The UK’s Air Accidents Investigation Branch (AAIB) implicated crew training in the crash of a Bermuda-registered Falcon 900EX at Stansted Airport on Feb. 9, 2004. The Falcon arrived at Kilimanjaro Airport in Tanzania, from London Luton, with an intermittent hydr#1 pump 3 display. The crew studied the minimum equipment list and determined that it could fly with only two operable hydraulic pumps. Because of limited maintenance facilities in Tanzania, the crew elected to defer addressing the defect until the airplane returned to Luton.
On the return flight the same warning light illuminated intermittently until it finally remained lit. Soon after, the pilots saw a noticeable loss of hydraulic contents. However, the crew stated that the pressure in the No. 1 system remained normal.
The Falcon was positioned to land on Runway 26 at Luton and the crew had selected the landing gear down. However, the “down and locked” light did not illuminate, so the crew began emergency extension checks.
The captain requested a diversion to Stansted Airport. The landing appeared normal, but as speed decayed the right gear collapsed and the aircraft came to rest on the grass infield. The two crewmembers and two passengers were uninjured.
The AAIB investigation noted that the crew used a checklist from FlightSafety International (FSI) marked “for training purposes only” and carrying a caution that the procedures were “for U.S.-registered aircraft only. For non-U.S.-registered aircraft consult AFM for alternate procedures.”
Examination of the hydraulic system showed fluid loss from No. 1 pump drain. Dassault sent both this pump and the No. 3 pump to the OEM for investigation, but they were overhauled rather than checked for failure, so the cause of failure could not be established.
AAIB Safety Recommendations
The AAIB made four safety recommendations as a result of the incident. The first was that Dassault review the minimum equipment list to ensure that it could not be misinterpreted. The crew mistakenly believed that it could operate with two of three hydraulic pumps serviceable. They had misunderstood Section 29.1 of the manual, which allows operation if two of three caution lights are operable. They had been misled by the fact that “caution lights” was in lower case, while the hydraulic pumps were listed in upper case.
In addition, the AAIB recommended Dassault amend the checklist in the flight manual to clarify the indications that crews could expect after the failure of either hydraulic system.
Investigators also recommended that FSI ensure that its training documents use the same procedures that crews will use in the aircraft. The training checklist for emergency gear extension called for sideslip after the pilots manually lowered the gear and stated that the downlock light should illuminate within 30 seconds. The flight manual stated that it would not illuminate for at least 30 seconds. This difference influenced the amount of aerodynamic force the crew applied to the gear.
The AAIB also concluded that FSI’s flight simulators did not truly reproduce the forces and procedures pilots would encounter in the airplane and recommended that FSI ensure that its simulators represent the correct pilot input.