Recent air ambulance crashes have raised questions about safety and standards, and there may not be enough experienced pilots. The N.Y. Times’ impact graphs:

The spike is putting a spotlight on a little-regulated and fast-growing sector of health care: the medical helicopter industry. There are an estimated 700 medical helicopters operating nationally, about twice the number flying a decade ago.

Medical helicopters were once nearly all affiliated with hospitals. But more generous federal reimbursements and changes in payment methods have attracted more operators, including publicly traded corporations and smaller concerns that in some cases set up outposts and market their services to rural emergency units and even homeowners.

Emergency medical helicopters do save lives, by speeding some patients to hospitals far faster than a ground ambulance could and by reaching remote areas. But the industry’s rapid, competitive growth may also be exacting a toll. Federal regulators and some doctors worry that the pool of skilled helicopter pilots has become drained and that some of those flying are making poor decisions. In addition, some companies are flying older helicopters that lack the instruments needed to help pilots navigate safely. Of the 27 fatal medical helicopter accidents that occurred between 1998 and 2004, 21 were at night and often in bad weather, according to federal statistics.

Recent air ambulance crashes have raised questions about safety and standards, and there may not be enough experienced pilots. The N.Y. Times’ impact graphs:

“You need to raise the bar and say this is where the bar is,” said Dr. Scott Zietlow, the medical director for the helicopter program at the Mayo Clinic. “If you can’t get over it, you can’t fly.”

Last month, the Federal Aviation Administration, after a meeting with helicopter operators, proposed steps to improve flight safety. They included helping pilots assess risks and providing them with up-to-date electronic equipment.

Separately, the National Transportation Safety Board has been examining medical helicopter safety and plans to issue recommendations to the Federal Aviation Administration, a safety board official said.