A damaged sensor may have set off the chain of events that led to the crash of the Ethiopian Airlines Boeing 737 Max 8 aircraft last month, killing all 157 aboard, according to a published report Wednesday.
A bird or debris may have damaged one of the plane’s two angle-of-attack sensors when the jetliner took off, which then caused the plane’s automated anti-stalling system to receive false readings. The system could then have kept pushing the plane’s nose down until it crashed, ABC News reported based on two anonymous sources.
The system, called the Maneuvering Characteristics Augmentation System or MCAS, was installed on the Max, the latest version of the 737, to compensate for engines that are heavier and placed more forward on the wings. The new location could cause the plane’s nose to rise under some flight conditions. MCAS was designed to automatically push it back down.
The ABC report follows one from the Wall Street Journal that, citing people briefed on the probe’s preliminary findings, said the pilots turned off MCAS but were still unable to reverse the plane’s trajectory. The system may even have switched itself back on moments before the crash, the report said.
The system has been at the center of the investigation of the Lion Air crash in October that killed 189 off of Indonesia and now, it would appear, in the Ethiopian crash shortly after takeoff from Addis Ababa.
Both flights crashed after drastic speed fluctuations during ascent. Both pilots made ill-fated efforts to return to their airport of origin after takeoff.
The latest crash is being investigated by French and Ethiopian authorities who are analyzing the plane’s flight data and cockpit recorders, but no findings have been released. The Ethiopian government has said they could issue a preliminary report on the crash this week.
The 737 Max was designed with two angle-of-attack sensors, but it took readings from only one to activate MCAS. Under the software changes that Boeing just announced in the wake of the accident, MCAS will initiate only when has readings from both sensors and it will disregard one if it is more than 5.5 degrees at variance with the other.
The pilots of the Ethiopian jet apparently switched off the power system that operates the plane’s horizontal stabilizer, which controls up-down motion, only to turn it back on, ABC News reported based on a single source. When the crew did, MCAS kicked in again, eventually forcing the jet into the ground with such force that it created a crater.
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MCAS kicked in and began pointing the nose downward before the plane surpassed 500 feet above ground, the Journal said. Pilots overrode the system by flipping two switches, then turned a manual wheel that directs the plane’s tail in an effort to raise the nose of the plane – procedures the Journal says were recommended by Boeing after the Lyon Air crash.
All efforts failed, and the aircraft crashed about six minutes after takeoff.
The 371 Boeing 737 Max jets flown around the world have been grounded pending further investigation. Also hanging in the balance are orders for more than 4,500 of the hot-selling planes. Boeing said it “paused” deliveries of the 737 Max although production continues.
The FAA said it expects to receive Boeing’s software improvement plan for the 737 Max aircraft in within weeks. The agency also promised rigorous review before approving installation of any proposed fixes.
This article originally appeared on USA TODAY: Bird hit on sensor could have doomed Ethiopian Airlines’ Boeing 737 Max jet, report says