Three On Board Were Killed
Federal safety investigators say the
test pilot aboard a Bombardier Challenger 604 test aircraft pulled
"too aggressively" on the yoke, causing fuel to slosh aft and
pushing the center of gravity out of the safety envelope.
"They were in the rear part of the range," he said. "When the
fuel migrated back, it shifted the center of gravity, which led to
the stall."
The report also blamed Bombardier for inadequate flight planning
procedures and both the FAA and Transport Canada for failing to
provide on-the-spot supervision during the October 10, 2000
test.
Test pilot Bryan Irelan, 33, and test engineer David Riggs, 48,
died soon after the accident. Eric Fiore, 43, also a test pilot,
died of his injuries 36 days later.
The NTSB report said the three crew members were indeed testing
the limits of the aft CG and had loaded their aircraft accordingly.
They were trying to obtain certification from the UK's Civil
Aviation Authority. Specifically, they were testing the Challenger
604's Pitch Feel simulator (PFS) function. PFS units replicate
aspects of the aerodynamic loads (absent in hydraulically driven
control systems) through artificial feel and centering units,
allowing the pilots to feel control input resistance. The units
increase control column, control wheel, and rudder pedal resistance
as the flight control surfaces are moved from their neutral
positions.
It wasn't set up to be a fun flight.
According to the NTSB Final Report, "The accident copilot
reportedly asked, 'why are we so far aft?'. The flight test
engineer responded that this configuration (with the production PFS
units) was previously flown on airplane number 5991 (the accident
airplane) with the CAA test pilot during the 1999 flight test. The
flight crew reportedly responded, 'okay.' The briefing continued
with a presentation comparing the characteristics of the production
PFS and modified PFS units. The pilot reportedly stated that the
airplane was going to 'handle like a pig.'"
Shortly after take-off from Wichita (KS) Mid-Continent Airport,
it became evident that Irelan was having trouble. The report
states, "At 1448:45, the tower issued a takeoff clearance and
instructed the flight crew to fly a heading of 230°.10 At
1449:21, the pilot stated, 'Okay, here we go,' and a sound similar
to an increase in engine RPM was recorded 2 seconds later. At
1449:29, the pilot stated, 'set thrust," and the copilot responded,
“thrust set" 6 seconds later. At 1449:37, the copilot called
out 'airspeed’s alive eighty knots.' At 1449:48 the copilot
called out 'V one' (takeoff decision speed) and 'rotate.' The pilot
responded, 'okay, we’re flying,' followed by the copilot
calling out 'V two' (takeoff safety speed)."
The report continued, "At 1449:51, the CVR recorded a sound
similar to stick shaker for 2.2 seconds, during which time the
pilot stated 'whew,' and the flight test engineer stated 'what are
you doing?'. The CVR then recorded the mechanical voice warning
'bank angle' and a sound similar to stall aural warning for 1.1
seconds at 1449:53.. 'Bank angle' was recorded at 1449:54 and again
at 1449:55. A sound similar to stick shaker was recorded for 0.15
seconds beginning at 1449:57, followed by 'bank angle' again at
1449:57.36. At 1449:58, and for the next 2 seconds, a sound similar
to stick shaker was recorded for 0.22 second, and the pilot stated,
'hang on.'"
"The recording ended at 1450:00," said the report. "Witnesses
reported seeing the airplane bank to the right after takeoff. They
stated that the airplane’s right wing rolled and impacted the
ground first and that the airplane exploded on impact. The airplane
crashed through an airport perimeter fence and came to rest
adjacent to a two-lane, north-south road."
The NTSB report says pilot Irelan
simply pulled back too hard during take-off. "The amounts of fuel
in the airplane’s center, three-in-line auxiliary fuel tanks
were not isolated from each other, which allowed fuel to move
freely through pipes between tanks, especially during acceleration
and rotation. Post accident calculations determined that the c.g.
moved aft as the airplane accelerated down the runway as fuel
shifted rearward in the auxiliary fuel tanks, tail tanks, and wing
tanks.
"By the time the airplane reached a pitch attitude of 13.8°
20 seconds after the start of the takeoff roll, the
airplane’s c.g. increased to at least 40.5 percent MAC,
according to Safety Board staff calculations. Although fuel some
migration is normal and expected in all airplanes, the
CL-604’s center fuel tank design allowed for significant fuel
migration above the range accounted for in the airplane’s
certified c.g. range limits. Safety Board staff also considered a
scenario that did not include fuel migration. Simulation testing
indicated that without the fuel migration factor, the
airplane’s c.g. would have been sufficiently forward to
prevent the airplane from pitching up sufficiently to trigger the
airplane’s stall protection system. Thus, the aft c.g.,
including the c.g. change during the takeoff phase, combined with
the high pitch attitude and pitch rate commanded by the pilot,
resulted in stall and loss of control.
"Moreover, the aft c.g. and the aggressive pitch control inputs
by the pilot eliminated the safety margin that the c.g. limit and
the lower pitch rate guidance of 3° per second were intended to
provide. Safety Board staff and Bombardier simulation studies
indicated that either restoring the c.g. margin or reducing the
pitch rate to 3° per second would have provided an adequate
safety margin."