69-17-01 MCDONNELL DOUGLAS DC-9 and BOEING 737: Amdt. 39-819. Applies to DC-9 airplanes equipped with AiResearch Model GTCP85-98D Auxiliary Power Unit (APU) Serial Numbers listed in AiResearch Telegraphic Bulletin No. 49A1761 dated July 1, 1969, or later FAA approved revision, and to Boeing 737 airplanes equipped with AiResearch Model GTCP85-129 APU serial numbers listed in AiResearch Telegraphic Bulletin No. 49A1760 dated July 1, 1969, or later FAA approved revision. \n\n\tCompliance required as indicated unless already accomplished. \n\n\tBecause of possible failure of the second stage impeller blades, the auxiliary power unit shall not be used as an alternate electric power source in place of a main engine driven generator until deficient impellers have been replaced. Pending replacement of the auxiliary power unit impeller, accomplishment of the following is required. \n\n\t1.\tWithin 10 hours time in service after the effective date of this Airworthiness Directive, install a placard in full view of the pilot to read: \n\n\tBoth main engine driven generators must be operative for takeoff. Only during in-flight emergency may the auxiliary power unit be used as an alternate electric power source. \n\n\t2.\tThis placard may be removed when the APU is replaced with an APU having satisfactory impeller blades, or when the APU is modified to incorporate an impeller with satisfactory impeller blades in accordance with the above AiResearch Telegraphic Service Bulletins. \n\n\tNOTE: Compliance with the inspection and speed reduction adjustments in these bulletins is optional. \n\n\tThis amendment becomes effective upon publication in the FEDERAL REGISTER for all persons except those to whom it was made effective immediately by telegram dated July 3, 1969.