In mid-2017 American F-35 fighters completed their first 100,000 flight hours. That is the point when a new aircraft is seen as mature. The F-22 reached that point in 2010. But the F-35, unlike earlier jet fighters, reached 100,000 flight hours without any crashes. However the F-35 did suffer three “Class A” accident (defined as an aircraft incident that killed someone or cost at least $2 million to repair). That’s a record low accident rate for a new aircraft but that rate may increase a bit before it settles down. F-35s are entering service in large numbers over the next few years and will be used operationally. Some are already operating near combat zones.
Even when there is no war going on flying warplanes, especially jet fighters. It is dangerous even when no one is shooting at you. A century ago, during World War I, pilots of fighters were more likely to die in an accident than from enemy fire. There have always been accidents and as aircraft got more expensive the U.S. Department of Defense came up with a more organized way to tracking aircraft mishaps. One big innovation was the different categories of accidents. Class A accidents included everything from total loss of the aircraft and the death of all on board down to expensive damage. The lower range was an accident that cost a certain amount of money that could be adjusted for inflation and such. Until 2010 a Class A accident repair costs had to be at least a million dollars. That cost has gone up over time. The high cost of building (and repairing) the F-22, and most other new warplanes (like the F-22), finally triggered the 2010 change that required repairs worth two million dollars to be considered a Class A accident.
Even with that by 2012 the F-22 accident rate was six per 100,000 hours flown, including some crashes but the rate came down year by year, as they always do. What was learned developing the F-22 was applied to the F-35. Among the aircraft the F-35 is meant to replace, the new fighter's safety record is par for the course or an improvement. The Navy's F-18 has averaged 2.84 Class As per 100,000 hours since 1990, while the F-16 lifetime rate is 3.45 per 100,000 hours.
New aircraft always have higher accident rates, which is how many hidden (from the design engineers and test pilots) flaws and technical problems are found. The F-35, like the F-22, is expected to eventually have an accident rate of 2-3 per 100,000 flight hours and this is part of a trend. There are exceptions, like the AV-8 Harrier vertical takeoff jet, which has a rate of 11-12. The F-35B version of the F-35 is replacing the AV-8 with the intention of having a much lower accident rate than the AV-8, but probably higher than the F-35A (that only operates from land bases) and the F-35C (that can operate from carriers but using a catapult, not vertical takeoff and landing). Only about 240 F-35s have been built so far and only the F-35A and F-35B are in service (the F-35C begins that in 2018). There are orders for some 2,400 F-35s, with nearly half of them for export customers. Production won’t hit 150 a year until 2020.
Combat aircraft are becoming more reliable, even as they become more complex. For example, in the early 1950s, the F-89 fighter had 383 accidents per 100,000 flying hours. A decade later the rate was in the 20s for a new generation of aircraft. At the time, the F-4, which served into the 1990s, had a rate of less than five per 100,000 hours.
Combat aircraft have gotten more reliable and easier to maintain, despite growing complexity, for the same reason automobiles have. Better engineering and more sensors built into equipment makes it easier for the user and maintenance personnel to detect potential problems. Aircraft used the computerized maintenance systems, currently common on new aircraft, long before automobiles got them. Unless you have a much older car that still runs, or a real good memory, you don't notice the enormous increase in automobile reliability. But older pilots remember because such changes are a matter of life and death if you make your living driving an aircraft. And commanders know that safer aircraft give them more aircraft to use in combat and more aircraft that can survive combat damage and keep fighting.