Only luck saved TWA’s Flight 840 after a 10-foot hole was blasted in the jetliner’s side by an explosive device during a flight over Greece, air safety experts and aeronautical engineers said Wednesday.
The Boeing 727 aircraft was descending and at an altitude of 15,000 feet when the bomb went off, triggering an explosive decompression in the pressurized passenger compartment and blowing out four passengers.
“An aircraft is exactly like a balloon, and once you get a hole in a balloon, it doesn’t just deflate. It explodes,” said Isaac Hoover, an airframe engineer and airline industry consultant.
“I think they are very fortunate,” he said of the surviving passengers and crew members.
If the bomb had gone off at a higher altitude, the decompression and resulting structural damage to the plane would have been worse. At some point, the damage would have caused a chain reaction of cracking and structural failure, experts explained.
In addition, heavy debris from the aircraft area blasted away could have caused major damage to delicate control surfaces, which would have destabilized the plane in flight. Such loss of controls have contributed to numerous accidents in the past, including the crash of a Japan Air Lines Boeing 747 last year killing 524, the worst single aircraft accident in aviation history.
“It was very likely that debris would have gone into an engine,” said Norman Birch, an independent aircraft accident investigator. “They were very lucky.”
Still, the hole in the side of the aircraft did not make the plane significantly more difficult to control.
“A hole in the side of an aircraft doesn’t particularly screw you up aerodynamically,” said Jerry Presba, an aircraft structures specialist. “A lot of worse things could have happened during the decompression.”
The hole caused somewhat greater drag, which was overcome by using additional engine power on landing, TWA officials said at a news conference in New York.
The hole was blown at floor level, about three rows in front of the point where the wing joins the fuselage. It appeared from photos examined by air safety experts that the force of the blast and the force of escaping cabin pressure burst the aircraft’s aluminum skin.
A 727 normally is pressurized to five or six pounds per square inch greater than the outside pressure at that altitude, Boeing spokesman Richard Schleh said. That amounts to about 36 tons of force, more than the weight of 36 subcompact cars, over the roughly 10-foot-by-10-foot area that was blown out by the bomb.
Photographs of the explosion showed likely damage to at least one and possibly three structural rings around the fuselage, rings known in the aircraft industry as “frame members.” These are spaced lengthwise about every two feet.
Commercial airliners are typically designed to sustain flight with one ring severed and several others seriously cracked, Hoover said.
In addition to structural peril caused by the bomb, debris from the explosion could have knocked out aircraft controls or caused catastrophic engine damage.
Damage caused by metal being sucked into the jet engines often is confined inside an engine, but it also can lead to serious safety hazards. For example, an engine fell off an American Airlines Boeing 727 last year when it was struck by a chunk of blue ice--frozen disinfectant from a leaky toilet.
Other Possible Damage
Debris would have traveled in an air flow over the wings and then down near the engines, Hoover said. But a flat piece of metal can behave in unpredictable ways.
It possibly could have damaged the wing or a control surface on the wing, known as an aileron. Less likely but still possible was damage to the 727’s tail or its control surfaces--the elevator and rudder.
TWA described the landing at Athens as “routine” and “uneventful.”
However, a 727 pilot for PSA remarked: “They were unbelievably lucky. There was tremendous potential for catastrophe.”
He said the bomb could very well have caused fatal structural damage if it had been placed in a different section of the aircraft.