Atlas Air Pilot Likely Reacted to Somatogravic Illusion

During the NTSB’s probe into the February 2019 crash of an Atlas Air Boeing 767 into a marshy area in Trinity Bay, Texas, the board determined the crew lost control of the airplane as it approached Houston’s George Bush Intercontinental Airport (IAH). The accident, an all-cargo flight, killed both pilots and also took the life of another airline pilot who was riding along in the jump seat.

The first officer was acting as the pilot flying on the leg to Houston that originated in Miami, Florida. As the heavy jet approached KIAH, the crew deployed the speed brakes and leading edge slats to increase the rate of descent. The captain was the pilot monitoring, though the Boeing’s autopilot and autothrottle system were engaged throughout the approach. Standard company procedure says the flying pilot should guard the speed brakes to ensure they are retracted when power is added to maintain level flight. The NTSB said the crew encountered light turbulence as they penetrated a deck of clouds associated with a cold front approaching Houston and continued the flight on solid instruments.

About 30 seconds prior to impact, as the aircraft descended through 6,300 feet headed to 3,000 feet, the flight data recorder indicated the go-around button was activated, possibly by the FO’s wrist while retracting the speedbrakes. The captain was distracted with other duties preparing for the approach. Activating the go-around button made the autopilot assume the crew wanted to climb and caused the command bars on the flight director to indicate the increase in nose pitch. Within a few seconds of the go-around mode’s activation, the first officer—believing the pitch up indicated the aircraft was stalling—shoved the control wheel forward.

The NTSB says, “Within seconds of go-around mode activation, manual elevator control inputs overrode the autopilot and eventually forced the airplane into a steep dive from which the crew did not recover. Only 32 seconds elapsed between the go-around mode activation and the airplane’s ground impact.” None of the flight data recorder information indicated the aircraft was anywhere near a stall at the time of the first officer’s reaction. The Board also cited the Atlas captain for failing to closely supervise the FO and also his failure to assume command of the aircraft when things began heading south.

The NTSB says, “Despite the presence of the go-around mode indications on the flight mode annunciator and other cues that indicated that the airplane had transitioned to an automated flight path that differed from what the crew had been expecting, neither the first officer nor the captain were aware that the airplane’s automated flight mode had changed.” Neither pilot communicated anything about the change with the other. The Board believes “the first officer likely experienced a pitch-up somatogravic illusion as the airplane accelerated due to the inadvertent activation of the go-around mode, which prompted him to push forward on the elevator control column.” A somatogravic illusion, also referred to as a vestibular or false sensation, can occur when no clear horizon is present, as in this case when the aircraft had just entered the clouds. The NTSB’s video recreation of the sequence of events during the final moments of Atlas Air 3591 and the Board’s abstract of the investigation offer a look at what probably happened in the cockpit.

Skybrary says, “The vestibular organs are part of the human body’s mechanism for achieving posture and stability. Changes in linear acceleration, angular acceleration and vertical acceleration (gravity) which occur as a result of flight control inputs, made to accomplish a change in the flight path, are detected by the vestibular system and may create either or both of these illusions. Whilst there are many situations in which these illusions can occur, one of the most likely, and certainly the most dangerous, is when the positive changes in acceleration, which accompany the initiation of a go around or the transition to initial climb after takeoff, are occurring. In both cases, the consequences can rapidly lead to CFIT if the condition is not recognized or to a [loss of control] if the situation is recognized but the complexities of recovery are mishandled.”

Aircraft accidents attributed to pilots reacting to these “seat of their pants” illusions have occurred in both commercial and general aviation operations. Another significant Part 121 loss took place in May 2010, as an Afriqiyah Airways Airbus A330 began a go-around in daylight from a non-precision approach at Tripoli. The crew also reacted to what they felt was happening rather than what their instruments indicated. The aircraft rapidly descended into the ground and was destroyed by impact forces and fire. All but one of the 104 occupants were killed.

While sensory illusions, stress, and startle response can adversely affect the performance of any pilot, the investigation revealed that in this case, the first officer of Atlas Air 3591 had earlier demonstrated fundamental weaknesses in his flying abilities and his response to stress that would have made it even more difficult for him to accurately assess the airplane’s state and respond with appropriate procedures after the inadvertent activation of the go-around mode.

In written comments found in the NTSB Docket on this accident related to remedial training session prior to the first officer taking his Boeing 767 type rating checkride, the instructor said the pilot’s, “Situational awareness was lacking. Procedures were incorrect. [Aircraft] Limitations were exceeded. Judgment was poor, CRM skills were poor. Steep turns exceeded all PTS limits. Non-precision procedures non-existent and a totally unstable approach resulted. Didn’t work well with pilot monitoring during in-flight emergency. Lack of confidence and tunnel vision were definite contributing factors.”

Additional evidence indicated the first officer had a long history of training performance difficulties as well as a tendency to respond impulsively and inappropriately when faced with an unexpected event during training scenarios at a number of different employers. The Board believes this indicated an inability to remain calm during stressful situations. The 1996 Pilot Record Improvement Act system was originally created in order to make it difficult for an applicant to be hired at a company without the hiring company being aware of those training issues. This accident showed the record system has no fallback when an applicant either lies or simply omits critical information from their application.

The NTSB determined the probable cause of this accident was “the first officer’s inappropriate response as the pilot flying to an inadvertent activation of the Boeing’s go-around mode, which led to his spatial disorientation and nose-down control inputs that placed the airplane in a steep descent from which the crew did not recover. Contributing to the accident was the captain’s failure to adequately monitor the airplane’s flightpath and assume positive control of the airplane to effectively intervene. Also contributing were systemic deficiencies in the aviation industry’s selection and performance measurement practices, which failed to address the first officer’s aptitude-related deficiencies and maladaptive stress response. Also contributing to the accident was the FAA’s failure to implement the Pilot Records Database (the NTSB had previously suggested) in a sufficiently robust and timely manner.

The NTSB issued six new safety recommendations following the investigation into the Atlas Air 3591 accident. The NTSB said the FAA should issue a safety alert for all Boeing 757/767 operators warning of the possibility of an inadvertent go-around activation when the pilot flying is in close proximity to the speed brake handle. The NTSB also wants to see the vulnerabilities of the current pilot record system that would include the results of all pilot training once it begins, regardless of the result and that the system be easily searchable by pilot certificate number. The Board reiterated its call for advanced cockpit video recorder systems for Part 121/135 aircraft.

On the human side of the equation, the NTSB reiterated to the FAA the urgent need to “require all Part 121 and 135 air carriers to obtain any notices of disapproval for flight checks for certificates and ratings for all pilot applicants and evaluate this information before making a hiring decision. To also require Part 121, 135, and 91K operators to document and retain electronic and/or paper records of pilot training and checking events in sufficient detail so the the carrier and its principal operations inspector can fully assess a pilot’s entire training performance. The Board also wants to see all training records provided to hiring employers as required under the PRIA and to develop a method of verifying the accuracy of those training records.”