Challenger 300 DC hydraulic pump filter failure, Geneva 2007

Final reportHydraulics

The short version

On the way into Geneva the crew switched the DC hydraulic pumps from OFF to AUTO as part of the in-range checklist. About two minutes later an L HYD DC PUMP FAIL caution came on. Nothing else looked wrong, and they only found the soot, the smell and a burned wire in the aft equipment bay after landing. That bay has no smoke or fire detection.

What happened

  1. The crew complete the in-range checklist. It includes moving the DC hydraulic pump switches from OFF to AUTO.

  2. About two minutes later the caution "L HYD DC PUMP FAIL" appears. There are no other abnormal indications.

  3. The crew continue and land at Geneva. The landing is otherwise uneventful.

  4. After deplaning, the crew see soot on the side of the fuselage, trailing aft from the battery bay door. They open the battery bay door and smell an acrid electrical fire odour.

  5. They open the rear bay and find soot and a burned wire on the positive terminal of the left DC motor pump filter assembly.

All times are local (central European summer time).

The Challenger 300 has a left and a right DC motor pump in the aft equipment bay. They add hydraulic capacity for takeoff and landing and give some backup for specific failures. In AUTO, a pump runs when its engine-driven pump fails, or when the flaps are not at zero and at least one generator is on line. Selecting OFF removes all electrical power from the pump. The aft equipment bay has no smoke detection, no fire detection and no fire suppression, and the regulations do not require any.1

Each pump has an electromagnetic interference (EMI) filter mounted on top: a sealed stainless steel box with two capacitors set in potting compound. On C-GFHR the capacitor on the positive terminal had overheated and melted the terminal stud completely. The filter had burned through at the bottom, and molten metal had built up on top of the pump. The pump had run 684.5 flight hours and 272 cycles. When investigators cut the filter open, the positive end of the capacitor was almost gone. The damage was consistent with a short circuit inside the capacitor.1

Why it happened

  1. The report found one cause: the capacitor on the positive terminal of the EMI filter on the left DC motor pump failed for unknown reasons, and the positive terminal melted and burned the wiring.1

  2. Selecting AUTO would have energised the pump. That possibly caused the filter to overheat, and the crew got the pump fail caution.

  3. There were no smoke or fire warnings because the aft equipment bay has no detection equipment, and none is required.

  4. It could not be determined when the melting or burning started or stopped.

  5. This was the first known failure of this kind in flight. At least two similar filter failures had happened on the ground in the previous year: aircraft S/N 20022 during ground runs in November 2006, and S/N 20023 while taxiing in April 2007. Those two filters came from the same batch. The date stamp on C-GFHR's filter was destroyed by the heat.

  6. Bombardier and Parker Hannifin, the pump maker, ran numerous tests and could not find the root cause.

The report lists the safety action taken. Bombardier sent an advisory wire on 13 July 2007 and issued AFM temporary revisions TR-44 (1 August 2007) and TR-44-1 (11 October 2007) restricting DC pump use in flight. Service bulletins from Bombardier (100-29-12 and 100-29-11) and Parker (955805-5-29-380) first called for overheat checks and then for a new filter. The new pump configuration, re-identified as P/N 955805-7, has no capacitor in the EMI filter.1

What a crew can take from it

  1. A pump caution can be the only sign of an overheat in a bay with no detection. On C-GFHR the crew had one caution and nothing else. A terminal melted and a wire burned in the aft bay, and the report could not say when. No warning could have told them, because nothing in that bay was watching for it. When an electric motor or its wiring fails in an unmonitored bay, think about heat and smoke as well as the lost function.

  2. Know which of your bays have detection. The aft equipment bay on this aircraft had no smoke detection, no fire detection and no suppression, and none was required. Know where your electric pumps, batteries and heavy wiring sit, and which areas can and cannot warn you.

  3. Use the switch to take the power away. The report says the OFF position removes all electrical power from the pump. When the QRH procedure for a failed electric pump allows it, selecting OFF stops current flowing to a component that may be overheating.

  4. Look for the evidence after landing. This crew saw the soot on the fuselage, opened the battery bay, smelled the burning and kept going until they found the burned wire. After any electrical or electric pump caution, walk round the aircraft and check the access doors near the failed system. Then write up what you saw for maintenance.

Study it on the course

Sources

  1. Transportation Safety Board of Canada. Aviation Investigation Report A07F0101, Hydraulic Pump Failure, Bombardier BD-100-1A10, C-GFHR, Geneva, Switzerland, 25 June 2007 (PDF). Released 21 August 2008.
  2. Aviation Safety Network, occurrence 349183.

Last updated 22 October 2026

For study only. Always use the approved AFM, QRH and operator procedures.