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A replacement life of 120 hours established for the quill shaft has been made mandatory by the airworthiness directive.

A reduction in the overhaul period of the transmiSSion and mix box is being conSidered

The problems of sudden stoppage and other abnormal loadings have been carefully investigated Measurement of stresses during such occurrences have indicated that looal stresses in drive system components do not exceed deSign stresses in such cases. Although such loadings are characterized by sharply defined peaks, it is not conSidered that the occur- rence of these loads is of suffiCient frequency to introduce a fatigue problem from this source


 * Material omitted which is not pertinent to the acc1dent ***

The FAA concurs that it is necessary to keep all operators, foreign and

domestic, advised of the situation in this case.

To this end, copies

of the emergency airworthiness directive were prOVided to the govern- ments of other countries using Vertol 107 helic0pters and to the

United States military serVices

In addition, the manufacturer has

directly prov1ded information concerning the necessary corrective

procedures to all operators to whom they had delivered Model 107 helicopters.

Enclosure

Sincerely yours,

/s/ D D. Thomas

D. D. Thomas Assoc1ate Administrator for Programs