DISTRIBUTION A. Approved for public release; distribution unlimited.
EN-SB-09-001, Page 1 of 13
Number: EN-SB-09-001
Date: 15 June 2009
Subject: Methodology for Determination of Equivalent Flight Hours and Approaches
to Communicate Usage Severity
References:
1. MIL-STD-1530C, Aircraft Structural Integrity Program, 1 Nov 2005.
2. Gallagher, J. P., “A Review of the Philosophies, Processes, Methods and
Approaches that Protect In-Service Aircraft from the Scourge of Fatigue Failures,”
ICAF 2007, Naples, Italy, May 2007.
3. Babish, C. A., “Implication of Usage Severity and Variability Based on an F-16 Case
Study”, ICAF 2007, Naples, Italy, May 2007.
4. NATO RTO-TR-AVT-125, “Future Airframe Structural Lifing: Methods, Applications
and Management”, December 2008.
5. AFRL-RX-WP-TR-2008-4373, “Recommended Processes and Best Practices For
Nondestructive Inspection (NDI) Of Safety-Of-Flight Structures”, October 2008.
Purpose:
Proper execution of an Individual Aircraft Tracking (IAT) Program requires an
understanding of the usage severity for each aircraft in the USAF fleet. Comparing
actual usage to a reference usage is important to understand the usage severity and to
assess the structural health and maintenance requirements for each “tail number”. For
the USAF, usage severity is determined by using the concept of Equivalent Flight Hours
(EFH) as described in the Aircraft Structural Integrity Program Task V of MIL-STD-
1530C (Reference 1). The purpose of this bulletin is to ensure that ASIP Managers and
structural engineers understand the process to determine equivalent flight hours and to
properly interpret and communicate usage severity.
Structures Bulletin
ASC/EN
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