A.2Concepts and Criteria
No single parameter by itself, without other data/information, can adequately qualify reliability. There are a number of variables, maintenance and operating statistics and general information about the operational experience of a particular power unit, which characterize propulsion system reliability. Engineering judgment must then be utilized to determine the adequacy and applicability of this data and information to ETOPS and to determine the suitability of the aeroplane for ETOPS. As an aid in making this judgment, statistical analysis will be used to help determine that the desired level of reliability is obtained.
The evidence must be such that it can be shown with high confidence that the risk of total thrust loss or loss to an extent that precludes continued safe flight, is acceptably low, i.e., at an appropriate level less than between 10-8 and 10-9 per hour during the relevant portion of the cruise.
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