National Transportation Safety Committee (KNKT) chairman Soerjanto Tjahjono speaks during Friday's press conference in Jakarta on the result of the investigation into last year's crash of Lion Air flight JT 610. (Antara Foto/Hafidz Mubarak A)

Indonesia Says Boeing's Lack of MCAS Manual Contributed to Lion Air Crash


OCTOBER 25, 2019

Jakarta. Indonesia's transportation safety regulator said the absence of specific guidance on the anti-stall system in the Boeing 737 MAX 8 played a role in the crash of a Lion Air passenger jet on Oct. 29 last year.

Flight JT 610 plunged into the Java Sea northeast of Jakarta, killing all 189 people on board, while en route to Pangkal Pinang in Bangka Belitung Province.

The National Transportation Safety Committee (KNKT) held a press conference in Jakarta on Friday to announce results of the yearlong investigation into the accident.

"The KNKT has concluded that several factors contributed to the accident, among them, the absence of pilot guidance on the MCAS in the manual, so the pilots had no knowledge of the MCAS," Nurcahyo Utomo, a KNKT official who was involved in the investigation, told reporters.

The anti-stall system, known as the maneuvering characteristics augmentation system, or MCAS, repeatedly forced the plane's nose down and the pilots were unable to regain control.

The fact that the MCAS relies on a single sensor also makes it very vulnerable to failure, Nurcahyo said.

"When the sensor is faulty, there is no backup system," he said.

The plane had experienced a problem before the ill-fated flight and it should have been grounded, he said. The earlier problem also involved the angle of attack (AOA) sensor that feeds information to the MCAS. Although the sensor was immediately replaced with another one, it was also faulty.

"The substitute AOA sensor had a calibration error, which went undetected during the previous repair," Nurcahyo said. However, it could not be determined in the investigation whether the new AOA sensor had been properly installed prior to the accident.

Moreover, key information from the earlier flight that also encountered problems was not recorded on the plane's flight history and maintenance books, so pilots and mechanics could not take appropriate actions, he said.

The information related to the plane's stick shaker and runaway stabilizer.

Another factor in the accident was the complicated situation in the cockpit amid repeated warnings from the MCAS and crowded communication with the air traffic controller, the official said.

The plane crashed only 13 minutes after taking off from Soekarno-Hatta International Airport in Tangerang, Banten.

About five months after the Lion Air accident, an Ethiopian Airlines Boeing MAX 8 also crashed, killing all 157 people on board. This crash was reportedly also caused by a problem involving the MCAS. 

Airlines worldwide have since grounded their entire 737 MAX 8 fleets.