What happened
While operating a Bombardier BD-100-1A10 (registration C-GFHR) from Prague, Czech Republic, to Geneva, Switzerland, the flight crew initiated the "in-range" checklist. This procedure involved switching the direct current (DC) hydraulic pumps from the "OFF" position to "AUTO". Approximately two minutes after this change, a cockpit caution message indicated a failure in the left hydraulic DC pump.
Despite the alert, the crew completed the flight to Geneva without further incident. However, after the aircraft arrived and passengers deplaned, the crew noticed soot trailing from the battery bay door. Upon inspecting the area, they detected an acrid electrical odor and discovered soot and a burned wire connected to the positive terminal of the left DC motor pump filter assembly.
The investigation
The investigation focused on the electromagnetic interference (EMI) filter assembly located on top of the DC motor pumps in the aft equipment bay. This assembly contains capacitors soldered to a stainless steel box. The investigation examined the electrical configuration of the pumps, which are designed to provide extra hydraulic capability during takeoff and landing.
Investigators noted that the aft equipment bay lacks smoke or fire detection systems, as such equipment is not required by regulation for this specific area. The investigation also reviewed several manufacturer advisories and service bulletins issued by Bombardier and Parker Hannifin Corporation following the event, which eventually led to a redesigned filter assembly that removed the capacitor entirely.