COLUMN ONE : To Some, the Sky Is Falling : Fuselage doors, turbine blades, even whole engines have plunged to earth from jetliners. FAA says incidents are so rare they aren’t a menace. But safety experts say debris is a potentially terrifying problem.

Each time a thundering jetliner passes overhead these days, Stacie Huffman warily scans the sky for plunging debris.

Only a twist of fate saved the high school sophomore from an aluminum part that a Delta Air Lines 727 dropped on her tennis match last April at Mt. Rainier High School near Seattle. A few seconds before her coach summoned her, Stacie was leaning on a fence at ground zero.

“There was a loud bang,” the 16-year-old girl recalled. “I turned around and this big piece of metal was crashing into the fence 10 feet away.”

Like cars losing hubcaps and mufflers on the freeways, airplanes periodically shed such objects as aluminum skins, access panels, fuselage doors, red-hot turbine blades, frozen sewage, cowlings, engine cones and even whole engines.

Hurtling toward Earth at hundreds of miles per hour, such fallout has punched gaping holes in roofs, crushed cars into pancakes, plunged into crowded swimming pools, smashed school desks, showered people with human waste, sent glass shards shooting through living rooms and set houses on fire.

Federal officials and aviation executives usually characterize these incidents as acts of God so rare that they aren’t a menace. But they acknowledge that no one knows with any certainty how often they occur or whether anyone has ever conducted a serious study of the problem.

No deaths or injuries have been reported in such incidents, but the Federal Aviation Administration is not even 100% certain of that. Nonetheless, some safety experts and those who have had close encounters with falling flotsam say it is a terrifying and potentially dangerous problem that needs attention.

“Nobody has been killed yet yet yet, but it will be a public relations disaster the day it finally happens,” said Chuck Miller, a noted air safety proponent and former government accident investigator. “Relying on statistical probability is a very shortsighted approach.”

Poor maintenance and bad design are major culprits, according to engineers. Increasing use of older aircraft, more prone to corrosion and metal fatigue, also may be contributing factors, they say. Toilets can leak sewage, which freezes at high altitude then falls off as ice.

While the skies have grown more crowded with flights, once vacant zones near big-city airports have filled up with industrial and residential development. As a result, falling debris is far more likely to be noticed.

Objects from all types of aircraft are being reported with what appears to be growing regularity; several serious incidents have occurred this year alone.

Data formerly kept by the military suggests that things fall off combat aircraft every day. The Navy recorded an average of 460 incidents per year during the 1980s.

In the commercial world, Boeing received 200 reports of structural parts falling off its planes between 1989 and 1994. McDonnell Douglas officials said only several incidents occur each year involving their planes.

Not to worry, say FAA officials who characterize falling debris as a statistically insignificant problem.

“It is a rare, rare event that this happens, but it does happen,” said Anthony J. Broderick, the FAA’s associate administrator for regulation and aircraft certification. “When you measure them in terms of probability, given millions [of] flights, it is very, very low.”

There have been a number of close calls, in which objects have landed just a few feet from people as they watched television, taught class or worked.

Mark Erp, who owns an auto body shop in St. Louis, was preparing to give a customer an estimate when a DC-9 engine cone from a TWA jetliner came barreling through the roof of his shop in 1989.

“It’s a day I’ll never forget,” he said recently. “It hit right in the center of the shop, gouged the floor, bounced up and left another big gouge where it landed.”

No one was injured. TWA at first denied that the nose cone came off one of its jets, but eventually acknowledged it was the airline’s and paid for damages, Erp said.

Ray Villeneuve was explaining a point of French grammar at Chino High School last March when a chunk of frozen sewage slammed through the roof of his classroom and smashed into his desk a few feet away.

“I had just set down a book on the desk and taken five steps away when it fell,” said the ex-Marine. “I know what incoming artillery sounds like and this sounded like a bomb.”

The Korean War veteran still worries about the potential health effects of being splattered with sewage. None of the 22 students in the class were hurt, but they were so scared that school officials brought in a counselor.

“I would say to the FAA: ‘Does it take somebody getting killed before they do something?’ ” Villeneuve added.

FAA officials deny that they take a casual attitude in handling falling debris. They say that anything that jeopardizes the safety of people on the ground also puts aircraft passengers at risk.

The FAA is supposed to investigate every report of a falling object, but Broderick says tracking down the offending aircraft is “generally impossible.” As with anything involving machines, he cautions: “I don’t know how it is possible to ensure 100% perfection.”

The agency has no records of ever fining an airline or undertaking disciplinary action against a pilot for dropping something, even in incidents that resulted in serious property damage.

Among the most serious cases occurred in 1983, when an engine malfunction aboard a DC-9 spewed hot turbine blades that set brush fires and burned 15 rooftops in Newport Beach. Steve Link’s home in the exclusive Dover Shores area was gutted. Link says he and his wife wonder whether the stress caused by the incident triggered a miscarriage.

“It was a very tough time,” Link said. “Ultimately, my wife couldn’t deal with it and we had to sell the house and move.”

Link said the airline disputed the damages, and he ultimately had to hire an attorney to reach a settlement with Republic Airlines, which was later bought out by another company.

Airlines often refuse to accept responsibility when they are accused and fight demands for property damage compensation.

“There is a lot of buck-passing when this happens,” said Barbara Beyer, president of the aviation consulting firm Avmark Inc. in Arlington, Va.

Executives at major airlines and their unions declined to talk publicly about the problem. However, one executive at a major airline acknowledged privately that the incidents “are major embarrassments.”

Neither the FAA nor the National Transportation Safety Board has ever studied why things fall off airplanes, although lax maintenance is most often blamed. Tools are sometimes left in the recesses of aircraft and rattle out during flight. Access panel doors are sometimes poorly secured and blow off.

Weak parts and age can also contribute to the problem. Hinges and latches may be flimsy and break. Fasteners fail then allow pieces of metal to separate. Jet engines have disintegrated because of weak components.

Airlines are also operating older aircraft that are more vulnerable to metal fatigue, stress corrosion and cracking that can result in delamination of aircraft skin, according to an executive at a major airline who did not want his name used. The average age of the commercial fleet, now about 15 years, has been advancing over the last decade.

“The older an aircraft, the higher the possibility a fatigue-related failure would occur, but that is an academic viewpoint,” Broderick said.

The biggest thing ever known to have fallen off a plane was caused by stress corrosion on a Boeing 737, operated by Aloha Airlines. The entire top of the forward fuselage plunged into the Pacific Ocean in 1988, killing a flight attendant and injuring 61 others before the plane landed. The incident prompted the FAA to intensify inspections and improve maintenance of older aircraft.

Nonetheless, Boeing and McDonnell Douglas officials say the Aloha incident and others like it were one-time failures, not tied to any trend.

The problem “doesn’t show up on our list of serious safety concerns,” a Boeing spokeswoman said.

Aly Samahy doesn’t buy that. A two-pound chunk of metal--later identified as a maintenance tool--fell from an aircraft and slammed through the skylight at his home in Chantilly, Va., in September. It showered the living room with glass and destroyed a valuable Oriental rug. After long complaining about airport noise, Samahy is worried about his safety as well.

“If it happens to me, it could happen to anybody,” Samahy said. “When something like this kills somebody, then it will be something they look at.”

A similar incident occurred in 1987, when a five-pound piece of polished steel crashed through the living room ceiling of Blanche Rebert in South-Central Los Angeles, while the 81-year-old woman was watching television.

Entire engines have fallen off at least several commercial and military aircraft in recent years, the result of ingesting foreign objects or old age, but no damage occurred on the ground.

Earlier this year, a propeller-driven American Eagle commuter plane lost a door over the Chicago suburbs and passengers aboard the plane had to pull a flight attendant to safety. The door was found in a river.

Among the Navy reports was a 1982 incident in which a 30-pound door from a helicopter plunged into a condominium swimming pool in Coronado, Calif., narrowly missing four swimmers and about a dozen sunbathers.

And since World War II, the military services have accidentally dropped 11 nuclear bombs, which were never recovered, according to a study released earlier this year by the Brookings Institution.

Local groups opposed to airport development have raised the debris issue. The Energy Department has done extensive research to ensure that nuclear bombs will not detonate if something were to plunge into a storage bunker.

In Japan, schools near Narita Airport require students to wear helmets at recess to protect them from parts and frozen sewage according to local authorities who have recorded 106 incidents of falling objects between 1980 and 1984 at Narita.

Some aerospace industry executives say problems of falling parts around the world show why the FAA should pay more attention to the problem.

“The FAA is dragging its feet,” said Michael Seville, chairman of Rancho Cucamonga-based PneuDraulics, a company that has invented a valve to stop sewage from leaking, then freezing into blue ice. “The approach the FAA has taken is air safety. That means they can drop blue ice on us.”

Meanwhile, Stacie, the tennis player from Seattle, said that despite an initial flurry of activity by the FAA and Delta after the part fell into her tennis match, officials never explained what happened.

Delta later identified the part as a faring, which helps smooth the airflow over a wing, and has stepped up inspections of the part. But “nothing was said to our tennis team,” Stacie said. “It was like, ‘Oh well.’ ”