Top Letters And Comments, April 12, 2019

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Boeing 737 MAX Accidents

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 Ethiopian 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.


I think your piece “MAX and the Press” does go some distance but many of your fellow press got it way off.

Two weeks to release the data from the FDR is way off. There are probably many parameters that could have correlated any suppositions early on.

We have not seen the Ethiopian Aviation Authority documents that were conveyed to Ethiopian Air. The FAA CANIC goes to the government NOT the carrier.

What OPS SPECs if any were modified by the Ethiopian authority to the carrier.

The documentation from carrier to the pilots, QRH, etc.

What data is there on maintenance of the aircraft?

What airport data is there reference what they purportedly hit? Is there a wildlife management plan as required by ICAO (Annex 14) for the airport?

And not to remove any blame from Boeing, what did they know about the System Safety Assessment hazard classification?

As a GA guy, you likely have flown aircraft with significant power to pitch coupling, this is not a new issue. However, I question pilot qualification in this case. A copilot with 200 hours.

And, similar systems exist on Airbus and other part 25 aircraft.

David Downey

Paul Bertorelli’s pieces on the Max issues to me illustrate why we don't want software engineers flying us in autonomous aircraft. I think we have confirmation where the ill-fated Indonesian aircraft's crew from the previous flight successfully headed off a disaster. Unfortunately, the second crew wasn't as adept at resolving the issue. The point being we need well trained humans in the loop.

Robert Mahoney

Boeing has pushed some of the detailed operation of the later 737s under the rug and come around to a KISS style that seems to now have bitten them. Old hands on another forum seem to think that of course the manual trim wheel gets stuck when airspeed as well as trim runs away. In that case a “roller coaster recovery” procedure used to be in the manuals for several early Boeing models — ease off yoke pressure, crank furiously, recover, ease off the yoke again, trim furiously, recover, etc., until neutral trim is regained. But item #1 on the memory check list is to reduce power to 85% or 80% of N1. POWER BACK is step one on the memory checklist for PPL training in any aircraft when the emergency has you nose down with speed increasing, and both accidents seem to have happened in clear air. So the attitude could be determined by looking out of the window. While stick shaker, spoken alarms, airspeed disagreements, a trim runaway that comes and goes, and all that would be pretty terrifying for anyone, Boeing did not apparently take the possibility of pilot/crew confusion into their failure scenarios, but assumed that the pilots would do the sensible thing. That may no longer be an acceptable model for certification.

Scott Kirkpatrick

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 2nd one, fatally. Perhaps it helps inform the Max conundrum.




Bill Tuccio

Certification Nomenclature

My day job consists of getting jet engines FAA certified. I note that folks (AvWeb and many others) are still using terms such as "FAR 23" to describe small airplane cert, or "FAR 91" for pilot stuff. It hasn't been "FAR" for more than a decade, since the regulations were moved under the Code of Federal Regulations umbrella. So while they remain federal regulations pertaining to aviation, they aren't "FARs."

"14 CFR part 23", or "14 CFR 23" would be acceptable (the FAA has a PowerPoint on it, of course!) but you can punt and say "Part 23" to keep the word count down (unless you are paid by the word, then use "Title 14 of the Code of Federal Regulations, part 33"!)

And that has painted me as a pedant, I'm sure!

R. K. Phillips