Nov. 5, 2018, © Leeham News: It was a week ago that Lion Air JT 610 crashed into the sea, just 13 minutes after takeoff.
The crash was the first involving the Boeing 737 MAX (in this case, the -8 model). The airplane was virtually new, having been delivered to the airline in August. Lion Air was not new to the 737, having flown the NG models for years.
Because the airplane crashed into the sea, recovery of the black boxes was not quick. The flight data recorder was recovered several days later but the cockpit voice recorder is still missing. The FDR data apparently has not yet been downloaded for a preliminary read. At least nothing has been made public, if it has.
Absent even a first-read of the FDR data, information about why the crash happened is sketchy.
We know the same airplane had airspeed mismatching the day before.
There was a report, but unconfirmed, there may have been an issue with the elevators, too. But until this is confirmed, I’m treating this as a rumor.
We know from Flighttracker24 JT 610 was at a lower altitude than normal at this point in the flight after departure, the altitude was erratic and so was the speed. Flighttracker also showed a virtually straight-down dive from 5,000 ft into the sea.
Bloomberg reported over the weekend it commissioned three experts to analyze the Flighttracker information. Each concluded, separately, that the plane was going +/- 600 mph on impact, with the nose-down attitude at least 45 degrees and maybe more.
So far, that’s about it.
Supposedly, Lion Air maintenance personnel fixed the airspeed mismatch issue from the day before, but this is unclear. Nothing definitive has pointed to the cause of the mismatch.
It could be faulty instrumentation.
It could be a fault with the pitot tubes that measures airspeed. This has happened before.
There were two Boeing 757 accidents traced to pitot tube malfunctions. Birgenair flight 301 sat on the ground for two days in Puerto Rico without the tubes covered. In this short time, mud wasps built a nest in the tubes. The walk-around didn’t detect this.
A speed mismatch was detected on the takeoff roll, but the pilot continued. As the airplane climbed through 4,700 feet, things began to go wrong, with the airspeed instrumentation mismatch between the pilot and captain and erratic airspeed indications appearing. (When I read the altitude in this accident summary and compared it with Lion Air’s altitude, the similarity was chilling.) The auto-pilot disengaged.
Events led to a stall and engine flame out and the airplane crashed, killing—get this—189 people on board, the same number as JT 610.
Eight months later, while Birgenair was still under investigation, Aeroperu Flight 603 crashed shortly after takeoff from Lima.
The cause was determined to be the failure of the ground crew to remove tape from the static ports that fed the airspeed and altitude to the cockpit instruments. The flight was at night and with no visual reference, the crew lost control and crashed.
Then there is Air France 447, an Airbus A330, that crashed June 1, 2009, in the South Atlantic. The pitot tubes collected ice at cruising altitude, causing airspeed mismatch instrumentation. The crew became confused, stalled the airplane and it pancaked into the Atlantic at high speed.
Pilots are supposed to be trained for deal with airspeed and altitude mismatches. A Delta Air Lines Boeing 767 aborted a takeoff at New York’s JFK on the takeoff roll when airspeed mismatch occurred. (Ironically, during a long taxi period to cool overheated brakes, the make gear nevertheless caught fire and an emergency evacuation on the taxiway was necessary.)
Without visual reference (such as with the Aeroperu flight), things become more difficult.
Still, a pilot for a US 737 operator emailed me and said instrument mismatch “is why we work on unreliable instrument scenarios in training.”
And, as another remarked, JT 610 was in broad daylight. Looking out the windows would have been useful.
There are very few answers and there are hundreds of questions.
We don’t know what was happening to the airplane. We don’t even truly know if this was instrumentation or something else.
We don’t know what was happening the in cockpit. We know the pilot radioed he wanted to return to the airport. Other than this, what was being said between the pilots, what were they seeing, hearing or thinking out loud?
The FDR will tell us what the airplane was doing, but as of this writing, we don’t have this information.
Did the pilots have a situation they couldn’t handle? Or did the pilots create a situation they couldn’t handle?
At this point we just don’t know.