4 ms·

mean time between failures < 60 minutes? If that's true, how can it be used for anything?

sandworm 12y ago
There are lots of things to fail. On most military aircraft it is rare to fly with every tiny system running at 100%. Five or things can break during a flight without any real risk. Not the engines, but something like a datalink antenna or camera system. If you include little things like tray-tables and seats getting stuck up/down, even the 747 probably has a failure rate measured in hours.
fit2rule 12y ago
Answer: it can't.
- venomsnake 12y ago
  It is good that JSF is shaping up nicely then ... /s
Wistar 12y ago
Good point. The less than 60 minutes figure came from a 2008 GAO report: http://www.gao.gov/new.items/d08467sp.pdf http://www.gao.gov/new.items/d08467sp.pdf The particular passage: " The Air Force also budgeted $132 million in fiscal years 2007 and 2008 for reliability and maintainability upgrades, $28 million more than the amount budgeted for fiscal years 2006 and 2007. Despite these efforts, the F-22A continues to operate below its expected reliability rates. A key reliability requirement for the F-22A is a 3-hour mean time between maintenance intervals, which is required by the time the program achieves 100,000 operational flying hours, now projected for fiscal year 2010. Mean time between maintenance is defined as the number of operating hours divided by the number of maintenance actions. Currently, the mean time between maintenance is less than 1 hour, or about half of what was expected by the end of system development in December 2005. There has been no significant change reported regarding the current mean time between maintenance since last year’s review" Wondering about that value and for the sake of being more accurate, always a good thing, I found a "F-22 Assertions and Facts" document used in the US Senate in 2009 to defend the F-22 program. It has substantially different numbers for the F-22. http://www.hatch.senate.gov/public/_files/F22AssertionsAndFacts.pdf http://www.hatch.senate.gov/public/_files/F22AssertionsAndFa... About maintenance ratio: "The F-22 is required to achieve 12.0 direct maintenance man-hours per flight hour (DMMH/FH) at system maturity, which is defined to be when the F-22 fleet has accumulated 100,000 flight hours. In 2008 the F-22 achieved 18.1 DMMH/FH which then improved to 10.5 DMMH/FH in 2009. It’s important to recognize this metric is to be met at system maturity, which is projected to occur in late 2010. So the F-22 is better than the requirement well before maturity." About F22 reliability: "Reliability is measured by Mean Time Between Maintenance(MTBM. One of the F-22 Key Performance Parameters (KPPs) is to have an MTBM of 3.0 hours at system maturity, which is defined to be when the F-22 fleet has accumulated 100,000 flight hours. Through 2008, F-22s averaged 2.0 hours MTBM while the fleet has accumulated 50,000 flight hours. The F-22 is on-track to meet or exceed 3.0 hours of MTBM at system maturity, projected to occur in late 2010, and the latest delivered F-22s, known as Lot 6 jets, are exhibiting an MTBM of 3.2 hours."

There are lots of things to fail. On most military aircraft it is rare to fly with every tiny system running at 100%. Five or things can break during a flight without any real risk. Not the engines, but something like a datalink antenna or camera system. If you include little things like tray-tables and seats getting stuck up/down, even the 747 probably has a failure rate measured in hours.

fit2rule 12y ago

Answer: it can't.

venomsnake 12y ago
It is good that JSF is shaping up nicely then ... /s

Wistar 12y ago

Good point. The less than 60 minutes figure came from a 2008 GAO report: http://www.gao.gov/new.items/d08467sp.pdf http://www.gao.gov/new.items/d08467sp.pdf The particular passage: " The Air Force also budgeted $132 million in fiscal years 2007 and 2008 for reliability and maintainability upgrades, $28 million more than the amount budgeted for fiscal years 2006 and 2007. Despite these efforts, the F-22A continues to operate below its expected reliability rates. A key reliability requirement for the F-22A is a 3-hour mean time between maintenance intervals, which is required by the time the program achieves 100,000 operational flying hours, now projected for fiscal year 2010. Mean time between maintenance is defined as the number of operating hours divided by the number of maintenance actions. Currently, the mean time between maintenance is less than 1 hour, or about half of what was expected by the end of system development in December 2005. There has been no significant change reported regarding the current mean time between maintenance since last year’s review" Wondering about that value and for the sake of being more accurate, always a good thing, I found a "F-22 Assertions and Facts" document used in the US Senate in 2009 to defend the F-22 program. It has substantially different numbers for the F-22. http://www.hatch.senate.gov/public/_files/F22AssertionsAndFacts.pdf http://www.hatch.senate.gov/public/_files/F22AssertionsAndFa... About maintenance ratio: "The F-22 is required to achieve 12.0 direct maintenance man-hours per flight hour (DMMH/FH) at system maturity, which is defined to be when the F-22 fleet has accumulated 100,000 flight hours. In 2008 the F-22 achieved 18.1 DMMH/FH which then improved to 10.5 DMMH/FH in 2009. It’s important to recognize this metric is to be met at system maturity, which is projected to occur in late 2010. So the F-22 is better than the requirement well before maturity." About F22 reliability: "Reliability is measured by Mean Time Between Maintenance(MTBM. One of the F-22 Key Performance Parameters (KPPs) is to have an MTBM of 3.0 hours at system maturity, which is defined to be when the F-22 fleet has accumulated 100,000 flight hours. Through 2008, F-22s averaged 2.0 hours MTBM while the fleet has accumulated 50,000 flight hours. The F-22 is on-track to meet or exceed 3.0 hours of MTBM at system maturity, projected to occur in late 2010, and the latest delivered F-22s, known as Lot 6 jets, are exhibiting an MTBM of 3.2 hours."