Challenger Incident Highlights Maintenance Check Flight Perils

Improper procedures led to test-flight incident, British investigators find

Following proper procedures is the foundation of aviation safety. It is arguably even more important when hangar-related work meets the flight line via a post-maintenance test flight.

A March 2014 incident involving a Bombardier Challenger on a post-maintenance flight at Biggin Hill Airport, Kent, England, underscores the perils of not following published protocol, a U.K. Air Accidents Investigation Branch (AAIB) report reveals.

Following routine scheduled maintenance, procedures called for an in-flight check of the air-driven generation (ADG), which provides backup power when the main generators fail. The two-pilot flight crew was accompanied by a maintenance engineer for the check, to be conducted during the aircraft’s downwind leg during a single circuit of the airfield.

The aircraft took off and, per the check procedure, maintained the takeoff flap setting of 20 deg. As the downwind leg began, the aircraft’s main generators were taken offline. The test checked out, but the crew did not put the main generators back online.

Instead of trouble-shooting the issue, the crew continued its approach, apparently unaware that the functions not powered by the ADG include flaps, ground spoilers, nosewheel steering and the brake anti-skid system. The routine flight deck warning and caution messages functioned, but did not prompt the crew to take action that might have led to restarting the generators.

Without these functions, the aircraft—its flaps still configured at the 20 deg. takeoff setting—landed fast, and the captain needed maximum wheel breaking to stop before running out of runway. The hard braking caused all four main landing gear tires to rupture; the main wheels and brakes were also damaged. The aircraft stopped near the runway end. 

Investigators determined that several factors contributed to the incident. Primarily, the flight crew and jump seat-riding engineer did not discuss a plan for the check flight before departure. The flight data recorder showed the flight lasted just 4 min, 31 sec., leaving little time to talk through the procedure before the downwind leg.

The pilots acknowledged that they did not review Bombardier’s recommended ADG flight-test procedures before departing. Post-incident interviews revealed that the pilots believed the engineer would talk them through the test procedures, so they neither reviewed the steps or had the quick-reference handbook standing by. 

“The flight crew embarked on a very short flight with no firm plan how to conduct the check, and a misunderstanding of the roles of the three people on board,” AAIB concluded. The report emphasizes the need for pilots conducting maintenance-check flights to have full pre-flight briefings, regardless of whether they say they understand the procedures. The maintenance organization involved—which was not identified—has changed its policies to implement the pre-flight briefings.

A version of this article appears in the December 1/8 issue of Aviation Week & Space Technology.

TAGS: Europe
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