Was the Lion Air disaster caused by the plane's own computer?

The crash of a Boeing 737 operated by Indonesia's Lion Air in late October was the second most fatal in the country's history. A standard preliminary report – released one month after the crash – confirms that the plane had problems on previous flights and notes that the pilots struggled with the aircraft's anti-stall automated system, but stops short of providing a definitive cause for the accident. There is a sneaking suspicion though: did the on-board computer crash the plane into the sea?

Marco Evers
November 28, 2018

Indonesian rescuers carry recovered debris of Lion Air flight JT610 for further investigation by the National Transportation Safety Committee Photo: Bagus Indahono / EPA-EFE

Flight JT-610 of the Indonesian low-cost airline Lion Air took off punctually at 6:21am local time on Monday, 29 October. On board the brand-new Boeing 737 Max 8 were 189 people, including two infants.

From Jakarta, the passengers were headed to the city of Pangkal Pinang, one hour north, but their journey would soon end in a terrible way. At 6:33am, the plane smashed nose first into the Java Sea.

The plane hit the water at between 600 and more than 1,000km per hour, which is why not much remained of JT-610 and its passengers. Divers were able to salvage tiny bits of debris and body parts at a depth of 30 metres.

Of the two flight recorders, investigators initially found only the data recorder. The other device, which records cockpit noises and conversations, remains missing. More than 200 emergency personnel searched for it. The ultrasonic transmitter on this device was fading, and officials worried that it would not be located before its signal disappeared.

The JT-610 crash is the second worst crash ever in Indonesia. Grieving relatives are stunned that the high-tech aircraft crashed despite being just 11 weeks old, with sufficiently experienced pilots flying in ideal weather.

As is customary internationally, aircraft accident investigators will present a preliminary report on the causes of the accident about a month after the crash (at the earliest) and a final report after about a year. Until then, the investigation can still take some unexpected turns. In this case, though, manufacturer Boeing has gone ahead with an extraordinary measure.

On 6 November, Boeing warned its customers worldwide in an “Operations Manual Bulletin” about a possible technical failure that Indonesian investigators had found. It apparently affects all 737 Max planes, the most modern version of Boeing’s best-selling craft. More than 4,500 of the planes are owned by airlines worldwide.

It was a fight to the death, man against computer

Over 200 of these 737 Max planes are in service with airlines that include Norwegian, United, Southwest and the holiday airline TUI. Each of them could be at risk of suffering a similar fate to JT-610.

The US Federal Aviation Administration (FAA) immediately heeded Boeing’s warning. An “urgent airworthiness directive” now requires all US operators of the 737 Max to inform their pilots of the aircraft’s special risk.

The JT-610 crew suspected even before takeoff that something was wrong with their aircraft. On its three previous flights, their colleagues had noticed, among other things, a faulty speed display. They had also experienced violent, sudden climbing and sinking.

Mechanics had tried several times to get the problem under control. The day before, they replaced an important sensor. Many airlines would have taken the aircraft out of service as a precautionary measure. Lion Air did not.

The Indonesian National Transportation Safety Committee (KNKT) investigator, Nurcahyo Utomo, holds a Boing 737 aircraft model as he answers questions from journalists during a press conference in Jakarta, Indonesia, 28 November 2018 Photo: Bagus Indahono / EPA-EFE

The drama began shortly after takeoff. The jet lost altitude. For minutes, it remained too low, at about 1,500 metres. It climbed, sank, climbed. The pilots reported to air traffic control that they wanted to turn around and fly back to Jakarta. Apparently they believed their situation was manageable since they didn’t report an emergency.

A few moments later, they watched helplessly as their plane dashed headlong towards the sea. The 737 Max uses software that is supposed to prevent crashes. With the help of two sensors at the bow, computers constantly analyse whether the aircraft is in immediate danger of a stall due to its position in the air stream.

As soon as the calculated angle of attack of the aircraft reaches an aerodynamically dangerous value, the computers intervene. They move the elevator downwards without any action on the part of the pilots, lowering the nose of the aircraft. The corrected angle of attack should guarantee that the aircraft has sufficient lift again.

The airline has had a number of accidents, some of which were due to pilot errors

This system, according to the Indonesian investigators’ scenario, failed in JT-610. It calculated – perhaps because of a defective sensor or faulty software – an incorrect angle of attack and fed it into the flight computer. As a result, the pilots received alarms and contradictory messages.

According to Boeing, the instruments of the captain and co-pilot can display different flight speeds and altitudes in such a case; at the same time, the warning of a stall can appear in the form of a loudly rattling control horn.

Under these circumstances, all that could happen in the cockpit was chaos – and while the pilots were still trying to discern the cause of their emergency, the computer kept steering the aircraft closer to the ground. Especially diabolical was the fact that, even if the crew managed to steer against it, the computer would, according to Boeing, try to lower its nose again only seconds later.

It was a fight to the death, man against computer.

After the crash, Boeing announced that the solution to this conflict was relatively simple: the pilots should fly manually, without autopilot, and flip two switches in the cockpit to turn off the automatic trim. That’s it. Two clicks.

Could the JT-610 crew have known that? Or didn’t they have a chance to see the root of the problem? According to Boeing, the rescue procedure is standard, at least for trimming problems. From the pilots’ point of view, though, it was probably unclear whether they had a primary trim problem or a speed problem. They didn’t have time to clarify such questions at 1,500 meters altitude.

The Indonesian investigators will now take a closer look at Lion Air’s pilot training. The airline has had a number of accidents, some of which were due to pilot errors. Lion Air has nevertheless become the country’s largest airline and continues to grow rapidly. The company operates over 100 aircraft, and has ordered 200 more from Airbus and Boeing.

Pilots of the 737 Max worldwide will be trained in a simulator so they can cope with the JT-610 accident scenario in the future. Whether the sensors or the computers of the 737 Max are particularly susceptible will probably be the subject of further investigations. At any rate, the FAA is not currently going as far as to order inspections or even temporary shutdowns of the 737 Max. This could change depending on the final report on JT-610.

Computers in the cockpit have undoubtedly made flying safer. Still, a number of accidents have been caused by sensors that delivered faulty data to computers.

Four years ago, the passengers of a Lufthansa Airbus A321 were more fortunate. On their way from Bilbao to Munich, the plane suddenly began to sink at over 1,000 metres per minute. The pilots were steering against it, but the computer ignored their control commands.

Three sensors on the outer skin of the aircraft had transmitted data on the angle of attack to the on-board computer. Of the three, two were frozen and provided false data. The computer wrongly assumed the aircraft was at an incorrect angle and did what it was programmed to do: press its nose down.

The captain saved the day in a creative way. He cut off the power supply to both computers. He immediately regained full control. The European air traffic control authority Easa then issued an urgent airworthiness directive that it made standard in all similar emergencies.

© 2018 Spiegel Online Distributed by The New York Times Syndicate
This article was published in the December 2018 edition of Southeast Asia Globe magazine. To subscribe to our newsletter, click here

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