In one of its longest investigations into a general aviation accident, the NTSB released its final report last month on the Oct. 10, 2000, crash of a Canadian-registered Bombardier Challenger 604 during a manufacturer’s test flight at Wichita Mid-Continent Airport. The two pilots and flight engineer died as a result of injuries sustained from the accident. News of the accident traveled fast throughout the industry because it occurred while nearly 30,000 business aviation people were gathered in New Orleans to attend the annual NBAA Convention.
The Safety Board determined that the probable cause of this accident was the pilot’s “excessive” rotation during an aft center-of-gravity takeoff, exacerbating a rearward migration of fuel during acceleration and takeoff that shifted the airplane’s c.g. beyond the aft limit, which caused the airplane to stall too close to the ground for a recovery.
Contributing to the accident, said the NTSB, “were Bombardier’s inadequate flight-planning procedures for the Challenger flight-test program and the lack of direct, on-site operational oversight by Transport Canada and the FAA.”
The purpose of the flight was to test a modified pitch feel simulator (PFS). Such a test required that the aircraft (C-FTBZ) be configured with an aft c.g., and it was loaded with 1,100 pounds of water ballast and 734 pounds of tail ballast. The mission was to collect data required to obtain British CAA certification of the Challenger 604.
A ground test with the modified PFS units was performed to determine the control-column travel needed to obtain full elevator deflection in both directions. 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 pilot moves control surfaces from their neutral positions.
Statements from preflight briefing participants indicated that the pilot asked the flight-test engineer to obtain a “risk analysis” from the Bombardier flight-test center’s manager of flight test operations and safety. The manager said–and this fact is one of the reasons the NTSB criticized Bombardier–that this was the “moment he first heard about the test flight.” Nevertheless, he assessed the flight’s risk level as low because the airplane would be operating within its c.g. range and because “the [PFS] modification was stabilizing.”
Despite the manager’s low-risk assessment, it was evident the pilots were concerned. After the briefing began with a description of the airplane’s configuration and the presentation of load sheet information, the copilot reportedly asked, “Why so far aft?” The flight-test engineer explained that this configuration with production PFS units had already been flown in C-FTBZ during a 1999 flight test. The flight crew reportedly responded, “OK.” But after a presentation was made comparing the characteristics of the production PFS and modified PFS, the pilot allegedly said the airplane was going to “handle like a pig.”
The NTSB’s final report criticized the preflight briefing from several viewpoints, including failure to follow Bombardier’s own procedures to discuss the test maneuvers in greater detail. Pitch-rate targets were also not discussed in the context of an aft-c.g. test flight. “Although the accident flight was to be conducted within the airplane’s c.g. [envelope], the c.g. was near the aft limit and [this item] should have been briefed to increase awareness of pitch-rate performance in this configuration,” the Safety Board said.
‘What are you doing?’
Weather was not a factor in this accident, the NTSB said, since VMC prevailed at the time. Wind was 190 degrees at 20 knots, gusting to 26 knots. Startup, taxi and the initial portion of the takeoff from Runway 19R proceeded uneventfully.
But bad things started happening as the airplane left the ground. After the copilot called “rotate,” the pilot responded, “OK, we’re flying,” followed by the copilot calling out “V2.” About three seconds later, the CVR recorded the sound of the stick shaker, during which time the pilot said, “whew,” and the flight-test engineer asked, “What are you doing?”
The CVR then recorded a computerized voice warning of “bank angle,” followed several seconds later by repeated stick-shaker sounds and “bank angle” warnings. At this time, the flight engineer repeated, “What are you doing?” followed by a sound similar to a stall warning and “bank angle” again. The CVR’s last words came from the pilot: “Hang on.” Witnesses reported seeing the airplane bank to the right before the right wing hit the ground and the airplane exploded. The pilot and flight engineer were killed. The copilot was seriously injured and died 36 days later.
The airplane’s center and three-in-line auxiliary fuel tanks were not isolated from each other, a configuration that allowed fuel to move freely through pipes between tanks, especially during acceleration and rotation. Post-accident calculations determined that the c.g., already near its aft limit for the intended mission, moved beyond that limit as the airplane accelerated down the runway and 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 degrees, about 20 seconds after the start of the takeoff roll, its c.g. had moved aft to at least 40.5-percent MAC, according to Safety Board calculations. Although some fuel movement is normal and expected in all airplanes, the 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,” according to the Safety Board.
Simulations indicated that without the fuel migration factor, the airplane’s c.g., although aft, would have been forward enough to prevent the airplane from pitching up sufficiently to trigger the stall-protection system. “Thus, the aft c.g. and the large c.g. change during the takeoff phase combined with the high pitch attitude and pitch rate commanded by the pilot,” resulting in a stall and loss of control.
“Moreover, the aft c.g. and the aggressive pitch-control inputs eliminated the safety margin that the c.g. limit and the lower pitch-rate guidance of three degrees per second [recommended in the Challenger operations reference manual] were intended to provide. Safety Board and Bombardier simulation studies indicated that either restoring the c.g. margin or reducing the pitch rate to three degrees per second would have provided an adequate safety margin.”
A History of Rapid Pitch Rates
According to FDR information, the airplane’s maximum pitch rate at rotation was 9.6 degrees per second (dps), more than three times the recommended 3-dps rate. A Safety Board review of the pilot’s previous takeoff technique showed that he had a history of “excessive” pitch rates during several takeoffs in the months before the accident, “including 6.5- and 6-dps pitch-rate takeoffs in a Challenger a month earlier; a 7.2-dps takeoff on a Challenger test flight two months before the accident; and an 8.3-dps takeoff in a Global Express, also about a month before the accident.
The accident pilot was certainly not the only Bombardier test pilot to use higher-than-recommended pitch rates. As part of its investigation, the Safety Board reviewed the telemetry of 50 flights by Bombardier flight-test center pilots, including several senior management pilots. The data indicated that they “routinely” used pitch rates that were more than double the recommended 3 dps.
During its investigation, the NTSB determined that the accident flight’s risk assessment was subject to several interpretations, depending on who was doing the assessing. “This disparity underscores the importance of a formal safety review and THA [test hazard assessments],” the Safety Board said, “especially when there are competing assessments.”
Although the flight never got to its test mission, the Safety Board noted that the risk assessment was made “minutes before the flight and did not take into account that the aircraft’s changes were to a flight-control system that was to be tested in flight for the first time during a complex maneuver.”
The Safety Board also believed that Bombardier did not properly qualify or prepare the pilots for the planned mission. Each pilot had logged more than 6,100 hours TT, but investigators noted that the pilot’s previous experience was “largely in routine, entry-level operational and production testing, rather than flight testing. Yet he was assigned as PIC to test airplane control performance and handling qualities in a complex flight-test maneuver that he had never flown.” As for the copilot, also an experienced test pilot, the flight was primarily to “familiarize himself with the Challenger, not to demonstrate flight-test procedures and maneuvers.”
After the accident, Transport Canada conducted a special-purpose audit of the flight-test center in Wichita. The audit report commended Bombardier “for documenting procedures for the safe conduct of flight tests [contained in Bombardier’s Standards and Procedures Manual 3000].” But “the audit revealed that company management does not always enforce the provisions of the manual.” The audit report noted that “documentation or specific procedures were unavailable to demonstrate that other engineering disciplines, potentially affected by the [PFS] modification, provided sufficient analysis to support safe operation of the aircraft.”
In a letter sent last November to the Transportation Safety Board of Canada, Bombardier refuted several conclusions and observations contained in Transport Canada’s post-accident audit. The company said it had “provided substantial proof that the subject documentation and procedures were readily available and that the required engineering oversight for the safe conduct of flight testing was beyond reproach.” In addition, Bombardier claimed that the audit “lacked specifics.” It also took corrective actions, according to Bombardier, including having the safety manager report directly to the executive vice president of engineering on safety issues and to the vice president of flight test on day-to-day issues.
Before this change, the safety manager did not report to senior management.
Accident History Recounted
Before the Oct. 10, 2000, accident, Bombardier and Learjet had suffered two fatal accidents, two nonfatal accidents and one incident, all involving flight testing. On April 3, 1980, a Challenger 600 was destroyed during stall testing near California City, Calif. The pilot was killed. The flight crew was troubleshooting a noise associated with stalls conducted during previous flight-test activities. The airplane went out of control during a stall, and the crew deployed the emergency spin-recovery parachute. According to the copilot and flight-test engineer, who were able to bail out, attempts to jettison the parachute didn’t succeed and the pilot never regained control of the airplane.
On July 26, 1993, another Challenger 600 was destroyed during lateral and directional stability testing near Byers, Kan. The two test pilots and flight-test engineer were killed. Investigators concluded probable cause to be the “captain’s failure to adhere to the agreed-upon flight-test plan for ending the test maneuver at the onset of pre-stall stick shaker, and the flight crew’s failure to ensure that all required switches were properly positioned for anti-spin chute deployment.”
A Global Express landed wheels-up on April 25, 1997, following avionics testing at Toronto, Canada. Investigation determined that the flight crew did not lower the landing gear and had not followed a landing checklist. The aural gear warning had been disarmed during the flight test and was not re-armed by the pilots following the test.
On Oct. 27, 1998, a Learjet 45 was destroyed after colliding with a pickup truck parked next to the runway during water ingestion testing near Wallops Island, Va. The probable cause of the accident involved “failure of the pilot to obtain/maintain alignment with the water pool, which resulted in a loss of control.”
Bombardier also reported a flight test-related incident that occurred on July 21, 2000, when the elevator of a Global Express jammed during its first production test flight. The pilots used a combination of thrust and pitch trim to maintain airplane control and landed uneventfully. A company investigation revealed that an unflagged rigging pin had not been removed before the flight.
The NTSB concluded that the accident and a disregard of risk-assessment procedures in place for the Challenger program attested to Bombardier’s lax oversight of its flight-test program. “Further, it is evident from the investigation that Bombardier’s operation of its flight-test program was deficient because the preflight briefing [for the subject accident of this report] was inadequate; because a relatively inexperienced flight-test pilot was chosen for a flight that involved a complex maneuver he had never flown (and in an aft-c.g. configuration greater than that of which he had never flown); because a build-up for the accident flight was not considered; and because the company failed to identify a history of its pilots’ practice of making high-rotation-rate takeoffs, which becomes even more critical in airplanes configured with an aft c.g.”
Transport Canada and the FAA didn’t escape harsh words by the NTSB either. Transport Canada had direct regulatory oversight of Bombardier’s flight-test center in Wichita involving the company’s Canadian-manufactured airplanes, but the last inspection of the facility occurred nearly a year before the accident, according to the Safety Board.
Although TC assigned a full-time inspector to the facility after the accident, “there was very little surveillance of the facility’s flight-test operations at the time of the accident,” claimed the NTSB.
A year after the accident, Transport Canada issued the findings of an audit asserting that Bombardier flight-test crews worked excessively long hours under mounting pressure to deliver new products to customers. Transport Canada insisted at the time that the crash did not trigger the audit.
In response to that audit, Bombardier claimed to have already implemented augmented safety precautions at its Wichita test facility by limiting work-week hours, hiring additional test pilots and increasing the number of crewmembers on some flight tests.
“There are no Canadian or U.S. regulations specific to the conduct of flight-test operations,” the NTSB report said. “Neither FAA nor TC regulations require Bombardier, or other flight-test operations, to have a flight-test policies and procedures manual” and “flight-test operations and the corporate safety culture they require would benefit from the adoption of TC- and FAA-approved flight-test standards and procedures,” according to the report. Transport Canada claims it is addressing the concerns.
At press time, the FAA was still reviewing the final report and declined to comment. A TC spokesman told AIN, “We will respond to the report as required within the next 90 days.” Since the accident, “we have been evaluating the best means by which flight-test operations could be more rigorously monitored and audited. To that end, we have drafted regulations to require the use of an approved flight-test operations manual by aircraft manufacturers, including Bombardier.” It has set no timetable for publication of the regulations.
‘Committed To Improving Safety’
Bombardier, whose Wichita operation hosts a well attended and respected corporate aviation safety seminar every year (called Safety Standdown), said it has revised the company flight-test standards and procedures manual used for the Challenger program.
“We are committed to improving safety,” a Bombardier spokesman in Wichita said. “We continually evaluate everything we do to make sure we can do it as safely as possible. We have a program called the safety risk-management process (SRM) that includes dedicated safety reviews and comprehensive flight-test hazard analyses where we try to assess what the risks are. I assure you that in the course of the more than three years since that accident we’ve continued to improve on the process.
“Whatever was in place on that day was not the same as it is today. Improvements in the process would have occurred regardless of whether or not an accident had occurred. As a point of clarification, the accident occurred on a routine takeoff. We never got to the test. These were two pilots with more than 6,100 hours of experience each. They knew how to take off in an airplane. Unfortunately, in this particular instance, we concur with the NTSB’s conclusion that the probable cause was the pilot’s excessive rotation during the takeoff.”
The information in the NTSB report about test pilots using excessive pitch rates on rotation “is now available to us and it is worthy of consideration,” the spokesman continued. “It’s not as if they [the briefing team and crew] don’t discuss pitch rates already at briefings. The Safety Board reviewed the telemetry on 50 flights. That’s probably something we hadn’t done up to that point, and therefore it is something we are now doing more routinely.”
Bombardier, Transport Canada and the FAA addressed the fuel shift/c.g. issue on the Challenger 604 four months after the accident. On Feb. 1, 2001, Bombardier issued a temporary revision to the Challenger flight manual changing the airplane’s aft c.g. limit from 38 percent MAC to 34.5 or 35 percent, depending on airplane weight. The same day, Transport Canada issued AD CF-2001-07 to make the revision permanent. The FAA issued emergency AD 2001-03-52 on February 2 to make the revision mandatory on U.S.-registered Challenger 604s.
In 2001, families of the crew killed in the crash filed a claim against four manufacturers of equipment installed in the aircraft. The lawsuit, alleging that defective equipment contributed to the crash, named Honeywell, Lucas Aerospace, Parker Hannifin and Rockwell Collins as defendants. Lucas Aerospace provided the pitch-feel system. The suit, which is still in active litigation for some of the parties, does not include Bombardier as a defendant.
Commenting on the lawsuit, a Honeywell spokesman told AIN, “The NTSB has confirmed our strong belief that no Honeywell products contributed to this unfortunate accident, and that the claims against Honeywell are without legal or factual basis.”
An NTSB spokesman said that the Safety Board is “considering” issuing one or more recommendation as a result of its investigation into this accident.