Answer by Thomas Zerbarini:
The specific numbers are closely guarded by each airline and not usually made public. Controlling cost and revenue is a big way airlines compete with each other. So, they don't want that information too readily available for public consumption.
You can get a great deal of information on an airline via their corporate filings and quarterly statements via the airlines website or the SEC website. Here is Delta's SEC filings webpage:
Some airlines will put together an overview or presentation report that summarizes their financial filings. Here is an example of such a presentation that was put together by a student for a report:
You'll find that the airlines will group together their operating costs and revenue in figures like Cost Available Seat Mile (CASM) and Revenue Available Seat Mile (RASM). In using the CASM they may carve out fuel or maintenance specifically to highlight a specific point.
Take a look at Delta's 10Q filing and you'll see each major expense including maintenance. The total expense is there, but you'll find that to deduce it down to hour or miles, there is not enough information to ascertain that information.