(Via Milinet)
U.S. News & World Report
June 19, 2000
A Dream Machine's Mysterious Moment
Behind the fatal crash of a V-22 tilt-rotor
By Richard J. Newman
It was a beautiful night to land an airplane on the desert
plateau.
As the brand-new V-22 transport aircraft commanded by Maj. John
"Boot" Brow flew toward Marana airport, just northwest of
Tucson,
Ariz., on April 8, it dipped over a moonlit mountain range and
into a
wide valley. Not a single cloud obscured the rugged landscape.
Advanced night-vision goggles gave Brow and his co-pilot, Maj.
Brooks
"Chuckie" Gruber, an excellent view of the airfield ahead.
As the plane slowed to land, its high-tech rotors pivoted from
the
forward-facing mode that made it fly like an airplane to the
upward-facing mode that converted it into a helicopter. The
pivot
went off without a hitch. But the pilots had a problem. As they
got
close to the airfield, the plane was higher than the flight plan
called for. The pilots hurried to descend. At some point, the
descent
exceeded 1,400 feet per minute-nearly twice the V-22's maximum
safe
descent rate of 800 feet per minute under landing conditions.
Loss of lift
The plunge produced a phenomenon known as "vortex ring state."
What
that means is that the aircraft was dropping so fast that the
air
flowing up through the rotors was moving as fast as the air
being
pushed down. Investigators believe the condition caused the V-22
to
completely lose lift. When it was just 245 feet off the ground,
the
aircraft flipped to the right and plummeted nose first to the
tarmac,
killing all 19 marines on board.
The crash, the military's worst since 1996, was all the more
sensational because it involved a V-22. The plane's
revolutionary
tilt-rotor engines, which allow it to fly with the speed and
range of
an airplane but take off and land like a helicopter, without a
runway, are so complex and expensive that the Pentagon tried to
kill
the program in the early 1990s. Congressional pressure kept it
going.
But Marine Corps officials say that an internal report, to be
completed this week, has found that the airplane performed
flawlessly
during the April 8 flight. "We're convinced there was no
mechanical
failure," says Brig. Gen. Emerson Gardner, one of the Marines'
V-22
experts. The probe results, he adds, have been reviewed and
validated
by NASA. The crash is not expected to affect the Marine Corps'
plans
to field its first squadron of 12 V-22s by next year. The
Pentagon
plans to buy 458 of the $65 million planes.
Instead, the Marines are grappling with a more puzzling
question: Why
did two of their most skilled and experienced pilots apparently
make
such an elementary mistake? Brow was an "all-star," says a
colleague.
Fellow pilots admired his "good hands," or precise air work.
Gruber,
the co-pilot, had logged even more time than Brow on the V-22
simulator. Yet they seem to have violated a basic tenet of
aviation.
"Do I have to tell you not to drink the drain cleaner underneath
the
sink?" wonders one V-22 pilot, likening the rapid descent to a
lapse
of common sense. "You can't imagine what these guys were
thinking,
that they couldn't land long or wave it off" and come around for
another landing.
The pilots' reasoning may remain a mystery. Military aircraft
have no
cockpit voice recorders. And Marine Corps officials say they
aren't
even sure which pilot was at the controls when the plane
crashed.
Whoever it was, some aviators speculate that he may have been
lulled
into complacency by the V-22's highly automated avionics and
powerful
engines. "Maybe he was so confident in the aircraft that he
figured
it could get him out of any situation," says one senior Marine
Corps
official. The V-22's critics question the safety of tilt-rotor
technology, but pilots say the aircraft handles like a dream
compared
with the 1960s-vintage CH-46 and CH-53 choppers it will replace.
Vortex ring state is one of the last things anybody expected to
cause
a safety problem. The Navy says the phenomenon has been a factor
in
only three helicopter accidents over the past 20 years. "Did we
focus
lots of training on this? No," says Gardner. That is likely to
change. The Marines are doing special tests on the V-22 to
determine
if there are any indicators, such as unusual shuddering or other
anomalies, which might signal that the aircraft is about to lose
lift. And scenarios such as those that Brow and Gruber
encountered
will be added to V-22 simulators. Still, "it's less than
satisfying,"
admits Gardner. "Will we ever know exactly what happened, and
why? I
don't think so."
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