Ethiopian pilots fought the 737 MAX flight controls almost from take-off, preliminary report shows
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April 4, 2019 at 11:59 am Updated April 4, 2019 at 1:26 pm
https://www.seattletimes.com/busines...ight-controls/
By Dominic Gates
Seattle Times aerospace reporter
The preliminary investigation into the crash of Ethiopian Airlines Flight 302 last month reveals that pilots began fighting against the Boeing 737 MAX’s new automatic flight control system barely a minute after leaving the ground, after a sensor failed immediately on take-off.
Boeing Chief Executive Dennis Muilenburg issued a statement Thursday from the Renton 737 factory expressing “the immense gravity of these events across our company,” and acknowledging the role the new Maneuvering Characteristics Augmentation System, or MCAS, played in the crash.
He pointed to the software fix and associated pilot training Boeing is working on.
“As pilots have told us, erroneous activation of the MCAS function can add to what is already a high workload environment. It’s our responsibility to eliminate this risk,” Muilenburg said. “We own it and we know how to do it.”
The “black box” flight recorder data shows that after MCAS swiveled the plane’s horizontal tail to push the nose sharply down three times in succession, the pilots hit the cut-off switches stopping the automatic action and tried to adjust the tail manually, according to the report by the Accident Investigation Bureau of Ethiopia’s Transport Ministry.
In doing so, they were following instructions provided by Boeing last November, following the crash of Lion Air Flight 610, on how to deal with such an inadvertent triggering of the new flight control system.
Ahead of the release of the full report, Ethiopian Transport Minister Dagmawit Moges held a news conference in the capital, Addis Ababa, that was almost entirely focused on vindicating the actions of the pilots. “The crew performed all the procedures repeatedly provided by the manufacturer but was not able to control the aircraft,” she said.
The report says that while trying to follow Boeing’s directions, about three minutes into the flight, the two pilots found that the manual system for moving the horizontal tail — also known as the stabilizer — “was not working.” This meant they couldn’t move the large stabilizer wheel in the cockpit that is connected via cables to the tail.
Flight-control experts told The Seattle Times earlier this week that was probably because the forces on the tail of the plane moving at high speed made it next to physically impossible to move the stabilizer wheel as Boeing had recommended.
All the while, the control column “stick shaker” was vibrating the control column, and various messages were telling the pilots and that their airspeed, altitude and pitch readings were unreliable. Two minutes into the flight, losing altitude, an audible warning sounded that the plane was too close to the ground: “Don’t Sink!”
About four minutes into the flight, the pilots gave up on the manual stabilizer wheel and switched the electric power to the tail back on, then used the thumb switches on the control column to pitch the nose back up.
But just five seconds later, MCAS kicked in again and once more pushed the nose sharply down.
Just 35 seconds later, six minutes after take-off, the plane rolled over before plowing into the earth in a “high energy impact” at a speed of approximately 575 miles per hour.
This sequence of events was triggered by the failure of the left angle-of-attack sensor on the outside of the fuselage, just 44 seconds after take-off, the data shows.
There are two such sensors one, either side of the aircraft, that measure the angle between the wing and the airflow. Only one is used to trigger MCAS. The data shows that both sensors showed normal readings on the ground during the take-off roll but deviated immediately after lifting off and in less than a minute were divergent by 60 degrees.
Ethiopian Airlines issued a statement Thursday backing the Flight 302 pilots, saying that they “followed the Boeing recommended and FAA approved emergency procedures to handle the most difficult emergency situation created on the airplane.”
“Despite their hard work and full compliance with the emergency procedures … they could not recover the airplane from the persistence of nose diving,” the statement added.
Boeing CEO Muilenburg said while the Ethiopian and Lion Air “tragedies continue to weigh heavily on our hearts and minds,” Boeing remains “confident in the fundamental safety of the 737 MAX.”
“When the MAX returns to the skies with the software changes to the MCAS function, it will be among the safest airplanes ever to fly,” he said.