Airworthiness Directive · Amendment 39-17722 · Turbine section
Sikorsky Aircraft Corporation (Sikorsky) Helicopters
This AD applies to Model S-70, S-70A, S-70C, S-70C (M), and S-70C (M1) helicopters with General Electric (GE) T700-GE-401C or T700-GE-701C part-numbered engines, certificated in any category.
We are adopting a new airworthiness directive (AD) for Sikorsky Model S-70, S-70A, S-70C, S-70C (M), and S-70C (M1) helicopters with General Electric (GE) T700-GE-401C or T700-GE-701C engines installed. This AD requires establishing new fatigue life limits for certain GE engine gas generator turbine (GGT) rotor parts. This AD was prompted by a reevaluation of the method for determining the life limit for certain GE engine GGT rotor parts and the determination that these life limits should be based on low cycle fatigue (LCF) events instead of hours time-in-service (TIS). The actions are intended to prevent fatigue failure of a GGT rotor part, engine failure, and subsequent loss of control of the helicopter.
You are responsible for performing each action required by this AD within the specified compliance time unless it has already been accomplished prior to that time.
(1) Before further flight, insert into the airworthiness limitations section of the maintenance manual or instructions for continued airworthiness the low cycle fatigue (LCF) limit diagrams shown in Figures 2 through 7 (pages 9 through 14) of GE T700 Turboshaft Engine Service Bulletin T700 S/B 72-0041, Revision 1, dated March 12, 2010, for helicopters with the GE T700-GE-401C engine, or Figures 2 through 4 (pages 10 through 12) of GE T700 Turboshaft Engine Service Bulletin T700 S/B 72-0038, dated October 1, 2008, for helicopters with the GE T700-GE-701C engine. The diagonal line on each diagram represents the new cycle life limit (a combination of full low cycle fatigue events (LCF1) and partial low cycle fatigue events (LCF2) as those terms are defined in the Accomplishment Instructions, paragraphs 3.A.(1) and 3.A.(2) of each service bulletin) for each gas generator turbine (GGT) rotor part. A combination of LCF1 and LCF2, which results in a number below the diagonal line of the applicable diagram for each engine, indicates that the part has not reached its fatigue life limit.
(2) Before further flight:
(i) Obtain the actual LCF1 and LCF2 count from the engine “history recorder” (HR);
(ii) Calculate the LCF1 and LCF2 fatigue retirement life for each GGT rotor part as follows:
(A) Determine the actual LCF ratio by dividing the total actual LCF2 cycle count obtained from the HR by the total actual LCF1 cycle count obtained from the HR. Add to the actual counts from the HR any actual additional fatigue cycle incurred during any period in which the HR was inoperative.
(B) Determine the LCF1 retirement life by dividing the maximum number of LCF2 events obtained from the applicable diagram for each engine by the sum of the actual LCF ratio obtained by following paragraph (e)(2)(ii)(A) of this AD plus the quotient of the maximum number of LCF2 events from the applicable diagram for each engine divided by the maximum number of LCF1 events from the applicable diagram for each engine.
(C) Determine the LCF2 retirement life by multiplying the actual LCF ratio obtained by following paragraph (e)(2)(ii)(A) of this AD times the LCF1 retirement life determined by following paragraph (e)(2)(ii)(B) of this AD.
(iii) Replace each GGT rotor part that has reached the new fatigue cycle life limit with an airworthy rotor part.
(3) For helicopters with the GE T700-GE-401C engine, if you cannot determine the number of low cycle fatigue events manually from the HR or by combining both manual and HR counts, then the life limit for the GGT rotor part is the hours TIS for the part as shown in Table 1 of GE T700 Turboshaft Engine Service Bulletin T700 S/B 72-0041, dated August 21, 2009.
(4) Before further flight, begin or continue to count the full and partial low fatigue cycle events and record on the component card or equivalent record that count at the end of each day for which the HR is inoperative.
