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Compliance required at first airplane overhaul or within six months after the effective date of the AD, whichever occurs first, unless already accomplished.

To prevent further failures of Pyrene fire extinguishers of the subject models, accomplish the following.

(a) Overhaul, inspect, and test the fire extinguishing systems that are equipped with electric discharge facility, in accordance with revised requirements in British Aircraft Corporation (Weybridge Division) Preliminary Technical Leaflets No. 256 (700 Series), No. 120 (800/810 Series), (Amendment TR 25 to Viscount Maintenance and Instruction Manuals and Amendment TR3 to the Accessories Manual cover the same subject). Subsequent overhaul of the fire extinguishing system must be carried out in accordance with these specified periods in the FAA-approved maintenance schedule.

(b) The spray ring system must be blown through with warm dry air to insure that the piping and discharge holes are free of obstructions during the overhaul of the airplane at periods specified in the FAA-approved maintenance schedule.

This directive effective October 3, 1965.