ABSTRACT
The United States Air Force (USAF) faces substantial challenges in operating airframes with exceptionally long service lives and, having recognized age as a factor in O&M costs as early as the 1960s (Johnson 1962), the USAF started comprehensive fleet lifetime O&M studies in the 1990s. While limited data in early studies contributed to a confused literature in the 60s and 70s, from Johnson (1962) to Marks and Hess (1981), large datasets and the application of more sophisticated analytical methods available to the USAF in recent years has enabled investigators to draw the cautious conclusion that age effects impact O&M costs. In particular, it was demonstrated in Ramsey et al. (1998) that heavy-maintenance workloads have increased with the chronological age of the KC-135 tanker aircraft, and an earlier RAND study (Hildebrandt and Sze 1990) estimated that, for every year increment in the age of a USAF mission design series, O&M costs increase on average by 1.7 perent. Further studies on age effects using commercial airline data (Ramsey et al. 1998; Dixon 2005), data from US Navy aircraft (Johnson 1993; Jondrow et al. 2002; Stoll and Davis 1993; Francies and Shaw 2000) and those of the USAF (Hildebrandt and Sze 1990; Kiley 2001; Pyles 2003; Keating and Dixon 2003) in the areas of workloads, material consumption, repairs per flight hour, mean time between failures, and
program depot maintenance all show positive growth with age. Investigators warn (Pyles 2003) that changing accounting practices, budget sluggishness, and relatively fixed maintenance-personnel requirements plague USAF and USN studies, creating a difficult environment in which to extract age effects from other pressures. Raymond Pyles’s 2003 RAND corporation investigation for the USAF on the impact of aging airframes on maintenance represents the most comprehensive study to date (Pyles 2003). Using regression methods that address several issues simultaneously, Pyles discovered a positive relationship between maintenance requirements-in nearly all activities-with airframe age. Not only did Pyles find that different maintenance tasks realize different age effects for the same airframe, but he also found that age effects correlate with aircraft complexity and fly-a-way costs.
