There simply is no useful argument to excuse a flight that descends below DH or MDA; you either have the runway or you don't. In this accident report, an aircraft decended below the glideslope, hit an obstruction, and still managed to continue to the airport. But although the pilot "lived to tell about it," an explanation eludes us.
August 29, 2001
This article appeared in the February 2001 edition of IFR Refresher and is reprinted here by permission.
From the very first day of our instrument training, we are taught never to descend below decision height (DH) or minimum descent altitude (MDA) unless the runway environment is in sight. It is a basic concept of instrument flight, and one that, when violated, often leads to a fatal accident.
The pilot of the aircraft involved in the accident that we are about to study was lucky. He walked away after his Cessna Caravan struck a utility pole 4,350 feet from the approach end of the runway. The flight was a contract freight operation with only the pilot on board. It departed Memphis, Tenn., at approximately 0400 EST on a February night in 1997 for a direct flight to the Cincinnati/Northern Kentucky Regional Airport (KCVG).
The weather at KCVG was reported as 700 feet overcast with 1/2 mile visibility in fog and drizzle. The wind was 200 degrees at four knots, and the surface temperature was 36 degrees. When the pilot was cleared to land on Runway 27, the controller told him that the RVR was 6,000 at the touchdown point and 3,000 at the rollout point. The midpoint RVR was not available. After the accident, the pilot told investigators that he picked up moderate icing, along with turbulence, sleet and snow, during the descent into the airport.
(Click for larger version of approach plate)
Taking a look at the approach plate for the ILS Runway 27 reveals that an airplane that is on the glideslope at DH will be four-tenths of a mile from the runway. With the visibility being reported at 1/2 mile that morning, it does not appear that there was a lot of room for error. The DH on that approach is 200 feet above the surface, or 1,075 MSL. If the aircraft's glideslope receiver or display equipment should become inoperative, the MDA for the approach becomes 1,420 feet MSL, or 545 feet above the surface.
When the Caravan pilot checked in with Cincinnati Approach he was at 9,000 feet. He immediately asked for lower because he was getting ice accumulation, though he did not specify the type or intensity of it.
The Cincinnati controller cleared him to 5,000 feet, and the pilot reported that he was out of the ice at 5,500 feet during the descent. The temperature at 5,000 feet was -1° C. He said that he was in snow at that altitude. The aircraft initially was vectored for Runway 36, but during the vectors the active was changed to Runway 27. The pilot acknowledged the runway change and the sequence that made him number four in line for the new runway. The pilot again asked for lower and was told to descend to 3,500 feet.
At a point one mile outside of the BLOCK intersection, 7.9 miles from the end of the runway, the pilot was cleared for the ILS approach. The controller instructed him to maintain 2,500 feet until established on the localizer. From this point until the aircraft landed on Runway 27 there were no calls that indicated that the pilot was having problems with the aircraft or that there was anything abnormal about the approach.
Witness Hears Strike
There was a witness near the accident scene, though his statement doesn't say exactly where he was located. He said, "I heard it hit something, then I heard him get back on the throttle. I thought he crashed, but when he hit, it nosed up and continued on toward the runway. He got so low the green and red lights on the plane disappeared. That's when I thought he crashed.
"He did come back up. At the time he hit the pole and wire he was idled way down. When he hit he throttled back up quickly and the engine sounded like it backfired a couple of times. The weather was foggy and misting."
I don't know what the weight of the aircraft was that morning, but if the witness is correct that the airplane descended closer to the ground after striking the pole, speculation would lead us to assume that the power of the Caravan's turboprop is what saved it. Had that airplane been powered by a piston, chances are that it would not have had enough power to recover from the strike.
The aircraft continued to the runway after striking the pole, landed, and the pilot taxied it to the freight ramp. No report of the accident was made for another two hours after the landing occurred.
Investigators found 192 feet of power line wrapped around the landing gear of the aircraft. The left aileron and left wingtip were missing from the aircraft, and they were found near the pole that was struck. The left main landing gear strut and left flap also were damaged. The pole was located 4,350 feet east of the approach end of the runway, about 100 feet to the left of the centerline, and stood only 27 feet above the surface.
The 29-year-old pilot held a commercial ticket with instrument and multi-engine ratings. He also was a certified flight instructor. He had 3,325 hours total time with 720 hours in the Caravan and 305 hours of instrument time, including 230 hours of actual instrument. He had flown 85 hours in the 30 days preceding the accident.
The pilot had the experience to be flying that night, though the radar archives detail a shaky ride down the glideslope. The airplane stopped descending at 1,900 feet for about 13.8 seconds, again at 1,500 feet for the same time, and it leveled off at 1,000 feet for about 9.2 seconds just before the loss of radar data.
In a statement to investigators, the pilot said, "After intercepting [the] localizer [I] continued ILS until approximately DH, where I then acquired the runway end strobe lights and descended to land. Somewhere during this descent, [I] felt [a] jolt to the aircraft but proceeded with the normal landing. Upon shutdown [I] noticed damage to the aircraft."
In his statement, the investigator who interviewed the pilot stated that "competency of the FAA-certificated airman is a factor. In fact, with all the evidence, facts and statements, this remains the sole factor in this accident. There is no reason why a pilot of an aircraft should ever be 27 feet above the ground over 4,000 feet from the runway in IMC conditions on a precision approach unless something was wrong. The PIC in his statement, and from my personal interview with him on the day of the accident, never indicated or even implied that anything was abnormal."
Why So Low?
The question that we have to ask is why was the pilot so low that night when the visibility was so poor?
Could the turbulence he reported have been a factor? He didn't bring the issue up in his statement, and there is nothing in the report to suggest that any other aircraft flying the approach that night suffered from turbulence severe enough to render them unable to remain on the glide path.
Was he guilty of deviating from FAR 91.13(a) as the investigator suggested in his report? That's the FAR that every pilot who gets violated for almost anything gets slapped with. The investigator said that the pilot excessively and carelessly deviated from the approach procedures to be so low as to strike the utility pole.
It would appear that since the pilot had no explanation of the course of events, he did fly his airplane in a careless and reckless manner. Certainly he knew that he was below the glideslope, and the radar data does not indicate that he attempted to climb back to it. It's possible that the pilot had some ground contact below him but not enough forward visibility to see the runway. He told the investigator in his statement that he had the runway environment in sight, but the investigator clearly did not believe him.
Perhaps he got below the glideslope inadvertently and tried to fly the airplane visually. The fact that he hit the pole 27 feet above the surface would indicate little or no forward visibility.
We know it took a great deal of power to keep the airplane flying after it struck the pole. The pilot told the investigator that the entire approach was normal except for a jolt that he felt somewhere along the descent. He didn't say anything about having to add power to overcome it or that it affected the airplane's flying stability. That tends to make one think that he knew exactly what he was doing, though he probably didn't understand how close he was to the ground until after he was told how high the pole was above the surface.
Not surprisingly, the NTSB attributed the accident to the "pilot's failure to maintain the airplane on the ILS glideslope, which resulted in a descent below the glide path." That should give us all pause to reflect on our own operations in low-visibility conditions and the intentions that we have before we begin the descent down the glideslope.
Sometimes commercial operators are under a fair amount of pressure to perform. This particular airplane was owned by Federal Express and leased to the pilot's employer, who flew it under contract to FedEx. Perhaps the pilot felt a sense of obligation to get into the Cincinnati airport that night, but everything was on his side had he flown the approach as published.
The ceiling was well above the 200-foot AGL DH. The visibility was at the minimum for the approach, but the RVR at the touchdown point was better than a mile. Chances are that the pilot would have had no problems locating the runway from a normal approach. In other words, there was no reason for him to bust minimums to make the landing that night.
For that reason the investigator called the pilot's competency into question. Not seeing any other explanation, it appears that he felt that the pilot botched the approach and descended below DH long before he should have, either intentionally or unintentionally. In either case, it was his view that enforcement action was necessary, and his report makes it clear it was taken.
The Buck Stops at DH
We all must have locked into our brains the fact that we never will descend below DH or MDA unless the required sightings are made during the approach. We should have the DH fixed in memory as we begin the descent down the glideslope, and we should be mentally ticking off how high above DH we are. If we get off the glideslope, we should make an attempt to get right back to it; however, a full deflection is an automatic go-around.
There is no question that the Caravan pilot had a full deflection of his glideslope needle that evening. At the point where the airplane struck the pole 27 feet above the surface, it should have been 290 feet above the surface.
This pilot was one of the lucky ones. Usually when we read about this type of accident, the airplane and all aboard are lost. Keep that in mind as you get ready for your next IFR trip. Decision heights and minimum descent altitudes are there for a reason. The reason is safety. You do not have the right to decide that you can conduct a safe operation below either if you do not have the approach lights or runway environment in sight.