Photo: CS-DFE at Zurich, from Aero Icarus (Creative Commons).

Eddie Sez:

One of the problems with small operators is the lack of functional check flight expertise. This problem can be exacerbated by aircraft manufacturers unwilling to share test procedures (also known as test schedules) for fear of liability problems. That is a recipe for a mishap, even with careful pilots who may not have considered every angle of an assigned task.

This crew was assigned the task of checking out a wheel brake that was causing the aircraft to pull to one side. They were concerned with keeping the aircraft on the runway during high speed tests but did not consider brake energy limits. They failed to consult brake energy charts and to consider the fact brake temperatures tend to rise for about 30 minutes after brake application. They exceeded brake energy limits by a wide margin. A design flaw in the airplane allowed hydraulic fluid to feed a brake fire, heavily damaging the airplane.

Before undertaking a functional check flight crews have a lot of work to do and may need to consider the possibility they are unqualified for the assigned duty. More about this: Normal Procedures & Techniques / Functional Check Flights.

What follows are quotes from the relevant regulatory documents, listed below, as well as my comments in blue.


Accident Report


Narrative

[AAIB CS-DFE, pg. 16]


Analysis

Photo: CS-DFE lower skin, flap, and tire damage, from AAIB, CS-DFE, figure 4.

[AAIB CS-DFE, pg. 23]

  • Both the left MLG brake units and the number three brake unit from the right MLG were removed and sent for disassembly and inspection at the manufacturer’s overhaul facilities.

  • The inspection found that all three units displayed severe heat damage after experiencing ‘exceptionally’ high brake energies. The elastomeric static and dynamic piston seals were completely destroyed (seal degradation would have started at a temperature of 183°C). The aluminium alloy housings within the brake piston assembly had melted, indicating temperatures in excess of 200°C and the pistons themselves were significantly deformed (Figure 5). The protective coating on the carbon discs had been removed indicating temperatures in excess of 1,200°C.

  • Using the recorded flight data, the manufacturer assessed that each of the left brakes had absorbed just under 18 MJ of energy and each of the right brakes just over 11 MJ2 from the cumulative effect of eight braked runs conducted during the incident.3 During certification the brakes had been tested up to 15 MJ on the aircraft and 16.4 MJ during brake qualification tests. Based on the data obtained from development testing with a fully worn heat sink, 16 MJ of brake energy was assessed to elevate the brake temperature by approximately 1,600°C.

Reason for test flight: operators manual vs. aircraft manual

[AAIB CS-DFE, pg. 25]

Flight crew's risk analysis

[AAIB CS-DFE, pg. 25]


Probable Cause

No probable cause was explicitly listed, though several recommendations were made from which causes can be inferred.

[AAIB CS-DFE, pg. 31]


See Also

Normal Procedures & Techniques / Functional Check Flights


References

Air Accidents Investigation Branch, Incident, Falcon 2000, CS-DFE, 12/2010.

Creative Commons