WASHINGTON/JAKARTA • The Lion Air pilots of a Boeing 737 Max passenger jet that experienced technical difficulties a day before a deadly crash in October last year had help from an unexpected source when the plane started to dive on its own - an off-duty pilot who happened to be riding in the cockpit.
The third pilot, who was seated in the cockpit jumpseat, correctly diagnosed the problem and told the crew how to disable a malfunctioning flight control system and save the plane, according to sources familiar with Indonesia's investigation.
The next day, under the command of a different crew facing what investigators said was an identical malfunction, the jetliner crashed into the Java Sea.
The new information on the earlier Lion Air flight represents a clue in the mystery of how some B-737 Max pilots faced with the malfunction have been able to avert disaster, while others lost control of their planes and crashed.
The presence of a third pilot in the cockpit was not mentioned in the Indonesian National Transportation Safety Committee's (NTSC) Nov 28 report on the crash and was not previously reported.
Sources said the so-called deadhead pilot on the earlier flight from Bali to Jakarta had told the crew to cut power to the motor driving the nose down, part of a checklist that all pilots are required to memorise.
"All the data and information that we have on the flight and the aircraft have been submitted to the Indonesian NTSC. We can't provide additional comments at this stage due to the ongoing investigation into the accident," Lion Air spokesman Danang Prihantoro said by phone.
The Indonesian safety committee report said the plane had multiple failures on previous flights and had not been properly repaired.
Representatives for Boeing and Indonesia's safety committee declined to comment on the earlier flight.
Three people with knowledge of the contents of a cockpit voice recorder on the doomed Lion Air flight said the pilots scoured a handbook as they struggled to comprehend why the jet was lurching downwards, but ran out of time.
The captain, 31, was at the controls of Lion Air Flight JT610 when the nearly new jet took off from Jakarta. The first officer, 41, was handling the radio, according to a preliminary report issued in November.
Just two minutes into the flight, the first officer reported a "flight control problem" to air traffic control and said the pilots intended to maintain an altitude of 5,000 feet, or 1,524m, the report said.
The first officer did not specify the issue, but a source said airspeed was mentioned in the voice recording.
Another source said an indicator showed a problem on the captain's display but not the first officer's.
The captain asked the first officer to check the quick reference handbook, which contains checklists for abnormal events, the first source said.
For the next nine minutes, the jet warned pilots it was in a stall and pushed the nose down in response, the report showed.
The pilots remained calm for most of the flight, the sources said. Near the end, the captain asked the first officer to fly while he checked the manual for a solution.
As the captain tried in vain to find the right procedure in the handbook, the first officer was unable to control the plane, two sources said.
The Indian-born captain was silent at the end, while the Indonesian first officer said "Allahu Akbar", or "God is greatest", a common Arabic phrase in the majority-Muslim country that is used to express excitement, shock, praise or distress.
The plane then hit the water, killing all 189 people on board.