LOS ANGELES - Radar data shows a piece of Alaska Airlines Flight 261 may have broken off seconds before the plane plunged into the Pacific Ocean, government investigators said today.
Analysis of radar and the flight data recorders portray a terrifying final 12 minutes, during which the MD-83 jetliner went into a 7,000-foot dive, then regained some semblance of control, then rolled upside down and plunged into the ocean.
The detailed description of the flight's end by the National Transportation Safety Board today didn't fix a cause for the Jan. 31 crash 10 miles off the Southern California Coast. All 88 passengers and crew aboard the flight from Puerto Vallarta, Mexico, to San Francisco were killed.
The new data showed the pilots struggling to fight a problem with the plane's horizontal stabilizer - the part of the tail that controls up-and-down motion - and a part suspected in the crash from the start of the investigation.
There was no immediate indication that the part which apparently came off the plane was a part of the stabilizer.
NTSB chairman Jim Hall displayed a chart at a Washington, D.C., briefing showing the plane's path as determined by radar. The chart marks a point right before the final plunge where radar picked up a reading that could indicate a piece separating from the plane and drifting with the wind as it fell into the Pacific.
``These primary radar hits might be indicative - and I emphasize might be indicative - of something coming off Flight 261 at this point,'' Hall said.
Navy ships have been sent to search the sea floor where the object would have landed, about four miles from the main body of the plane's wreckage, Hall said.
Hall said video mapping of the crash site was complete and an 8-foot section of the left horizontal stabilizer and some portions of the central stabilizer had been recovered.
The remains of three of the 88 victims had been positively identified and the families notified, Hall said.
Meanwhile, concern over the safety of MD-80-series aircraft like the Alaska Airlines MD-83 that crashed Jan. 31 may be leading pilots to become overly cautious about testing their planes' rear stabilizers.
In the week since the crash that killed 88 people, three U.S. jetliners have returned to their gates because of stabilizer problems.
Airline officials said Monday at least two of the incidents probably can be traced to pilots inadvertently overheating the motors by repeatedly testing the equipment.
``It may be that some pilots are being overly cautious and are running through their checks several more times than they typically do,'' said Jack Evans, an Alaska Airlines spokesman.
The horizontal stabilizer is a moveable, 40-foot wing mounted high on the aircraft's tail. It guides the up-and-down motion of the plane during flight, and is controlled by two motors that turn a jackscrew, similar to the mechanism that controls garage door openers.
During a flight, the motors make more than 100 adjustments, slightly changing the pitch as the airliner uses fuel and as other conditions shift.
On the ground, the motors can last up to 90 seconds before overheating and shutting down. It is usually not a problem in-flight because of the cold temperatures at higher altitudes.
The motors should become operative again after cooling down for several minutes, said John Thom, spokesman for Boeing, which bought McDonnell Douglas, maker of the MD-80 series planes, in 1997.
``We are getting the word out there (to pilots) to make sure you give enough time for these motors to cool down if you do go through the check again,'' Evans said.
On Tuesday, Boeing issued recommendations that any pilot with a stabilizer problem simply complete the operating manual checklist and, if that doesn't work, attempt no more troubleshooting.
``Priority should be given to landing at the nearest suitable airport or where maintenance can be performed,'' Boeing said in an update to operators of the DC-9, MD-80, MD-90 and Boeing 717.
Another, apparently unrelated, incident involving an Alaska Airlines jetliner occurred Monday night when an MD-80 made an emergency landing at San Francisco International Airport moments after takeoff because sparks were seen flying from an engine.
It was not clear today what caused the problems with the plane, which had come from Puerto Vallarta, Mexico, stopped in San Francisco, then headed on to Seattle - the same flight path as Flight 261.
No injuries were reported, and passengers traveling to Seattle were put on another plane.
On Saturday, an Alaska Airlines MD-83 jet returned to the airport in Reno, Nev., minutes after taking off for Seattle. The NTSB is investigating, but the airline said it was probably caused by an overheated stabilizer motor.
On Thursday, an Alaska MD-80 taxiing toward the runway in Seattle experienced ``intermittent problems'' with the stabilizer motor. After returning to the gate, the parts were swapped out and the plane took off without incident.
An American Airlines MD-83 flight out of Phoenix returned to the gate last week with a stabilizer problem, but investigators said it may have been caused by a faulty control switch in the cockpit.
Pete Harkovitch, a passenger on the jet that had to return to Reno, said he will avoid MD-80s until investigators figure out what happened to Flight 261.
``I was terrified,'' said the 42-year-old Fairbanks, Alaska, resident, who flies two to three times a month. ``It was too close to the other accident that killed so many innocent people. If MD-80s look like they're trouble-free, then I'll go back on them, but if I had to fly tomorrow, I'd take something else.''
AP Staff Writer Tom Verdin contributed to this report.