Before Lion Air plane crashed, pilots struggled to fix faulty sensor

Before Lion Air plane crashed, pilots struggled to fix faulty sensor

Before Lion Air plane crashed, pilots struggled to fix faulty sensor

"During the flight from Denpasar to Jakarta, the plane experienced a technical problem, but the pilot chose to continue the flight", Mr Nurcahyo Utomo, KNKT sub-committee head for air accidents, said yesterday. "In our view, the plane was not airworthy", he said on Wednesday.

He said the pilots on the flight from Bali the previous day should not have flown the plane to Jakarta, but should have turned back.

An Indonesian policeman holds wreckage recovered from Lion Air flight JT610 which crashed into the sea, at Tanjung Priok port in Jakarta, Indonesia, October 29, 2018.

Lion Air, Indonesia's largest airline, has a notoriously flawed safety record.

Nurcahyo Utomo, aviation head at the National Transport Safety Committee, said it was "too early to conclude" whether the anti-stall system had contributed to the crash.

"What they were focused on was keeping the airplane in the air", said Clint R. Balog, a pilot and aeronautics expert at Embry-Riddle Aeronautical University.

Boeing said that "the appropriate procedure to address unintended horizontal stabiliser movement" was contained in the relevant flight manuals.

The aircraft maintenance log shows that since Oct 26, there had been six reports of problems, including faulty sensor readings.

Much remains unknown about the doomed flight, including why a plane that had encountered problems with the sensors was permitted to fly in the first place.

The report also raises questions about how the problems on the flight the night before the crash were reported to mechanics.

The report by Indonesia's safety commission did not draw conclusions about why the crew lost control of the plane, but it repeated earlier recommendations that pilots be better versed in emergency procedures and aware of past aircraft problems. His last words captured were "five thou", as he asked to be cleared to 5,000ft (1,500m).

The black box data is consistent with the theory so far on what happened to Flight 610: Sensors on the fuselage sent incorrect information to the plane's anti-stall system and, due to that erroneous information, the system forced the nose down again and again.

A policeman stands guard near the wreckage of Lion Air's flight JT610 at Tanjung Priok port in Jakarta
Image A policeman stands guard near the wreckage in Jakarta

The Maneuvering Characteristics Augmentation System (MCAS) ― an automated modification new to the model that crashed ― activated and directed the jet's nose down to prevent a stall, Utomo said.

Information provided to American Airlines from Boeing since the crash, Tajer said, "specifically says that pulling back on the control column in the Max will not stop the runaway if MCAS is triggered".

The pilots also faced a difference between left and right angle of attack readings of about 20 degrees that again continued throughout the flight.

The plane's automatic safety system repeatedly pushed the plane's nose down, according to a draft of a preliminary report by Indonesian authorities.

It is essentially software that helps push down the nose if the aircraft's computers detect a high angle of attack. "This condition is considered as un-airworthy condition" and the flight should have been "discontinued". In a statement Tuesday, Boeing said it could not discuss the crash while it is under investigation but reiterated that "the appropriate flight crew response to uncommanded trim, regardless of cause, is contained in existing procedures".

Boeing's statement did not make any reference to a revised anti-stall system introduced on the 737 MAX, which United States pilots and Indonesian investigators say was missing from the operating manual.

The report provided new recommendations to Lion Air on safety on top of earlier recommendations about the flight manual that have already been implemented by Boeing.

"Why is the airplane flying passengers?" said John Cox, president of consulting company Safety Operating Systems and a former airline pilot who participated in multiple accident probes.

Preliminary reports deal with facts surrounding an accident and an analysis will not come until the full report.

Indonesian investigators expect to fly to the US later this week to gather more information about the Boeing aircraft and its components, including discussing the MCAS safety feature with Boeing engineers to understand how it may have contributed to the accident, Utomo said.

The search for the cockpit voice recorder continues and the committee told Lion Air, which has taken a number of safety actions, to improve aspects of its safety culture.

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