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.
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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:
- Why is the pilots’ decision to use electric trim “inexplicable”
- 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 McDonaldFrom 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.
NTSB CASES:
ERA12FA127
ERA14FA045Bill 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
