The government ordered U.S. airlines Friday to inspect 1,440 Boeing jets to determine if they have a potentially faulty fuel pump that could cause an explosion.

The Federal Aviation Administration's emergency order stressed that no serious incidents have been linked to problems with the pumps, which are made by Hydro-Aire Inc. of Burbank, Calif., and were installed in January and April on Boeing 737s, 747s and 757s.

The airlines were given four days to inspect their fleets. The FAA estimated 1,250 pumps could have a problem with wires that were placed too close to a rotor and can chafe. Since one plane can have several pumps, it was not immediately clear how many aircraft might have the flaw.

Ron Wojnar, the FAA's deputy director of aircraft certification services, said any airlines that installed Hydro-Aire's pumps in the Boeing models since January are being ordered to keep enough fuel in the tanks to cover the devices even when the planes bank or encounter turbulence in flight.

"This is not an unsafe condition," he said, explaining that the submersion would prevent any sparks from igniting fuel vapors.

The FAA's inspection order affects 515 of the 737s, 247 of the 747s, and 678 of the 757s operated by U.S. carriers.

Foreign airlines operate about 2,100 of the jets. The FAA is sending advisories about the pumps to its counterpart agencies in those countries.

The FAA will issue a follow-up directive in a few weeks, instructing carriers to repair or replace any faulty pumps, Wojnar said.

The pumps are located in the center fuel tank under the fuselage. Some planes may also have pumps in wing tanks.

Boeing spokeswoman Liz Veridier said her company sent the airlines a bulletin Wednesday ordering the pumps replaced on 116 new planes that had been put into use this year.

Greg Ward, president of Hydro-Aire, said the problem appears to have occurred while the pumps were being assembled. Hydro-Aire, meanwhile, has X-rayed all of the pumps that had not yet been shipped to Boeing--about 150 pumps--and found about 3 percent contained the wiring problem, Ward said.

He said one pump that the company took apart after it was returned by an airline contained a wire that had been rubbed by a nearby rotor, creating concern of a potential spark.

"When you have fuel covering the pump there's no oxygen, so there can be no fire," he said.

Other 737s, 747s and 757s were ordered to fly only with their tanks full enough to cover the pumps until further inspections could be carried out, said Boeing's Veridier.

The problem was detected on three planes that had pumps short out and stop working, giving the crew an indication of low pressure in the tank, said FAA spokesman Les Dorr.

The British carrier easyJet sent the pump back to Hydro-Aire on Aug. 12 after the crew of one of its Boeing 737s detected low pressure, Dorr said. A week later, a Northwest Airlines 747-400 reported a low pressure indication and found the same problem, he said. A China Southern Airlines 747-400 experienced the same trouble.

The National Transportation Safety Board ruled that an explosion in the center fuel tank of TWA Flight 800 caused it to crash off the coast of Long Island in 1996. It said vapors in the partly empty tank probably were ignited by a spark in wiring.

The Paris-bound Boeing 747 exploded in a fireball at 13,700 feet, minutes after leaving John F. Kennedy International Airport. All 230 people on board were killed. "All of our pumps that were on Flight 800 were recovered and not found to be contributors to the crash," Ward said.