An oldie, but a goodie
Role of Stabilizer in Alaska Crash Questioned
By Tim Dobbyn
WASHINGTON (Reuters) - A stabilizer problem alone would probably not have caused Monday's crash of an Alaska Airlines MD-83 off the coast of southern California, pilots and others familiar with the plane said on Tuesday.
A problem with stabilizer trim radioed from Flight 261 was about the only clue available early on to investigators trying to determine what caused Monday's crash. But pilots and safety experts said it sounded more like a symptom than the primary cause.
``I've had the trim fail. It's annoying but it isn't dangerous,'' said a pilot with 12 years experience on the closely related DC-9.
``We are trained for a jammed stabilizer,'' he said. ``I think there was an additional factor.''
The Alaska Airlines plane carrying 88 people plunged into the Pacific Ocean after requesting an emergency landing at Los Angeles airport en route from the Mexican resort of Puerto Vallarta to San Francisco and then on to Seattle. No survivors were found despite a massive search.
``There has really been nothing in the history of the airplane that would indicate it would be susceptible to this kind of (stabilizer) problem,'' said David Stempler, Air Travelers Association president and publisher of the Airline Accident Report Card.
Some pilots speculated that a fire in the rear or more serious damage to the tail than the Alaska Airlines crew realized, could have caused the crash.
In the MD-83 type of aircraft, the whole horizontal stabilizer, which is the cross piece mounted above the vertical tail piece, is driven electrically to trim the aircraft's nose up or down and compensate for movement inside the aircraft by passengers and other weight changes.
If the system malfunctions, the nose of the plane could pitch suddenly up or down but the pilot can hit a switch to stop the motion of the stabilizer, pilots said.
The crew can then use the elevators, movable panels on the trailing edge of the stabilizer that are controlled by cables on the MD-83, to correct the plane's attitude.
The stabilizer has a primary electric motor that obeys trim instructions from the pilot and a lower-powered ``alternate'' motor than responds to autopilot commands, said Boeing Co. (NYSE:BA - news) spokesman John Thom. The full range of stabilizer movement is 14.3 degrees.
In 1995 the Federal Aviation Administration asked operators of DC-9's and MD-80 series planes to inspect and replace certain primary motors because of a manufacturing defect that could cause premature failure, documents show.
Alaska Airlines (NYSE:ALK - news) spokesman Jack Evans could not immediately confirm the airline had done that specific piece of work but he said the company acted on all FAA orders within required deadlines.
In February 1999 another of the airline's fleet of MD-80s reported flight control difficulties during takeoff from Fairbanks International Airport.
According to a National Transportation Safety Board report, the pilot said the plane's nose failed to rise as he pulled back on the control column until he applied excessive pressure.
The plane continued to Anchorage for an emergency landing during which the pilot said the elevator controls felt sluggish. No one aboard was hurt.
But pilots who have flown the twin-engined MD-80 series expressed skepticism that a malfunctioning stabilizer at cruising altitude could cause the crash alone.
``In that phase of flight I've never heard of a runaway stabilizer situation that couldn't be recovered,'' said a pilot with a major airline who spent five years flying MD-80s.
``A fire could have damaged the flight controls or a mid-air collision taken out the tail but at the moment it's just a mystery,'' the pilot said.
The Coast Guard reported hearing a pinging noise that may be from the plane's flight data or cockpit voice recorder. Both devices will be critical to determining what went wrong.