A major reason American military helicopters, mainly the AH-64 gunship and transports like the UH-60 and CH-47 are so popular is because they have high readiness rates (percentage of available aircraft able to do their job). These tend to be very high, often 80 percent or more. This has been the case for over fifty years, even for older (in terms of years and flight hours) aircraft. This has proved to be decisive in keeping these older designs selling.
Europe sought to build competitive military helicopters but were never able to match American readiness rates. This is surprising, because European commercial aircraft (AirBus) can do it. But the Tiger helicopter gunship and NH90 transport, meant to compete with the AH-64 gunship and UH-60 have failed. The Tiger entered service in 2003 and the NH90 in 2007 and their low availability rates recently became a public scandal (embarrassing debate in the French parliament) when it was revealed the Tiger had a 21 percent readiness rate (5.5 year average) and the NH90 had a readiness rate of 40 percent. This came despite years of efforts by the users and manufacturers to raise that rate. The users, who frequently operate from bases shared with American (or European) troops using AH-64s and UH-60s note the differences and are unhappy, as are the troops they support. Those European troops, when given a choice, prefer to be supported by American helicopters. Users of the Tiger and NH90 blame most of the problems on their logistical systems, which take far longer to deliver spare parts than their American counterparts. But even when that is not a problem the European helicopters have a hard time achieving and sustaining readiness rates of 50-60 percent.