AD 71-21-07

71-21-07 de HAVILLAND: Amendment 39-1310. Applies to de Havilland Model DHC- 6 Airplanes, Serial Numbers 6 through 289 certificated in all categories and incorporating Flitetronic Type PC 15 or PC 15A Inverters.

Compliance required within the next 250 hours' time in service after the effective date of this AD unless already accomplished. To prevent a total loss of AC power in the event of a fault occurring in an AC circuit, accomplish the following:

(a) Comply with Accomplishment Instructions 1 and 2 (a) through 2(e) of de Havilland Service Bulletin No. 6/263 dated 5 October 1970, Revision B dated 29 January 1971.

(b) Remove slow-blow fuses not replaced in (a) and replace with:

(1) Littlefuse type 312 of the same rating for the 26-volt supply except that ratings greater than 2 amps shall be replaced with Littlefuse 312002.

(2) Littlefuse type 312 or Bussman type MB of the same rating for the 115 Volt supply, except that ratings greater than 1 amp shallbe replaced with Littlefuse 312001 or Bussman MB01.

(c) Comply with Accomplishment Instructions 3 through 6 of de Havilland Service Bulletin No. 6/263 dated 5 October 1970, Revision B dated 29 January 1971 for PC 15 and PC 15A inverter without a suffix letter after the serial number. Inverters which do not meet the requirements of the overload function test must be replaced, prior to further flight, with an inverter with a suffix letter after the serial number. Equivalent methods may be used provided they are approved by the Chief, Engineering and Manufacturing Branch, FAA Eastern Region.

Upon request with substantiation data submitted through an FAA maintenance inspector, the compliance time specified in this AD may be increased by the Chief, Engineering and Manufacturing Branch, FAA Eastern Region.

This amendment is effective October 12, 1971.