70-08-03 SIKORSKY: Amdt. 39-974. Applies to Sikorsky type S-61A/L/N/R helicopters certificated in all categories.
Accomplish the following within the next 10 heater hours in service, unless already accomplished, and every 15 heater hours in service thereafter:
A. Remove and inspect combustion air inlet duct backfire check valve Bobrick Co. P/N 9660-1-1 or 40064-32 for distortion, missing flappers, or other obvious damage.
B. Replace defective valves before further operation of the heater with a part inspected in accordance with paragraph A above. Upon replacement inspect all heater inlet air ducting for evidence of fuel contamination. Any fuel contamination must be eliminated before further heater operation.
C. Upon submission of substantiating data through an FAA maintenance inspector, the Chief, Engineering and Manufacturing Branch, FAA Eastern Region may adjust the repetitive inspection intervals specified in this AD to permit compliance at an established inspection period of the operator.
D. For the purpose of this AD, compliance time may be based on helicopter hours in service if the owner or operator cannot document heater operating time.
This amendment is effective April 23, 1970, and was effective March 17, 1970 for all recipients of the telegram dated March 17, 1970 which contained this amendment.