Airworthiness Directives; Bombardier, Inc. Model DHC-3 Airplanes

The FAA adopts a new airworthiness directive (AD) for certain Bombardier, Inc. Model DHC-3 airplanes modified with A.M. Luton's Supplemental Type Certificate (STC) number SA3777NM. This AD requires you to inspect the wiring for the heating blankets on P<INF>3</INF> and P<INF>Y</INF> pneumatic lines and the push-to-test function lights to ensure that they are wired to the correct schematic; replace the circuit breaker switch as applicable; and replace the flight manual supplement currently in use with Revision G, dated March 28, 2001 (incorporates Revision I of Sheet 1 of Drawing 20075, "Electrical System Schematic," dated October 10, 2000). This AD is the result of mandatory continuing airworthiness information (MCAI) issued by the airworthiness authority for Canada. We are issuing this AD to detect and correct wiring installed in accordance with an incorrect drawing, which shows the pneumatic heating blankets to the P<INF>3</INF> and P<INF>Y</INF> pneumatic lines wired in series with the indicator lights, rather than parallel. This can result in reduced current for the heating blankets and loss of pneumatic line heating, which can lead to loss of engine power or reverse propeller overspeed governing protection and ultimately loss of control of the airplane.