UK Safety Board Concerned about Avionics Corrosion

The UK Air Accidents Investigation Branch (AAIB) recently issued a sweeping recommendation that the EASA, FAA, Transport Canada and other aviation agencies amend requirements for the design and installation of electronic components in aircraft to take into account fluid and moisture contamination, as a source of common cause failures. This recommendation stems from a November 2005 incident involving a 2004 Bombardier Challenger 604 (registration VP-BJM) that experienced autopilot pitch and stabilizer trim failure due to corrosion of the horizontal stabilizer trim control unit (HSTCU) circuit board. There were no injuries, but the crew declared an emergency and made a no-flap emergency landing at London Heathrow Airport. According to the AAIB, moisture created by humid air condensing on the cooling motherboard during repeated prolonged flight at altitude over time corroded the solder, leading to the HSTCU’s eventual failure. While the incident occurred on a Challenger, the AAIB is concerned that avionics motherboards on other aircraft could be affected in a similar manner. Bombardier has since issued a fix and installed specially coated HSTCU motherboards in the affected 366 in-service Challenger 604s at no cost to operators.