The fiery collision of two airplanes on a Los Angeles runway early this month was the sixth consecutive major domestic airline crash in which more passengers survived than died.

Since Dec. 7, 1987, when a disgruntled former airline employee shot the pilot of a Pacific Southwest jet, sending it into a dive over California and killing all 43 aboard, there has not been a major passenger airline crash in U.S. airspace in which everyone aboard died. This includes the crash of United Flight 232 at Sioux City, Iowa, on July 19, 1989, in which 111 were killed but 187 survived even though the plane broke up and skidded down the runway in a ball of flame.

While aviation safety specialists are leery of declaring a trend, improvements in the air traffic control system, in crew training and in jetliners -- many of them implemented after disastrous crashes in the 1970s and 1980s -- may be paying dividends.

Cabin safety measures, particularly fire retardants and passenger escape routes, also may have increased the number of survivors in at least three of the last six crashes. There is also some anecdotal evidence that passengers are looking around for emergency exits and paying more attention to safety instructions, perhaps prompted by the flow of news stories about survivable crashes.

"I think the answer may be that we have eliminated or greatly reduced the large accident producers," said Capt. Dave Simmon, United Airlines' director of flight safety. "This is significant. It really shows us the way to go in the future."

The common thread in the last six crashes is that all but one took place on airport grounds, including ground collisions at Detroit on Dec. 3, 1990, and Los Angeles on Feb. 1. In all six, the pilot was in control of the plane until almost the last second, including an Avianca Boeing 707 that ran out of fuel and essentially belly-flopped at relatively low speed into a Long Island, N.Y., neighborhood in January 1990.

"If you can be in a landing attitude or near a landing attitude, especially on a flat surface like a runway, you've got a good chance of having a fairly good number of survivors," Simmon said.

Boeing Commercial Aircraft Co. statistics show that the majority of crashes happen on takeoff or landing. But chances of survival are far better if the crash takes place on the runway rather than a few hundred feet off airport grounds where buildings or trees can become killers.

There are numerous ways to "count" airline accidents. The broadest count would include such incidents as planes striking pedestrians on the runway. Commuter airline and general aviation accidents would run up the total, as would all-cargo airlines or incidents involving planes with crews but no passengers. According to National Transportation Safety Board statistics, 1,960 people have died in crashes of major U.S. carriers worldwide in the last 11 years, including the bombing of Pan American Flight 103 over Lockerbie, Scotland, on Dec. 21, 1988.

Confining the count to U.S. airspace and counting only crashes in which an airliner carrying passengers was destroyed by the impact or burned afterward, 528 passengers and crew have lived and 242 have died in the last three years, compared to the previous eight years when more than 1,000 died and 116 survived.

If this phenomenon continues, the United States will have separated itself from the rest of the world in airline safety.

Worldwide, for instance, one of the major causes of crashes has been "controlled flight into terrain," in which a pilot flies a perfectly airworthy plane into a mountain or into the ground. But that type of accident is rare in U.S. airspace. There have been incidents involving non-major airlines, such as a small commuter plane operated by Aloha Island Air that flew into a mountain on Oct. 29, 1989. But the last involving passenger fatalities on a major airline was May 8, 1978, when a National Airlines jet ditched in Escambia Bay near Pensacola, Fla.

There also has not been a midair collision in the United States since the Aug. 31, 1986, collision between an Aeromexico DC-9 and a small plane over Cerritos, Calif.

"I think everything's moving toward a safer in-air environment," said Bob Baker, executive vice president for operations for American Airlines.

Baker, Simmon of United Airlines and others in government and industry point to a steady progression of improvements and federal regulations throughout the quarter-century of the jet age, most of them prompted by disastrous crashes.

"I've got to believe those rules had an effect," said Anthony J. Broderick, the Federal Aviation Administration's associate administrator for regulation and certification.

Among the recent examples:

The 1986 Cerritos crash led the FAA to impose stringent airspace controls on general aviation aircraft around the 27 busiest U.S. airports, requiring planes within those terminal control areas to have "Mode-C" transponders, devices that automatically report location and altitude to air traffic control radar.

The rule became effective in stages between July 1989 and the end of 1990, and Baker noted that reports of near-collisions "went down like an elevator" in 1990.

By the end of 1993, all commercial aircraft must also be equipped with the Traffic Alert and Collision Avoidance System (TCAS), which tells pilots to take evasive action when other aircraft are too close.

One of the major requirements to grow out of the Dec. 1, 1974, Trans World Airlines crash on Mount Weather, Va., was the ground-proximity indicator. This device, now required on all U.S. airliners, warns a pilot audibly when an airplane is approaching the ground too fast.

Simmon said the "ground prox," coupled with air traffic control improvements growing out of the TWA crash, have all but eliminated "controlled flight into terrain" crashes in the United States.

Baker said the FAA's Central Flow Control Facility, which regulates air traffic through the country in an effort to prevent airborne holding, can also take credit for preventing midair incidents. "They have never let the system get full of airplanes," he said.

The 1982 Air Florida crash into the 14th Street Bridge and a 1987 Continental crash at Denver have led to better de-icing fluids, Simmon said, which last longer as airplanes wait for takeoff.

Wind shear, a rapid change in air movement, has been responsible for numerous crashes in the jet age. But there has not been a wind shear crash since a Delta Lockheed L-1011 crashed at Dallas-Fort Worth on Aug. 2, 1985. During that time, airlines have put pilots through an intensive training and awareness program to teach them to avoid wind shear and to survive it if necessary.

Airline crew training has intensified in all areas in the last decade, particularly after accidents caused by crew error such as failing to set the wing flaps properly for takeoff.

"We have been applying the lessons learned, and it has helped," said John J. Nance, a pilot and aviation author.

Except for the United crash at Sioux City, none of the six major accidents has involved a mechanical defect, possibly an indication of improved maintenance.

One effect of so many airport-related accidents has been to point out a major weakness in the air traffic system -- ground control. The FAA has announced plans to standardize runway markings and signs, and to develop a new generation of ground-control radar and safety devices.

Baker said it is past time. "That's been on the mill at the FAA for 10 years," he said. He called the current ground radar system "a piece of junk."

The recent accidents have also led o renewed emphasis on survivability after the initial impact. Airliners have been outfitted with fire survival devices, such as less flammable interior materials and floor-track lighting to help passengers find exits. Automatic fire extinguishers and smoke detectors have been placed in lavatories.

Seats designed to withstand an impact nine times the force of gravity are being replaced by seats that can absorb 16 times gravity's force. New escape slides also deploy faster, a far cry from the slides of decades ago that were little more than glorified bedsheets.

"Where we are today is way beyond the '70s technology," said Jim Likes, Boeing's payload systems director. "I've been here since 1960, and I don't remember a time in that period when we haven't had something going on improving interiors."

Feb. 1, 1991 -- USAir Boeing 737 collides with commuter plane on the runway at Los Angeles. 34 killed, 67 survive.

Dec. 3, 1990 -- Northwest 727 collides with McDonnell Douglas DC-9 on runway at Detroit. Eight killed, 34 survive on burned DC-9.

Jan. 25, 1990 -- Avianca 707 runs out of fuel, crashes on Long Island. 73 killed, 85 survive.

Sept. 20, 1989 -- USAir 737 crashes on takeoff from LaGuardia Airport. two killed, 61 survive.

July 7, 1989 -- United DC-10 crash-lands at Sioux City, Iowa, after engine explosion. 111 killed, 187 survive.

Aug. 31, 1988 -- Delta 727 crashes on takeoff from Dallas-Fort Worth. 14 killed, 94 survive.