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Volume 26, Number 15b
April 10, 2019
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737 MAX Update: Stocks Downgraded, Orders Plummet
Marc Cook

Boeing released sales data for the 737 MAX line that reveal there were no new orders for the troubled jet in March, and simultaneously said that deliveries and orders for all 737 models fell in the first quarter. Overall orders were down by nearly half, to 95 from 180 in the first quarter of 2018.

After delivering 184 aircraft in the first quarter of 2018, Boeing released just 149 this year; of those 89 were for all variants of the 737. Boeing has halted deliveries of all MAX variants until software updates can be completed and approved and announced earlier that it would cut production of the MAX from 52 to 42 units a month.

Boeing has orders for more than 5000 of the single-aisle airliner on the books, though several airlines have indicated their intention to cancel or slow the delivery of the MAX. Indonesian airline Garuda has officially canceled its order of 50 MAX aircraft.

On Monday, Wall Street downgraded both Boeing’s and Southwest Airlines’ stock based on the continuing 737 MAX saga and the continuing capacity disruptions to carriers using the troubled jet. Boeing’s stock is currently trading at around $370 a share from a high of $440 in late February. Market analysts say the company’s slide has obliterated more than $20 billion in market capitalization. Bank of American Merrill Lynch on Monday changed its recommendation on Boeing from buy to neutral, resulting in a 4% drop in stock value that day. Analysts are now predicting a much longer recovery period for Boeing, believing that the MAX will remain grounded for another six to nine months. And that’s likely to be in the U.S. alone. Currently, Canada, China and the European Union are signaling that they want to independently verify the aircraft before permitting it to fly in their countries again.

Spirit AeroSystems, which builds components for the 737 MAX, saw its stock prices fall from a recent high of $99 a share on March 1 to $84 a share today, is among several contractors likely to feel the pinch of the 737 MAX slowdown.

The same can be said for domestic airlines having the 737 MAX in their fleets. Although the MAX makes up only 4% of Southwest’s fleet, market analysts believe the extended grounding of the aircraft will negatively impact the airline’s schedule and revenue. Southwest itself said that it expects to lose $150 million in the first quarter due to a variety of factors including the MAX grounding.

American Airlines has announced that it will cancel all of its MAX-based flights through June 5. The airline has 24 of the aircraft expected to fly roughly 90 flights a day.

AVweb Insider: MAX And The Press
Paul Bertorelli

If Boeing wanted bad press for itself, it couldn’t have done any better than the unfolding drama of two hull losses of the 737 MAX 8 within five months and the slow drip of daily coverage on what crash investigators are learning. Overall, I give the daily press a B+ for its coverage. It has generally been fair, accurate and technically competent.

But as I write this, there’s a story circulating in print and broadcast that appears to be flat out wrong in the detail that’s important to this kind of coverage. In fact, reader Don Dillman emailed me to say that we—well, me—got the headline wrong on a recent story. It said that the Ethiopian Airlines pilots followed Boeing’s recommendations on disabling the MCAS after experiencing uncommanded trim. But that’s not correct. They initiallyfollowed Boeing guidelines by using the stab trim cutout switches, but then—inexplicably—re-engaged electric trim, and thus the MCAS stall protection subsystem that appeared to be causing the runaway trim in the first place.

I explained this correctly in the story, but I couldn’t make it fit in the headline. I went back into the story and tweaked it. We can do that in online publishing. In newspapers, it awaited the second edition or the next day’s fish wrapper. But broadcast outlets, including NPR, are still getting it wrong, without the nuance of the pilots using the cutouts and then re-engaging them for reasons we can’t, at this point, grasp.

Just to review, by requirement of AD, following the Lion Air MAX crash in Indonesia in October, Boeing sent out a detailed bulletin explaining how to handle an MCAS abnormal, including what indications pilots should expect to see. These included continuous or intermittent stick shaker on the affected side only, an airspeed and or altitude disagree warning, a minimum speed bar and increasing nose-down stick force.

The response is typical of a runaway trim condition. Boeing said to disengage the autopilot and use electric trim as required. If relaxing the control column causes the trim to move, set the electric trim cutout switches to disable the trim. If the trim still moves—I’m not sure how it could—then the pilots can hold the trim wheels and trim by hand. As we’ve reported, the 737 MAX 8 is a bit of a throwback, in that it has large trim wheels on either side of the pedestal between the pilots. It can be manually trimmed, albeit somewhat laboriously. Either way, Boeing said to leave the stab trim switches in cutout for the remainder of the flight.

If The Wall Street Journal’s reporting on the FDR output is correct, the Ethiopian pilots first followed the procedure by using the trim cutouts. But then they re-engaged the electric trim, allowing the ostensibly malfunctioning MCAS subsystem to get at the stab trim and start cranking the nose down again. But this is not what Boeing recommended, ergo, they didn’t follow the procedure.

This is an important detail because ignoring it suggests that there’s something seriously amiss that isolating the electric trim can’t correct. It’s not impossible that this is the case, but there’s no evidence to suggest that it is. As journalists, we owe it to our readers to get this as right as possible. Including the headlines.

Note to Readers: No, it's not something you said. Because of persistent denial of service attacks against AVweb, we're moving the site to another platform. The commenting section will be unavailable for a time. We apologize for the inconvenience, but the site will be better for it in a week or two. In the meantime, if you have a comment, email us and we'll append it to the blog.

From one armchair accident investigator to another…

I just finished reading the Preliminary Report from the Ethiopian AIB. I have come to the astonishing conclusion that one or both of the flight crew did not understand once the stab trim cutout switches are in cutout, you MUST use the manual trim wheel to adjust the stabilizer trim. At 41:50, the First Officer should be cranking away on the manual trim wheel and not fussing with the electric trim switches on the yoke. If you zoom in and study the chart on page 26, you will find that at no time during the flight was the stabilizer trim adjusted using the manual trim wheel.

Contributing Factors: I suspect there is confusion about the meaning of the term “Use Manual Trim”. Boeing thinks it means use the manual trim wheel. The First Officer seems to have thought it means use the trim thumb switches on the yoke. When the trim switches didn’t work, someone turned the electric trim system back on in a last ditch effort to regain trim control. Unfortunately, that let the MCAS devil back into the cockpit. Also, the final paragraph of the Runaway Trim procedure can lead one to believe the using electric trim to correct an unexplained out-of-trim condition is an acceptable procedure. Paragraph 3 says leave it in cutout for the remainder of the flight, but the final paragraph tends to conflict. It would probably be best if Boeing deleted that final paragraph.

Jeff Moffatt

Your post says “Boeing said to disengage the autopilot and use electric trim as required.”So what wasn’t clear to me was:

  1. Why is the pilots’ decision to use electric trim “inexplicable”
  2. We have been told that MCAS is only active with the autopilot off, so why “disengage the autopilot”

Take it for what it’s worth – I’m sure you’re getting tons of half-baked armchair feedback.

Aarohi Vijh

Most of the mail we're getting is fully baked, as are your questions. As noted in today's story, the pilots already had disagree alerts and stick shaker on one side before engaging the autopilot. I'm told by pilots consulting with us that enaging the autopilot at that stage is not good practice.

Your reporting is usually very objective, to the point and factual. But I have to take issue with many of the strong definitive-sounding statements you make in today’s article about the 737 MAX.

Title: "Investigators Fault MCAS In Ethiopian Crash”. Absolutely not. For starters, the entire preliminary report by the ECAA does not mention MCAS at all. Search for it. You will not find MCAS anywhere in that report. They refer to automatic aircraft nose down trim, but not MCAS. Presumably the AND could be caused by MCAS or some other subsystem. Yet to be determined. So no, they did not fault MCAS. They do not even mention MCAS. Even the Minister was asked repeatedly about MCAS at the press conference, and never ever blamed MCAS, only said that the pilots were unable to override the system. Further, this is a preliminary report. The investigators do not identify causes, nor contributing factors. They are not assigning blame. Not yet. Your title is way too sensationalist and not at all reflective of what the investigators have said.

Then, in your article you say that "the data also showed the pilots re-engaged electric stabilizer trim” and that “they […] inexplicably re-engaged electric trim” and that "pilots using the cutouts and then re-engaging them for reasons we can’t, at this point, grasp". No, the data does not show that. Not the data is in the prelim report, anyway. It shows that manual electric trim again became operative, which suggests that the circuit was reestablished. It does not say that the pilots took any action to reestablish that circuit. You could write that you surmise that the pilots may have re-enabled the system, but you should not say definitively that the pilots did, nor should you claim that the data shows that they did. Because it doesn’t.

Then you claim that "the pilots can hold the trim wheels and trim by hand”. Perhaps. Theoretically. At the gate. Notice here that these guys carried a great deal of speed and the aircraft was very out of trim, causing great aerodynamic forces on the out-of-trim tail section. It is quite possible that a pilot would not have the physical strength to turn the wheel by hand. It is also possible that neither pilot had any free hands to go crank that wheel, because both were pulling on the columns just to keep the nose up. Notice that the report states "At 05:40:44, the Captain called out three times “Pull-up” and the First-Officer acknowledged”. "At 05:41:30, the Captain requested the First-Officer to pitch up with him and the First-Officer acknowledged.” "At 05:43:04, the Captain asked the First Officer to pitch up together and said that pitch is not enough.” This to me indicates that the captain (pilot flying) was not able to exert enough force and requested help from the second column. Also from the report "The data indicates that aft force was applied to both columns simultaneously several times throughout the remainder of the recording”. So there. Is it quite possible that the guys were exerting all their force on the columns to keep it flying and had no free hand to crank the trim wheels. “The pilots can hold the trim wheels and trim by hand” is all nice and good at the gate, but perhaps not here. Further, if they really need to trim up and had no hands to turn the trim wheels, it is quite possible that, as a last resort, they would reenable electric trim so that could trim up electrically. This goes back to our previous paragraph and perhaps explain why they may have re-engaged the electric trim, those famous "reasons we can’t, at this point, grasp”.

Let me quote a famous certain Paul Bertorelli: "As journalists, we owe it to our readers to get this as right as possible. Including the headlines.” Please do. Thanks.

Paulo Santos

We'll have to agree to disagree. The preliminary report clearly says the pilots re-engaged electric trim to moved the trim nose-up from 2.1 to 2.3 units.

--Paul Bertorelli

Another facet of this preliminary report that the media is missing – and I don’t fault most them as they are often not aviation experts nor qualified B737 pilots – is that from the moment the aircraft lifted off it had an unreliable airspeed emergency. Disparity between the Captain and FO airspeed indicators, the stall warning (stick shaker), etc. The crew of that Ethoipean flight did not do the recall (memory drill) for that emergency which would later come back to haunt them.
The first thing you do is set the attitude appropriate for the phase of flight (in this case 10 degrees on the attitude indicator) and an appropriate power setting (for the Max I think it is 85%). They did not do this and as we will see later, with the thrust at 100% the aircraft goes really, really fast and is nay impossible to trim.
The other questionable action is not leaving the aircraft in the same configuration (flaps extended) and return to Addis Abba (a maintenance base) to get the unreliable airspeed fixed. Why one would want to continue on a 1 hour flight in stick shaker is beyond me.
Nevertheless, the flaps were selected up and the MCAS failure appeared (which might have been associated with the unreliable airspeed). As the preliminary report states, the airspeed reached between 305 and 340 kts on the RH airspeed indicator and 20-25 kts more on the LH airspeed indicator; meanwhile the engines are at 100% N1 thrust.
As any aviator would know, trim forces increase with airspeed at roughly the square of the velocity; twice the airspeed, four times the aerodymanic force, all things being equal.
Rather than flying the aircraft which includes managing the speed, the aircraft was racing around at Vmo (velocity max operating) with the overspeed clacker going. In addition to not dealing with the thrust right after take-off and the unreliable airspeed indication and setting 85%, 100% N1 caused the speed to increase, making manual trim difficult if not impossible.
As a general observation, I think the media will have to be on the lookout for national bias in this accident as well as the Lion Air one too. Both accidents point directly at professional pilots not being able to handle irregularities that should be easily handled.
Ed McDonald
From a 14,000 hour pilot with 10,000 hours in B737 here. I commend you for your last article and would agree with Ed MacDonald's post. On the Lion Air accident, we can give the crew some slack for dealing with an unknown fault at the time which affected several aircraft systems.
However, in the Ethiopian accident, the crew had all the symptoms of an MCAS failure but did not apply the recommended procedure by Boeing. First the crew wasted precious time trying to engage the autopilot, while the checklist calls to disengage it. Retracting the flaps was also a big, big mistake, which enabled MCAS logic to kick in. If you have stick shaker and IAS disagree alerts, leave the flaps at 5 and come back to land and go have a beer later.
The checklist calls for the Stab Trim Cut Out switches to be left in the OFF position for the REMAINDER OF THE FLIGHT, to Trim the aircraft manually and "ANTICIPATE TRIM REQUIREMENTS. " This is a key statement here. The crew never touched the throttles which were left at takeoff thrust (94.1% N!) allowing the aircraft (which was now level and sometimes descending) to accelerate beyond VMO, making manual trim very difficult if not impossible, due to high aerodynamic forces.
Also, Boeing is skeptical at the possibility of an Ethiopian biased report as they try to protect themselves. A complete FDR and CVR superimposed transcript will reveal exactly what was said and done at specific times in that cockpit. At this time, from the released FDR transcript (CVR was not released) we can only suspect that in a last act of desperation, one of the pilots re-engaged the Stab Trim Cut Out Switches which doomed the flight.

Eduardo Letti

Great work on Max articles. Aviation and investigations can be harsh on pilots. Here are just two examples of "scary as shit" moments where pilots were judged harshly. In the second one, fatally. Perhaps it helps inform the Max conundrum.


Bill Tuccio

I read carefully your report on cockpit activities during the Ethiopian MAX crash and conclude mostly that Boeing does not have a clue what is going on with the aircraft. I think the cg was far enough aft of the neutral point to make the aircraft violently unstable in both the pitch-up and pitch-down senses. Initially the pilot tried to fight the divergences with porpoising, but in the end the pitch-down moments on the fuselage, wings, engine cowls, and tail were too great to be much affected by the pilot's efforts to counteract them with either stabilizer or elevator.

Boeing engineers can and should replicate the event by sliding a paper clip back and forth along a paper airplane. Based on my experience teaching aerodynamics at UCLA and UA up to 1998, I doubt they have the mathematical acumen to understand the fundamentals.
Steve Crow

China To Join FAA 737 MAX Review Panel
Marc Cook

China, the first country to ground the Boeing 737 MAX after the fatal crash of Ethiopian Flight 102 last month, is set to join the FAA’s review panel. Former NTSB chairman Christopher Hart is running the program, which is expected to run for about three months. The FAA agreed to create an international review board last week as the aviation authorities in several countries indicated skepticism at the certification process that approved the 737 MCAS stability system in the first place.

China joins the European Aviation Safety Agency (EASA) and regulators from Canada, UAE, Australia, Brazil, Singapore, Ethiopia and Indonesia on the review panel. Of the 371 737 MAX aircraft in circulation, Chinese airlines operate 97 of them. Southwest Airlines has the largest U.S. fleet, at 34 aircraft.

Detonation Concerns Behind Superior's Buyback of XP-400 and XP-382 Engines
Marc Cook

Last month, Superior grounded the XP-400 and XP-382 Experimental-class engines after crankshaft breakages were believed to be set off by detonation. Approximately 150 engines were affected. At the time, the company asked those already flying the engine to immediately ground the aircraft and for those still in construction to return the engines.

Superior is refunding the purchase price of the engine as well as paying for return shipping. “We’re sending customers a crate and having it picked up for them,” said Superior’s VP of Sales and Marketing Scott Hayes in this podcast from Sun ’n Fun. “We’re about a third of the way through contacting owners now,” he said.

Unfortunately for both builders and those who were flying these engines, Superior is not paying for the effort of engine removal or any costs incurred changing to a different brand or configuration of engine. This is an especially knotty problem with the angle-valve XP-400, whose only comparable engine is either the Lycoming IO-360 or IO-390. Hayes says that a replacement from Superior for the XP-400 is at least a couple of years away. “The buyback program is eating a lot of our R&D funds,” he says.

The XP-382, a hopped-up version of the parallel-valve IO-360, is a close fit for a wide range of available engines, though its claim of 200 HP will be tough to match with most versions of this platform.

Regarding the XP-400, Hayes says, “We’ve seen pistons that are free of any deposits whatsoever. What that tells us is that we’re on the edge of incipient detonation. Because you should have some combustion deposits. People think that’s awesome but it’s the sign of an issue.” It’s not compression ratio alone, as the XP-400 has a listed 8.9:1 ratio, the same as the Lycoming IO-390. The key difference, beyond the inevitable detail differences from the way Superior and Lycoming make cylinders and crankshafts, is that the XP-400 is essentially a stroked version of the venerable IO-360, where the Lycoming IO-390 gets its increased displacement through a marginally larger bore.

When asked about the effect of ignition timing on these detonation margins, Hayes pointed out that “the advanced timing that some ignition systems can get to—some can go out to 32 degrees—you can get into an area that’s no man’s land. But we’ve also seen some traditional mags that were advanced and we’ve seen similar issues. So I think you need a little more margin of safety. When we originally started off, these engines were timed at 25 degrees. We did a whole bunch of studies around it and if we reduced to 20 [degrees], the pressures in the cylinders go down significantly.”

Superior did publish a service bulletin in January recommending owners retard the ignition timing of the XP-400 from 25 degrees to 20. (Incidentally, that’s the same recommendation Lycoming has for the certified version of the IO-390.) It also recommended the most conservative of ignition curves for electronic ignitions.

Further confusing the issue is that one of the engines that failed was marked for the 20-degree ignition advance but “we couldn’t verify where the timing was set,” said Hayes. “The data plate said one thing but the physical evidence said something totally different.” It would not be the first time a magneto was mis-timed or intentionally advanced, which is permissible under the experimental rules.

“We’ve done a ridiculous amount of metallurgy around the crankshaft itself and found absolutely nothing,” says Hayes, including subsurface issues. He goes on to say that the engine was subsequently highly instrumented with pressure transducers reading the combustion chambers, running it in various configurations, and “we were unable to come up with a specific issue other than seeing signs of incipient detonation,” he said.

To a great degree, Superior’s buyback program and general approach to the issue has been greeted positively by the homebuilt community.

Lt. Col. Dick Cole, Last of Doolittle's Raiders, Passes at 103
Marc Cook

And then there were none. The last surviving member of the Doolittle Raiders died today at the age of 103. Retired Lt. Col. Richard E "Dick" Cole was Jimmy Doolittle’s copilot in the lead bomber during the 1942 raid on Tokyo. He was there by chance, as Doolittle’s original copilot became ill before the mission launched.

Cole was interviewed by in 2016 about the raid, and was asked how he felt to help lead the bombing mission on Tokyo. “I guess I felt the same way as the rest of the people aboard,” he told HistoryNet. “There was a lot of jubilation and so forth, and then it got kind of quiet as people realized what they were getting mixed up in. But nobody jumped ship and nobody bailed.” Cole described what it was like just before the bomb run. “As we were flying over the Japanese countryside, I was impressed by the beauty of the place, and as we came over Tokyo I was amazed that nobody was jumping us and that there was no ack-ack. This was the first time that any of us who were on the raid had seen combat, and I thought, ‘So far, so good.’"

Launched on April 18, 1942, the so-called Doolittle raid was a success mainly in the sense that it boosted morale in the dark days after Pearl Harbor, and was a dramatic show of force demonstrating that U.S. air forces could attack mainland Japan. Sixteen B-25 Mitchell bombers were launched from the USS Hornet that Saturday morning, having been modified to carry significantly more fuel than normal, at the expense of defensive weapons. The raid was conceived with no way to return, so the bombers were expected to continue into China. All crash landed but 77 of the 80 crewmen survived the raid.

Carl Dietrich Out, Chao Jing In As Terrafugia CEO
Marc Cook

Terrafugia has named Chao Jing as its new CEO, replacing co-founder Carl Dietrich. Described as “a professional business leader with extensive experience working in international companies,” Jing will help drive Terrafugia toward its first deliveries this summer.

According to the company, the new CEO will also have a fresh CFO, Huaibing Wang, who has “over 20 years of experience in various finance leadership positions in both automotive and industrial businesses.” Of his departure, the company offered its “appreciation and thanks” to Dr. Dietrich for seeing Terrafugia through its initial growth.

Such a change of management structure is little surprise since it was purchased by Chinese automaker Geely (also owner of Volvo and Lotus) and signals a clear shift from primarily development into manufacturing.

The Terrafugia Transition made its first public flights in 2013. The current model is a folding-wing two-seater powered by a Rotax 912iS and a top speed of 100 MPH. Last year, Terrafugia announced updates for the production machine, including Dynon avionics and a BRS whole-airframe parachute. Prices have not been released.

Terrafugia apparently has big plans for flying cars. The TF-2 concept (see video below) is an eight-motor eVTOL that could form part of a multi-mode transportation system.

The Mysteries Of Altimetry
Luca Bencini-Tibo

At one a.m. local time on November 11, 1995, an MD-83 was making a VOR instrument approach to RWY 15 at Bradley Field (KBDL) in Windsor Locks, Connecticut, when it struck trees on a ridge line about 2.65 miles from the runway threshold. Before we continue, let’s review a few altimeter terms.

Altimeter Settings

There are three types of “altimeter settings” and we’ll refer to them using ICAO terms based on the Morse “Q” codes:

  1. “QNH” is the altimeter setting that we get from ATIS and in METARs.
  2. “QNE” refers to altimeter setting of 29.92 IN of Hg above 18,000 feet MSL (in the US) for flight levels rather than altitudes.
  3. “QFE” is an altimeter setting that allows the altimeter to read zero feet on the airport surface.

Today, typically only gliders set the altimeter to zero feet AGL on the ground. Previously it was common for airlines (including the one involved in the Bradley incident) to have one of two altimeters set to QNH and the other to QFE. With QFE, most ILS CAT I approaches would indicate 200 feet at DA/H.

It was a dark night at Bradley; winds were gusty with heavy rain. The relevant weather issue in this incident was the atmospheric pressure that was falling rapidly. The flight was using the altimeter with the QFE setting and it was set 76 feet too high—meaning that the airplane was actually 76 feet lower when it read zero feet.

The NTSB report cited descending below the MDA (actually the MDH) without adequate visual runway references as the probable cause. A contributing factor was the “failure of the BDL approach controller to furnish the flight crew with a current altimeter setting and the flight crew’s failure to ask for a more current setting.”

Even though using the QFE altimeter did not directly result in the accident, the airline involved abandoned the practice of using an altimeter set to QNH and another one set to QFE. Only QNH would be used below 18,000 feet MSL.

The MD-83 successfully landed at Bradley but suffered extensive damage. One of the 72 passengers received minor injuries during deplaning; none of the crew members were injured. (The VOR approach is no longer available at Bradley).

Value Of The Altimeter

When in IMC, out of the six-pack instruments or its equivalent in glass, the altimeter is perhaps the most important one followed closely by the attitude indicator. The altimeter provides vertical clearance from the ground when flying at charted and assigned altitudes and horizontal clearance with other airplanes.

Also, single-engine airplanes typically don’t have a backup for an altimeter unless the GPS-derived altitude is used, which is not accurate. In other countries, usually two altimeters are required for IFR.

Luckily, altimeter failures are not common; the most likely failure mode is a clogged static port. Some airplanes have two static ports, one on each side of the fuselage to equalize the static pressure during uncoordinated flight. Most planes also have an alternate static source vented to the cabin or to an unpressurized part of the airplane. (Not to be confused with an alternate air source for the engine intake.)

Aneroid (pressure) altimeters are essentially barometers. It is an indirect measurement instrument since it senses atmospheric pressure but provides the units in feet rather than pressure.

The case is vented to the “outside” through the static port; as pressure in the case changes, the aneroid wafers expand or contract, and through a series of gears, moves the pointers on the face. The primary factor impacting the accuracy of an altimeter is atmospheric pressure. It was not until 1928 that Paul Kollsman developed the “sensitive” altimeter, which could be adjusted to reflect atmospheric pressure—what we call “altimeter setting.” Today we honor him with the Kollsman window found on all altimeters.

Regulatory Requirements

For IFR operations, the well-known FAR 91.411 applies: “Within the preceding 24 calendar months, each static pressure system, each altimeter instrument, and each automatic pressure altitude reporting system has been tested and inspected and found to comply with appendices E and F of part 43 of this chapter;” (Note Appendix E of Part 43 goes in great detail of how to do the inspection by an approved shop).

Of course, the inspection and results need to be documented in the airplane’s logbook. Since our instrument student days, we know that when on the ground we set the current altimeter setting in the Kollsman window: it should be plus-or-minus 75 feet from the field elevation. If it is, we are good to go, but we don’t make any correction to the altimeter setting. If it isn’t, then are we grounded for IFR.

The 75-foot discrepancy is not in the regulations, it is in AIM 7-2-3. In case of a mishap involving an altimeter, let’s not forget one of the catch all regulations: FAR 91.7: the need to “operate a civil aircraft unless it is in an airworthy condition.” If the altimeter is outside the acceptable 75-foot range, this might be interpreted as not being airworthy.

To test if we are complying with the 75-foot tolerance, we need to know the airport elevation. Of course, we can find the elevation on the airport diagram or on an approach chart. The airport elevation is the highest point of an airport’s usable runways. But be careful. A few years ago, runways 10R and 28L of Fort Lauderdale/ Hollywood International (KFLL) were extended and, due to space limitations, runway 28L threshold area goes over highway US 1; cars now pass beneath the runway. An upslope of the runway was required. Suddenly, the airport elevation went from about 8 feet to 65 feet. Well, 65 feet is the elevation of the threshold area of runway 28L.

Unless you are at the threshold of runway 28L, use the elevation of about eight feet as reference for the altimeter check: -67 to 83 feet. Be sure you have a good idea of the correct elevation on the airport where you are making the check.

Types Of Altitudes

What adds to the complexity of altimetry are different “types” of altitudes:

Indicated Altitude is altitude shown on the altimeter using the local altimeter setting.

True Altitude is the actual height above MSL. Elevations of airports, obstructions, mountain tops are true altitudes.

Pressure Altitude is what the altimeter shows when set to 29.92 inches of Hg. It defines flight levels and is used in the US when flying above 18,000 feet MSL. It is also an input in determining density altitude and true airspeed.

Density Altitude is pressure altitude corrected for non-standard temperature and it is the altitude the airplane “feels”—engines and airfoils. It also determines performance such as take-off distance and climb rate. It also corrects indicated airspeed taking in consideration temperature and pressure altitude to compute true airspeed.

Absolute Altitude is really a height, an AGL value. Examples are: Height Above Touchdown (HAT) and Threshold Crossing Altitude (TCH).

Altimetry Errors

Altimeters have several errors but we will focus on two potential errors: non-standard pressure and temperatures. When we fly below 18,000 feet MSL, we fly using indicated altitudes. The safety problem arises when flying from an area of higher pressure to an area of lower pressure without adjusting the altimeter setting. The well-known “high to low, hot to cold, watch out below” applies. FAR 91.121 states that below 18,000 feet MSL, the altimeter setting needs to be set to a station along the route “within 100 NM of the aircraft.” When pressure is changing rapidly upwards and downwards (for example when crossing a front), the altimeter should be reset more frequently and to the nearest reporting station.

When going to a lower-pressure area from a higher-pressure area without updating the altimeter setting, the indicated altitude will result in a lower true altitude. It could impact ground clearance and create opposing traffic conflict.

Part 2 will address the impact of altimetry during approaches to certain airports when the temperatures are extremely cold.

Read Part 2

NTSB reference to BDL incident: DCA96MA008

Luca Bencini-Tibo ATP/CFII, is a FAASTeam Lead Rep, aircraft owner and is a graduate of MIT with an MBA from Harvard.

This article originally appeared in the November 2018 issue of IFR Refresher magazine.

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Lycoming 'When can an engine give you 200 extra flying hours?'
Video: AirCam Gen-3 Triple Seater
Marc Cook

Phil Lockwood explains the differences in the new Gen-3 AirCam first shown at Sun 'n Fun 2019. More powerful engines allow for a gross-weight increase and the possibility of a third seat. Sorry, back-seat drivers; there are only controls in the front two seats!

Video: That's All Brother At Sun 'n Fun
Kate O'Connor

The historic C-47 "That's All Brother" stopped in at Sun 'n Fun 2019 before heading overseas this summer as part of the D-Day Squadron, the American contingent participating in the Daks Over Normandy flyover which will be crossing the English Channel to commemorate the 75th anniversary of D-Day on June 6, 2019. Pilot and member of the Commemorative Air Force Tom Travis discussed the significance of the aircraft, its recovery and restoration, and the reasons behind maintaining warbirds with AVweb at the show.

Accident Probe: Full Frontal
Joseph E. (Jeb) Burnside

During my primary training, one of my mentors was fairly adamant about the threat of weather. If I had the skills, wisdom and experience, and the airplane was in good condition with sufficient fuel, he would point out, the only other big thing that could be a safety-of-flight problem was weather. The primary concerns he expressed included thunderstorms and their turbulence, low ceilings that engendered scud running and fog that blanketed the airport.

As I gained more experience, including an instrument rating, my weather understanding never really progressed beyond those big three hazards, plus airframe icing as I logged more IMC. It was more a matter of convincing myself I didn’t need that additional knowledge—I’d already made up my mind that I wasn’t going to fly in those conditions—than an outright refusal to learn more. On one of my first forays into IMC as the pilot in command, I learned a hard lesson on cold fronts.

The thing about cold fronts is they can combine many of the aforementioned weather hazards into a single package. As the colder, denser air slides under the warmer mass, lifting occurs. And it can be enthusiastic. In many situations, the only reasonable thing to do is land and let the cold front pass, then launch into cooler, clearer air.

Warm fronts, as their name implies, typically mean warming, stable, slow-moving air, along with lowered visibilities and perhaps an occasional air-mass thunderstorm.

The thing is, aviation meteorology is pretty good at identifying and predicting both kinds of fronts. Checking the surface analysis immediately shows their position and type while the prog charts give us a pretty good idea of where they’re headed. The only real trick is checking and understanding the weather situation, especially when launching on a night flight in winter.


On November 19, 2016, at about 1902 Eastern time, a Ryan Navion A impacted wooded terrain while maneuvering near New Gretna, N.J. The private pilot was fatally injured and the airplane was substantially damaged. Night visual conditions prevailed.

Earlier, the accident pilot and another pilot flew their airplanes to dinner at Hummel Field (W75) in Saluda, Va. After dinner, they both added fuel and departed about 1730 for separate destinations, with the accident pilot headed for the Ocean County Airport (MJX), Toms River, N.J. While en route, they communicated with each other. On reaching his destination, the friend-pilot experienced wind shear and advised his friend of the conditions. The accident pilot acknowledged the warning. The friend radioed the accident pilot again about 1830 to check on him, and he replied that he had reached the Delaware Bay. No further communications were received from the accident pilot.


A review of weather information and FAA radar data revealed the accident flight proceeded on a relatively direct course until about 1849, when it encountered the leading edge of a cold front. During the following 13 minutes, the flight completed numerous course deviations, including three complete left circuits and two right circuits, before impacting wooded terrain. During the last three minutes of radar data, the airplane’s altitude varied between 2100 and 200 feet MSL as it completed the two right circuits and one of the left circuits, before impacting terrain. The last target was recorded at 1902:36, when the airplane was about 2000 feet southeast of the accident site, at 525 feet MSL.

The debris path extended about 420 feet, where the main wreckage came to rest inverted with both wings separated. The right main and nose landing gear were extended; the left main landing gear had separated. Control-cable continuity was confirmed from the cockpit to the wing roots, and to the empennage, where they exhibited broom-strawing consistent with overload. The propeller remained attached to the engine. Both propeller blades exhibited S-bending, chordwise scratching, leading edge gouging and tip curling, consistent with being under power at impact.

The accident pilot’s destination was about 16 miles northeast of the accident site. At 1856, recorded weather there included wind at five knots, three statute miles of visibility in mist and clear skies. Meanwhile, the Atlantic City (N.J.) International Airport, about 14 miles southwest of the accident site, recorded wind from 290 degrees at 24 knots, with gusts to 31 knots, at 1730, about the time the pair took off.

The accident pilot’s friend reported obtaining a weather briefing about 1630 via Flight Service for both flights, and telling him that the weather was forecast to deteriorate near his destination airport between 1900 and 1930. The friend also reported plotting a route on the pilot’s iPad using Garmin Pilot. A search of Flight Service records did not reveal any contact from either airplane’s registration numbers on the day of the accident, and neither ForeFlight nor Garmin had a current subscription for the accident pilot.

The 75-year-old private pilot was not instrument-rated. He had owned the airplane since 1993.

Probable Cause

The NTSB determined the probable cause(s) of this accident to include: “The pilot’s inadequate preflight weather planning and in-flight weather evaluation, which resulted in an encounter with a strong cold front and the pilot’s subsequent loss of airplane control.” Yes, this accident ultimately will be attributed to losing control. As the NTSB highlights, inadequate weather planning and evaluation also play major roles. What does that tell us?

One thing it tells us is this accident has a longish chain. It started with the pilot not having an instrument rating. It lengthened with a night flight and got stretched even more by the pilot’s failure to obtain and understand a preflight weather briefing or letting his electronic flight bag do it for him. Along the way, considerations like being relatively close to the airplane’s base and perhaps a warm, familiar bed—along with a very familiar airplane—may have combined to lure the accident pilot into a false sense of security. His last warning about the weather in front of him was literally radioed to him by his pilot friend.

Applying even basic risk management principles to this flight— one conducted at night, without a weather briefing and without an instrument rating—would have rung some loud bells. Put aside the natural peer pressure of two pilots flying more or less together, it’s always up to you to brief the weather conditions. Don’t expect even a good friend to do it for you.

Cold Front Characteristics

According to the FAA’s Pilot’s Handbook of Aeronautical Knowledge (PHAK, FAA-H-8083-25B), “A typical cold front moves in a manner opposite that of a warm front. It is so dense, it stays close to the ground and acts like a snowplow, sliding under the warmer air and forcing the less dense air aloft. The rapidly ascending air causes the temperature to decrease suddenly, forcing the creation of clouds. The type of clouds that form depends on the stability of the warmer air mass. A cold front in the Northern Hemisphere is normally oriented in a northeast to southwest manner and can be several hundred miles long, encompassing a large area of land.

“Prior to the passage of a typical cold front, cirriform or towering cumulus clouds are present, and cumulonimbus clouds may develop. Rain showers may also develop due to the rapid development of clouds. A high dew point and falling barometric pressure are indicative of imminent cold front passage.

“As the cold front passes, towering cumulus or cumulonimbus clouds continue to dominate the sky. Depending on the intensity of the cold front, heavy rain showers form and may be accompanied by lightning, thunder, and/or hail. More severe cold fronts can also produce tornadoes....”

Aircraft Profile: Ryan Navion A

Image: FlugKerl2 - CC BY-SA 3.0

Engine: Continental E-185

Empty Weight: 1782 lbs.

Maximum Gross Takeoff Weight: 2750 lbs.

Typical Cruise Speed: 135 KTAS

Standard Fuel Capacity: 40 gal.

Service Ceiling: 15,600 feet

Range: 430 NM


Jeb Burnside is the editor-in-chief of Aviation Safety magazine. He’s an airline transport pilot who owns a Beechcraft Debonair, plus half of an Aeronca 7CCM Champ.

This article originally appeared in the November 2018 issue of Aviation Safety magazine.

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