Two days after an Alaska Airlines jetliner plunged into the ocean near Los Angeles, an American Airlines jet returned unexpectedly to Phoenix. Within four days, Alaska Airlines experienced a rough landing in Reno, Nev., and a postponed flight in Seattle.
All four airplanes reported the same problem: a jammed horizontal stabilizer trim on the tail, crucial to keeping the plane level.
The emergencies - all involving MD-80-series jets - are prompting some passengers and pilots to wonder if it's time to ground the fleet until its safety is confirmed. But aviation experts, from the Federal Aviation Administration (FAA) to watchdog groups, see such action as premature.
"We most definitely should not jump to conclusions," says Aaron Gellman, director of Northwestern University's Transportation Center in Evanston, Ill.
Whether or not the FAA eventually takes special action, last week's Alaska Airlines crash, coupled with the emergency landings, has put a spotlight on the agency's system of correcting mechanical problems on commercial jets.
The FAA routinely issues "airworthiness directives," often at the rate of one or two a day, which are similar to automobile recalls except that compliance is mandatory.
On the Alaska jetliner that crashed, maintenance was scheduled for June in response to one such directive. Experts at this point are divided on whether this issue had any impact on last week's crash.
The directive called for checking for corrosion on hinge plates in horizontal stabilizers on McDonnell-Douglas MD-80 aircraft (including the MD-83 version). But that issue was not seen as an immediate threat to safety, so airlines had until November to comply.
On rare occasions, the FAA issues an emergency directive, grounding an entire fleet until the problem is solved.
One such directive was issued after an American Airlines jet lost an engine and crashed near Chicago's O'Hare International Airport in 1979. Until investigators discovered why an engine would break away, all DC-10s were grounded.
But with Flight 261, "we're not sure if the report of the stabilizer problem was a symptom or a cause of the problem or, in fact, if it was the stabilizer at all," says David Stempler, president of the Air Travelers Association.
Mr. Stempler was instrumental in the grounding of all DC-10s after the 1979 crash. He says he would be the first to call for the grounding of the MD-80s, named for their manufacturer McDonnell-Douglas, if he could point to a particular problem. But he has too many unanswered questions.
Especially disturbing to many experts are reports of two loud bangs in the rear of Flight 261, indicating trouble with more than the horizontal stabilizer.
"These are exceedingly safe airplanes, and even when they run into problems, as shown in Phoenix and Reno, they're able to land safely. So something is unique about this situation," Stempler says. "You don't want to start grounding airplanes until you know what the specific problem is."
In response to last year's corrosion directive, Alaska Airlines has so far done the required work on 10 of its 35 MD-80s.
Air-safety experts say such corrosion would not have been the sole cause of Flight 261's crash. But some speculate that the problem may have increased malfunction of the horizontal stabilizer.
"It appears that the initial problem was with the horizontal stabilizer trim, which was not directly related to the hinge within the airworthiness directive," says R. John Hansman, a professor of aeronautics and astronautics at the Massachusetts Institute of Technology. Corrosion, he adds, "would not directly cause the stabilizer to trim full up [as occurred], but it's possible it may have occurred indirectly."
Moreover, experts don't necessarily view the recent emergency landings with concern.
"Pilots, like other humans, get skittish. And problems in one airplane will be subject to greater sensitivity by the crews of other airplanes," says Mr. Gellman.
Indeed, airline officials say recent stabilizer troubles could stem from pilots overheating the motors by repeated testing.
Industry experts stress that as many of 500 airworthiness directives are issued each year - and most are fixed without incident.
Unlike automobile recalls, when the registered owner of an airplane receives an air-worthiness directive, "you must follow the directions ... or you're not allowed to fly your airplane," says Tony Broderick, an aviation-safety consultant and former FAA official.
Once a problem is detected - one significant enough to require action beyond routine maintenance - the FAA and the manufacturer analyze risks, leading to a service bulletin similar to the recall instructions that get sent to garages. It details the steps airlines must take to fix the problem and the deadline - which can be months or even years.
"The fundamental desire is to have compliance before it would be expected that the problem would become an issue in any other airplane," Mr. Broderick says.
Boeing, which now owns McDonnell-Douglas, estimated that the work for this particular corrosion directive would cost about $7,000, and take 117 hours, per airplane.
"It's very expensive for airlines to pull an airplane out of service to do an inspection, particularly a major thing where you have to take an airplane apart," Mr. Hansman says. "From a cost/benefit standpoint, they prefer to do it during normal maintenance."
Once the wreckage of Flight 261 is retrieved from the Pacific Ocean and analyzed, the cause of the crash should become clearer. The Alaska flight has a tremendous amount of information to draw from, including the cockpit voice recorder, the flight data recorder, radar coverage, and communications with air-traffic controllers and Alaska Airlines maintenance departments.
The radar record suggests that a piece, possibly from the tail, may have fallen from the plane about 4 miles before it crashed.
Whatever the FAA does, "the rate of mechanical accidents in airplanes has been going down for the past 40 years," says Hansman. In fact, one of his colleages at MIT likes to describe it this way: If you were to randomly get on an airplane every day, it would be 15,000 years before you had a fatal accident. "So it's a very, very safe system," he says.
(c) Copyright 2000. The Christian Science Publishing Society