The U.S. Army recently made much of the fact that their UH-60 transport helicopters have been in the air for over 900,000 hours without a "material failure" breakdown. Much of this was due to the efforts of the ground crews, but a lot of it because the UH-60 built on the experience of the Vietnam era UH-1, and was built to be safer, and more reliable.
In the 1980s, the UH-60 began replacing the Vietnam era UH-1 "Huey" transport helicopter. Not only was the new design more effective, they were a lot safer, and expensive. By 2005, the U.S. Army had retired all of its UH-1s. The results of this shift were dramatic. The number of accidents went from over a thousand a year in the early 1990s, to less than 200 a year now. The accidents were more expensive, because the AH-64 and UH-60 were more expensive (costing more than three times as much.) But a lot of that money went into making the new choppers safer, and more survivable, for their crews, when they did get into trouble. At its peak, there were nearly 400 UH-60s operating in Iraq.
The U.S. military currently has over 2,000 UH-60 helicopters, with most of them (about 1,700) in the army. These have flown over six million hours so far, but it has taken over two decades to refine the design and maintenance procedures to achieve such a long run of failure free flying. The manufacturer expects the UH-60 to reach a million problem free flight hours by the end of the year. The ground crews, in doing their part, have managed to make the UH-60s 84 percent "mission capable" (available for use.) This is very high, for most combat aircraft are doing well if they are 70-80 percent mission capable.
The UH-60 was safer, and sturdier, in combat. Since 2003, the United States has lost about 70 helicopters in Iraq. Most of them belonged to the U.S. Army, the rest were marine or civilian (mainly security contractors.) During the peak period of combat (2005-2007), helicopters were fired on about a hundred times a month, and about 17 percent of the time, the helicopters were hit. Most of these were UH-60s. But few of the helicopters hit were brought down, much less destroyed. Contrast this with Vietnam (1966-71). There, 2,076 helicopters were lost to enemy fire (and 2,566 to non-combat losses), most of them UH-1s, or the gunship variant, the AH-1. In Vietnam, helicopters flew 36 million sorties (over 20 million flight hours). In Vietnam, helicopters were about twice as likely to get brought down by enemy fire. As in Iraq, the main weapons doing this were machine-guns. Today's helicopters are more robust, partly because of Vietnam experience, and are more likely to stay in the air when hit, and land, rather than crash. The 1960s was also a period of learning how to use helicopters on a large scale, in a combat environment. That experience also went into developing safer ways to fly, and use, helicopters in combat.
For example, in Iraq, aircraft losses to ground fire have been declining every year, since 2003, mainly because of improved defensive tactics. Moreover, the most vulnerable aircraft, helicopters, have been spending more time in the air. In 2005, U.S. Army aircraft (mainly helicopters) flew 240,000 hours over Iraq. That increased to 334,000 hours last year, and went to over 400,000 hours in 2007, after which it plateaued and declined because the terrorists were defeated. The more time helicopters are in the air, the more opportunities someone has to shoot at them. And the more robust the helicopters, the less likely they are to be brought down by enemy action, or, especially, because of "material failure."