Investigators link crash to sensor

JAKARTA, Indonesia — Pilots fought against an automated system that pitched a Boeing jetliner’s nose down repeatedly because of a faulty sensor until they finally lost control and plunged into the Java Sea last month, Indonesian investigators said Wednesday.

At a news conference, safety officials said they were still struggling to understand why the plane crashed, killing all 189 people on board.

The National Transportation Safety Commission’s Nurcahyo Utomo said investigators were trying to figure out from interviews with engineers why they certified that the Boeing 737 MAX 8 was airworthy and whether they had followed required maintenance procedures. Pilots of previous flights had reported problems with control systems on the brand-new jet.

The board issued a preliminary report that stopped short of declaring a probable cause of the crash — the investigation is continuing — but it provided new details about the pilots’ struggle to fly the highly automated jet and Lion Air’s inability to fix problems with sensors on the plane.

Sensors that measure speed were flushed and checked, and an electrical plug was cleaned before the fatal flight. Mechanics, however, did not check a sensor that measures whether the nose of the plane is pointing up or down.

That Angle of Attack sensor gave faulty readings throughout the short flight, triggering a system that automatically pointed the plane’s nose down more than two dozen times, with pilots responding by manually fighting to correct the pitch. Pilots even asked air traffic controllers to tell them how fast and high they were flying.

The malfunctions and warnings from the plane’s control system appeared to overwhelm the pilots almost as soon as the jet became airborne, said another investigator, Ony Suryo Wibowo.

In a statement after the release of the report, U.S.based Boeing declared that the MAX, its newest plane, is safe.