Inspection Urged For 747 Cargo Doors -- Ntsb Cites Accidental Opening

The National Transportation Safety Board has called for inspection of the wiring of cargo doors on 360 late-model Boeing 747s, rekindling a controversy about the potential for the doors to come open in flight with disastrous results.

The NTSB's recommendation was prompted by a June 13 incident at New York's John F. Kennedy Airport involving a 4-year-old United Airlines 747-200B jumbo jet. As ground workers prepared the plane for a flight to Tokyo, a stray electrical signal from chafed and blackened wires unlatched the aft cargo door and lifted it open with no one operating the switches.

Because of that incident, United has taken the extraordinary step of disconnecting all potential sources of power to the cargo doors prior to departure of all 747 flights. The Chicago-based airline, which operates 48 jumbo jets, lost nine passengers when a 747 cargo door tore off in flight two years ago.

After the cargo doors on United jets are closed, latched, locked and checked, a mechanic now climbs into a small hatch just behind the front wheel, called a "hog hole," and pulls a small black button, opening a circuit breaker. This disconnects the wire bundles in and around the forward and aft cargo doors from all sources of electricity.

"United has implemented this procedure on all 747s in order to maximize the safety of the operation until a permanent fix can be applied," said United spokeswoman Sara Dornacker. "It is extraordinary, but it does have FAA approval."

Dave Duff, spokesman for the Federal Aviation Administration, could not say whether other airlines are taking similar precautions. To date, no 747 operators have been required by the FAA to similarly disconnect cargo-door power; nor has the agency asked airlines to inspect a flawed conduit blamed in the New York incident and now known to be susceptible to potentially dangerous cracking.

The NTSB, which investigates accidents but has no enforcement powers, called for sweeping inspection of the wiring in an Aug. 28 letter to FAA Administrator James Busey.

Boeing forwarded a copy of that letter to airlines worldwide, but has taken no other formal action, said company spokesman Christopher Villiers.

The FAA's Leroy Keith, the Renton-based executive responsible for issuing safety orders, declined a request for an interview and prohibited FAA technical experts from being interviewed.

"We have received the NTSB recommendation, we have evaluated it and we are looking at different options," said Duff. "We will have a response back in the near future."

In the New York incident, the cargo door was shut and latched - but the locks had not yet been set in place - when the latches suddenly rotated open and the door swung open. The powerful electric motors that lift the 800-pound door continued to run for several seconds after the door was fully open, until a mechanic cut off power by pulling a circuit breaker.

Boeing spokesman Villiers downplayed the hazard posed by potentially chafed and burned cargo-door wires on 747s operated by other airlines.

Villiers said reinforced steel locks that airlines and Boeing began installing in the past two years now are on all 851 747s in commercial service. He said that, even if a stray electrical signal inadvertently activated the door-opening sequence in flight, the steel locks would keep the door shut tight. He also noted that additional electronic sensors that warn the flight crew if the door is not properly locked have been ordered, although neither he nor the FAA could say how many aircraft currently have the sensors installed. Airlines have until Nov. 30 to install them.

In lab tests in 1987, Boeing discovered that a stray electrical signal could drive 747 cargo-door latches open; the latches simply bent the weak aluminum locks out of the way.

In late 1988, the FAA ordered stronger steel locks as replacements for the old aluminum ones, but granted some airlines up to two years to make the $2,000-per-aircraft change.

Authorities believed several switches that direct power to and around the door would have to short-circuit to enable stray electricity to open the door, and that such a complicated failure was virtually impossible.

But the New York incident proved that the door-opening sequence can be activated with power coming from certain bare wires - even with the switches functioning as expected, according to the NTSB. This revelation may change conclusions drawn previously by the NTSB about the United accident two years ago, said relatives of victims killed in that case.

On Feb. 24, 1989, the front cargo door of United Flight 811 tore off in flight near Honolulu, sending nine passengers, including 24-year-old Lee Campbell and 61-year-old Mary Handley, to their deaths. The plane was a 19-year-old 747-100 with weak lock sectors, scheduled to be changed sometime in the next 18 months. After that accident, the FAA ordered steel locks installed on all 747s within 30 days.

More than a year later, in April 1990, the NTSB ruled that Flight 811's cargo door must have been improperly shut before takeoff, even though ground workers and the flight crew testified that the door had been routinely closed, latched and locked.

But then in September 1990, the cargo door, long believed to hold the most telling evidence of what really happened, was recovered from the ocean floor. Boeing analyzed the door in Seattle and sent the results to the NTSB, where the case has remained in limbo. The NTSB reportedly will hold a hearing early next year on those results.

Evidence on Flight 811's door - and now the recent door-opening incident in New York - have sparked new suspicion that a stray electrical signal may have caused the Honolulu accident, said relatives of Campbell and Handley who have been closely tracking the issue.

Campbell's father, Kevin Campbell, believes 747 cargo doors, even with steel locks, have the potential to come open in flight, tearing off huge chunks of the fuselage and cabin floor, as happened on Flight 811.

"It can still occur," said Campbell. "This is why United is pulling the circuit breakers before flights."

Campbell is a retired New Zealand car-dealership owner with a background in mechanical engineering. He and his wife, Susan, have spent more than $100,000 and thousands of hours investigating the accident.

Campbell said his theory about hazards posed by the door are derived from research and from extensive discussions with officials at the NTSB and United.

According to Campbell, a stray electrical signal could, at any point during flight, begin to push the cargo-door latches partially open if the steel locks are even slightly out of adjustment. (Steel locks in perfect adjustment are designed to prevent any movement of the latches, but Campbell said the locks can, over time, move out of adjustment.)

With the latches and locks thus slightly misaligned, a phenomenon called "hoop stress" would be nullified. The door is designed so that as the plane swells under pressurization, forces are created that help to snugly seat and reinforce the latches and locks in a perfectly aligned position.

With the latches and locks misaligned, pressurization from inside the plane would add to the force of the motor trying to drive the latches open. The door would begin to flex and strain, and, at some point, the latches could break or slip loose, and pressurization would blast the door explosively into the airstream.

"It's a remote possibility, sure; but we know that remote possibilities have a way of happening," Campbell said. "If something can go wrong, eventually it will go wrong."

If it turns out that numerous Boeing 747s have chafed or burned cargo-door wires, it would mean passengers on those planes are relying solely on perfectly adjusted steel locks to keep the planes safe, he said.

"You're down to one more failure before disaster," he said.

Just how many jumbo jets may be involved won't be known unless the FAA follows through on an order to inspect wiring on all 747s delivered after 1981 as called for by the NTSB, which identified those 360 jets as having the suspect conduit.

The FAA sometimes rejects recommendations from the NTSB; it did so most recently early in the investigation of a Boeing 767 that crashed in Thailand last May. The NTSB, early on, called for banning the use of thrust reversers on some Boeing jets. Only after Boeing made the suggestion did the FAA concur.

Campbell pointed out that older 747s may be prone to chafed wires, as well, since they use the same door and similar wire systems. Older cargo doors may, in fact, be more prone to stray electrical signals than newer ones, since they have been opened and closed many more times, increasing the likelihood of wear and tear, he said.

Patricia Gabrielse, of Tacoma, said Boeing and the FAA should be moving more aggressively to define the current hazard posed to the public and, in the meantime, require reasonable precautions, such as those now being taken by United, to reduce the risk of a door opening in flight.

Gabrielse, the daughter of Flight 811 victim Handley, said her mother, a successful Dale Carnegie franchise owner, might still be alive if the FAA had not been persuaded by Boeing and the airlines to stretch out the deadline for installing steel locks.

"When the industry is allowed to so heavily influence safety regulations, I think that's a significant problem that continues to put all of us unnecessarily at risk when we fly," she said.

HOW 747 CARGO DOORS OPERATE UNTIL CHAFED WIRES RECENTLY CAUSED THE CARGO DOOR ON A UNITED 747 TO MYSTERIOUSLY UNLATCH AND LIFT OPEN, AUTHORITIES BELIEVED IT WAS VIRTUALLY IMPOSSIBLE FOR A STRAY ELECTRICAL SIGNAL TO BYPASS SEVERAL SWITCHES IN AND AROUND THE DOOR TO BEGIN THE DOOR-OPENING SEQUENCE.

747-200B

1. HOW THE LATCHES WORK

Electric motors lower and shut the 800-pound door; eight "latch cams," evenly spaced along the bottom edge of the door, connect with eight "latch pins" mounted on the fuselage.

PROPERLY LOCKED Boeing contends new steel lock sectors prevent the latch cams from rotating open, even if the latch cams - activated by a stray electrical signal - tried to do that in flight.

SLIGHTLY MISALIGNED One safety advocate contends that latch cams powered by a stray signal could rotate partially open against out-of-alignment lock sectors. Pressurization would add opening forces to the moving latches. The door would flex and strain until the latches burst free of the latch pins, blasting the door open.

2. DOOR LATCHED AND LOCKED

A motor rotates the cams around the pins, securing the door. A ground worker depresses a lever on the outside of the door, which mechanically swings the eight lock sectors into place over the latch cams, blocking them from rotating open. The sequence, which takes less than 30 seconds, is reversed to open the door.