In Ethiopia Crash, Faulty Sensor on Boeing 737 Max Is Suspected – The New York Times

Regulators around the world grounded the Max this month, and airlines are not expected to use them soon. On Friday, Southwest Airlines said it planned its flight schedule through May without its 34 Max jets.

Boeing said it could not comment on the black box findings until investigators released their official report, per international aviation agreements. Rosemount Aerospace, a subsidiary of the industrial giant United Technologies based in Burnsville, Minn., made the sensor. A United Technologies spokeswoman did not immediately respond to requests for comment.

Angle-of-attack sensors are highly reliable and have been used on passenger jets for years, but like any aircraft component, they can fail. Given that, former Boeing and Rosemount engineers said it was surprising that Boeing would allow a single sensor to activate a crucial system that pushes the aircraft toward the ground.

The sensors, which are effectively wind vanes on the jet’s nose, have malfunctioned in the past, for a variety of reasons, including bird strikes, according to the former engineers. They have also been broken by jetways that attach to the plane for passengers to board and exit the plane.

The sensors can also malfunction if water pools around them and then freezes when the plane reaches a certain altitude, the engineers said. The sensors have built-in heaters to prevent freezing at such high altitudes, but they sometimes do not work quickly enough or can fail outright.

“Generally speaking, aviation components are highly reliable,” said Mel McIntyre, a retired Boeing engineer who worked with such sensors for years. “But everything can fail. Nothing is invincible.” Mr. McIntyre declined to comment further on any specifics of the 737 Max.