BY : The Associated Press

The dreaded BANG! came from deep within the F-16's lone engine, shaking the warplane as it made passes over an Arizona bombing range last December. Then came the alarming loss of thrust.

Two attempts to restart the engine failed. Having exhausted their options, the pilot and his student bailed out, parachuting to safety before the plane slammed into the Sonoran Desert, a $21 million loss for taxpayers.

Not all F-16 pilots have been so lucky recently. The accident rate for this workhorse fighter has risen over the past few years, and two pilots have died in the past year, according to an Associated Press review of Air Force documents.

In the fiscal year that ended Sept. 30, there were 10 "Class A" F-16 accidents — crashes that resulted in death, loss of the aircraft or damage of more than $1 million. (An 11th F-16 crash was counted separately as a combat loss by the military because the pilot was strafing enemy trucks at the time.)

The total was up from nine the previous year, five the year before that and just two the year before that.

The number of crashes has gone up even though the total number of hours flown has dropped steadily over the past five years.

An Air Force official said that one factor appears to be human error, and that pilots and maintenance crews must stay on guard against complacency. Pilot error was blamed for three accidents and the Iraq combat crash last year.

"I liken the problem to a really good football team that drops its guard," said Col. Willie Brandt, the chief of the Aviation Safety Division at the Air Force Safety Center and an F-16 pilot now flying combat missions in Iraq. "We started well this year and were on track, but have slipped a little. If I have a concern it is in the trend I see there."

The rate of Class A accidents this year — 3.18 per 100,000 hours flown — was the highest since 2001, when it was 3.85 because of a rash of engine failures.

The Class A accidents last fiscal year include crashes that happened during training in the United States and Italy. The total also includes several crashes that happened during sorties in Iraq while the pilots were not engaging the enemy.

One expert said that it may be that as the Iraq war drags on, the stress of combat is taking a toll on the 1,300 F-16s in the U.S. fleet, and their pilots.

"That might be putting wear and tear on the planes," said John Pike, director of the Washington-based military think tank Globalsecurity.org. "It might be putting wear and tear on crews."

The F-16 is known in Air Force circles as the "lawn dart" for its tendency to plunge back to Earth when its single engine flames out, and in most years, engine failure causes more accidents than any other factor. But pilot error was responsible for about the same number of F-16 accidents as engine failure in the past year.

An Air Force-wide increase last fiscal year in destroyed aircraft has spurred the service to redouble its efforts to confront human error, Brandt said.

The Air Force Safety Center housed at Kirtland Air Force Base in New Mexico now has a full-time flight surgeon, an aviation physiologist, a life-support specialist and two aviation psychologists on the staff, Brandt said.

"They are constantly immersed in trying to find ways to improve the human side of aviation," he said.

One problem safety experts are on guard against is exhaustion amid the day-and-night sorties F-16 pilots are flying in Iraq.

Ohio Air National Guard Maj. Kevin Sonnenberg, 42, died in June when his F-16 crashed shortly after takeoff from an air base in Iraq. Investigators found he became disoriented while flying in a dust storm at night.

Before taking off at 12:25 a.m., Sonnenberg had complained to his roommate that he was having trouble sleeping, according to an investigation. His squadron mates also said Sonnenberg appeared "slightly fatigued," but investigators found no proof fatigue was responsible for his misjudgments.

Despite the heavy flying responsibilities in the war zone, pilot fatigue is not a widespread problem, Brandt said. The Air Force has strict guidelines governing rest for its pilots, he said.

Pilots must take at least 12 hours off before showing up for duty, and duty on a flying day is limited to 12 hours, or 10 hours at night.

The F-16s damaged or destroyed in fiscal 2006 were worth about $112 million altogether.

The current crash rate remains lower than that seen during the 1980s and 1990s. In the late 1990s and the early part of this decade, engine problems caused the number of F-16 Class A crashes to spike to as many as 18 in one year. Experts pinpointed the problem, fixed it and brought the accident rate down.

There is no indication of such a problem today, Brandt said.

"If I thought there was an issue with the age or safety of the aircraft, I wouldn't fly it, and neither would most of my friends," he said in an e-mail.

A constant challenge, Brandt said, is squeezing the human-error factor out of the crash equation.

"We have aircraft piloted by human beings, designed by human beings, and maintained by human beings," said Brandt. "We are the most combat-tested, combat-experienced force on the planet, and we learn more about ourselves and our business every day. But still we are human and make mistakes."