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
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
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"
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
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
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 email@example.com, Jon Emont at
firstname.lastname@example.org and Andrew Tangel at
(END) Dow Jones Newswires
January 21, 2021 02:47 ET (07:47 GMT)
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