The early focus in the Alaska Airlines crash is on the plane's tail-mounted horizontal stabilizer, which has had difficulties on MD-80s.
The problem was a jam in the plane's tail, the pilots of Alaska Airlines Flight 261 told air traffic controllers.
The pilots descended from 31,000 feet and struggled for more than six minutes Monday to bring their MD-80 jetliner under control. They tried to solve the problem while high over the Pacific Ocean and then asked for an immediate landing in Los Angeles. They requested to stay over water as they configured the plane for landing, an ominous comment that hinted at their dire situation.
But the plane suddenly fell from about 17,000 feet and crashed, apparently killing all 88 people on board.
Rescue crews continued to search for survivors in the Pacific near Point Mugu, Calif., but it was unlikely anyone could have survived the impact or the chilly water. Search teams recovered several bodies Tuesday and said they heard pinging signals from one or both of the plane's flight recorders.
As the National Transportation Safety Board released the first details about the crash, investigators began to focus on the horizontal stabilizer, the top portion of the MD-80's distinctive T-shaped tail. They are especially interested in the stabilizer because the pilots reported it was jammed.
The stabilizer helps pilots control the plane in two ways:
It moves the entire stabilizer through a process called trimming, which allows it to adjust the 40-foot device to make a flight smooth and steady.
It moves panels on the stabilizer called elevators to make the plane climb and descend.
The MD-80's stabilizer has been the subject of safety inspections because of previous difficulties.
In October, Boeing warned airlines about a problem caused by de-icing fluid that congeals and freezes in the plane's elevators. Boeing said there had been two incidents on MD-80s in Europe last winter in which de-icing fluid dried to a residue and then became wet and solidified. That froze the elevators, preventing pilots from moving them properly.
"The gel swells to many times its original size and can freeze during the next flight leg, potentially restricting the movement of flight control surfaces," a Boeing engineer wrote in an October 1999 article sent to airlines. A copy was obtained by the St. Petersburg Times.
That article referred to all types of planes, but MD-80s were singled out because of the European incidents. The official MD-80 maintenance manual was updated with a "Precaution Note" that urged mechanics to inspect vulnerable areas for residue of de-icing fluid.
It's not clear how recently the accident airplane had been deiced. Officials from Boeing and Alaska Airlines did not return telephone calls Tuesday.
Separately, the Federal Aviation Administration has issued four "Airworthiness Directives" over the past 12 years calling for inspections or fixes to the horizontal stabilizer.
However, it's far too early to say if de-icing fluid or the other tail problems played a role in Monday's crash.
NTSB investigators emphasized they are exploring all possibilities about the crash.
It's also not clear how the stabilizer could jam.
When a plane is at a cruise altitude _ in Flight 261's case, 31,000 feet _ the pilots usually rely on the autopilot to trim the plane.
When pilots are flying the plane by hand at a lower altitude, they make their own adjustments by moving switches on their control wheels.
There are several safeguardsto prevent problems in the trim system. The switches are designed so pilots cannot move them inadvertently, there are backup switches and circuit breakers, and the system makes a buzzing sound so pilots know when the trim is being adjusted.
One malfunction is called "runaway trim," when an electrical glitch causes the trim to move the stabilizer as far as it will go. That can make the plane suddenly climb or dive, until pilots regain control.
But that is extremely rare. Three MD-80 pilots said they had never encountered that problem in thousands of hours flying the airplane.
Pilots are trained to recover from jammed stabilizers, said Jack O'Brien, director of training for Largo-based Southeast Airlines, which flies MD-80s. They can overpower the stabilizer problem by forcefully pushing or pulling their control column.
Bill Sorbie, a retired MD-80 pilot from US Airways, said that kind of jam is "nothing that's catastrophic, nothing you can't handle."
But Sorbie and other pilots said the situation could have turned catastrophic for the Alaska Airlines crew if there were other malfunctions such as a frozen elevator or a fire in the tail.
Trouble in the tail
Tailspan of MD-80: 40 ft. 2 in.
Pilots of Alaska Airlines Flight 261 reported problems in the tail of their plane shortly before it crashed in the Pacific Ocean on Monday.
The horizontal stabilizer is the top part of the MD-80's distinctive T-shaped tail.
- Elevators, rear panels on the stabilizer, point the plane's nose up or down.
- The elevators are controlled by the pilot pushing or pulling on the control column/yoke
The pilot moves or "trims" the entire stabilizer to make a flight smooth and steady. It needs to be adjusted throughout the flight to account for changes in the weight of the plane and air conditions.
Sources: News reports, Federal Aviation Administration
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Text that accompanies drawing explaining the final moments of Flight 261 not available electronically. Please see microfilm.