The aviation regulator DGCA has told Jet Airways and SpiceJet to check all their Boeing 737 Max aircraft for an issue that could lead to “significant altitude loss”, a week after a brand new plane of the same model plunged into the sea minutes after take-off in Indonesia.
The US watchdog Federal Aviation Administration and Boeing have issued advisories on what could be done to prevent similar incidents involving the Boeing 737 Max, after the Indonesian Lion Air flight crash that killed all 189 on board.
Jet Airways and SpiceJet are the only airlines in India that fly the Boeing 737 Max.
“Both the documents (FAA and Boeing) address erroneous high angle of attack sensor input and corrective action for the same as it has potential for repeated nose-down trim commands of the horizontal stabiliser,” said a senior Directorate General of Civil Aviation official, who asked not to be named.
Angle of attack is a technical term that refers to the angle between the oncoming air or relative wind and a reference line on the airplane or wing, according to Boeing. Sometimes, the reference line is a line connecting the leading edge and trailing edge at some average point on the wing.
The DGCA official said if the condition is not addressed, it could cause the flight crew to have difficulty in controlling the airplane. The condition can even lead to “excessive nose-down attitude, significant altitude loss, and possible impact with terrain (plane crash),” said the official.
Based on initial investigation of the Lion Air plane crash, the FAA issued an emergency “airworthiness directive” on Wednesday. Boeing also released a bulletin about the issue on Tuesday.
The DGCA official said changes to the flight manual have to be done within three days after getting the airworthiness directive from the US watchdog; the manual contains procedures to be followed by the flight crew.
“The DGCA has ensured that all Indian operators are aware of the FAA AD and have taken appropriate corrective action,” he added.
Comments from Jet Airways and SpiceJet were awaited.
Indonesian investigators said on Wednesday the plane had experienced instrument failures on four flights, including on one journey where both the angle of attack (AOA) sensor and the airspeed indicator were affected.
Soerjanto Tjahjono, head of Indonesia’s National Transportation Safety Committee, told reporters that after one flight from Bali to Jakarta — the last flight before the crash — the left and right AOA sensors were found to disagree by 20 degrees.