"In July 2009, the Air Force reported that the F-22 requires more than 30 hours of maintenance for every flight hour, with the total cost per flight hour of $44,000.[165] The Office of the Secretary of Defense puts that figure at 34 hours of maintenance per single hour of flight at a cost of $49,808 per hour of flight.[165] However, a Lockheed spokesman says that the variable cost per flight hour is only $19,000,[164] with a direct maintenance man hours per flight hour of 18.10 in 2008 and 20.48 in 2009.[164] The Pentagon requirement is for 12 hours of maintenance per flight hour.[164] The F-22 also reportedly encounted a critical failure every 1.7 hours.[N 2] The F-22 had required maintenance every 0.97 flight hours in 2004. This improved to 3.22 flight hours per maintenance event in production Lot 6 aircraft.[164]"