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US emergency directive after Boeing jet crash in Indonesia

The FAA said erroneous data from the “angle
of attack” sensor, which helps prevent the plane from stalling
and diving, could cause flight crew to have difficulty
controlling the airplane and lead to “excessive nose-down
attitude, significant altitude loss, and possible impact with
the terrain”.

The US Federal Aviation Administration issued an emergency
airworthiness directive on how to handle erroneous data from a
sensor that investigators believe malfunctioned on a new Boeing
jet that plunged into the sea in Indonesia, killing all 189
people on board. The directive gives regulatory weight to
Boeing’s safety bulletin that it sent to operators of Boeing
737 MAX 8 and MAX 9 planes based on findings from the ongoing
Indonesian investigation into the October 29 crash of a Lion
Air jet. FAA directives are usually followed by other airline
regulators internationally.

The FAA said erroneous data from the “angle of attack” sensor,
which helps prevent the plane from stalling and diving, could
cause flight crew to have difficulty controlling the airplane
and lead to “excessive nose-down attitude, significant altitude
loss, and possible impact with the terrain”. The directive
instructs airlines to make specific changes to flight manual
procedures for responding to the problem. Boeing’s bulletin
said it was directing flight crews to existing guidelines.

Indonesian investigators on Wednesday said the sensor was
replaced on the Lion Air plane the day before its fatal flight
and may have compounded other problems with the aircraft. The
2-month-old Boeing 737 MAX 8 crashed into the Java Sea 13
minutes after takeoff from Jakarta. Both that flight and its
October 28 flight from Bali to Jakarta had erratic speed and
altitude shortly after takeoff. Indonesia’s National
Transportation Safety Committee earlier this week announced the
plane had a malfunctioning airspeed indicator on its last four
flights, based on analysis of the flight data recorder.

Chairman Soerjanto Tjahjono said the airspeed indicator and
sensor problems are related. Lion Air’s first two attempts to
address the airspeed problem didn’t work, and for the jet’s
second-to-last flight the “angle of attack” sensors were
replaced, Tjahjono said. On that October 28 flight, from Bali
to Jakarta, the pilot’s and copilot’s sensors disagreed by
about 20 degrees. The plane went into a sudden dive minutes
after takeoff, from which the pilots were able to recover. They
decided to fly on to Jakarta at a lower-than-normal altitude.
On the fatal flight, the plane hit the water at very high speed
after the flight crew had been cleared to return to the airport
several minutes after takeoff.

“The point is that after the AOA (sensor) is replaced, the
problem is not solved but the problem might even increase. Is
this fatal? NTSC wants to explore this,” Tjahjono said. Airline
safety experts said pilots are trained to handle a plane safely
if those crucial sensors fail and backup systems are generally
in place as well. There are audio signals and physical warnings
that can alert the pilot to malfunctioning equipment or other
dangers, said Todd Curtis, director of the Airsafe.com
Foundation.

“They should have been completely engaged in what was going on
inside that cockpit, and any kind of warning that came up, they
would have been wise to pay attention to it,” Curtis said.
Investigators are likely focused on how a single sensor’s
failure resulted in a faulty command that didn’t take into
account information from a second sensor, said John Cox, CEO of
Safety Operating Systems.

“We don’t know what the crew knew and didn’t know yet,” Cox
said. “We will.” Indonesia’s search and rescue agency has
extended the search until Sunday. Body parts are still being
recovered and searchers continue to hunt for the cockpit voice
recorder. Indonesia’s transportation safety committee said it
had agreed with Boeing on procedures that the airplane
manufacturer should distribute globally on how flight crews can
deal with the sensor problems.

The flight procedure recommendations to Boeing were based on
how the flight crew responded to problems on the
Bali-to-Jakarta flight, said investigator Nurcahyo Utomo. Lion
Air is one of Indonesia’s youngest airlines but has grown
rapidly, flying to dozens of domestic and international
destinations.

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