AIRCRAFT ACCIDENT REPORT
Adopted: June 7, 1979
UNITED AIRLINES, INC.
McDONNELL-DOUGLAS DC-8-61, N8082U
DECEMBER 28, 1978
About 1815 Pacific standard time on December 28, 1978, United Airlines, Inc., Flight173 crashed into a wooded, populated area of suburban Portland, Oregon, during an approachto the Portland International Airport. The aircraft had delayed southeast of the airportat a low altitude for about 1 hour while the flightcrew coped with a landing gearmalfunction and prepared the passengers for a possible emergency landing. The planecrashed about 6 nmi southeast of the airport. The aircraft was destroyed; there was nofire. Of the 181 passengers and 8 crewmembers aboard, 8 passengers, the flight engineer,and a flight attendant were killed and 21 passengers and 2 crewmembers were injuredseriously.
The National Transportation Safety Board determined that the probable cause of theaccident was the failure of the captain to monitor properly the aircraft’s fuel state andto properly respond to the low fuel state and the crewmember’s advisories regarding fuelstate. This resulted in fuel exhaustion to all engines. His inattention resulted frompreoccupation with a landing gear malfunction and preparations for a possible landingemergency.
Contributing to the accident was the failure of the other two flight crewmembers eitherto fully comprehend the criticality of the fuel state or to successfully communicate theirconcern to the captain.
1. FACTUAL INFORMATION
1.1 History of the Flight
On December 28, 1978, United Airlines, Inc., Flight 173, a McDonnell-Douglas DC-8-61(N8082U), was a scheduled flight from John F. Kennedy International Airport, New York, toPortland International Airport, Portland, Oregon, with an en route stop at Denver,Colorado.
Flight 173 departed from Denver about 1447 1/ with 189persons on board, including 6 infants, and 8 crewmembers. The flight was cleared toPortland on an instrument flight rules (IFR) flight plan. The planned time en route was 2hrs 26 min. The planned arrival time at Portland was 1713.
According to the automatic flight plan and monitoring systems 2/the total amount of fuel required for the flight to Portland was 31,900 lbs. There was46,700 lbs of fuel on board the aircraft when it departed the gate at Denver. This fuelincluded the Federal Aviation Regulation requirement for fuel to destination plus 45 minand the company contingency fuel of about 20 min. During a postaccident interview, thecaptain stated that he was very close to his predicted fuel for the entire flight toPortland “…or there would have been some discussion of it.” The captain alsoexplained that his flight from Denver to Portland was normal.
At 1705:47, Flight 173 called Portland Approach and advised that its altitude was10,000 ft 3/ and its airspeed was being reduced. Portlandresponded and told the flight to maintain its heading for a visual approach to runway 28.Flight 173 acknowledged the approach instructions and stated, “…we have the fieldin sight.”
At 1707:55, Portland Approach instructed the flight to descend and maintain 8,000 ft.Flight 173 acknowledged the instructions and advised that it was “leaving ten.”At 1709:40, Flight 173 received and acknowledged a clearance to continue its descent to6,000 ft.
During a postaccident interview, the captain stated that, when Flight 173 wasdescending through about 8,000 ft, the first officer, who was flying the aircraft,requested the wing flaps be extended to 15, then asked that the landing gear be lowered.The captain stated that he complied with both requests. However, he further stated that,as the landing gear extended, “…it was noticeably unusual and (I) feel it seemed togo down more rapidly. As (it is) my recollection, it was a thump, thump in sound and feel.I don’t recall getting the red and transient gear door light. The thump was much cut ofthe ordinary for this airplane. It was noticeably different and we got the nose gear greenlight but no other lights.” The captain also said the first officer remarked that theaircraft “yawed to the right….” Flight attendant and passenger statementsalso indicate that there was a loud noise and a severe jolt when the landing gear waslowered.
At 1712:20, Portland Approach requested, “United one seven three heavy, contactthe tower (Portland), one one eight point seven.” The flight responded,”negative, we’ll stay with you. We’ll stay at five. We’ll maintain about a hundredand seventy knots. We got a gear problem. We’ll let you know.” This was the firstindication to anyone on the ground that Flight 173 had a problem. At 1712:28, PortlandApproach replied, “United one seventy – three heavy roger, maintain five thousand.Turn left heading two zero zero.” The flight acknowledged the instructions.
At 1714:43, Portland Approach advised, “United one seventy three heavy, turn leftheading, one zero zero and I’ll just orbit you out there ’til you get your problem.”Flight 173 acknowledged the instructions.
For the next 23 min, while Portland Approach was vectoring the aircraft in a holdingpattern south and east of the airport, the flightcrew discussed and accomplished all ofthe emergency and precautionary actions available to them to assure themselves that alllanding gear was locked in the full down position. The second officer checked the visualindicators on top of both wings, which extend above the wing surface when the landing gearis down-and-locked.
The captain stated that during this same time period, the first flight attendant cameforward and he discussed the situation with her. He told her that after they ran a fewmore checks, he would let her know what he intended to do.
About 1738, Flight 173 contacted the United Airlines Systems Line Maintenance ControlCenter in San Francisco, California, through Aeronautical Radio, Inc. 4/According to recordings, at 1740:47 the captain explained to company dispatch andmaintenance personnel the landing gear problem and what the flightcrew had done to assurethat the landing gear was fully extended. He reported about 7,000 lbs of fuel on board andstated his intention to hold for another 15 or 20 minutes. He stated that he was going tohave the flight attendants prepare the passengers for emergency evacuation.
At 1744:03, United San Francisco asked, “okay, United one seventy three….Youestimate that you’ll make a landing about five minutes past the hour. Is that okay?”The captain responded, “Ya, that’s good ball park. I’m not gonna hurry the girls. Wegot about a hundred sixty five people on board and we…want to…take our time and geteverybody ready and then we’ll go. It’s clear as a bell and no problem.”
The aircraft continued to circle under the direction of Portland Approach in atriangular pattern southeast of the airport at 5,000 ft. The pattern kept that aircraftwithin about 20 nmi of the airport.
From about 1744:30 until about 1745:23, the cockpit voice recorder (CVR) containedconversation between the captain and the first flight attendant concerning passengerpreparation, crash landing procedures, and evacuation procedures. During his initialinterview, the captain indicated that he neither designated a time limit to the flightattendant, nor asked her how long it would take to prepare the cabin. He stated that heassumed 10 or 15 minutes would be reasonable and that some preparations could be made onthe final approach to the airport.
At 1746:52, the first officer asked the flight engineer, “How much fuel wegot…?” The flight engineer responded, “Five thousand.” The first officeracknowledged the response.
At 1748:38, Portland Approach advised Flight 173 that there was another aircraft in itsvicinity. The first officer advised Portland Approach that he had the aircraft in sight.
At 1748:54, the first officer asked the captain, “…what’s the fuel shownow…?” The captain replied, “Five.” The first officer repeated,”Five.” At 1749, after a partially unintelligible comment by the flight engineerconcerning fuel pump lights, the captain stated, “That’s about right, the feed pumpsare starting to blink.” According to data received from the manufacturer, the totalusable fuel remaining when the inboard feed pump lights illuminate is 5,000 lbs. At thistime, according to flight data recorder (FDR) and air traffic control data, the aircraftwas about 13 nmi south of the airport on a west southwesterly heading.
From just after 1749 until 1749:45, the flightcrew engaged in further conversationabout the status of the landing gear. This conversation was interrupted by a headingchange from Portland Approach and was followed by a traffic advisory from PortlandApproach.
About 1750:20, the captain asked the flight engineer to “Give us a current card onweight. Figure about another fifteen minutes.” The first officer responded,”Fifteen minutes?” To which the captain replied, “Yeah, give us three orfour thousand pounds on top of zero fuel weight.” The flight engineer then said,”Not enough. Fifteen minutes is gonna – really run us low on fuel here.” At1750:47, the flight engineer gave the following information for the landing data card:”…Okay. Take three thousands pound, two hundred and four.” At this time theaircraft was about 18 nmi south of the airport in a turn to the northeast.
At 1751:35, the captain instructed the flight engineer to contact the companyrepresentative at Portland and apprise him of the situation and tell him that Flight 173would land with about 4,000 lbs of fuel. From 1752:17 until about 1753:30, the flightengineer talked to Portland and discussed the aircraft’s fuel state, the number of personson board the aircraft, and the emergency landing preparations at the airport. At 1753:30,because of an inquiry from the company representative at Portland, the flight engineertold the captain, “He wants to know if we’ll be landing about five after.” Thecaptain replied, “Yea.” The flight engineer relayed the captain’s reply to thecompany representative. At this time the aircraft was about 17 nmi south of the airportheading northeast.
At 1755:04, the flight engineer reported the “…approach descent check iscomplete.” At 1756:53, the first officer asked, “How much fuel you gotnow?” The flight engineer responded that 4,000 lbs remained, 1,000 lbs in each tank.
At 1757:21, the captain sent the flight engineer to the cabin to “…kinda see howthings are going….” From 1757:30 until 1800:50, the captain and the first officerengaged in a conversation which included discussions of giving the flight attendants ampletime to prepare for the emergency, cockpit procedures in the event of an evacuation afterlanding, whether the brakes would have antiskid protection after landing, and theprocedures the captain would be using during the approach and landing.
At 1801:12, Portland Approach requested that the flight turn left to a heading of 195deg. The first officer acknowledged and compiled with the request.
At 1801:34, the flight engineer returned to the cockpit and reported that the cabinwould be ready in “another two or three minutes.” The aircraft was about 5 nmisoutheast of the airport turning to a southwesterly heading. Until about 1802:10, thecaptain and the flight engineer discussed the passengers and their attitudes toward theemergency.
At 1802:22, the flight engineer advised, “We got about three on the fuel andthat’s it.” The aircraft was then about 5 nmi south of the airport on a southwestheading. The captain responded, “Okay. On touchdown, if the gear folds or somethingreally jumps the track, get those boost pumps off so that…you might even get thevalves open.”
At 1802:44, Portland Approach asked Flight 173 for a status report. The first officerreplied, “Yeah, we have indication our gear is abnormal. It’ll be our intention, inabout five minutes, to land on two eight left. We would like the equipment standing by.Our indications are the gear is down and locked. We’ve got our people prepared for anevacuation in the event that should become necessary.”
At 1803:14, Portland Approach asked that Flight 173 advise them when the approach wouldbegin. The captain responded, “…They’ve about finished in the cabin. I’d guessabout another three, four, five minutes.” At this time the aircraft was about 8 nmisouth of the airport on a southwesterly heading.
At 1803:23, Portland Approach asked Flight 173 for the number of persons on board andthe amount of fuel remaining. The captain replied, “…about four thousand, well,make it three thousand, pounds of fuel,” and “you can add to that oneseventy-two plus six laps-infants.”
From 1803:38 until 1806:10, the flightcrew engaged in a conversation which concerned(1) checking the landing gear warning horn as further evidence that the landing gear wasfully down and locked and (2) whether automatic spoilers and antiskid would operatenormally with the landing gear circuit breakers out
At 1806:19, the first flight attendant entered the cockpit. The captain asked,”How you doing?” She responded, “Well, I think we’re ready.” At thistime the aircraft was about 17 nmi south of the airport on a southwesterly heading. Theconversation between the first flight attendant and the captain continued until about1806:40 when the captain said, “Okay. We’re going to go in now. We should be landingin about five minutes.” Almost simultaneous with this comment, the first officersaid, “I think you just lost number four…” followed immediately by advice tothe flight engineer, “…better get some crossfeeds open there or something.”
At 1806:46, the first officer told the captain, “We’re going to lose anengine….” The captain replied, “Why?” At 1806.49, the first officer againstated, “We’re losing an engine.” Again the captain asked, “Why?” Thefirst officer responded, “Fuel.”
Between 1806:52 and 1807:06, the CVR revealed conflicting and confusing conversationbetween flight crewmembers as to the aircraft’s fuel state. At 1807:06, the first officersaid, “It’s flamed out”
At 1807:12, the captain called Portland Approach and requested, “…would likeclearance for an approach into two eight left, now.” The aircraft was about 19 nmisouth southwest of the airport and turning left. This was the first request for anapproach clearance from Flight 173 since the landing gear problem began. Portland Approachimmediately gave the flight vectors for a visual approach to runway 28L. The flight turnedtoward the vector heading of 010 deg.
From 1807:27 until 1809:16, the following intracockpit conversation took place:
1807:27 – Flight Engineer: “We’re going to lose number three in a minute, too.”
1807:31 – Flight Engineer: “It’s showing zero.”
Captain: “You got a thousand pounds. You got to.”
Flight Engineer: “Five thousand in there…but we lost it.”
1807:38 – Flight Engineer: “Are you getting it back?”
1807:40 – First Officer: “No number four. You got that crossfeed open?”
1807:41 – Flight Engineer: “No, I haven’t got it open. Which one?
1807:42 – Captain: “Open em both – get some fuel in there. Got some fuel pressure?”
Flight Engineer: “Yes sir.”
1807:48 – Captain: “Rotation. Now she’s coming.”
1807:52 – Captain: “Okay, watch one and two. We’re showing down to zero or a thousand.”
Flight Engineer: “Yeah.”
Captain: “On number one?”
Flight Engineer: “Right.”
1808:08 – First Officer: “Still not getting it.”
1808:11 – Captain: “Well, open all four crossfeeds.”
Flight Engineer: “All four?”
1808:14 – First Officer: “Alright, now it’s coming.”
18 08:19 – First Officer: “It’s going to be – on approach though.”
Unknown Voice: “Yeah.”
1808:42 – Captain: “You gotta keep ’em running….”
Flight Engineer: “Yes, sir.”
1808:45 – First Officer: “Get this…on the ground.”
Flight Engineer: “Yeah. It’s showing not very much more fuel.”
1809:16 – Flight Engineer: “We’re down to one on the totalizer. Number two is empty.”
At 1809:21, the captain advised Portland Approach, “United seven three is going toturn toward the airport and come on in.” After confirming Flight 173’s intentions,Portland Approach cleared the flight for the visual approach to runway 28L.
At 1810:17, the captain requested that the flight engineer “reset that circuitbreaker momentarily. See if we get gear lights.” The flight engineer complied withthe request.
At 1810:47, the captain requested the flight’s distance from the airport. Portlandapproach responded, “I’d call it eighteen flying miles.” At 1812:42, the captainmade another request for distance. Portland Approach responded, “Twelve flyingmiles.” The flight was then cleared to contact Portland tower.
At 1813:21, the flight engineer stated, “We’ve lost two engines, guys.” At1813:25, he stated, “We just lost two engines – one and two.”
At 1813:38, the captain said, “They’re all going. We can’t make Troutdale.”
At 1813:46, the captain told the first officer, “Okay. Declare a mayday.” At1813:50, the first officer called Portland International Airport tower and declared,”Portland tower, United one seventy three heavy, Mayday. We’re – the engines areflaming out. We’re going down. We’re not going to be able to make the airport.” Thiswas the last radio transmission from Flight 173.
About 1815, the aircraft crashed into a wooded section of a populated area of suburbanPortland about 6 nmi east southeast of the airport. There was no fire. The wreckage pathwas about 1,554 ft long and about 130 ft wide.
The accident occurred during the hours of darkness at latitude 45031’21″Nand longitude 122029’59″W. The elevation of the accident site was 285 ft.
1.2 Injuries to Persons
1.3 Damage to Aircraft
The aircraft was destroyed.
1.4 Other Damage
Two unoccupied homes were destroyed. Telephone lines were cut and high-tensionelectrical powerlines were damaged.
1.5 Personnel Information
The crewmembers were properly certificated and qualified for the flight (See AppendixB.)
1.6 Aircraft Information
The aircraft was certificated and maintained in accordance with Federal AviationAdministration (FAA) requirements. The gross weight and center of gravity were withinprescribed limits for the approach and landing. There was no usable fuel in the aircraftwhen it crashed.
The figures below illustrate the aircraft’s approximate takeoff gross weight,approximate landing weight, and the approximate pounds of fuel remaining upon arrival inthe vicinity of the Portland International Airport; these figures are based on normaloperations.
Zero fuel weight from weight manifest
Total fuel on board from fuel service form
Aircraft weight before departure from gate at Denver
Fuel consumption on taxi
Takeoff gross weight
Fuel consumption en route to Portland, based on flight plan
Landing weight at Portland
Zero fuel weight from weight manifest
Fuel remaining at Portland
Throughout the landing delay, Flight 173 remained at 5,000 ft with landing gear downand flaps set at 15 deg. Under these conditions, the Safety Board estimated that theflight would have been burning fuel at the rate of about 13,209 lbs per hour – 220 lbsper min. At the beginning of the landing delay, there were about 13,334 lbs of fuel onboard.
A new type of fuel quantity indicating system was retrofitted to this aircraft on May12, 1978. The retrofit was authorized by Change Order Authorization No. 2-4849. With thenew system installed, there are eight individual tank quantity gages. Each of these gageshas three digits which are seven-segment incandescent lamps. On these individual tankgages, the digital reading is multiplied by 100 to obtain the total amount of fuel in thetank.
The totalizer gage receives input from each individual tank gage and displays the totalfuel available on three digital readouts. However, this digital reading must be multipliedby 1,000 to obtain the value of the total amount of fuel on board. The smallest incrementof change that can be indicated on the individual tank gages is 1,000 lbs. The smallestincrement of change on the totalizer is 1,000 lbs.
Before the implementation of the change order, each individual tank gage displayed fivedigits which were read directly to obtain the amount of fuel in each tank.
The change order also replaced the flight engineer’s totalizer gage, which haddisplayed six digits read directly for total fuel on board.
According to United Airlines, the primary purposes of installing the fuel quantityindicating system were (1) to reduce erroneous system indications because of stray pickupof 400 Hz signals in the fuel quantity indicating system wiring, and (2) to reduceindication errors from current leaks across the elements of the capacitive probes andcompensators.
After the accident, United Airlines determined that the aircraft was burning fuel inaccordance with the automatic flight plan and monitoring system. In October 1978, fuelburnoff examination indicated that the aircraft was not consuming fuel as fast aspredicted; it was 1.04 percent less than predicted. In addition, another method fordetermining burnout was begun by United engineers. Each trip’s total burnout was dividedby total time. For December 1978 these aggregate values verified that this aircraft’s fuelconsumption was within 1 percent of the plan.
The aircraft was also equipped with a fuel flow indicator for each engine whichdisplayed, in hundreds of pounds, the hourly rate of fuel being used by the engine. Theseindicators were located on the pilot’s forward engine instrument panel along with otherengine monitoring gages.
1.7 Meteorological Information
Surface weather observations taken before and after the accident at PortlandInternational Airport by National Weather Service personnel were:
1655 – 4,500 ft scattered; visibility – 30 mi; temperature – 300F; dewpoint – 130F; wind – 3400 at 8 kns; altimeter setting – 30.16 in Hg.
1755 – Clear; visibility – 15 mi; temperature – 290F; dewpoint – 13 F; wind – 0100 at 11 kns; altimeter setting – 30.17 in Hg.
1829 Local – Clear; visibility – 15 mi; temperature – 280F dewpoint – 120F; wind – 3500 at 11 kns; altimeter setting – 30.19 in Hg; AIRCRAFT MISHAP.
1.8 Aids to Navigation
During his deposition, the captain stated that he had set the Portland VORTAC, which islocated 9.2 nmi north-northeast of Portland International Airport, in both of his VORreceivers. He stated also that he was receiving distance measuring equipment information.
No communications difficulties were reported.
1.10 Aerodrome Information
Runway 28L at Portland International Airport is hard surfaced and is 11,014 ft long and150 ft wide. The published touchdown zone elevation and field elevation are 19 ft and 26ft, respectively. The runway is equipped with high intensity runway edge lights,centerline lights, and visual approach slope indicator lights. The airport has two otherrunways. Runway 10L/28R, which is parallel to runway 28L, is 8,004 ft long and 150 ftwide. It is the primary instrument runway. Runway 02/20 is 7,000 ft long and 150 ft wide.It is used mainly as a crosswind runway.
The airport is located near the south shore of the Columbia River southeast ofPortland. The terrain southeast of the airport is characterized by low rolling hills,which rise from the river valley.
1.11 Flight Recorders
N8082U was equipped with a Fairchild model 5424 flight data recorder (FDR), serial No.6043. The recorder showed no outward evidence of damage. The foil recording medium was notdamaged; all parameter and binary traces were present and active with no evidence ofrecorder malfunction or recording abnormalities. Electrical power to the recorder wasterminated about 44 sec before the aircraft crashed. A readout was made of the final 15min 44.7 sec of the recorded traces. This readout covers the 15 min of flight before allparameter traces – altitude, airspeed, magnetic heading, and vertical acceleration -ceased to be recorded and continues for an additional 44.7 sec where all binary tracesbecame atypical.
N8082U was also equipped with a Sundstrand model V557 CVR, serial No. 1427. Therecorder was removed from the aircraft and the entire tape was transcribed. The quality ofthe recording was good. (See Appendix D.)
1.12 Wreckage and Impact Information
The aircraft first struck two trees about 100 ft above the ground. These trees wereabout 1,554 ft from the point where the wreckage came to rest. About 541 ft farther alongthe flightpath on a heading of about 345 deg, the aircraft struck two trees about 85 ftabove the ground. About 400 ft farther, the right wing struck a tree about 45 ft above theground. About 225 ft beyond that point, the left outer wing struck a tree about 8 ft abovethe ground. The aircraft then struck and destroyed an unoccupied house which was locatedabout 1,230 ft from the first tree. Pieces of the aircraft’s left wing structure werelocated just beyond the house.
The two main landing gear and the nose section of the aircraft first struck a 5-ftembankment next to a city street about 1,275 ft from the first tree. The aircraftcontinued across the street and came to rest on a heading of 330 between some trees and ontop of another unoccupied house. The tail of the aircraft came to rest about 1,350 ft fromthe first tree. Just after crossing the street, the vertical stabilizer struck a series ofhigh tension cables, which ran parallel to the street.
The fuselage, from about the fifth row of passenger seats forward, sustained severe,extensive impact damage in a generally rearward direction. The cockpit upper structure,which included the cockpit forward windows, had separated and was found to the right ofthe fuselage just forward of the inboard end of the right wing. The cockpit floorstructure, which included portions of the crew seats, sections of the instrument panel,and the nose tunnel structure with the nose gear assembly partially attached, hadseparated and rotated to the right and aft. This structure was in a partially invertedposition. All portions of the fuselage structure were accounted for and all of thestructural damage was caused by impact with the ground and the numerous large trees in theimmediate area.
The lower left side of the fuselage, between the fourth and sixth rows of passengerseats and below window level, had been torn away. The remainder of the underside of thefuselage sustained heavy damage from contact with several large trees and tree stumps. Thepassenger cabin interior, from row 6 to the aft bulkhead, was relatively intact. Atseveral points along the fuselage, windows were smashed and the fuselage had been dentedby large trees and separated portions of the main landing gear.
The empennage showed moderate impact damage. The vertical stabilizer leading edge hadbeen damaged by high tension cables at three points just forward of the upper threerudder-to-stabilizer hinge points.
The left wing had separated from the fuselage about 3 ft outboard from the fuselageattachment point. The No. 2 engine had separated from its pylon and was located adjacentto the wing trailing edge. The No. 1 engine remained attached to a section of left wingstructure. A 7-ft-long section of the left wingtip had been sheared off and was found nearthe first house.
The right wing separated about 5 ft from the fuselage. A 2-ft opening was evidentbetween the fuselage and wing leading edge structure. The wing leading edge, from a pointabout 5 ft outboard from the leading edge inboard end, was cut and torn aft to the frontspar assembly. A large section of right wing leading edge structure had separated duringthe impact sequence and was also found near the first house.
A section of right wing with the No. 3 engine and pylon attached was located justforward of the right horizontal stabilizer. The outboard wing section, which included theNo. 4 engine, was to the right of the fuselage.
All four engines were inspected and found to be capable of operation. None showed signsof rotation at impact
Both main landing gear were fully extended but were torn from their mountingstructures. They were located near main wreckage. Inspection of the right main landinggear retraction mechanism showed corrosion in the threads of an attachment eyebolt. Theeyebolt was pulled out of the actuator cylinder piston. The nose landing gear was fullyextended and remained attached to the nose tunnel structure.
1.13 Medical and Pathological Information
A review of the flightcrew’s medical records revealed no evidence of medical problemsthat might have affected their performance.
The 10 persons who were killed in the crash died from impact trauma. Toxicologicalanalyses showed no acidic, neutral, or basic drugs or ethanol in the blood taken from theflight engineer and first flight attendant
There was no fire.
1.15 Survival Aspects
The accident was partially survivable. The 10 occupants killed in the crash werelocated between the flight engineer’s station in the cockpit and row 5 in the passengercabin. All of the passengers who were killed had been located on the right side of thecabin. That section of the aircraft was destroyed during the accident sequence.
The most seriously injured passengers were seated in the right forward portion of thecabin near an area of the fuselage which appeared to have been penetrated by a large tree.These persons were seated near those passengers who were injured fatally. Some seriouslyinjured passengers were seated in the rear cabin near the trailing edge of the wings. Thefuselage in this area had been penetrated and the floor and seats had been disrupted.
Some passengers sustained serious injuries during the evacuation. Two passengerssustained fractures and others sustained lacerations and abrasions when they either fellfrom exits or as they climbed through debris outside the aircraft in order to reach theground. As a result of the accident, 22 persons were admitted to hospitals with seriousinjuries ranging from multiple fractures of extremities and fractures of cervicalvertebrae, to observations for possible injuries.
The plane crashed in the jurisdiction of Multnomah County Rural Fire ProtectionDistrict No. 10. Three fire departments sent personnel and equipment to the scene: ThePort of Portland (Airport) Fire Department; Multnomah RFPD No. 10, and the City ofPortland Fire Bureau. A total of 39 fire units and 108 on-duty fire personnel responded tothe scene. Numerous off-duty fire personnel from all fire departments also responded tothe scene. Because there was no fire, the basic fire service functions were search andrescue, extrication, triage, emergency medical care, precautionary foaming of someaircraft parts and surrounding area, laying standby firefighting water supply lines,transporting or assisting ambulatory victims to a nearby church, setting up area lighting,providing some interagency radio communications, and setting up the on-scene command post.
Although there were many occupied houses and apartment complexes in the immediatevicinity of the accident, there were no ground casualties and no postcrash fire, injuredpersons were transported to nearby hospitals by helicopter and ambulance.
The aircraft was equipped with 10 floor level exits, each provided with automaticallyinflatable emergency escape slides. In addition to slides at the boarding doors (1L and5L) and at the two galley service doors (2R and 5R), slides were located at the six”jet escape” floor level exits (1R, 2L, 3L, 3R, 4L, 4R). The “jetescape” doors were hinged at the bottom and were designed to swing down and outwardwhen opened. Movement of the door actuated the automatic inflation of the escape side.
The slide from exit 1L was found wrapped around a tree at the left wing. The slidesfrom exits 3L and 3R were found packed and uninflated. These exits were reportedly blockedby debris outside the aircraft. The slide at exit 1R reportedly inflated inside the cabinand extended across the aisle and lodged against seat 8C. The door was prevented fromopening fully because of cockpit and forward cabin debris outside the aircraft. The slideat exit 2R also reportedly inflated inside the cabin and blocked the cabin aisle. The exitdoor was displaced inward when the plane hit a tree.
The slide at exit 4R reportedly inflated inside the cabin when the door was opened by apassenger. The slide inflated upward and partially blocked the exit opening. Because ofdebris outside the fuselage, the exit door was prevented from opening fully. The passengerwho opened the door reported that about 10 persons used this exit before the slide waspushed out the exit and onto debris. The remaining escape slides reportedly deployedoutside the aircraft and inflated but were punctured or torn by debris during theevacuation.
The escape slides were removed from the accident site and were examined on January 3,and on January 9, 1979. No discrepancies were found in the installation, maintenance,manufacture, or design of the escape slides.
The evacuation was completed in about 2 min. Except for seats at rows 20 through 22which were torn loose from the floor attachments, there was only minor disruption of thecabin furnishings aft of row 6. The emergency lights provided adequate illumination duringthe evacuation.
1.16 Tests and Research
1.16.1 Retract Cylinder Assembly
The Safety Board examined the piston rod and the mating end from the right main landinggear retract cylinder assembly at its metallurgical laboratory in Washington, D.C. Theexamination showed that the primary cause of the separation of the rod end from the pistonrod was severe corrosion cause by moisture on to the mating threads of both components. Asa result of the corrosion, the joint was weakened to such an extent that only acomparatively low tensile load was required to pull the rod end out of the piston rod. Thepattern of mechanical damage indicated that all of the rod threads had been engaged andthat the rod end had been pulled straight out of the piston rod without any significantrotation.
1.16.2 Fuel Control Test
Functional testing of the fuel controllers from each of the four engines was conductedat the company’s maintenance base. No discrepancies or out-of-tolerance conditions werefound.
1.16.3 Aircraft Systems Examinations
During the week of January 8, 1979, the following examinations were conducted at thecompany’s maintenance facility:
(1) Fuel Flow indicators
The shop examinations confirmed that the four indicators were indicating zero fuel flow. The front face, case, and electrical connections were all damaged and none could be operated or tested before being repaired. After minor repairs to the electrical connections only the flow meter for the No. 2 engine became operable, and it met the linearity specifications.
(2) Fuel Quantity Gages
During the wreckage salvage, the eight fuel quantity gages were recovered. AU units were damaged and repairs were attempted on each. Three gages could be repaired sufficiently to allow functional testing.
The No. 4 main tank gage was given a lamp check, segment check, and self-test check and all were within specification. In addition, a linearity check was made at full, at 1,000 lbs, at 500 lbs, and at empty. The results were within specifications. The No. 4 alternate tank gage and the No. 2 main tank gage were tested in the same manner, and the results were within specifications. The other tank gages were not operable because of damage and, therefore, could not be tested.
(3) Totalizer Gage
The glass face was broken, the electrical connector bent, and the case punctured. The damage was too extensive to enable repair for testing.
(4) No. 1 Main Fuel Tank Capacitance Probes
The five capacitance probes from the No. 1 main fuel tank were examined according to company specification. All units were within specification except probe No. MR 28062, serial No. 525856-31X. This unit did not meet resistance tolerance specification when wet.
(5) Tank Reference Capacitors
One of these units is located in each main tank. All four units were recovered and, when tested, met specifications.
(6) Right Main Landing Gear Down-Lock Switch
This switch is activated when the gear reaches a down-and-locked position. A similar switch was installed on the left main landing gear. A comparison of the damage to the two switch cases showed that the switch from the right landing gear had been damaged apparently by an internal part that pushed the case outward and had distorted it. Electrical tests of the switch and attached wiring indicated an intermittent short circuit when the switch was shaken. X-rays of the switch showed that a large spring had become free of its mounts within the switch case. Normally this spring returns the down-lock switch to the gear-not- down position when the landing gear is refracted. The switch case was cut open and several coils of the spring were found spread apart. When the spring and switch case damages were matched, one end of the spring fit into the distorted portion of the case. The other end of the spring touched wiring terminal No. 8 of the microswitch and marks indicative of electrical arcing were found on the spring where it contacted terminal No. 8.
(7) Left Main Landing Gear Down-Lock Switch
The spring of the left main landing gear down lock switch was tree of its mounts. The coils of this spring were not bent and no marks similar to electrical arcing were found.
(8) Landing Gear Warning and Interlock Circuit Breaker
When examined in the field, this circuit breaker appeared to be mechanically extended or electrically open. There was some mechanical damage. Later, shop tests verified that the circuit breaker was open. It could be operated mechanically and it opened and closed the electrical circuit properly.
(9) Distance Measuring Equipment
Two distance measuring equipment units, Collins Model 860E-2, serial No. 3954 (No. 1) and serial No. 617 (No. 2), were opened in the company maintenance shops and the distance modules were removed. When connected to a test panel, the mileage readouts were 16.05 nmi for the No. 1 unit and 16.0 nmi for the No.2 unit. Both units were selected to channel 113X, which corresponds to a VOR frequency of 116.60 MHz.
1.16.4 Fuel Quantity System Error
Upon request, United Airlines provided the Safety Board with an error analysis of thefuel quantity indicating system for the accident aircraft. Analyses were prepared forthree different assumptions. The first analysis assumed that all errors were at theirlimits and in the same direction. The second analysis assumed that all errors were attheir limits but were distributed randomly with respect to sign (root-sum-squareanalysis). The third analysis was a probable error analysis. All errors in this analysiswere those associated with empty or near empty tanks.
These analyses indicated the following:
Sum of Indicators
High Error Lbs
Low Error Lbs
High Error Lbs
Low Error Lbs
1.16.5 Fuel Burn Time History
At the request of the Safety Board, Douglas Aircraft Company and United Airlinesstudied fuel burn performance for the accident flight. In both studies, the fuel on boardat the gate in Denver was 46,700 lbs. The fuel remaining at cruise at 35,000 ft was almostidentical in both studies. United’s calculations of fuel burn rate for the descent from35,000 ft to the 5,000 – ft holding altitude were 13 percent lower than Douglas’.However, United’s fuel burn rate while in the holding pattern was 14 percent higher thanDouglas’. This disparity was a result of different interpretations of meteorological andFDR data which resulted in differing mach values. Both studies had similar fuel remainingvalues when both flight recorders ceased operation; Douglas had calculated 178 lbs andUnited had calculated 73 lbs. Both studies compared favorably to the fuel burn timehistory computed by the Safety Board using information from the automatic flight plan andmonitoring system and CVR data.
A correlation of CVR information with both fuel burn studies shows the observed andcalculated fuel remaining values to be in agreement The CVR transcript indicated anobserved fuel remaining value of 5,000 lbs about 1749. The Douglas figure for that timewas 5,250 lbs and United’s was about 6,000 lbs. If the totalizer accumulated probableerror of 885 lbs was applied, the calculated and observed fuel remaining values would bein agreement. In addition, the two studies indicated that the accident aircraft’s fuelconsumption was normal during the accident flight
Although both studies had similar fuel remaining values when the aircraft lost itsengine power, the Safety Board believes that the Douglas’ study more closely approximatesthe fuel burn during the 5,000-ft hold period. Therefore, fuel remaining computations forthis period are predicated on the manufacturer’s figures of a calculated fuel burn of13,209 lbs per hour (220 lbs per min). According to the manufacturer’s study, the aircraftentered into the hold with about 13,334 lbs of fuel.
1.17 Other Information
1.17.1 Responsibility of the Crew
Excerpt from United Airlines Flight Operations Manual, paragraph 6.2, June 30,1978:
“16. Except as otherwise specifically directed by the captain, all crew members noting a departure from prescribed procedures and safe practices should immediately advise the captain so that he is aware of and understands the particular situation and may take appropriate action.”
1.17.2 United Airlines Flight Operations Bulletin 22-76, Fuel Policy DomesticFAR 45 Minute and Overwater/International 30 Minute Reserve Fuel.
“FAR 121.639 (C) does not specify in detail how the aforementioned requirements are to be calculated. United Airlines has established the following criteria for computing required fuel.
a. Weight – The operating weight empty of the airplane plus maximum structural payload or maximum space payload, whichever is smaller, plus the weight of the 45 minutes of reserve fuel.
b. Speed – Long range cruise speed.
c. Altitude – 25,000 Feet
d. The ability to loiter at 5,000 feet at clean holding speed for 45 minutes.”
“From the aforementioned criteria is derived the following DC-8-61 fuel requirements.
1. Fuel required for 45 minutes cruising at long range cruise at 25,000 feet is 8,300 pounds.
2. Fuel required for 45 minutes holding clean at 5,000 feet is 7,800 pounds.
3. FAR 45 minute reserve: 8,400 pounds.”
1.17.3 Excerpts From United Airlines DC-8 Flight Manual
“Landing Gear Lever Down and Gear Unsafe Light On
If the visual down-lock indicators indicate the gear is down then a landing can be made at the captain’s discretion.”
(Dated January 1, 1974, pg. 1-44.)
“Landing Gear Apparently But Not Conclusively Down
If possible, have tower visually check. If there is reasonable indication that the gear is down then the landing can be made assuming gear is down. Do not taxi the airplane until gear locks have been installed.”
(Dated January 2, 1974, pg 1 – 44-59.)
“Preparation For Evacuation
1. Notify ground station of emergency.
2. Advise the First Flight Attendant as to:
a. nature of emergency and expected landing conditions,
b. time available for preparation,
c. signal for taking protective position,
d. signal to be used if evacuation is not necessary,
e. other special instructions.
3. Determine from the First Flight Attendant:
a. the passenger load,
b. number of infants, invalids, and other passengers who would be given special consideration.
4. Direct all nonessential cockpit members to move to the cabin and assist Flight Attendants as requested.
5. Review the EVACUATION Emergency procedure.
6. Make an announcement to the passengers as appropriate.
7. Accomplish the CABIN INSPECTION CHECKLIST below when advised by the First Flight Attendant that cabin preparations are completed.
8. Depressurize the airplane when below 10,000 feet.
9. Insure that – the emergency exit lights switch is in the armed position.
10. Avoid landing, if possible, until emergency equipment and crews are standing by.
11. Advise the First Flight Attendant when approximately five minutes from landing.
12. Advise the passengers and Flight Attendants when to assume the protective position.
13. If evacuation is necessary, accomplish the EVACUATION Emergency Procedure.”
(Dated September 27, 1975, page 1 – 19.)
“Cabin Inspection Checklist
1. All Flight Attendants briefed on station, duties, and signals.
2. Passengers reseated as required and seats to be used by crew vacated.
3. Helper passengers briefed on station, duties, and exit operation.
4. Passengers briefed on:
a. Protective position and signal to assume position.
b. Seatbelts tight and low.
c. How to unfasten seat belts.
d. Assigned exits and when and how to leave the airplane.
5. Passengers’ glasses, dentures, high heels, and other possible hazardous items removed and stowed. Loose objects stowed in secure stowage areas.
6. Internal doors and curtains secured open.
7. Meal service furnishings in appropriate secure area.
8. Seat backs upright and tables stowed. Pillows and blankets distributed for impact protection.”
(Dated September 27, 1975, page 1-20)
1.17.4 Excerpts From United Airlines Maintenance/Overhaul Manual
“Fuel Quantity Indicator System – Tolerance
a. All tanks at empty, +/- 150 pounds.
b. Tank at full #1 & #4 Main +/- 400 pounds
#1 & #4 Alt +/- 225 pounds
#2 & #3 Main +/- 400 pounds
#2 & #3 Alt +/- 250 pounds”
(Dated January 19, 1976, page 201.)
1.17.5 Main Landing Gear Retract Cylinder Assembly
Although the purpose of the main landing gear retract cylinder assembly is to raise thelanding gear during the refract cycle, the hydraulic action of the cylinder acts as abuffer during the extend cycle to moderate the rate of extension and prohibit the landinggear from free falling to the down-and-locked position.
McDonnell-Douglas Corporation issued an All-Operator Letter, AOL 8-141, in July 1967,Main Landing Gear Retract Cylinder Assemblies, DC-8 Aircraft. The letter advised, all DC-8operators that several cylinder end fittings had been found with fractures in the threadroots. To alleviate this condition, the eyebolt threads were changed from machined torolled-type threads. The letter also recommended sealing the threads with a corrosionresistant compound.
On March 27, 1968, McDonnell-Douglas issued Service Bulletin No. 32-131, DC-8 SC 1681,Landing Gear Extension and Retraction -Replace Main Landing Gear Retract Rod Assemblies.This bulletin provided information on the replacement of the retract cylinder rod endassemblies with machined threads with rod end assemblies with rolled-type threads.
In 1973, United Airlines instituted a gamma ray inspection program for the main landinggear retract actuating cylinder and rod ends on the DC-8 aircraft. The purpose ofinspection was to detect thread corrosion in the cylinder. The cylinder threads on themain landing gear refract actuators of the accident aircraft were last inspected using thegamma ray injection on April 2, 1977.
In order to provide additional threads and a longer eyebolt on actuator cylinders foundwith corrosion damage, the retract cylinder was to have been modified as provided for inthe United Airlines Maintenance Manual dated January 2, 1974. The right main landing gearretract actuator on the accident aircraft had not been modified.
1.17.6 Dispatcher Responsibility and Authority
Under the provisions of United Airlines Flight Operations Manual, the flight dispatcherresponsibility after the aircraft is airborne is limited to computation of fuel estimateunder only two conditions – when contact is not established within 20 min and during ahijacking.
1.18 New Investigation Techniques
The flightcrew was properly certificated and each crewmember had received the trainingand the off-duty time prescribed by applicable regulations. There was no evidence ofmedical problems that might have affected their performance.
The aircraft was certificated and maintained according to applicable regulations. Thegross weight and c.g. were within prescribed limits. Except for the failure of the pistonrod on the right main landing gear retract cylinder assembly and the failure of thelanding gear position indicating system, the aircraft’s airframe, system; structures, andpowerplants were not factors in this accident.
The investigation revealed that fuel was burned at a normal rate between Denver andPortland. The aircraft arrived in the Portland area with the preplanned 13,800 lbs of fueland began its delay at 5,000 ft with about 13,334 lbs.
The first problem which faced the captain of Flight 173 was the unsafe landing gearindication during the initial approach to Portland International Airport. This unsafeindication followed a loud thump, an abnormal vibration, and an abnormal aircraft yaw asthe landing gear was lowered. The Safety Board’s investigation revealed that the landinggear problem was caused by severe corrosion in the mating threads where the right mainlanding gear refract cylinder assembly actuator piston rod was connected to the rod end.The corrosion allowed the two parts to pull apart and the right main landing gear to fallfree when the flightcrew lowered the landing gear. This rapid fall disabled themicroswitch for the right main landing gear which completes an electrical circuit to thegear-position indicators in the cockpit. The difference between the time it took for theright main landing gear to free fall and the time it took for the the left main landinggear to extend normally, probably created a difference in aerodynamic drag for a shorttime. This difference in drag produced a transient yaw as the landing gear dropped.
Although the landing gear malfunction precipitated a series of events which culminatedin the accident, the established company procedures for dealing with landing gear systemfailure(s) on the DC-8-61 are adequate to permit the safest possible operation and landingof the aircraft. Training procedure; including ground school, flight training, andproficiency and recurrent training, direct the flightcrew to the Irregular Proceduressection of the DC-8 Flight Manual, which must be in the possession of crewmembers while inflight. The Irregular Procedures section instructed the crew to determine the position ofboth the main and nose landing gear visual indicators. “If the visual indicatorsindicate the gear is down, then a landing can be made at the captain’s discretion.”The flight engineer’s check of the visual indicators for both main landing gear showedthat they were down and locked. A visual check of the nose landing gear could not be madebecause the light which would have illuminated that down-and-locked visual indicator wasnot operating. However, unlike the main landing gear cockpit indicators, the cockpitindicator for the nose gear gave the proper “green gear-down” indication.
Admittedly, the abnormal gear extension was cause for concern and a flightcrew shouldassess the situation before communicating with the dispatch or maintenance personnel.However, aside from the crew’s discussing the problem and adhering to the DC-8 FlightManual, the only remaining step was to contact company dispatch and line maintenance. Fromthe time the captain informed Portland Approach of the gear problem until contact withcompany dispatch and line maintenance, about 28 min had elapsed. The irregular gear checkprocedures contained in their manual were brief, the weather was good, the area was voidof heavy traffic, and there were no additional problems experienced by the flight thatwould have delayed the captain’s communicating with the company. The company maintenancestaff verified that everything possible had been done to assure the integrity of thelanding gear. Therefore, upon termination of communications with company dispatch andmaintenance personnel, which was about 30 min before the crash, the captain could havemade a landing attempt. The Safety Board believes that Flight 173 could have landed safelywithin 30 to 40 min after the landing gear malfunction.
Upon completing communications with company, line maintenance and dispatch, the captaincalled the first flight attendant to the cockpit to instruct her to prepare the cabin fora possible abnormal landing. During the ensuing discussion, the captain did not assign thefirst flight attendant a specified time within which to prepare the cabin, as required bythe flight manual. In the absence of such time constraint, the first flight attendant wasprobably left with the impression that time efficiency was not necessarily as important asthe assurance of thorough preparation.
The Safety Board believes that any time a flight deviates from a flight plan, theflightcrew should evaluate the potential effect of such deviation on the aircraft fuelstatus. This flightcrew knew that the evaluation of the landing gear problem andpreparation for an emergency landing would require extended holding before landing.
The flightcrew should have been aware that there were 46,700 lbs of fuel aboard theaircraft when it left Denver at 1433 and that there was about 45,650 lbs at takeoff at1447. Regardless of whether they were aware of the actual fuel quantities, they certainlyshould have been aware that the initial fuel load was predicated on fuel consumption forthe planned 2 hr 26 min en route flight, plus a reserve which includes sufficient fuel for45 min at normal cruise and a contingency margin of about 20 min additional flight.
Therefore, the crew should have known and should have been concerned that fuel couldbecome critical after holding. Proper crew management includes constant awareness of fuelremaining as it relates to time. In fact, the Safety Board believes that proper planningwould provide for enough fuel on landing for a go-around should it become necessary. Suchplanning should also consider possible fuel-quantity indication inaccuracies. This wouldnecessitate establishing a deadline time for initiating the approach and constantmonitoring of time, as well as the aircraft’s position relative to the active runway. Suchprocedures should be routine for all flightcrews. However, based on available evidence,this flightcrew did not adhere to such procedures. On the contrary, the cockpitconversation indicates insufficient attention and a lack of awareness on the part of thecaptain about the aircraft’s fuel state after entering and even after a prolonged periodof holding. The other two flight crewmembers, although they made several commentsregarding the aircraft’s fuel state, did not express direct concern regarding the amountof time remaining to total fuel exhaustion. While there is evidence to indicate that thecrew was aware of the amount of fuel remaining at various times, there is no evidence thatthe onboard quantity was monitored in relation to time remaining during the final 30 minof flight. The Safety Board believes that had the flightcrew been aware of the fuel state,comments concerning time to fuel exhaustion would have been voiced. However, there wasnone until after the aircraft was already in a position from which recovery was notpossible.
In analyzing the flightcrew’s actions, the Safety Board considered that the crew couldhave been misled by inaccuracies within the fuel-quantity measuring system. However, thoseintracockpit comments and radio transmissions in which fuel quantity was mentionedindicate that the fuel-quantity indicating system was accurate.
Had the flightcrew related any of these fuel quantities to fuel flow, they should havebeen aware that fuel exhaustion would occur at or about 1815. Other evidence that thecaptain had failed to assess the effect of continued holding on fuel state was provided byhis stated intentions to land about 1805 with.4,000 lbs of fuel on board. Just minutesearlier, at 1748:56, he was made aware that only 5,000 lbs remained. During the 16 minbetween the observation of 5,000 lbs and 1805, the aircraft would consume at least 3,000lbs of fuel. Further evidence of the flightcrew’s lack of concern or awareness wasprovided when just after his observations of 4,000 lbs remaining about 17 min before thecrash, the first officer left the cockpit at the captain’s request to check on the cabinemergency evacuation preparations. Upon his return, about 4 min later, he gave the captainan estimate of another 2 or 3 min for the completion of the cabin preparation. At thistime, the aircraft was in the general vicinity of the airport. In the initial interviewwith the captain, he stated that he felt the cabin preparation could be completed in from10 to 15 min and that the “tail end of it” could be accomplished on the finalapproach to the airport. Certainly there was nothing more to do in the cockpit. All of thelanding gear check procedures, as prescribed in the approved flight manual and recommendedby company line maintenance, had been completed and dispatch had been notified and hadalerted Portland company personnel of the problems.
Under these circumstances, there appears to have been no valid reason not todiscontinue their heading inbound toward the airport in order to make their previouslyestimated landing time. However, about 1801:12, the first officer accepted and the captaindid not question a vector heading which would take them away from the airport and delaytheir landing time appreciably. Moreover, after the turn was completed none of theflightcrew suggested turning toward the airport. Thus, it was at this time that the crew’scontinuing preoccupation with the landing gear problem and landing preparations becamecrucial and an accident became inevitable.
The Safety Board also considered the possibility that the captain was aware of the fuelquantity on board, but failed to relate the fuel state to time and distance from theairport and intentionally extended the flight to reduce the fuel load in order to reducethe potential of fire should the landing gear fail upon landing. The Safety Board couldfind no evidence, however, to support such a theory and believes that had he so intended,the captain would have advised the first officer and the flight engineer. Therefore, theSafety Board can only conclude that the flightcrew failed to relate the fuel remaining andthe rate of fuel flow to the time and distance from the airport, because their attentionwas directed almost entirely toward diagnosing the landing gear problem. Although on twooccasions the captain confirmed with the company that he intended to land about 1805 andthat he would be landing with about 4,000 lbs of fuel, this estimated time of arrival andlanding fuel load were not adhered to, nor was the expected approach time given toPortland Approach. This failure to adhere to the estimated time of arrival and landingfuel loads strengthens the Board’s belief that the landing gear problem had a seeminglydisorganizing effect on the flightcrew’s performance. Evidence indicates that their scanof the instruments probably narrowed as their thinking fixed on the gear. After the No. 4engine had flamed out and with the fuel totalizer indicating 1,000 lbs, the captain wasstill involved in resetting circuit breakers to recheck landing gear light indications.
It was not until after it became apparent to the crew that total engine flame out wasimminent that the captain was concerned and, in fact, may have been confused as to theamount of fuel which actually remained. About 6 min before all engines stopped, thecaptain stated that there was 1,000 lbs of fuel in the No. 1 main tank, and the flightengineer agreed with him. At this same time, the captain began to describe the gageindication as changing from 1,000 lbs to zero lbs. Since the No. 1 main tank gage does notchange its indication from 1,000 lbs to zero lbs directly, but decreases in increments of100 lbs, the captain must have read the gage indication incorrectly. Actually, the actionhe described was that of a gage changing from 100 lbs to zero lbs.
The company had recently changed the fuel quantity gages on this aircraft from a directreading digital-type to a three-figure indicator that had to be multiplied by a factor of100 to get the actual individual tank values. In addition, the new totalizer gage, of thesame three-figure presentation as the individual tank gages, had to be multiplied by afactor of 1,000 to get the actual total fuel. During the stressed situation, the captainand the flight engineer may have mixed up these multipliers and used 1,000 when readingthe individual tank gages instead of 100. However, there is no evidence from previouscomments that such a mistake was made. By the time such confusion was indicated, theaccident was inevitable.
The Safety Board believes that this accident exemplifies a recurring problem – abreakdown in cockpit management and teamwork during a situation involving malfunctions ofaircraft systems in flight. To combat this problem, responsibilities must be divided amongmembers of the flightcrew while a malfunction is being resolved. In this case, apparentlyno one was specifically delegated the responsibility of monitoring fuel state.
Although the captain is in command and responsible for the performance of his crew, theactions or inactions of the other two flight crewmembers must be analyzed.
Admittedly, the stature of a captain and his management style may exert subtle pressureon his crew to conform to his way of thinking. It may hinder interaction and adequatemonitoring and force another crewmember to yield his right to express an opinion.
The first officer’s main responsibility is to monitor the captain. In particular, heprovides feedback for the captain. If the captain infers from the first officer’s actionsor inactions that his judgement is correct, the captain could receive reinforcement for anerror or poor judgement. Although the first officer did, in fact, make several subtlecomments questioning or discussing the aircraft’s fuel state, it was not until after theNo. 4 engine flamed out that he expressed a direct view, “Get this…on theground.” Before that time, the comments were not given in a positive or direct tone.If the first officer recognized the criticality of the situation, he failed to conveythese thoughts to the captain in a timely manner.
The flight engineer’s responsibility, aside from management of the aircraft systems, isto monitor the captain’s and first officer’s actions as they pertain to the performance ofthe aircraft, that is, takeoff, landing, holding speeds, and range of the aircraftconsidering time and fuel flow. Although he informed the captain at 1750:30 that anadditional “fifteen minutes is really gonna run us low on fuel here,” there isno indication that he took affirmative action to insure that the captain was fully awareof the time to fuel exhaustion. Neither is there an indication that, upon returning to thecockpit at 1801:39, he relayed any concern about the aircraft’s fuel state to the captain.Although he commented that 3,000 lbs of fuel remained, he failed to indicate timeremaining or his views regarding the need to expedite the landing.
The first officer’s and the flight engineer’s inputs on the flight deck are importantbecause they provide redundancy. The Safety Board believes that, in training of allairline cockpit and cabin crewmember, assertiveness training should be a part of thestandard curricula, including the need for individual initiative and effective expressionof concern.
In order to determine whether the captain had received all available assistance duringthe emergency, the Safety Board evaluated the actions of the company dispatcher and hisrole relative to the accident sequence. According to the tape of the conversation betweenthe captain, the company dispatcher, and company line maintenance personnel, the captainhad advised the dispatcher that he had 7,000 lbs of fuel aboard and that he intended toland in 15 or 20 min. The dispatcher then checked with the captain to ascertain a specifictime for the landing and the captain agreed that 1805 was “a good ballpark.” Thedispatcher, according to his interview after the accident, then relayed this landing timeand the aircraft’s status to the company personnel in Portland. He also stated that hisassessment of the situation was that of the fuel remaining upon landing would be low butthe landing could be made successfully at 1805. The Safety Board believes that, with theinformation given to him by the captain, the dispatcher acted properly and in accordancewith company procedures.
Crew Resource Management
In a number of airline accidents investigated by the Safety Board in the 1960s and 1970s, the Board detected a culture and work environment in the cockpit that, rather than facilitating safe transportation, may have contributed to the accidents. The Board found that some captains treated their fellow cockpit crewmembers as underlings who should speak only when spoken to. This intimidating atmosphere actually led to accidents when critical information was not communicated among cockpit crewmembers. A highly publicized accident in 1978 provided the impetus to change this situation.
On December 28, 1978, as a result of a relatively minor landing gear problem, a United Airlines DC-8 was in a holding pattern while awaiting landing at Portland, Oregon. Although the first officer knew the aircraft was low on fuel, he failed to express his concerns convincingly to the captain. The plane ran out of fuel and crashed, killing 10.
As a result of this accident and others, the concept of cockpit resource management, now called crew resource management (CRM), was born. Following pioneering work by the National Aeronautics and Space Administration (NASA), the Safety Board issued recommendations to the FAA and the airline industry to adopt methods that encourage teamwork, with the captain as the leader who relies on the other crewmembers for vital safety-of-flight tasks and also shares duties and solicits information and help from other crewmembers. United Airlines was one of the first airlines to adopt this concept, which is endorsed by pilot unions and is now almost universally used by the major airlines (as well as in other modes of transportation). The Board has also recommended and the FAA has acted to implement CRM for regional and commuter airlines.
The value of CRM was demonstrated on July 19, 1989, when a United Airlines DC-10 experienced a catastrophic engine failure over Iowa that destroyed the aircrafts hydraulic systems, rendering it virtually uncontrollable. The cockpit crew and a deadheading captain who was a passenger worked as a team to bring the aircraft down to a crash landing at Sioux City. Although more than 100 people perished, almost 200 survived a situation for which no pilots in the world had ever been trained.
1. The flightcrew was properly certificated and qualified for the flight.
2. The aircraft was certificated, maintained, and dispatched in accordance with Federal Aviation Regulations and approved company procedures.
3. Except for the failure of the piston rod on the right main landing gear retract cylinder assembly, with the resulting damage to the landing gear position indicating system switch, there was no evidence of a failure or malfunction of the aircraft’s structure, powerplants, flight controls, or systems.
4. The aircraft departed Denver with the required fuel aboard of 2 hrs 28 min for the en route flight and with the required FAR and company contingency fuel aboard of about 1 hr.
5. The aircraft began holding about 1712 at 5,000 ft with its gear down; this was about 2 hrs 24 min after it departed Denver.
6. The landing delay covered a period of about 1 hr 2 min.
7. All of the aircraft’s engines flamed out because of fuel exhaustion about 1815 – 1 hr 3 min after it entered into hold and 3 hrs 27 min after it departed Denver.
8. Fuel exhaustion was predictable. The crew failed to equate the fuel remaining with time and distance from the airport.
9. No pertinent malfunctions were found during examinations of the fuel-quantity measuring system.
10. A new digital fuel-quantity indicating system was installed on this aircraft on May 12, 1978. This was in accordance with a DC-8 UAL fleetwide retrofit program.
11. Evidence indicates that the fuel quantity indicating system accurately indicated fuel quantity to the crew.
12. The fuel gages are readily visible to the captain and the second officer.
13. The captain failed to make decisive timely decisions.
14. The captain failed to relate time, distance from the airport, and the aircraft’s fuel state as his attention was directed completely toward the diagnosis of the gear problem and preparation of the passengers for an emergency landing. The gear problem had a disorganizing effect on the captain’s performance.
15. Neither the first officer nor the flight engineer conveyed any concern about fuel exhaustion to the captain until the accident was inevitable.
3.2 Probable Cause
The National Transportation Safety Board determined that the probable cause of theaccident was the failure of the captain to monitor properly the aircraft’s fuel state andto properly respond to the low fuel state and the crewmember’s advisories regarding fuelstate. This resulted in fuel exhaustion to all engines. His inattention resulted frompreoccupation with a landing gear malfunction and preparations for a possible landingemergency.
Contributing to the accident was the failure of the other two flight crewmembers eitherto fully comprehend the criticality of the fuel state or to successfully communicate theirconcern to the captain.
4. SAFETY RECOMMENDATIONS
As a result of this accident, the Safety Board has issued the following recommendationsto the Federal Aviation Administration:
“Issue an Operations Alert Bulletin to have FAA inspectors assure that crew training stresses differences in fuel-quantity measuring instruments and that crews flying with the new system are made aware of the possibility of misinterpretation of gage readings. (Class II-Priority Action) (A-79-32)”
“Emphasize to engineering personnel who approve aircraft engineering changes or issuance of Supplemental Type Certificates the need to consider cockpit configuration and instrumentation factors which can contribute to pilot confusion, such as the use of similar-appearing instruments with different scale factors. (Class II-Priority Action) (A-79-33)”
“Audit Supplemental Type Certificate SA3357WE-D for completeness, especially in the area of system calibration after installation. (Class II-Priority Action) (A-79-34)”
“Issue an operations bulletin to all air carrier operations inspectors directing them to urge their assigned operators to ensure that their flightcrews are indoctrinated in principles of flightdeck resource management, with particular emphasis on the merits of participative management for captains and assertiveness training for other cockpit crewmembers. (Class II, Priority Action) (A-79-47)”
BY THE NATIONAL TRANSPORTATION SAFETY BOARD
/s/ JAMES B. KING
/s/ ELWOOD T. DRIVER
/s/ FRANCIS H. MCADAMS
/s/ PHILIP A. HOGUE
Investigation and Hearing
The Safety Board was notified of the accident about 2130 e.s.t. on December 28, 1978.The investigation team went immediately to the scene. Working groups were established foroperations, air traffic control, witnesses, human factors, powerplants, structures,system; maintenance records, weather, cockpit voice recorder, flight data recorder, andperformance.
Participants in the on-scene investigation included representatives of the FederalAviation Administration, United Airlines, Inc., Douglas Aircraft Company, Air Line PilotsAssociation, Professional Air Traffic Controllers Association, Association of FlightAttendants, International Association of Machinists, Multnomah County Sheriff’s Office,and Port of Portland.
2. Public Hearing
There was no public hearing held in conjunction with this accident investigation.
The captain was deposed at the Federal Aviation Administration’s Rocky MountainRegional Headquarters in Denver, Colorado, on March 6,1979. Parties to the depositionincluded representatives of the Federal Aviation Administration, United Airlines, Inc.,Douglas Aircraft Company, and the Air Line Pilots Association.
2/ A computer printout which predicted the amount of fuel that would be used between several identifiable en route points. The flightcrew was able to check the actual fuel used against the predicted fuel use at each of these points.