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Indonesia Plane Crash Inquiry Focuses on Possible Aircraft Problems

JAKARTA, Indonesia — Indonesian investigators on Wednesday broadened the possibilities of what may have contributed to the fatal crash of a Boeing 737 Max 8 last week, suggesting there were aircraft problems that may have played a role in the new plane’s nose-dive into the sea.

Haryo Satmiko, the deputy head of Indonesia’s National Transportation Safety Committee, said in an interview that he had held several discussions with Boeing officials after the crash about the possibility that inaccurate readings fed into the Max 8’s computerized system could make the plane enter a sudden, automatic descent.

“This case is something for Boeing to reflect upon,” Mr. Haryo said.

Boeing appeared to dispute the Indonesian official’s assertion. The company said in a statement on Wednesday that the aircraft’s manual explains how to respond to errant data that might be received, and that Boeing had issued a worldwide bulletin about following correct procedure to all operators of the plane on Tuesday.

Still, the possibility of errant data pitching the plane into an abrupt descent added to a series of potential issues that may have combined to doom the plane. Investigators are also looking into the possibility of faulty airspeed indicators and flawed maintenance in the plane’s short life.

All 189 people aboard died when the Lion Air Flight 610 plunged into the Java Sea less than 15 minutes after takeoff on Oct. 29.

In its statement, Boeing did not discuss sudden diving as a potential problem with the 737 model, which only entered commercial operations last year and for which more than 4,500 orders have been placed globally.

But the statement said that Boeing had been told by the Indonesian transportation safety committee that Flight 610 had “experienced erroneous input” from one of its “angle of attack” sensors. Those instruments, on the nose of the plane, gauge the degree of an aircraft’s ascent or descent and help determine whether the plane might be stalling.

The Boeing statement said that its bulletin had alerted operators to “existing flight crew procedures” for handling false readings from the Max 8’s angle of attack sensors.

Boeing officials in Jakarta, the Indonesian capital, would not give further details when asked for comment on Wednesday.

John Cox, the former executive air safety chairman of the Air Line Pilots Association in the United States and now the chief executive of Safety Operating Systems, a consulting firm, said that unlike previous versions of the Boeing 737, the Max 8 has an automated system that can take control of the aircraft and cause it to point its nose down sharply without any instruction from the pilot.

Mr. Cox, who flew earlier generations of the Boeing 737 for 15 years, said that the system is designed as an automatic response if the plane’s sensors detect a stalling danger.

He said that his understanding of Boeing’s advice to air carriers was that it was reminding them of the operating manual’s instructions on what flight crews should do to manually disengage the automatic system if it is malfunctioning. “There is a defined procedure for pilots to do” if the plane incorrectly pitches its nose downward in response to a flawed stall warning, he said.

Angle of attack information is also used on the latest 737 models to help calculate the airspeed of the plane, said Ony Soerjo Wibowo, an air safety investigator for the Indonesian government.

Soerjanto Tjahjono, the head of the national transportation safety committee, said on Wednesday that it was not fair to fault Boeing for a possible systemic problem with the Max 8.

“We cannot yet say that there is a design flaw with the plane,” he said, adding that the plane only developed a problem with the angle of attack sensor after technicians on the Indonesian island of Bali changed it for the jet’s penultimate flight.

The potential issue with inaccurate angle of attack data adds to problems previously reported with the Lion Air plane.

On Wednesday, Indonesian transport officials confirmed that the flight data recovered from the downed jet last week showed that the plane had experienced problems with its airspeed indicator on its final four flights.

“In principle, if the airspeed indicator malfunctions, it can cause different anomalies for a pilot,” said Mr. Haryo, the deputy head of Indonesia’s National Transportation Safety Committee. “The malfunction of this airspeed indicator could confuse the pilot on how to respond and could even cause disorientation or loss of control.”

Mr. Ony, the air safety investigator, said that on the plane’s third-to-last flight, from the eastern Indonesian city of Manado to Bali, the plane, which was delivered to Lion Air in August, had recorded no airspeed data at all.

Following Boeing’s troubleshooting manual, technicians in Bali changed the plane’s angle of attack sensors, Mr. Ony said, and the plane was declared fit to fly on to Jakarta.

The plane’s stopover in Bali was relatively brief. Once in the air, the plane again experienced problems with its airspeed indicator and recorded an issue with its angle of attack sensor, according to Indonesian investigators, who were relying on information retrieved from the plane’s flight data recorder.

Data from online flight-trafficking services show that the flight experienced a roller-coaster takeoff that would indicate that the airspeed problems occurred early in the flight.

However, the plane did not return to the Bali airport, as some pilots said would be normal procedure for such problems.

On the flight’s touchdown in the Indonesian capital late on Oct. 28, maintenance crews went to work and tackled a problem with the plane’s pitot tubes, external probes that record relative airspeed, according to maintenance logs viewed by Indonesian aviation experts. This problem was declared solved and the plane was again judged fit to fly, according to the maintenance log.

Mr. Ony said that part of his investigation centered on why the plane had not been grounded by Lion Air, given that it had experienced multiple airspeed problems.

“This is strange,” he said in an interview on Wednesday. “We found several events that we should investigate but they didn’t report them.”

Lion Air is Indonesia’s largest carrier and one of the world’s fastest-growing low-cost airlines.

Mr. Haryo said that the investigation was focusing on three different components: possible problems with the plane, possible human error by those who operated and maintained the plane, and the overall management of the airline.

Lion Air has had a spotty safety record since it began commercial operations in 2000, racking up at least 15 major safety lapses, including a fatal air crash in 2004.

It is not clear what specifically could have caused the nose-dive problem that Indonesian officials said Boeing had discussed with them. But generally speaking, the faster a plane travels, the more lift it experiences.

To compensate for the lift, a pilot will edge the nose of a plane downward. If incorrect airspeed or angle-of-attack information is being transmitted to computerized systems, then the plane might automatically nose dive, even if automatic piloting systems are disengaged, said Indonesian aviation experts closely following the case.

The plane slammed into the sea at such high speed that the jet fractured upon impact, in some cases disintegrating into a fine powder, Indonesian investigators said.

“There was no problem with the engine,” Mr. Haryo said, referring to the speed with which the plane entered the water and an initial examination of an engine part that has been retrieved from underwater.

On Tuesday, Indonesian investigators spent hours interviewing technicians who had tried to repair the airspeed indicator problems by installing multiple spare parts and who had cleared the plane for its final flight from Jakarta to the small city of Pangkal Pinang, Mr. Haryo said.

Those interviews, along with conversations with other aviation technicians, have led Indonesian investigators to conclude that the manual Boeing has published on how to deal with a faulty airspeed indicator contains insufficient information, Mr. Haryo said.

“For example, the manual book is lacking in these respects: If this indicator is having a problem, what should be done, how should it be fixed, what should a pilot do?” Mr. Haryo said. “All these are still lacking, so our recommendation is to complete the manual.”

Air crashes are rarely caused by a single factor, aviation experts say. Instead, a combination of external issues, such as bad weather or multiple technical faults, can catalyze pilot confusion and a fatal chain of events.

If there is a problem with the Max 8 that causes the plane to record inaccurate data or to nose dive after processing that faulty information, it would not be the first time that similar problems have manifested themselves after a new model is put into operation.

Airbus, for instance, experienced a problem with the computerized filtering of air data that is believed to have caused a relatively new model of the A330 to dive suddenly. In 2008, Qantas Flight 72, en route from Singapore to Perth, began processing incorrect speed and angle of attack readings. The plane’s autopilot disengaged, but the aircraft abruptly and violently pitched downward, causing serious injuries among the passengers and crew.

Source: NYT > World

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