AD 63-21-03

63-21-03 HILLER: Amdt. 631 Part 507 Federal Register October 15, 1963. Applies to Models UH-12D and UH-12E Helicopters.

Compliance required as indicated.

Due to fatigue cracking and brazed doubler separation of main rotor blade, Parsons P/N's 2253-1101-02 and 2253-1101-03, inspect the top and bottom surfaces of each blade after removing paint in the area adjacent to the outboard end of the steel doubler brazed to the leading edge spar (approximately 27 inches from the blade root end), for doubler separation and for cracks in the leading edge spar near the end of the doubler as follows:

(a) For all main rotor blades, conduct a visual inspection of the affected areas with a 4 to 6-power magnifying glass within 10 hours' time in service from the effective date of this AD and daily thereafter. When inspecting for cracks or separation in the lower surface, the blade tip must be supported in a manner to remove all droop from the blade.

(b) For all main rotor blades, conduct a dye penetrant inspection of the affected areas within the next 10 hours' time in service after October 15, 1963, and thereafter at intervals not to exceed 25 hours' time in service from the last dye penetrant inspection for blades, Serial Number 1269 and below, and at intervals not to exceed 100 hours' time in service from the last dye penetrant inspection for blades, Serial Number 1270 and above.

(c) In the event of any unusual main rotor vibration that cannot be corrected by normal tracking, balancing or rigging procedures, conduct a dye penetrant inspection of the affected areas. In addition, inspect for cracks the bolt hole and adjacent milled surfaces of the main rotor blade fork P/N 52110-3 by means of a dye penetrant inspection or FAA approved equivalent. For this inspection remove nut, washer and pin. Replace cracked forks before further flight.

(d) Main rotor blades with cracks or doubler separation must be removed from service before further flight.

(e) The repetitive visual and dye penetrant inspections required by this AD may be discontinued after the installation of blades. Parsons P/N 2253-1101-04.

(Hiller Service Information Letter No. 3037A covers this subject.)

This supersedes AD 60-17-02.

This directive effective October 15, 1963.

Revised April 8, 1966.