Boeing : Indonesia Plane Crash Probe Centers on Engine Control Problems

By Andy Pasztor, Jon Emont and Andrew Tangel

Investigators suspect malfunctioning engine controls and pilot efforts to troubleshoot the problem likely played a major role in an Indonesian airliner's fatal plunge into the Java Sea earlier this month, according to people familiar with the details.

Information downloaded from the Sriwijaya Air jet's flight-data recorder, the people said, points to pilots trying to deal with a problem affecting an automatic throttle system on the twin-engine, 1990s-era Boeing Co. 737. The recorder, which is one of the plane's two black boxes, was retrieved a few days after the crash.

The data indicates the so-called autothrottle system--which automatically adjusts fuel flow and thrust to maintain the path set by pilots--wasn't operating properly on one engine at some point during the Boeing 737-500's climb away from the nation's capital, Jakarta, on Jan. 9, according to some of the people familiar with the matter.

Instead of shutting off the system, they said, the flight-data recorder indicates pilots tried to get the stuck throttle to function. Such engine-control malfunctions can create significant differences in power between engines, making a twin-engine jet harder to control and it could potentially distract pilots from maintaining a safe flight.

Twin-engine aircraft such as the 737 are designed to fly safely on a single engine and pilots are trained to do that in various situations. But large differences in thrust between engines, according to pilots and safety experts, require swift pilot recognition of the problem, which would ideally be followed by quick responses and manual commands.

Haryo Satmiko, deputy head of Indonesia's national transportation safety committee, confirmed the probe is looking into an autothrottle problem. He said investigators may obtain specific information about the pilots' handling of the autothrottle after listening to the cockpit-voice recorder, which authorities are trying to retrieve from the crash site. That device--the plane's second black box--could shed more light on what pilots were saying on the flight deck as they responded to the malfunction.

Bloomberg earlier reported that investigators were looking at a malfunctioning automatic throttle.

Those familiar with details of the probe, along with safety experts tracking it, said it was too early to draw definitive conclusions about why two experienced pilots lost control of the jet, or what other factors may have contributed to the crash. Information from the flight-data recorder is under further analysis, while pilot records and maintenance files also are being examined.

Investigators haven't detailed the primary focus of their probe, though they have said both engines were putting out power when the jet hit the water, killing all 62 people on board. They also have said the location of debris indicates the plane was intact when it hit the water.

A Sriwijaya spokeswoman said "we can't respond to technical matters because we haven't yet received an official statement from" national investigators.

Pilots on a previous flight in the same jet experienced a similar autothrottle problem, according to one person briefed on the matter, but the discrepancy apparently wasn't written up as required in the jet's maintenance log. A spokeswoman from the airline declined to comment.

Autothrottles have been widely available in aviation for decades. They are standard equipment on all types of airliners and using them is like second nature to commercial pilots.

The systems are more transparent, easier for pilots to understand and also in other ways are substantially different from the defective automated flight-control system, called MCAS, that led to a pair of fatal crashes of two Boeing 737 MAX jets in 2018 and 2019.

Pilots are routinely trained to activate and turn off autothrottles. By contrast, MCAS systems installed on the 737 MAX fleet initially weren't mentioned in any pilot or training manuals. Under some circumstances, the 737 MAX's automated feature would repeatedly and strongly push down a plane's nose without any pilot input.

Air-safety regulators in the U.S., Europe and Canada have approved hardware, software and training fixes and MAX jets have returned to commercial service.

Based on the information available so far, the officials said, pilots' attention to autothrottle problems on the Sriwijaya jet appears to have kicked off the sequence of events that resulted in the jet veering off course, pilots failing to respond to radio transmission from air-traffic controllers and eventually plunging into the water.

One veteran safety expert and former 737 pilot said in the event of an autothrottle malfunction, the plane's autopilot likely would have turned the plane to keep it on its designated track while compensating for the difference in thrust between left and right engines. Autopilots are complex computers that manipulate flight-control systems in conjunction with autothrottles to keep planes on correct courses, altitude and speed.

If the autopilot was suddenly turned off or shut off on its own, safety experts said, aerodynamic forces could have forced the Indonesian jet's nose to drop and made it difficult to control. That is one of the leading scenarios investigators are examining, according to one of the people familiar with the probe.

Write to Andy Pasztor at [e-mail], Jon Emont at [e-mail] and Andrew Tangel at [e-mail]

(END) Dow Jones Newswires

01-21-21 0247ET