A 1994 plane crash may provide clues to why a Wyoming company's
air tanker broke apart in June, causing a crash that killed three
men hired to fight fires in California.
Investigators are still combing the wreckage of a C-130A that
plummeted to the ground near Walker, Calif., on June 17. Hawkins &
Powers Aviation Inc., of Greybull, owned the plane.
A video showed the wings coming off after the plane dropped fire
retardant.
Since 1960, 14 fatal crashes have involved firefighting planes
under contract with the U.S. Forest Service.
The June crash in California and a 1994 wreck north of Los
Angeles are apparently the only ones involving C-130s, and some
similarities exist between the two accidents.
On Aug. 13, 1994, the right wing of a C-130A came off in mid-air
moments before the plane went down in mountainous terrain near
Pearblossom, Calif.
Just before the wing came off, witnesses saw a flash and then a
fireball near where the wing connects to the fuselage. Three people
were killed.
The National Transportation Safety Board said the explosion was
probably caused by fuel that leaked from a pressurized fuel line
system, possibly because of a faulty O-ring gasket, and ignited.
NTSB officials say they will search for similarities between
that crash and the one this summer in California.
"Right now we're looking at the Walker crash as a unique
accident, but we know the Pearblossom accident is out there," NTSB
spokeswoman Lauren Peduzzi told the Billings (Mont.) Gazette. "We
will look for similarities and if there are broader, more systemic
problems, we'll incorporate that into our safety recommendations."
She said it could be nine months to a year before a final report
is issued.
Five C-130s are expected to remain grounded for the rest of the
fire season until more is known about the crash.
Peduzzi said the two crashes could have quite different causes,
even though the circumstances may seem similar.
"We haven't made any definitive determination of cause in the
Walker, Calif., crash," she said. "We're aware of the problems
with the O-rings and we'll look at that."
The planes involved were made by Lockheed in 1956, delivered to
the Air Force and later converted into firefighting air tankers by
private companies.
In the 1994 crash, the NTSB said an O-ring may have been
flattened or dried out because the plane was in long-term storage
in the desert. The fuel from the pressurized system probably
ignited when it reached an engine or other hot surface, the report
said.
But in 1997, a former NTSB investigator took a second look at
the Pearblossom crash and reached a different conclusion.
Douglas Herlihy brought a team of investigators together to
climb to the crash site and sift through the wreckage.
In a paper published in 1999, he said the O-ring theory wasn't
supported by evidence at the site, the plane's maintenance records
or "universal maintenance knowledge."
Instead, he said, the plane probably crashed for a number of
reasons: flexing of the wing at a speed faster than recommended by
the manufacturer, pilot error and turbulence in 102-degree weather
while flying over mountains.
He theorized that the wing flexed violently, causing the
propeller cables and engine control cables to be pulled. In an
instant, he said, engine No. 3, the inboard engine on the right
side, went from 3,500 horsepower moving forward to 2,200 horsepower
in reverse thrust.
The bulkhead holding the fuel above the engine was ripped open,
fuel leaked and ignited when it hit the engine, he suggested.
Most likely, Herlihy wrote, the explosion occurred after the
plane's structural failure, not before as suspected by the NTSB.
As the investigation into the June crash continues, fire
officials and aviation managers are taking a more cautious
approach, especially after a second plane crashed at the Big Elk
fire in Colorado in July.
The Forest Service issued a directive last week requiring all
air tankers to carry 15 percent less retardant in the hopes of
reducing stress on planes in flight.
Federal officials are also examining the nation's aerial
firefighting technology, including an air tanker fleet whose
average age is approaching 50 years. New safety recommendations
could be proposed this fall.

(Copyright 2002 by The Associated Press