A review of the newly released interim report on a wake vortex encounter shows how close a Bombardier Challenger 604 came to crashing into the sea in January. While flying over the Arabian Sea, the pilots temporarily lost control of their twin-turbine business jet when it flew into the wake from an Airbus A380 flying in the opposite direction that was 1,000 feet overhead and slightly to the right.
Approximately a minute after the two aircraft passed each other, the Challenger hit turbulence from the A380’s wake and quickly went out of control. Before the crew regained control at FL240, the aircraft had exceeded several design load limits, rolled several times, dropped 8,700 feet, lost vital avionics (including attitude displays) and the left engine had to be caged. The pilot-flying explained that since the sky and the ocean were almost the same blue color, he had been able to recognize the aircraft's flight attitude only “with the help of the clouds.”
After the crew regained control, they declared an emergency and diverted to an alternate airport, where they made a normal landing. Although no external damage could be seen (in contrast to that in the cabin), Bombardier determined that the airframe structure could not be restored to airworthy condition. Two passengers were severely injured and one passenger and the flight attendant sustained minor injuries.
Were it not for a few clouds in an otherwise completely blue sky, the outcome of the loss-of-control accident involving a German-registered Bombardier Challenger 604 on January 17 this year could have been a plunge into the Arabian Sea. As it was, several passengers were seriously injured from the gyrations of the aircraft after it encountered wake vortices from an Airbus A380 and the aircraft itself was severely damaged. Those clouds helped the crew regain control, preventing a crash that surely would have been fatal for all nine aboard.
Germany’s BFU, lead investigator of the mishap, issued an interim report last month that shows just how close the German-registered twinjet came to crashing after the pilots temporarily lost control following the encounter with wake turbulence from the passing A380. According to the report, the A380, flying southeast in the opposite direction at FL350, passed 1,000 feet overhead and slightly to the right of the Challenger, which was flying northwest. At this point, the aircraft was 500 nm from the nearest land.
Forty eight seconds after the two aircraft passed each other and with the A380 some 15 nm away, the Challenger suffered an upset caused by the wake vortex from the larger aircraft and quickly went out of control. The crew regained control of the aircraft at FL240, but not before the flight guidance and attitude reference avionics failed, the FDR recorded large control surface and spoiler deflections and acceleration, a 10,000-foot loss of altitude, and the left engine had to be caged until the crew had fully regained control of the aircraft.
The PIC stated that a Tcas alert drew his attention to the opposite traffic when it was about six nm from the Challenger. He recognized the aircraft as an A380 and informed his copilot. The PIC told investigators that a “short time” after the A380 had passed them in the opposite direction, the Challenger was hit by the airliner’s wake turbulence. “The airplane shook briefly, then rolled heavily to the left and the autopilot disengaged,” the PIC said. Both pilots applied right aileron to stop the rolling motion, but the airplane continued to roll to the left, “completing several rotations.”
Subsequently, the inertial reference system (IRS), FMS and attitude indicators failed. At the time of the upset, both pilots had their lap belts fastened and the copilot was wearing his shoulder belts. The PIC told investigators he lost his headset during the rolling motion of the airplane. The Quick Reference Handbook (which contained emergency procedures and other checklist items) had “flown around the cockpit and was damaged.” Individual pages were “scattered around the cockpit.”
'With the help of the Clouds'
The PIC explained that since the sky was blue and the ocean’s surface almost the same color, he had been able to recognize the aircraft’s attitude only with the help of the clouds. Both pilots were eventually able to regain control of the airplane at FL240 using aileron inputs and, later, rudder and slight elevator deflection.
The PIC said that N1 and N2 on the left engine had "run apart," and that N1 had decreased severely. The ITT exceeded 1,000 degrees C, and the indication flashed red. Subsequently the crew shut down that engine. Drawing on memory, the pilots were able to reactivate one IRS in attitude mode. Then they used the cross bleed of the right engine to restart the left. After the second IRS was reactivated and position and heading had been entered manually into the FMS, they re-engaged the autopilot. It was by now 17 minutes since onset of the wake encounter.
The flight attendant told investigators what was happening in the cabin while the pilots were fighting to regain control of the aircraft and relight the engine. She had been standing in the middle of the cabin preparing food service when the chaos erupted. Four of the six passengers were also standing. It was these five people standing who incurred the injuries in the accident. In her recollection, the airplane “turned three times around its longitudinal axis,” during which time the standing occupants were thrown against the ceiling and the seats. Using the first aid kit on board, she attended to the injured passengers.
One passenger suffered head injuries and a broken rib; another passenger incurred a fractured vertebra. Two passengers and the flight attendant sustained minor injuries: bruising and a fractured nose, respectively. The two other passengers and the pilots were uninjured.
With the aircraft back under control, the crew declared an emergency and diverted to an alternate airport where they made a normal landing. Although there was no external damage visible,
Bombardier later determined that the airframe could not be restored to airworthiness as it had exceeded the certification design load limits during the upset.
Unlike the exterior, the inside of the cabin showed damage to the seats and the paneling, as well as traces of blood. The armrests of the four seats in the front, installed in club arrangement, were either deformed or fractured. On the left side of the cabin, two oxygen masks had fallen from their casings.
The Challenger was equipped with a CVR that had a two-hour recording loop. Because the flight lasted for another two hours after the accident, the recording carried no conversation or sounds at the time of the accident.
Wind No Factor in this Wake-vortex Encounter
To help avoid wake vortices encounters, the interim report closed with a recap of recommended RVSM lateral offset procedures and a reiteration of the findings and recommendations of an international ad-hoc working group. The working group was established in 2003 to establish safety requirements to ensure that wake vortex risks from the A380 “will be acceptable.”
In part, the working group concluded: at cruise speeds, the vortex trajectory crosses the flight level 1,000 feet below, and 10 to 20 nm behind, the generating aircraft “in calm wind conditions.” At the approximate time of the wake vortices encounter that caused this accident, the wind at the Challenger’s cruising altitude of FL340 was estimated as 20 knots from the northwest—a nearly straight-on headwind for the Challenger.
The BFU expects to release the final report before year-end.
A review of aircraft accident data shows no other clearly defined accident involving wake vortices striking a business jet in cruise. On the other hand, there have been several incidents in which business jets encountered wake turbulence on approach or climb-out. The last known fatal business jet accident resulting from a wake vortex happened a quarter century ago.
On Dec. 15, 1993, the crew of an IAI 1124A Westwind operated by Martin Aviation on a passenger charter flight from La Verne, Calif., to Santa Ana, Calif., lost control of the aircraft and it crashed 3.5 nm north of Santa Ana Airport. The pilots were making a visual night approach behind a 757-200. The Westwind was destroyed by the impact and all five occupants were killed. The NTSB concluded that wake turbulence from the 757 brought the Westwind down.