Investigators at the crash site of the doomed Ethiopian Airlines flight have found new evidence that points to another connection to the earlier disaster involving the same Boeing jet.
The evidence, a piece of the Boeing 737 Max 8 jet that crashed in Ethiopia last weekend killing 157 people, suggests that the plane’s stabilizers were tilted upward, according to two people with knowledge of the recovery operations. At that angle, the stabilizers would have forced down the nose of the jet, a similarity with the Lion Air crash in October.
Although the crash investigations are still in the early phases, the new evidence potentially indicates that the two planes both had problems with a newly installed automated system on the 737 Max jet intended to prevent a stall.
This evidence ultimately contributed to American regulators’ decision to ground the 737 Max this week, according to the two people who spoke on the condition of anonymity. The Federal Aviation Administration said it had found physical evidence from the Ethiopian crash that, along with satellite tracking data, suggested similarities between the two crashes.
As the investigations continue, Boeing has also been racing to finish a software update for the 737 Max aircraft, which is expected by April. Boeing and the Federal Aviation Administration have continued to stand by the safety of the plane. Yet Boeing’s update will modify features of the jet around the automated system that investigators have suggested might have played a role in the Lion Air crash.
The new evidence found at the crash site in Ethiopia, a piece of equipment known as a jackscrew, controls the angle of the horizontal stabilizers. The stabilizers can be triggered by the automated system, known as MCAS.
The stabilizers could have been tilted upward for other reasons. Authorities in France are analyzing the black boxes of the Ethiopian Airlines plane for more information.
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The planes flew in similar erratic patterns, suggesting to experts that an automated system might have malfunctioned on both flights.
Indonesian and American authorities are also looking into whether MCAS contributed to the Lion Air crash that killed 189 people in October. In that disaster, the automated system, possibly based on faulty sensor readings, may have repeatedly pushed the nose of the plane down, creating a struggle between the new flight control system and the pilots.
After the Lion Air crash, Boeing backed the safety its planes and 737 Max aircraft continued to crisscross the planet. In the background, Boeing has been working on a software update for the planes.
Boeing designed the 737 Max as an updated, more fuel-efficient version of its best-selling 737 aircraft. The Max’s engines were bigger and mounted farther forward on its wings, a configuration that could push the nose upward toward a stall in certain circumstances. To compensate for that, Boeing installed MCAS to automatically push the nose down to counteract those forces, in the hopes of making the 737 Max safer and able to handle like its predecessors.
That similarity was part of Boeing’s pitch to the F.A.A. and airlines: Because the plane handled like previous 737s, pilots would not need to be retrained to fly it. Regulators and carriers agreed, and the pilots’ 737 Max training typically amounted to a course on an iPad and a few white papers.
The automated system, which may have pushed down the nose of the aircraft in the Lion Air crash, activates if just one of two sensors mounted on the aircraft’s exterior says the nose is too high. That means a single malfunctioning sensor could force the plane in the wrong direction, as has been theorized in the Lion Air crash.
Boeing is updating the software to require data from both sensors for the system to kick in, according to pilots at several major airlines and two lawmakers briefed on the matter.
Modern aircraft are built with backups and redundancies for virtually every crucial component. So when something breaks — as things often do — it won’t threaten the safety of a flight. Boeing’s software fix indicates that the plane maker shipped the 737 Max with a single point of failure, a potentially dangerous anomaly in aviation, and the Federal Aviation Administration approved it.
Such a single point of failure on a modern jet is rare and far riskier than having backup systems, said Michael Michaelis, the top safety official at American Airlines’ pilots union and a 737 captain. “A single point of failure on a significant system that points my nose towards the ground?” he said. “Now that to me seems just a little bit over the line.”
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Boeing has also said its software fix would cause the automated system to push the nose down at a slower rate, Mr. Michaelis said. The system currently pushes the nose down by 2.7 degrees in 10 seconds, Mr. Michaelis said. “That’s a pretty aggressive pitch down,” he said, particularly just after takeoff.
The update will also deal with another concern in the wake of the Lion Air crash: pilots fighting with MCAS.
Investigators have said it appears that the Lion Air pilots repeatedly pulled the plane’s nose back up after the automated system pushed it down. This continued until it was too late and the aircraft slammed into the Java Sea.
The system is designed to push down the nose of the aircraft if sensors are saying it is necessary — overriding what pilots may be trying to do. The software update would limit the number of times MCAS tries to push down the nose, preventing it from struggling with a pilot, according to the pilots.
Boeing has indicated the software fix will “make an already safe aircraft even safer.” The F.A.A. has said it expects to tell airlines “no later than April” to incorporate the software fix.
Pilots at American Airlines, Southwest Airlines and United Airlines said they still generally felt comfortable flying the 737 Max jets, in part because they are now aware of the automated system. Boeing did not fully disclose the system to pilots until after the Lion Air crash.
Reviews of tens of thousands of 737 Max flights at American, Southwest and United showed the automated system never activated, presumably because their pilots never forced the noses of their aircraft too high. Some pilots said they were concerned the system could be activated by a single inaccurate sensor, pushing the plane toward the ground right after takeoff, when the margin for error was thin. But they added that in that situation, they could always flip a switch to automatically turn off systems like MCAS.
“It is of course a concern for pilots,” said James LaRosa, a United Airlines’ 737 pilot. “But if it happened to me or our pilots, I know that our pilots would react.”