Pilots are complaining that their airline bosses, desperate to cut costs, are forcing them to fly uncomfortably low on fuel.

Safety for passengers and crews could be compromised, they say.

The situation got bad enough three years ago, even before the latest surge in fuel prices, that NASA sent a safety alert to federal aviation officials.

No action.

Since then, pilots, flight dispatchers and others have continued to sound off with their own warnings, yet the Federal Aviation Administration said there is no reason to order airlines to back off their effort to keep fuel loads to a minimum.

"We can't dabble in the business policies or the personnel policies of an airline," said FAA spokesman Les Dorr. He said there was no indication safety regulations were being violated.

The September 2005 safety alert was issued by NASA's confidential Aviation Safety Reporting System, which allows air crews to report safety problems without fear their names will be disclosed.

"What we found was that because they carried less fuel on the airplane, they were getting into situations where they had to tell air traffic control, 'I need to get on the ground,"' said Linda Connell, director of the NASA reporting system.

With fuel prices now their biggest cost, airlines are aggressively enforcing new policies designed to reduce consumption.

In March, for example, an airline pilot told NASA he landed his regional jet with less fuel than required by FAA regulations. "Looking back," he said, "I would have liked more gas yesterday." He also complained that his airline was "ranking" captains according to who landed with the least amount.

A month earlier, a Boeing 747 captain reported running low on fuel after meeting strong headwinds crossing the Atlantic en route to John F. Kennedy International Airport in New York. He said he wanted to stop to add fuel but continued on to Kennedy after consulting his airline's operations manager, who told him there was adequate fuel aboard the jet.

When the plane arrived at Kennedy, the captain said it had so little fuel that had there been any delay in landing, "I would have had to declare a fuel emergency" - a term that tells air traffic controllers a plane needs immediate priority to land.

The last major U.S. air crash attributed to low fuel was on Jan. 25, 1990, when an Avianca Boeing 707 ran out while waiting to land at Kennedy. Seventy-three of 158 aboard were killed.

FAA regulations require airliners to take off with enough fuel to reach their destination or an alternate airport, plus another 45 minutes of flight. The regulations also say it's up to dispatchers and pilots to decide the size of fuel loads, with pilots making the final call.

Spare fuel beyond the minimum required by FAA is often added to airliners to allow for weather or airport delays. That adds weight, which burns more fuel and increases a plane's operating cost. A Washington-to-Los Angeles flight by an Airbus 320 with 150 passengers burns about 29,500 pounds, or 4,300 gallons, of fuel. That costs about $14,600. Adding an additional 1,500 pounds, about 219 gallons, would cost about $750 more.

Complaints about airlines scrimping on fuel aren't limited to those submitted to the NASA system.

Labor unions at two major airlines -- American Airlines and US Airways -- have filed complaints with FAA, saying the airlines are pressuring members not to request spare fuel for flights.

American notified dispatchers on July 7 that their records on fuel approved for flights would be monitored, and dispatchers not abiding by company guidelines could ultimately be fired.

American said its fuel costs this year were expected to increase to $10 billion, a 52 percent over 2007. "The additional cost of carrying unnecessary fuel adversely affects American's financial success," the airline told dispatchers in a letter.

Union officials responded that "it appears safety has become a second thought" for the company.

At US Airways, the pilots' union took out an ad in USA Today on July 16 charging that eight senior captains had been singled out by the company for requesting extra fuel and had been required to attend training sessions. The union said the training order was a message to other pilots not to request extra fuel.

American and US Airways blame the complaints on heated labor negotiations -- both are in contract talks with the complaining unions.

"It's not a safety issue; it's a contract issue," said John Hotard, a spokesman for American.

US Airways said in a statement to its employees that the eight captains had been adding fuel "well in excess of the norm."

FAA spokeswoman Laura Brown said the agency has conducted several analyses of airline fuel practices but found no instances of the minimum being violated or pilots' fuel requests being denied.

"We didn't see any proposed changes we thought needed to be made," Brown said.

Department of Transportation Inspector General Calvin Scovel recommended in April that the FAA take a nationwide look at airline fuel practices. Five months later, the agency is still developing a survey to send to its inspectors at each airline and has no schedule for sending it out.

Scovel also said the number of pilots reporting low fuel on approach to Newark Liberty International Airport tripled from 2005 to 2007. More than half were Continental Airlines flights, the dominant carrier at Newark.

He suggested the airline was pressuring pilots "to either not stop for fuel when needed or to carry insufficient amounts of fuel." His letter cited two bulletins from Continental's management urging pilots and flight crews to cut back on fuel, including one that noted "adding fuel indiscriminately reduces profit sharing and possibly pension funding."

But Scovel's review of 20 Newark-bound flights - out of 151 reporting low fuel on approach in 2007 - found none with less than 45-minutes worth of spare fuel.

Former National Transportation Safety Board Chairman Jim Hall said the situation merits an industrywide investigation by Scovel.

"It's a safety-of-flight issue and it needs to be treated as such," said Hall, now a transportation safety consultant. "If dispatchers and pilots are saying the airlines are pressuring them, and it's having a chilling effect on the decisions they make every day in regard to the fuel loads, and it looks it's like eroding the authority of the pilot in command, then that issue needs the attention of the government regulators who are there to oversee the system."