Washington: One day before a Lion Air jet went down near Jakarta last year, pilots on the same Boeing Co. 737 Max jet, which had been suffering repeated failures on recent flights, made a startling decision:
In spite of a malfunctioning airspeed indicator, they chose to ignore procedures and take off for their destination anyway, according to two people familiar with the incident.
The plane landed safely, but the previously unreported decision to fly represents another in a series of missed opportunities to prevent the Oct. 29 crash that killed 189.
“It’s obviously not acceptable,” Roger Cox, a former airline pilot who worked as an investigator at the U.S. National Transportation Safety Board, said of the decision to continue the earlier flight. “It wouldn’t be approved by anyone anywhere.”
The flight with the faulty airspeed indicator is expected to be outlined in a report by Indonesian investigators that’s scheduled for release Friday, according to the people who asked not to be named discussing the details of the flight.
The accident investigation by Indonesia’s National Transportation Safety Committee found plenty of fault by Boeing and the U.S. Federal Aviation Administration for questionable design decisions and lax oversight that led to a pair of deadly crashes in less than five months and the worldwide grounding of the jet.
But the probe has also highlighted a series of miscues and malfunctions with the jet that weren’t adequately addressed, according to findings presented Wednesday to family members of victims.
For example, a different device, the sensor that triggered the Oct. 29 accident, was faulty before it was installed on the plane and went undetected. Investigators were unable to to conclude if mechanics performed a mandatory test that would have discovered the problem, according to the briefing to family members.
Pilots the evening before encountered the identical failure that led to the crash but didn’t adequately document it so it could be repaired, family members were told. The cockpit crew on the fatal flight showed “deficiencies” in flying skills, communication and executing emergency checklists.
Lion Air hasn’t commented on the NTSC findings released to family members and airline spokesman Danang Prihantoro didn’t respond to calls asking about the Oct. 28, 2018 Manado-to-Denpasar flight.
The circumstances of that flight was described by two people briefed on the incident who weren’t permitted to speak about it.
Later that day, the crew on a flight of the same plane from Denpasar to Jakarta were saved when an off-duty pilot hitching a ride in the cockpit told them how to disable an automated system driving down the nose of the jet — the same failure that occurred the next morning in the crash.
The earlier Oct. 28 flight involved a different set of failures.
The 737 has separate instruments for the captain and copilot that calculate the necessary information to fly within safe limits, such as speed and altitude. There is also a third backup system in case either of the two fails.
The three-month-old Lion Air jet had been experiencing problems on these systems for several days before the accident, according to the people and a preliminary report on the crash released last November. On at least four of those flights, the flight-data recorder on the plane showed that there were “invalid” airspeed readings from the captain’s instruments.
In most of those earlier cases, the failures occurred after the plane reached high altitudes.
But not included in last year’s preliminary report was the fact that on the Manado-to-Denpasar flight the data recorder shows that the captain’s speed reading wasn’t functioning properly as the plane taxied and took off.
In fact, instruments in the cockpit indicated that the captain’s speed and altitude data weren’t functioning from the moment the crew started the engines, according to one of the people briefed on details of the investigation.
Having fully functioning speed and altitude readings are critical to safely operating an aircraft. In a modern jetliner such as the 737 Max, the data feed everything from the autopilot to emergency warning systems.
In addition to checking the cockpit instruments, Boeing’s flight manual for the 737 and other models requires that pilots check the speed readings during takeoff. Boeing calls for it to occur at 80 knots (92 miles per hour or 148 kilometers per hour), which is well below takeoff speed.
Cox, who didn’t have direct knowledge of the Indonesian investigation’s conclusions and was speaking generally about pilot practices, said every airline he’s familiar with around the world has a similar procedure.
“One of the things you always look for is what we call ‘airspeed alive,’” he said. A jet’s speed readings don’t function during slow-speed taxiing, so both pilots monitor their instruments as they accelerate for takeoff to ensure they are working properly, he said.
“Cross checking your instruments on takeoff roll is one of the most critical tasks you have during takeoff,” he said.
The responsibility of the pilots and the airline didn’t start at the takeoff, Cox said.
Pilots are expected to read their plane’s maintenance log before each flight and the captain has to decide whether the plane is safe. The instrument problems from prior flights had been noted in the Lion Air jet’s logbook, according to the November crash report by Indonesian investigators.
Seeing those notations should have have been a red flag, Cox said.
“You don’t intentionally operate with any airspeed indicator inoperative,” he said. “That’s fundamental. That’s common sense. It’s true of any aircraft at any time.”
If there’s an indication that one of the pilots’ instruments has failed or the two readings don’t agree, the crew is required to abort the takeoff, he said.
After the plane arrived in Denpasar on the island of Bali on Oct. 28, a mechanic determined that a device known as an “angle-of-attack” sensor, which the plane uses to help calculate airspeed and altitude, was at fault and it was replaced.
However, the new one wasn’t properly calibrated, something the mechanic failed to detect, according to the findings presented to family members.
Photos that purported to document the repair were given to investigators after the crash. But investigators said they couldn’t verify their accuracy, Bloomberg News reported earlier. Some of the photos may have been taken of a different aircraft, according to people familiar with that incident.
The malfunctioning sensor prompted a feature on the plane known as Maneuvering Augmentation Characteristics System to repeatedly drive down the nose.
With the help of the off-duty pilot riding in the jumpseat, pilots on the next flight on Oct. 28 to Jakarta were able to disable the nose-down commands, but didn’t fully describe the failure after they landed and it wasn’t fixed.
Pilots who took off the next morning in the plane weren’t able to diagnose the issue and crashed after about 11 minutes.
Also read: International experts fault regulators who cleared 737 Max’s fatal design changes