DEPARTMENT OF TRANSPORTATION

Federal Aviation Administration

14 CFR Part 39 

[Docket No. 89-ASW-29; Amendment 39-6458, AD 90-01-04] 

Airworthiness Directives; Sikorsky Model S-61 Series Helicopters.

AGENCY: Federal Aviation Administration (FAA), DOT. 

ACTION: Final rule.  

DATES: Effective February 5, 1990. 

90-01-04   SIKORSKY AIRCRAFT: 
	Amendment 39-6458.   Docket No. 89-ASW-29. 
	Applicability:   Sikorsky Model S-61 series helicopters certificated in any category, equipped with part number (P/N) S6110-23300 main rotor head. 
	Compliance:   Required within the next 150 hours' time in service after the effective date of this AD, unless already accomplished. 
	To prevent possible failure of the main rotor hub upper plate, which could result in the loss of the helicopter, accomplish the following: 
	(a)   Conduct a one-time inspection of the main rotor head, P/N S6110-23300, installed with a bifilar assembly, P/N S6112-23039, as follows: 
		(1)   Remove main, rotor fairing to provide access to the upper hub arms. 
		(2)   Loosen the bifilar attachment bolt (NAS630-84) and nut (EB108) a minimum of two turns, one bolt at a time. 
		(3)   Using a 0.010-inch feeler gage or equivalent, insert tip of feeler gage between washer stackup and bifilar lug.   Accomplish this check on both sides of lug. 
			(i)   If tip of feeler gage does not contact shank of attachment bolt, washer stackup and lug clearance are acceptable.   Torque attachment nut to 1,690 inch-pounds. 
			(ii)   If tip of feeler gage contacts shank of attachment bolt, reshim bifilar support assembly to provide a 0.000 to 0.004 inch clearance.   Torque attachment nut to 1,690 inch-pounds maximum. 

	NOTE:   The Sikorsky Model S-61 Maintenance Manual contains shimming instructions. 

		(4)   Repeat the requirements of paragraphs (a)(2) and (3) individually on the four remaining hub arms for each bifilar support assembly attachment hardware. 
		(5)   Reinstall main rotor fairing. 
	(b)   Conduct a one-time visual inspection for cracks in area of the 10 main rotor hub upper plate arm bifilar attachment bolt holes.   Conduct a visual inspection for cracks on the outside surfaces of each of the 5 hub arms, adjacent to the 10 bifilar attachment holes.   The rotor head does not requiredisassembly for these inspections. 
		(1)   If a crack indication is found by the visual inspection, clean immediate area and reinspect using a dye penetrant or equivalent inspection method. 
		(2)   If a crack is verified, remove main rotor hub assembly prior to further flight, and replace with an airworthy component. 
	(c)   Upon request, an alternate means of compliance which provides an equivalent level of safety to the requirements of this AD may be used when approved by the Manager, Boston Aircraft Certification Office, Engine and Propeller Directorate, Aircraft Certification Service, 12 New England Executive Park, Burlington, Massachusetts 01803, telephone (617) 273-7118 
	(d)   Upon submission of substantiating data by an owner or operator through an FAA Aviation Safety Inspector, the Manager of the Boston Aircraft Certification Office may adjust the compliance time specified in this AD. 

	NOTE:   Sikorsky Aircraft Co. Alert Service Bulletin No. 61B10-46, dated February 7, 1989, pertains to this subject. 

	This amendment (39-6458, AD 90-01-04) becomes effective on February 5, 1990. 

FOR FURTHER INFORMATION CONTACT:  Donald F. Thompson, Airframe Branch, Boston Aircraft Certification Office, Engine and Propeller Directorate, Aircraft Certification Service, Federal Aviation Administration, 12 New England Executive Park, Burlington, Massachusetts 01803, telephone (617) 273-7113.