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."

FMI: www.ntsb.gov/publictn/2004/AAB0401.pdf