Lion Air flight 610: In the Cockpit
On the 29th of October 2018, Lion Air flight 610, a Boeing 737-8 (MAX) crashed at Tanjung Karawang, West Java after departing from Jakarta. This crash was the first public sign that there was something wrong with the Boeing 737-MAX; the initial domino in a cascading sequence of events that uncovered an unbelievable quagmire of corporate malfeasance and corruption. At the time, the crash was blamed on faulty maintenance and the incompetence of the pilots. It took a second crash of a passenger flight full of innocent people, just a few months later, to focus attention on Boeing and even then, Boeing and the FAA furiously defended the aircraft. By now, everyone has heard of the massive grounding of the aircraft around the world as a result of concerns with MCAS, the Maneuvering Characteristics Augmentation System specific to the Boeing 737 MAX.
Over the past year, we’ve gone over the events leading up to that fateful day. I have tried to keep the posts as stand-alone as possible but I’m afraid that to understand the background to the situation in the cockpit, you really need to have read both Lion Air 610: The Faulty AOA Sensor and Lion Air flight 610: The Previous Flight. The primary resource for this sequence of events is the final report released by the Komite Nasional Keselamatan Transportasi (KNKT).
The flight crew arrived at the Soekarno-Hatta International Airport in Jakarta on the morning of the 29th of October in order to prepare for Lion Air flight 610 to Depati Amir Airport in Pangkal Pinang. The morning seemed routine as the flight crew did their pre-flight briefing. They discussed the taxi route, runway in use, intended cruising altitude and the fact that the Automatic Directional finder (ADF) was unserviceable. There was no discussion logged related to the previous flight or the issues logged in the Aircraft Flight and Maintenance Log (AFML). The previous flight crew had not reported the extent of the issues they had faced but if they had, it would not have mattered, as it appears this morning’s flight crew didn’t bother to check.
As they completed the Before Taxi checklist, the digital flight data recorder recorded a pitch trim of 6.6 units. Because the configuration of the aircraft will define what “in trim” means, those units can’t be used to understand if the aircraft is pitching up or down but it does allow us to have a relative understanding of how the trim changed during the flight. The units of pitch trim are constantly recorded by the FDR: I won’t list every pitch trim change, but it is useful to look at the units at key points, so we can get a feeling for how pitch trim, and thus the pitch, were changing during the flight.
The ground controller issued a taxi clearance for flight 610 and told the crew to contact Jakarta Tower. Jakarta Tower told them to line up on runway 25 left, where the crew performed the Before Takeoff checklist. The captain was to be Pilot Flying with the first officer as Pilot Monitoring.
Jakarta Tower issued the take-off clearance and the first officer read it back. At 06:20 local time (23:20 UTC), the FDR recorded that the TO/GA (takeoff/go-around) button was pressed and the engines spooled up for take-off.
Fifteen seconds later, the first officer called out 80 knots. They did not know a faulty AOA (Angle of Attack) sensor had been installed but the problems related to this started immediately. The AOA sensors measure the angle between the wing’s mean aerodynamic chord and the direction of relative mean. As they prepared to lift off, the flight data recorder recorded a difference angle between the left and right AOA sensors. The flight director (F/D) on the captain’s display showed 1° down while on the first officer’s display, the flight director showed 13° up. Related: the airspeed on the captain’s display showed 140 knots while the first officer’s was 143 knots.
The first officer called “rotate” and the nose lifted ready to climb.
At that moment, the captain’s control column stick shaker activated.
A stick shaker consists of an electric motor and an unbalanced flywheel connected to the control column. An electrical current is sent when the AOA reaches unsafe values, which causes the stick shaker to vibrate and shake the control column. This alerts the pilot that the AOA urgently needs reducing. Once the AOA decreases, the electrical signal stops and the stick shaker stops.
The stick shaker is meant to be a warning that you can’t miss that something is wrong: effectively it means that the aircraft does not have enough energy to maintain flight. It requires an immediate response. The response could be to increase the power or to reduce the pitch (so the aircraft stops climbing and is able to increase the airspeed) or both.
So, as the aircraft reached take-off speed, the captain’s control column began vibrating violently. It would continue to shake for most of the flight.
Then the take-off configuration warning sounded. The first officer, in his role of Pilot Monitoring, called out to draw the captain’s attention to the warning: “Takeoff Config”. The captain muttered as he tried to work out what was going wrong. At that moment, the flight data recorded that the Boeing 737 MAX was pitched nose-up 7°.
The aircraft became airborne.
As they began to climb away from the runway, the first officer called out “Auto Brake Disarm” as a part of his take-off duties. Then he told the Captain that they had an IAS (indicated airspeed) Disagree, which meant the aircraft had conflicting information about the speed at which it was travelling through the air. The captain’s display showed an indicated air speed of 164 knots while the first officer’s display had an indicated airspeed of 173 knots. The IAS DISAGREE message displayed for the remainder of the flight.
The first officer asked what the problem was and whether the captain intended to return to the airport. The captain did not acknowledge or respond to the first officer’s question. It was perhaps not the best moment to ask such a question but the interaction gives us a clear first view of the cockpit management resources that day: the first officer doesn’t understand what is happening and looks to the captain for guidance, which the captain does not give.
The first officer called out “auto brake disarmed” again which this time was acknowledged by the captain. The landing gear lever moved to the UP position.
Jakarta tower asked the flight crew to change frequency to the Terminal East controller.
The first officer advised the captain that the ALT DISAGREE message had appeared, meaning that the aircraft had conflicting information about its altitude. The altitude on the captain’s primary flight display indicated 340 feet and the first officer’s indcated 570 feet. The captain acknowledged this.
The first officer switched frequencies and contacted the Tower East controller, who replied that they had identified the aircraft on the radar display and to please climb to flight level 270 (27,000 feet).
The first officer asked the Tower East controller to confirm the aircraft altitude as shown on the radar display. The controller responded that the aircraft altitude showed as 900 feet. The captain’s altimeter showed 790 feet and the First Officer’s showed 1,040 feet. It was 90 seconds since they had bcome airborne.
The captain asked the first officer to perform the memory items for airspeed unreliable.
The first officer didn’t respond. Instead, he asked the captain which altitude he should request from the Tower East controller. He suggested that the captain should fly downwind, which the captain rejected.
The captain twiddled the heading bug to start a turn to the left and told the first officer to request clearance to any holding point.
The first officer contacted Tower East to ask for clearance “to some holding point for our condition now”, explaining that they had a flight control problem.
The controller didn’t offer a clearance. When asked later, the controller only remembered that the flight crew had reported a flight control problem but not that they’d asked for a holding point. Communication seemed to be breaking down all around.
Everything was happening too quickly in the cockpit. Suddenly, the first officer realised they were still flying with the flaps extended and asked whether the captain wanted flaps 1, which the captain agreed. The first officer adjusted the flaps from flaps 5 to flaps 1. About ten seconds later, the captain asked the first officer to take control. The first officer responded with “Standby,” presumably meant as “give me a second.”
The Tower East controller watched the flight on the radar display and noticed that the aircraft had descended by about 100 feet. He called to ask their intended altitude; effectively verifying whether they meant to be descending.
The captain’s altimeter indicated 1,600 feet and the first officer’s indicated 1,950 feet. The first officer asked whether he should continue the flap reconfiguration. When the captain agreed, he moved the flaps into the UP position. The captain’s indicated airspeed showed 238 knots while the first officer’s indicated airspeed was 251 knots. Realising that the controller was still waiting for an answer, the first officer asked the captain if 6,000 feet was the altitude they wanted. “5,000 feet,” said the captain.
He made the call and the controller responded that they should climb to 5,000 feet and turn left to a heading of 050°. The first officer acknowledged.
That was when the Extended Ground Proximity Warning System sounded with a call of BANK ANGLE, BANK ANGLE. The aircraft roll had reached 35° right as the flaps reached the fully retracted position.
In the midst of all this chaos, the automatic trim suddenly activated for about ten seconds, trimming the aircraft nose down. This was the MCAS activating, a system which neither the captain nor the first officer knew anything about. At the same time, the horizontal stabilizer pitch trim decreased from 6.1 units to 3.8 units.
The captain shouted “Flaps 1” and the flaps began extending. The main electric trim moved the stabilizer in the aircraft nose up (ANU) direction for five seconds, which would have been the captain correcting for the nose down movement and putting the aircraft back into the climb. The pitch trim increased to 4.7 units.
This is very interesting because the MCAS stability augmentation function, meant to improve the aircraft’s handling characteristics, would kick in under very specific circumstances:
- The aircraft’s AOA value (as measured by either AOA sensor) exceeded a specific threshold,
- the aircraft was in manual flight (autopilot not engaged),
- the flaps were fully retracted.
If all three of these were true, the MCAS responded to the AOA value by moving the stabiliser trim nose down. Because one of the AOA sensors was faulty, the MCAS was incorrectly attempting to move the stabiliser trim nose down. The captain may not have understood exactly what was going on but he certainly had concluded that the issue had started when the flaps were fully retracted and responded by calling for flaps set to the initial setting. It seems likely that he set them himself as the flaps started extending immediately as he called out.
As they reached 5,000 feet, the flight officer called out the altitude. The selected altitude on the Mode Control Panel had been set to 11,000 and over the next six seconds, it was decreased to 5,000; one of the flight crew belatedly setting their desired altitude.
Suddenly, the aircraft descended at a rate of up to 3,570 feet per minute, immediately losing about 600 feet of altitude. The pitch trim was at 4.4 units. The flaps stopped extending as they reached position 1.
The captain’s control column stick shaker finally stopped. The left AOA recorded 18° up and the right AOA sensor recorded 3° down. The aircraft continued to plummet. The barber pole appeared on the captain’s flight display.
The “barber pole” appears on the pilot flight display for a quickly recognisable indication that the speed is too high or too low. The maximum operating speed, that is the maximum speed at which the aircraft is safe to manoeuvre without fear of breaking up, is called VMO. This speed has to be calculated, as it is modified by the aircraft configuration, atmospheric conditions and altitude. In most aircraft, the VMO needle which indicates the maximum operating speed has red and white stripes, hence the name.
The Boeing 737 MAX has a flat panel display which also uses the barber poles (in red and black instead of red and white) to show the minimum speed, with yellow bands in the middle to show where manoeuvring capability begins to decrease.
The low speed barber pole appeared on the captain’s pilot flight display, with the top of the pole at 285 knots. The stick shaker and the speed barber poles were both giving the flight crew wrong indications that their airspeed was too low, caused by the fact that they were being fed the wrong AOA data from the faulty sensor. Two minutes had elapsed since take-off.
The first officer asked the controller to relay the speed indicated on his radar display. The automatic trim activated nose-down again, this time for eight seconds. The Extended Ground Proximity Warning System sounded again with an urgent warning: AIRSPEED LOW – AIRSPEED LOW.
The controller reported that the ground speed of the aircraft as shown on the radar display was 322 knots. The Captain’s PFD indicated 306 knots and the first officer’s showed 318 knots. Their airspeed was not low.
Someone in the cockpit, almost certainly the captain, selected flaps five and the flaps began to extend again from position 1 to position 5. At the same time, the captain commanded nose up for five seconds, with the pitch trim recorded at 4.8 units. The automatic nose-down trimming had ceased.
I hate to split things into two without making them stand-alone but in this case, there wasn’t much of a choice. I’ll be back next week with the second half of this post in which we follow the situation in the cockpit of Lion Air 610 until the fatal crash of the flight.