know there were dragons lurking beyond
a descent rate of 800 feet per minute at 40
knots or less, so why test? “There was no
practical need for any rotorcraft that we
knew of to have to exceed that boundary
anyway,” one of the Osprey’s developmental test pilots in those days told me.
The flight clearance placard setting the
limits on how the MOTT could fly the
Osprey simply adopted the standard from
helicopter flight manuals. “Avoid descent
rates of 800 fpm (feet per minute) or
greater at airspeeds less than 40 KCAS,”
it said, “KCAS” being the abbreviation for
“knots calibrated air speed.” Precisely what
might happen if a pilot flew beyond that
edge of the envelope wasn’t spelled out in
the MOTT’s flight clearance placard, but
there was no need to go into detail. The
rule was labeled a “Warning,” which meant
failing to observe it risked loss of the aircraft and death. For pilots, “Warning” is
the flight manual equivalent of a skull and
crossbones.
At his May 9 news briefing, McCorkle
was asked whether the Osprey that
crashed had been “descending within the
flight envelope.”
“He was descending over a thousand
feet per minute,” McCorkle said, noting
that the recommended limit was no more
than 800 feet per minute at 40 knots or
less. Why the pilot had descended so fast
was still being studied, McCorkle said.
The right rotor of the Osprey, he added,
might have gone into vortex ring state only
when the pilot moved his control stick to
the right four seconds before the crash. “I
think that that’s probably what caused it,”
McCorkle said.
“Is it correct to say that pilot error is to
blame for this accident?” a reporter asked.
“No, it’s not correct to say that,”
McCorkle said. “I would really appreciate
it if you wouldn’t speculate on that until
after the mishap board has reported out.
We feel like we have enough information
to say that it was not mechanical. There are
a lot of things the board is looking at. And
why was the pilot at this rate of descent?
Why was he in this position at this time?
And it would be very inappropriate at this
time to say that it was pilot error.”
The main thing McCorkle wanted
people to understand was that the crash
wasn’t being blamed on a flaw in the
Osprey. Developmental test pilots at Pax
River were going to do a full range of tests
to explore where the edge of the Osprey’s
envelope for going into vortex ring state
lay, he said. Meanwhile, OPEVAL would
go on. “We have waited really a heck of a
long time to put the airplane back into the
air,” McCorkle said.
The Right Stuff
Once upon a time, test pilots like the famed
Chuck Yeager tugged on a helmet and
squeezed into a flight suit, strapped on an
X-model aircraft, then bet their lives they
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APRIL 2010 | ROTOR & WING MAGAZINE
