French, U.S. Investigators: Ethiopian MAX Report Downplays Human Factors

The Ethiopian Airplane Accident Investigation Bureau (EAAIB) final report on the March 2019 fatal Boeing 737 MAX accident that triggered the model’s global grounding leans on erroneous information in analyzing how the pilots reacted and does not dig deeply enough into pilot-performance issues, investigators from France and the U.S. said.

EAAIB’s report on Ethiopian Airlines Flight 302 (ET 302), released Dec. 23, sheds little new light on the 737 MAX saga. The agency concluded that faulty data from a broken angle of attack (AOA) sensor activated the aircraft’s automated maneuvering characteristics augmentation system (MCAS) that directed the horizontal stabilizer to repeatedly point the 737-8’s nose down, and the pilots did not maintain control. Ten contributing factors focus on flaws in MCAS’s design and Boeing’s incorrect conclusion that pilots would respond appropriately if the system activated erroneously, with one blaming Boeing for inadequate responses to questions raised following the first 737-8 fatal accident, Lion Air Flight 610, in October 2018.

France’s BEA and the U.S. NTSB generally agree with EAAIB’s analysis of MCAS’s role in the accident. But the 330-page report sheds little light on why the ET302 pilots were not better prepared for an MCAS-related malfunction, despite significant communication about the system—including how to counteract it—following the Lion Air accident. Both agencies contend that EAAIB’s lack of focus on flight deck human factors aspects paints an incomplete picture of the ET302 accident and, more importantly, short-changes broader efforts to improve pilot training and competency.

“Shortcomings relating to the crew’s actions, particularly in the first phase of the flight, is not accompanied by a thorough analysis of the reasons for the behaviors observed, in relation with their training, their experience and the company organization with regard to the training and knowledge acquisition principles,” BEA said in comments on a draft version of the report released with the final report.

Much of BEA’s analysis focuses on the 1 min. 15 sec. period between the first sign of trouble—a stick-shaker stall warning triggered by the faulty AOA data—and the initial activation of MCAS. The stall warning plus two other visual messages triggered by the bad AOA data that appeared soon after on both the captain’s and first officer’s primary flight displays (PFDs)—indicated airspeed (IAS) disagree and altitude (ALT) disagree—should have prompted specific responses from the pilots. 

“On the activation of the stick shaker, the flight crew must apply the approach to stall or stall recovery procedure, which is a memory item,” BEA said. As documented in the 737 MAX pilot manual and quick-reference handbook, the first steps in each procedure “are to hold the control column firmly, disengage the autopilot and autothrottle and then smoothly apply a nose down input,” the French agency added. But the only change in the aircraft’s state was nose-down inputs.

EAAIB’s report suggests the crew acted per Boeing’s recommended training, which is usually done with the autothrottle already disengaged. Further, Boeing’s training protocol does not cover “how to conduct an approach to stall training with the autopilot not engaged nor for a stall condition during departure,” EAAIB added.

Recognition of an IAS Disagree fault should prompt pilots to run a specific checklist that includes disengaging the autopilot, autothrottle, and locking in specific pitch and power settings. None of this was done, nor were the warnings acknowledged by either pilot.

“Non-normal procedures related to erroneous AOA inputs instruct the crew to disengage both the autopilot and autothrottle, thereby preventing the erroneous AOA inputs from affecting flight control and throttle movements,” the NTSB said in its comments. “The observable flight deck effects associated with erroneous AOA inputs include the activation of the stick-shaker and the annunciation of the IAS Disagree and ALT Disagree messages.”

Contention On Disagree Prompts 

Ethiopian investigators contend the IAS and ALT Disagree prompts—which are not captured by the aircraft’s flight data recorder—never appeared on either PFD. But both BEA and NTSB insist conditions were met to trigger both prompts, a position validated in tests during the investigation and by the absence of evidence that the systems malfunctioned. 

“Given that the conditions were met for the IAS Disagree and ALT Disagree messages to be annunciated to the crew members, their lack of conversation or action in response to the annunciations should be explored in the context of the flight deck environment, workload, crew experience, and training,” the NTSB said. “The report’s assumption that those messages did not appear, which is contrary to Boeing’s description of the alerting system and the results of simulator testing during the investigation, severely limits the opportunity for recognizing and addressing potential crew training and experience improvements.”

Added BEA: “There were no crew exchanges on the [cockpit voice recorder] regarding the IAS Disagree or ALT Disagree messages, which supports the conclusion that the IAS Disagree and ALT Disagree messages were most probably not seen by the crew throughout the flight.”

While the crew had no way of understanding the predicament unfolding, leaving the autothrottle connected—it remained at takeoff thrust due in part to the system failures—helped set the stage for MCAS to overwhelm them. Once the conditions for MCAS activation were met—manual flying with the flaps up—the erroneous AOA data triggered unneeded nose-down inputs. 

EAAIB said the pilots were aware of Boeing’s post-Lion Air directive, later mandated by global regulators including Ethiopian officials, that instructed crews on how to respond to an erroneous MCAS activation. Among the instructions: counter the nose-down inputs with manual nose-up trim, and if the cycle does not stop, disconnect the automatic trim motor and use a manual wheel to move the horizontal stabilizer. 

“If the crew had conducted the procedure [as described], the crew would have used manual electric trim to reduce control forces. However, FDR data show minimal crew use of manual electric trim,” the NTSB said.

The crew disconnected the automatic trim motor, but the aircraft’s airspeed, which had increased due to the faulty AOA data’s effects, meant the forces on the horizontal stabilizer were too strong to move the trim wheel. The crew then re-engaged the trim motor—in direct contrast to the MCAS activation response directive.

EAAIB cited the high-stress scenario as the reason the pilots did not follow procedures.

“During abnormal situations, flight crews are assumed to be capable of maintaining control of the flight path and performing a rapid diagnosis that will allow them to identify the correct response and actions to apply,” the EAAIB report said. “However, a significantly unusual abnormal situation can lead to a total loss of understanding. The stick shaker here represented a major disruption in managing the situation and the rapid onset of multiple inconsistent cues and abnormalities. As a consequence, the effectiveness of the crew’s [crew resource management] was seriously affected.”

While EAAIB acknowledged some human-factors shortcomings, its report spends little time dissecting their ramifications. The final report’s text also did not include BEA’s or NTSB’s comments, appending them via a weblink instead—an unusual step that suggests notable disagreement between the two agencies and EAAIB. Both BEA and the NTSB took the equally unusual step of releasing their submissions publicly once the final report was out.

“[A]ppropriate crew management of the event, per the procedures that existed at the time, would have allowed the crew to recover the airplane even when faced with the uncommanded nose-down inputs,” the NTSB said in its comments. “The absence of flight crew performance information limits the opportunity to address broader and equally important safety issues.”