Airworthiness Directives; Hiller Aircraft Corporation Model UH- 12, UH-12A, UH-12B, UH-12C, UH-12D, UH-12E, CH-112, H-23A, H-23B, H- 23C, H-23D, H-23F, HTE-1, HTE-2, and OH-23G Helicopters

This amendment supersedes an existing airworthiness directive (AD), applicable to Hiller Aircraft Corporation Model UH-12, UH-12A, UH-12B, UH-12C, UH-12D, UH-12E, CH-112, H-23A, H-23B, H-23C, H-23D, H- 23F, HTE-1, HTE-2, and OH-23G helicopters, and UH-12D and UH-12E helicopters converted to turbine engine power in accordance with Supplemental Type Certificate (STC) Nos. SH177WE and SH178WE, having a certain control rotor blade spar tube (blade spar tube) or cuff installed, that currently requires inspections of the blade spar tube and cuff for cracks, and repair or replacement as necessary. This amendment requires inspections of the blade spar tube and cuff for corrosion or cracks, or elongation, corrosion, burrs, pitting or fretting of the bolt holes, and repair as necessary, and defines specific intervals in which the inspections must be performed. This amendment is prompted by analyses that show that the amount of calendar time that elapses between the current repetitive inspections may allow corrosion to develop. The actions specified by this AD are intended to prevent separation of the control rotor blade assembly and subsequent loss of control of the helicopter.