78-10-04 AIRESEARCH MANUFACTURING COMPANY OF ARIZONA: Amendment 39-3216. Applies to AiResearch Model TSCP700-4B and -5 Auxiliary Power Units (APU's) which have first stage compressor disks P/N's 969600-1 or -2 installed, of the serial numbers listed.
Disk Serial No.
7-03501-2503
7-03501-2531
7-03501-2504
7-03501-2532
7-03501-2506
7-03501-2538
7-03501-2507
7-03501-2545
7-03501-2510
7-03501-2546
7-03501-2511
7-03501-2548
7-03501-2513
7-03501-2549
7-03501-2514
7-03501-2558
7-03501-2519
7-03501-2582
7-03501-2522
7-03501-2588
7-03501-2523
7-03501-2599
7-03501-2526
7-03501-2606
7-03501-2527
7-03501-2619
7-03501-2718
7-03501-2529
7-03501-2743
Compliance required before accumulating a total of more than 3000 cycles on the first stage compressor disks, or within the next 300 cycles after the effective date of this AD, whichever occurs later, unless already accomplished:
To prevent a high energy release of first stage compressorblades and disk parts due to the possible fatigue failure of the disk, accomplish the following:
(a) Remove the first stage disk from the compressor section of the APU and replace with like serviceable part.
(b) For the purposes of this AD:
(1) A cycle is defined as a start and acceleration to at least 95% high pressure spool (N2) rpm followed by a shutdown, during which low pressure spool (N1) rpm reaches, or exceeds, 97% rpm nominal. If, in any start, operating and shutdown sequence, the low pressure spool (N1) is prevented from exceeding 91% rpm nominal, only one half of a cycle must be recorded.
(2) Operators who have not kept a record of operating starts on individual disks may assume two starts have occurred for each recorded APU operating hour of service, or any other cycle per hour ratio approved by the operators' assigned FAA maintenance inspector, provided the request contains substantiating data to justify the alternative ratio.
(3) Operators whohave not kept a record of APU operating hours of service shall estimate hours of APU operation equating APU operation to airplane hours time in service using a ratio approved by the operator's assigned FAA maintenance inspector and justified by substantiating data.
NOTE: AiResearch Service Bulletin TSCP700-49-5016 dated April 25, 1978 refers to the same subject.
This amendment becomes effective May 30, 1978.