Older fleets cost more to maintain per flight hour, on one age slope for every aircraft class. At any age the wide-body curve sits well above the narrow-body one and the regional curve a little below it.
What this shows: The chart plots Narrow-body, Wide-body and Regional on a vertical axis of Maintenance cost ($/hour).
Conditions and method
Status: descriptive (the age slopes are pooled across aircraft categories because the per-category differences are jointly insignificant, so the categories differ only in level).
Maintenance expense divided by airborne (flight) hours, for one carrier’s aircraft of one type in one year; the age is the average age of those aircraft. The fit uses 2,565 such observations and explains 28% of the variation in the log of their cost per hour.
The three curves share one age slope and differ only in level, because the differences between the categories’ age slopes are jointly insignificant.