Plane crash investigators focus on faulty device
Indonesia
Indonesian officials are providing the strongest hints yet that a faulty airspeed indicator played a role in the deadly crash of a Lion Air jet into the Java Sea.
Investigators said that one of the so-called black boxes showed that the airspeed indicator on the Boeing jet malfunctioned on its last four flights, including the October 29 crash that killed all 189 people on board.
Airspeed indicators have been around for decades to tell pilots how fast they are flying. They are paired with separate indicators measuring the degree to which the nose is pointed up, down or level.
Modern jetliners have redundant measurements to help pilots spot and disregard a single reading that looks unlikely and possibly erroneous.
Speed-measuring systems consist of tubes and sensors that measure air pressure generated by the plane’s movement and compare it with surrounding air pressure. They fail occasionally, especially in bad weather at high altitude, when the tubes located under the plane’s nose can become jammed with ice, preventing air from reaching the sensors. The October 29 Lion Air flight took off in good weather.
Frozen pitot tubes were blamed for the 2009 crash of Air France Flight 447, which killed all 228 people on board. The year before, the US Air Force said moisture in sensors caused the 2008 crash of a B-2 stealth bomber on Guam; both pilots ejected safely. In 2015, a wasp nest plugged the sensors on an Allegiant Air jet leaving St Petersburg, Florida, forcing pilots to cut the flight short and land in Orlando.
Pilots train in simulators to learn how to notice potentially faulty readings and work around them. They learn the normal power settings and attitude, or nose-up and nose-down settings, for each of the various phases of a flight. A problem with the airspeed system should not result in a crash under most circumstances, according to safety experts.
‘‘If you were driving down the interstate and the speedometer failed, would you expect to crash the car?’’ said John Cox, a former airline pilot and now a safety consultant.
He said a faulty airspeed system might have contributed to the crash, but that based on what we know so far, it shouldn’t be considered the cause of the crash.
Safety experts said investigators will look at why Lion Air didn’t ground the plane if it experienced recurring problems with the sensors and subject it to more rigorous inspection and testing until the problem was fixed.
Alan Diehl, a pilot and safety consultant, said the report that the same problem happened four times and was never fixed suggests that the problem may have been intermittent, making it harder to pin down.
‘‘Intermittent failures are very difficult for maintenance personnel to trouble-shoot because a lot of times they just say, ‘Cannot duplicate,’ and they write it up that way,’’ Diehl said.
The pilots’ actions will also be studied. Data transmitted from the plane and captured by flightradar24.com indicates that the plane continued flying at high speed away from the airport to which they intended to return, which Cox said seemed unusual. –AP