Airworthiness Directive · Amendment 39-17923 · Pneumatic
Bombardier, Inc. Airplanes
This AD applies to Bombardier, Inc. Model DHC-8-400, -401, and -402 airplanes, certificated in any category, serial numbers 4001 through 4446 inclusive.
We are adopting a new airworthiness directive (AD) for certain Bombardier, Inc. Model DHC-8-400 series airplanes. This AD was prompted by reports of failure of the high pressure shutoff valves (HPSOVs) causing the timer and monitor unit (TMU) to become inoperative since the HPSOV and the TMU are on the same circuit breaker. This AD requires a wiring modification to segregate the HPSOV power supply from the TMU. We are issuing this AD to prevent an inoperative TMU, which could result in the loss of the automatic de-icing mode, and lead to an increased workload for the flight crew and loss of control of the airplane.
You are responsible for having the actions required by this AD performed within the compliance times specified, unless the actions have already been done.
Within 2,000 flight hours or 12 months after the effective date of this AD, whichever occurs first: Do a wiring modification to segregate the HPSOV power supply from the TMU, by incorporating Bombardier ModSum Package 4-110595, Revision C, dated May 14, 2013, in accordance with the Accomplishment Instructions of Bombardier Service Bulletin 84-36-04, Revision B, dated January 2, 2014.
