AD 53-12-01

53-12-01 HILLER: Applies to All UH-12, UH-12A, UH-12B, HTE-1, HTE-2, H-23A and H-23B Helicopters Incorporating Horizontal Stabilizers With Short Spar Inserts or Without Spar Inserts.

Compliance required as indicated below.

Replacement of the horizontal stabilizer assembly, P/N 37001 on the above helicopters has been found necessary to prevent fatigue failure of the stabilizer spar. (Hiller Service Bulletin No. 26 covers this procedure.)

(a) Stabilizer assemblies P/N 37001-9 incorporating short spar inserts (5.75 inches) must be removed from service when they have accumulated 300 hours total time. The replacement stabilizer is identified as 37001-14 and incorporates a long spar insert.

(b) Stabilizer assemblies P/N 37001-7 (without spar insert and identified as 37001) must be removed from service when they have accumulated 1,600 hours total time. The replacement stabilizer is identified as 37001-12 and incorporates a long spar insert.

(c) Stabilizer assemblies P/N 37001-12 and -14 incorporate long spar inserts (10.29 inches). Attachment to the aft bulkhead socket is made by two AN 174-17 bolts. The total service life of these assemblies is not limited.