2 Airlines, Boeing Call for Jet Inspections

Alaska Airlines and American Airlines said Wednesday that they will inspect all 318 of their MD-80 and MD-90 series jetliners for damage to the horizontal stabilizer, the part that apparently failed in last week’s crash of Alaska’s Flight 261.

A few hours later, the Boeing Co., which has taken over the McDonnell-Douglas firm that built the planes, said it will ask all the other airlines flying the planes to follow suit.

The inspections were announced after the National Transportation Safety Board said that Flight 261’s stabilizer jackscrew--recovered Tuesday night from the ocean floor off Anacapa Island--showed signs of damage.

During radio conversations with maintenance personnel and air traffic controllers in the minutes before the Jan. 31 crash, the pilots of Flight 261 said they were having difficulty controlling the plane because of problems with the stabilizer--the wing-like structure on the tail of the plane that controls the up-and-down pitch of the nose.

NTSB Chairman Jim Hall said it was not known whether the damage to the jackscrew occurred during the flight or as a result of the jetliner’s impact with the ocean, but at least two veteran air-safety consultants said some of the damage appeared to have occurred well before the crash that killed all 88 on board.

Alaska Airlines, which has 34 MD-80s and MD-90s, said the visual checks should be completed by this morning and are expected to cause only minimal delays.

American Airlines, which flies 284 of the aircraft, said its inspections will take about a week.

“This voluntary inspection should alleviate public concerns following the Alaska Airlines accident,” American Vice Chairman Bob Baker said.

More than 2,000 of the sleek, twin-engine jetliners and their precursor, the DC-9, are flown around the world. Boeing’s request would affect more than 60 airlines.

Elliot Brenner, a spokesman for the Federal Aviation Administration, said Boeing would ask the airlines to check their planes during overnight stops or when routine maintenance is required. He said inspections are not mandatory, but most carriers are expected to comply promptly.

“This is the right thing to do and a very prudent action,” Brenner said. “It is important to take every opportunity available to look at these airplanes.”

Boeing issued an advisory Monday to pilots of MD-80s and MD-90s recommending an emergency landing if following a standard checklist fails to resolve a stabilizer problem.

“It seems like the prudent thing to do at this point,” said a company spokesman.

The jackscrew recovered Tuesday is a thick, threaded bolt about two feet long. Two motors spin the jackscrew, pushing the leading edge of the stabilizer up and down. The wings of the jetliner serve as a fulcrum, so when the leading edge of the stabilizer tips up, the plane’s nose tips down, and vice versa.

Although problems with the stabilizer may have begun shortly after the plane took off--possibly continuing for as long as two hours--the situation worsened dramatically about 12 minutes before the crash, when the stabilizer suddenly jammed in the full nose-down position.

Gene Daub, a senior air crash investigator with the FAA’s Transportation Safety Institute in Oklahoma City, said that is when at least some of the jackscrew damage may have occurred.

The NTSB displayed photographs of the jackscrew on its Web site Wednesday, and after looking at the pictures, Daub noted that some of the threads appear to have been stripped spirally from the jack shaft, indicating that the nut riding up and down the shaft had stopped moving smoothly.

One possibility, he said, is that an automatic turnoff mechanism failed when the stabilizer reached its full nose-down position and the motors continued to turn the shaft. Another possibility, he said, is that some dirt or other foreign material fouled the threads, grinding them off until the stabilizer jammed.

Brenner said the inspections requested by Boeing will focus on both the turnoff switches and the possibility that something fouled the threads.

Barry Schiff, a retired Trans World Airlines pilot and air safety consultant, said he was “80% sure” that much of the damage shown in the NTSB pictures occurred while the plane was still in the air.

Both he and Brenner said it was hard to tell what, if any, damage occurred before the stabilizer jam, and how the earlier problems reported by the flight crew related to it. They said it also was unclear whether any of the damage was related to a loud noise heard just before the plane began its final, minute-long plunge into the Pacific.

“All the problems are probably related somehow, but exactly how and why, who knows?” Schiff said.

Daub suggested that the final dive may have been precipitated by a stall of the steeply pitched horizontal stabilizer. In a stall, the stabilizer would lose the aerodynamic properties that normally tend to press it down, keeping the nose up and the plane in equilibrium. The plane would dive nose down, and pilots say recovery would be extremely difficult.

Radar data show that a piece apparently broke off the plane just before the final dive, but investigators say they still don’t know what it was. The Navy has launched an undersea search for this piece where it apparently landed, about four miles from the main debris field.

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Key Part Damaged

Investigators are examining the damaged threads of a 2-foot-long jackscrew pulled from the crash site. The jackscrew raises and lowers the leading edge of the MD-83’s horizontal stabilizer, which pilots reported was not functioning properly before the crash.

Sources: National Transportation Safety Board, The Boeing Co.; compiled by RICHARD O’REILLY/Los Angeles Times