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AIRWORTHINESS DIRECTIVE

For the reasons set out in the background section, the CASA delegate whose signature appears below issues the following Airworthiness Directive (AD) under subregulation 39.1 (1) of CAR 1998. The AD requires that the action set out in the requirement section (being action that the delegate considers necessary to correct the unsafe condition) be taken in relation to the aircraft or aeronautical product mentioned in the applicability section: (a) in the circumstances mentioned in the requirement section; and (b) in accordance with the instructions set out in the requirement section; and (c) at the time mentioned in the compliance section.

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DHC-3 (Otter) Series Aeroplanes

AD/DHC-3/38 Electrically Heated Engine Pneumatic Lines 12/2002

Applicability: DHC-3 “Turbo Otter” aircraft, all series, modified in accordance with A.M. Luton, United States Federal Aviation Administration (FAA) Supplemental Type Certificate (STC) No. SA3777NM or with Transport Canada Aviation equivalent Supplemental Type Approval No. SA89-32.

Requirement: 1. Inspect the electrical wiring to the P3 and Py engine pneumatic line heating blankets and to the P3 heater warning light to determine if they are wired in a parallel configuration. Sheet 1 of Drawing No. 20075 “Electrical System Schematic” Rev. I dated 10 October 2000 (hereafter referred to as ‘The Drawing’) as referenced in A.M. Luton Service Information Letter SIL-00-10-10 dated 22 March 2001 (hereafter referred to as the ‘SIL’) illustrates the correct wiring configuration. If the inspection determines that lines are correctly wired in a parallel configuration, proceed to Requirement 3.

Note 1: CASA recommends that the electrical inspection of the wiring include a continuity check of the heating blanket line(s) to ensure that they are serviceable. Then, after selecting the P3 heater switch to the “On” position, if the line(s) quickly feel warm to the touch, this is an additional indication that the line(s) are correctly configured.

2. If, as a result of the Requirement 2 inspection, it is determined that the P3 and Py engine pneumatic line heating blankets and the P3 heater warning light are incorrectly wired, modify the wiring to the configuration shown on The Drawing.

Note 2: CASA recommends that a similar test be performed as described in Note 1 after modifying the wiring.

3. Inspect the circuit breaker switch for the heated engine pneumatic lines circuit ensuring the following:

If the engine installation utilizes both P3 and Py heated pneumatic lines, unless already accomplished, install a 7.5 Amp circuit breaker switch in accordance with The Drawing. Potter & Brumfield part number (P/N) W31- X2M1G-7.5, as referenced in the SIL, is an acceptable circuit breaker switch.
If the engine installation utilizes only a P3 heated pneumatic line, unless already accomplished, install a 5.0 Amp circuit breaker switch in accordance with The Drawing. Potter & Brumfield P/N W31-X2M1G-5.0 is an acceptable circuit breaker switch.