Nonmilitary government agencies operate more aircraft than the world's largest airline but are subject to little federal safety oversight - a situation accident investigators say has contributed to air crashes and deaths.

Federal, state and local agencies own or lease more than 2,400 nonmilitary planes and helicopters for fighting forest fires, chasing crooks, conducting scientific research and other tasks. By comparison, the world's largest airline -- created by the merger of United and Continental -- and its regional carriers operate fewer than 1,300 planes.

But unlike United, Continental and other commercial airlines, government agencies are mostly left to police the safety of their flight operations themselves. The Federal Aviation Administration has long said it doesn't have the authority to apply regulations to other government agencies.

From 2000 through the first eight months of this year, the National Transportation Safety Board investigated at least 349 accidents, resulting in 135 deaths, involving aircraft owned by or operated under contract for government agencies. Problems uncovered in some of those accidents have prompted the board to host a forum beginning Wednesday aimed at getting the FAA and other government officials to discuss ways to address the problem.

"The issue for us is who is responsible (for safety). We have cases now where we ask that question and no one seems to know," said Tom Haueter, director of NTSB's office of aviation safety.

The NTSB isn't the only one confused. John Allen, the head of the FAA's flight standards, told a gathering of private and public aviation officials earlier this year that even his inspectors are sometimes uncertain of their role.

FAA officials have asked Congress to clarify the situation but the request "isn't a high priority," Allen said.

Part of the problem is that safety regulations written with commercial and private aviation in mind don't address government operations that are sometimes inherently risky.

"They're landing on dirt strips out in the middle of nowhere. They're shooting coyotes from the air. ... Some of the stuff is really kind of intense flying. If you're down low enough for a guy to shoot a coyote, that's pretty low," Haueter said.

Assigning responsibility for safety oversight becomes even murkier when private contractors operate flights for government agencies, an increasingly common occurrence.

The FAA published new guidance for government agencies and contractors in March, but safety investigators and contractors said there are still many gray areas.

The NTSB forum was spurred in part by the agency's two-year investigation of the August 2008 crash of a firefighting helicopter near Weaverville in Northern California. Nine people were killed and four others injured. The company that operated the flight misrepresented the performance capabilities of its helicopters in order to win a U.S. Forest Service firefighting contract, and then gave misinformation to its own pilots, causing them to underestimate the aircraft's weight, NTSB's investigation found.

The board faulted the Forest Service for not ensuring the helicopter operator was following safety regulations as promised in its contract. It also faulted the FAA, whose inspectors checked the safety of aircraft the contractor used for nongovernment work, but ignored helicopters used for government assignments.

Other Accidents That Have Raised Concern:

- A New Mexico state police helicopter crashed while attempting to rescue a lost hiker near Santa Fe, N.M., in June 2009. The pilot and the hiker were killed and a highway patrolman seriously injured. State police placed greater importance on completing missions than on making certain they were carried out safely, the board said. The agency also didn't employ enough pilots to safely operate around the clock, which indirectly put pressure on pilots to fly missions despite not having had enough rest.

- A Maryland state police medical evacuation helicopter crashed at night in poor weather while attempting to transport two auto accident victims in September 2008. The pilot, two medical workers and one of the accident victims were killed. The second accident victim was severely injured. The board questioned the agency's decision to dispatch the helicopter, saying police should have assessed the potential risks first.

Cases like the Weaverville accident involving a deliberate disregard for safety are rare, said Matt Zucarro, president of Helicopter Association International, whose members include government contractors.

"If you look at (contractor) aircraft performing government operations, the civilian ones, as well as government-operated aircraft, they have a very good safety record," Zucarro said. "Generally the operators have their standards and they aren't going to mitigate or diminish them because they get a request from a government agency for something."

FAA inspectors may not have the authority to demand safety information from contractors whose work for the Defense Department is classified secret, Allen told contractors at the meeting, which was hosted by the helicopter association.

"You are seeing more and more contracting in support of government services," he said. "The regulatory framework is slow to catch up."

Allen cited the example of a contractor transporting special forces troops in Afghanistan who was asked by the military to carry cargo containing ammunition on the plane as well. FAA regulations don't permit ammunition on passenger-carrying aircraft.

"You need to educate your air crews not to be enticed to operate outside the regulations in the heat of battle," he warned.