AD 78-26-01

78-26-01 DETROIT DIESEL ALLISON: Amendment 39-3373. Applies to Model 250-C28B engines installed in but not limited to Bell Model 206L-1 rotorcraft certificated in all categories. Compliance required as indicated, unless previously accomplished. To preclude possible engine power loss resulting from electromagnetic interference, accomplish the following: (A) Before further flight accomplish the following unless the engine electrical system has been previously modified in accordance with Detroit Diesel Allison Commercial Engine Bulletin 73-2003. (1) Pull the N2 overspeed circuit breaker and secure by wrapping with tape or placing a Ty-Wrap around the breaker stem. (2) Install placard which states "Eng Ovsp Circuit Deactivated" in 1/4" or larger letters adjacent to N2 overspeed circuit breaker. Note: The engine overspeed test outlined in Section 2 of the RFM will no longer function with the circuit breaker deactivated. (B) Not later than February 1, 1979 modify the engine electrical system in accordance with Detroit Diesel Allison Commercial Engine Bulletin 73-2003 unless previously accomplished. Concurrent with the accomplishment of CEB 73-2003 reactivate the N2 overspeed control by engaging the N2 overspeed circuit breaker and removing the placard "Eng Ovsp Circuit Deactivated," and remove the No. 4 plug from the outlet vent of the N2 overspeed solenoid valve if installed in accordance with Detroit Diesel Allison Commercial Service Letter 2008. The Detroit Diesel Allison Commercial Engine Bulletin identified in this directive is incorporated herein and made part hereof pursuant to 5 U.S.C. 552(a)(1). The Detroit Diesel Allison Commercial Engine Bulletin incorporated herein may be obtained upon request to Detroit Diesel Allison, Division of General Motors Corporation, P.O. Box 894, Indianapolis, Indiana 46206. This document may also be examined at the FAA Great Lakes Region, 2300 East Devon Avenue, Des Plaines, Illinois 60018 and at FAA Headquarters, 800 Independence Avenue, S.W., Washington, D.C. 20591. A historical file on this AD which includes the incorporated material in full is maintained by the FAA at its headquarters in Washington, D.C. and the Great Lakes Region. (Detroit Diesel Allison Commercial Service Letter 250-C28B CSL-2008 also pertains to this subject.) This amendment becomes effective upon publication in the Federal Register, as to all persons except those persons to whom it was made immediately effective by the air mail letter dated November 3, 1978, which contained this amendment.