Updated at 5:20 a.m. ET
A series of failures and missteps on the ground and in the cockpit resulted in the crash of a Boeing 737 Max in Indonesia last year that killed all 189 passengers and crew aboard, a new report released Friday concludes.
A key finding in the report by Indonesia's National Transportation Safety Committee is that while a design flaw in an automated flight-control system, known as MCAS, was the primary cause of the crash, a faulty sensor, inadequate maintenance, poor pilot training and a failure to heed previous problems with the same aircraft were all contributing factors.
On Oct. 29, 2018, Lion Air 610 took off from Jakarta bound for Pinang, Indonesia, but 13 minutes into the flight the plane suddenly nosed into the Java Sea, killing everyone aboard. The following March, an Ethiopian Airlines 737 Max also crashed shortly after takeoff from Addis Ababa, killing all 157 people aboard.
Following the Ethiopian crash, aviation authorities and airlines around the world ordered all Boeing 737 Max passenger planes grounded pending an investigation into the twin disasters.
A subsequent probe linked the crashes to the Maneuvering Characteristics Augmentation System, or MCAS — a system unique to the Boeing 737 Max. In both planes, the automated system acted on faulty sensor data indicating an impending stall that caused the plane to repeatedly nose down, forcing the pilots to scramble to compensate, investigators found.
A report issued earlier this month sharply criticized both Boeing and the Federal Aviation Administration for the way the 737 Max was developed and certified to fly. The Joint Authorities Technical Review - a panel assembled by the FAA and made up of both U.S. and international civil aviation authorities - said that Boeing did not include any information about MCAS in pilot or training manuals.
"The design and certification of the MCAS (Maneuvering Characteristics Augmentation System) did not adequately consider the likelihood of loss of control of the aircraft," the report said. "A fail-safe design concept and redundant system should have been necessary for the MCAS."
It said the aircraft maker withheld crucial details about the system from the FAA, which was responsible for certifying the aircraft.
Friday's report in Indonesia echoed the criticism of both Boeing and the FAA. Among other things, it found that Boeing changed the parameters on MCAS without informing officials, increasing the automated system's maximum limit for moving the plane's horizontal stabilizer from 0.6 degrees to 2.5 degrees.
"[T]he higher limit caused a much greater movement of the stabilizer than was specified in the original safety assessment document," the report found.
Indonesian investigators also faulted Boeing for not detecting and fixing an MCAS software glitch that resulted in a key warning light not working.
Overall, the company and the FAA were cited in the report for failing to "adequately consider the likelihood of loss of control of the aircraft" if MCAS malfunctioned. "A fail-safe design concept and redundant system should have been necessary for the MCAS."
In a statement released early Friday, Boeing said its engineers were working with the FAA and other global regulators to fix software problems and other issues that may have led to the crashes.
Since the Lion Air accident, "[the] 737 Max and its software are undergoing an unprecedented level of global regulatory oversight, testing and analysis," it said, adding that it was "updating crew manuals and pilot training, designed to ensure every pilot has all [the] information they need to fly the 737 Max safely."
Pilots and ground crew share the blame
But the report also cites a series of other shortcomings on the part of flight and maintenance crews of the Lion Air 737.
It points to a crucial sensor that measures the plane's angle of attack, or AOA, and feeds data to MCAS. There are two on each plane. The day before the crash, a faulty, second-hand AOA sensor, repaired by Xtra Aerospace in Miramar, Fla., was installed on the plane by ground crew.
The report indicates that the sensor — which proved to be 21 degrees out of calibration — was probably not tested prior to flight, but investigators "could not determine with any certainty that the AOA sensor installation (was) successful," because 31 pages of the plane's October 2018 maintenance log are missing.
Indonesian investigators found that just after the sensor was installed the day before the crash, a different crew had experienced the same problems with MCAS as on the later, fatal flight. Unaware of the MCAS system — and with the help of a third pilot sitting in the jump seat — they managed to cut off power to the tail and resume control.
Standard operating procedures meant that the crew should have returned and landed the plane immediately, but instead they continued to their destination.
Upon landing, the captain did not report the most serious problems the crew had encountered, which would have required the plane to be grounded.
Instead, Flight 610 on Oct. 29 took off at 6:20 a.m. local time. Soon after takeoff, the pilot struggled to counteract repeated nose downs as a result of MCAS and the data the faulty sensor was feeding it.
When the problems surfaced on Flight 610, the pilot asked the first officer to perform an Airspeed Unreliability checklist that should have indicated which of the plane's two AOA sensors was reading incorrectly. The first officer should then have directed the pilot to engage the autopilot, which disables MCAS.
It took the co-pilot four minutes to locate the checklist because he was "not familiar with the memory item," the report concludes. During training at Lion Air, the first officer had shown unfamiliarity with standard procedures and weak aircraft handling skills, according to the report.
The pilot reportedly countered the nose dives more than 20 times before, apparently needing a break, turning the controls over to the co-pilot, who quickly lost control of the aircraft, which plunged into the sea.