Whenever some new research is done and technology comes to the market there are always issues and the technology gets better and improved with time one example of it is the Russian MiGs they use to have a lot of problem in 80s . Recent example is Chinese Z-10 helicopter Engine has a problem of running in under powered condition usually it carry up to 16 guided air-to-ground missiles (i.e HJ-10), but it is limited to eight the weight to power ratio also cause performance issue in the field the empty weight of Z-10 is 5000 kg the engine Z 10 is using WZ 9 can support typically a helicopter in the range of 3000 kg can now China is developing a new Engine for a utility helicopter with a french company Safran (WZ-16). WZ-16 is to have a take-off output power of at least 1240 kW, and continuous operation output of over 1100 kW. F 22 Raptor also had a lot of issues the issue of Oxygen tank was solved a few years ago .Yes, it was resolved several years ago. Unlike other aircraft that carry a finite LOX (liquid oxygen) supply, the F-22 has an "On Board Oxygen Generating System" (OBOGS). Previously if OBOGS malfunctioned intermittently, the pilot could not detect if it was imperceptably generating insufficient oxygen, and thereby cause the pilot to develop a slow onset of hypoxia that could lead to blackout before anything could be remedied. The solution was to issue a retrofit contract to add finite LOX units configured with an oxygen sensor to automatically dispense oxygen if it detects OBOGS is not providing enough. The retrofit contract was done two years ago and there's been no hypoxia incidents for over two years.
but still USA is not manufacturing any more F 22 and 187 units built ,production stopped due to high price which is 67 billon $. USA thinks F22 is stealth one but critics says it is never used in full scale war.Maintaince cost of F22 is very high. Time required for maintaince is also more .
next time please do some research and than do argument