JAKARTA, Indonesia — 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.
Boeing and aviation regulators in the United States, clearly worried that an unforeseen situation may have confronted the cockpit crew, also took steps on Wednesday to strengthen emergency procedures in the operations manual of the new plane, one of the most popular in commercial aviation.
The developments suggested that multiple causes may have combined to create a fatal cascade of problems for Lion Air Flight 610, which plunged into the Java Sea less than 15 minutes after takeoff on Oct. 29, killing all 189 people aboard.
Haryo Satmiko, the deputy chief 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 did not comment on Mr. Haryo’s assertion. But the company said in a statement on Wednesday that the aircraft’s manual explains how to respond to errant data, and that Boeing had issued a worldwide bulletin about following correct procedures to all operators of the plane on Tuesday.
The Federal Aviation Administration of the United States reinforced the Boeing bulletin on Wednesday by issuing an “Emergency Airworthiness Directive” addressing the possibility of erroneous data from instruments on the plane that could cause it to pitch downward, “making the aircraft difficult to control.”
The directive ordered operators of the Max 8 to ensure that the onboard flight manuals include the procedures on how pilots should handle such a situation.
The possibility of errant data pitching the plane into an abrupt descent added a new element to what investigators have been scrutinizing, including faulty airspeed indicators and possibly flawed maintenance.
The 737 model entered commercial operations only last year. More than 4,500 orders have been placed globally.
Boeing’s statement said that it had been told by the Indonesian transportation 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 — meaning it is pointed too high for its current speed.
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.
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 pilot instruction.
Mr. Cox, who flew earlier generations of the Boeing 737 for 15 years, said that the system was designed as an automatic response if the plane’s sensors detect a stalling danger.
His understanding of Boeing’s advice to air carriers, he said, 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 malfunctioned. “There is a defined procedure for pilots” if the plane incorrectly pitches its nose downward in response to a flawed stall warning, Mr. Cox said.
Angle of attack information is also used on the latest 737 models to help calculate airspeed, 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 developed a problem with the angle of attack sensor only 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 of the 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.
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 airborne, the pilots again experienced problems with the 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 flight-trafficking services show that the flight experienced a roller-coaster takeoff indicating early airspeed problems. However, the plane did not return to the Bali airport, as some pilots said would be normal procedure.
On the flight’s touchdown in the Indonesian capital late on Oct. 28, maintenance crews 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 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, with at least 15 major lapses, including a fatal air crash in 2004.
Incorrect readings from either — or both — the airspeed probes and the angle of attack sensors could cause autopilot systems to disengage and leave pilots confused about what exactly is happening.
Flight 610 crashed into the Java Sea, northeast of Jakarta, after less than 15 minutes, following an erratic takeoff that mirrored the problem on its flight from Bali. The flight crew requested permission to return to the Jakarta airport but never turned around.
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.
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.
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 a new aircraft model has faced such problems.
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.
Australian transport investigators eventually focused on a software limitation of the A330’s computer system, which they said had caused the accident. Procedures were quickly put in place to avoid a similar outcome.
“It’s really hard to find some faults in testing, so it has happened that problems are only discovered after the plane is put into service,” said Gerry Soejatman, an Indonesian aviation expert. “Sometimes weird things happen, and you just can’t anticipate it.”
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