DENVER -- In large block letters, the United Airlines wind shear training manual leaves pilots with this sobering thought: "IT IS VITAL TO RECOGNIZE THAT SOME MICROBURSTS CANNOT BE SUCCESSFULLY ESCAPED WITH ANY KNOWN TECHNIQUES."

Effective today, new Federal Aviation Administration rules mandate that all airline and commuter pilots have read that line and have been told, in effect, don't be a hero. If the weather looks suspicious, avoid it.

More importantly, the rules require that airline pilots receive hours of training in classrooms and on simulators on how to survive wind shear, a sudden shift of wind that has killed thousands of passengers over the years, 535 of them in the last decade.

The most violent form of wind shear, called a microburst, occurs when a rapidly descending column of cold air fans out as it hits the ground, robbing a plane of airspeed.

Microbursts and the explosive forces they create were not understood, even by meteorologists, just 15 years ago. United and the Boeing Commercial Airplane Co. pioneered wind shear research and training, and a number of pilots working in the United Training Center here give the airline's program credit for their existence today.

Whether by luck or a growing awareness brought on by the industry's training programs, which have now been made mandatory by the FAA, there has been no U.S. airline wind shear crash since Delta Flight 191 crashed at Dallas on Aug. 2, 1985.

A crucial turning point in the fight to survive wind shear, most authorities agree, came at 1:34 p.m. on May 31, 1984, as United Flight 663, bound for Las Vegas, left Denver's airport. By all accounts, Capt. Gary Gore and 104 passengers and crew members came within inches of death.

As the Boeing 727 sped down Runway 35L at Stapleton International Airport on a typically partly cloudy High Plains day, its airspeed indicator showed a steady acceleration. Then as Gore began raising the nose wheel to lift off, the indicator suddenly began running backwards.

Gore looked at his instruments. "The eyes were telling the brain, but the brain said, 'That can't be,' " he said.

Gore had been one of the volunteer test pilots developing new wind shear survival techniques on aircraft simulators at United's training center here. Behind him was Capt. John Perkins, then head of the 727 training program and a key management official in developing the wind shear survival program, who was taking a turn as flight engineer because of a crew shortage. To his right was copilot Newt Rueter, a former Strategic Air Command pilot.

Keeping his plane on the runway and slamming the throttles ahead to the full "firewall" position, Gore watched the end of the runway race toward him. With Perkins giving "verbal encouragement," as he said, Gore pointed the 727's nose high into the air as the 2,000-foot runway hashmarks flitted past. The plane pitched up almost enough to stall.

"That was about the only chance we had," Gore said. Still, the plane did not lift off.

Gore said the world began moving slowly, "almost like a dream," and both he and the copilot thought death was imminent. Perkins, sitting back in the flight engineer's seat, could not see the ground. "It wasn't terrifying to me because I couldn't see out," he said.

"We never really lifted off the runway," Perkins said. "We just rolled off the end of the runway and flew." The National Transportation Safety Board later determined that the jet was so close to the ground that the blast from the tail-mounted engines scorched the grass for 600 feet beyond the end of the runway.

When wind shear cannot be avoided, the training program teaches pilots essentially to forget some of the things they have been taught about flying. Normally, when a plane loses airspeed, a pilot will allow the plane to follow its natural tendency to lower its nose to gain speed. Simulator tests showed, however, that the best chances of surviving wind shear are to push the nose up to almost "stick-shaker," or stall attitude, with full throttle. On takeoff, this may even require dragging the tail on the runway.

Straight ahead of Flight 663 that spring day was the hill that claimed a Continental jet under similar conditions a few years before. But the United plane emerged from the microburst into turbulent air and "we just shot up like an elevator," Gore said. The shaken crew circled the airport and brought the plane safely back to Stapleton.

Although the crew did not know it at the time, the 727's tail raked an array of antennas at the end of the runway. One antenna spar was thrust like a javelin through the fuselage. One antenna was ripped off just inches above its concrete base.

"I was out there a day later with Perkins and we looked at how close that sucker came to wiping out with a concrete pole," said John McCarthy, director of the research applications program at the National Center for Atmospheric Research (NCAR) in Boulder, Colo., one of the developers of the wind shear-detecting radar.

Their narrow escape not only gave the training program a boost but gave the National Transportation Safety Board and others a platform to demand that the government move ahead with then-experimental new wind shear-detecting radar.

Five days after the incident, McCarthy said, he received a call from the FAA asking if NCAR could develop a doppler radar -- a device to see the movement of air -- to protect Stapleton from further wind-shear incidents. The Denver radar has now had several summers of successful tests, including an operational test this past summer in which at least one pilot said his plane was saved by a warning from the radar. The government now has plans to deploy doppler radars at major airports throughout the country.

The safety board was mildly critical of Flight 663's decision to take off under circumstances conducive to wind shear, but it left no doubt that United's fledgling training program saved lives. "The successful performance of the flight crew . . . can be attributed to United's program of providing thorough flight training in this area," the board said.

The search for wind shear survival techniques dates to the crash of Eastern Flight 66 at John F. Kennedy International Airport in New York on June 24, 1975, killing 113, a notorious disaster that led the aviation industry to believe that some unknown weather phenomenon was snatching death from the sky. Microbursts are so violent and short-lived that they simply had not been "discovered." In later years, the toll included 145 passengers and crew on Pan Am Flight 759 and eight on the ground at Kenner, La., on July 9, 1982, and 134 aboard Delta Flight 191 at Dallas in 1985.

"We saw a lot of things we didn't understand and didn't like," said Dave Simmon, United's safety director, who in the early 1980s was manager of the 727 training program at Denver and is given much of the credit for developing the wind shear program.

The first rule of the training program is simple: "Avoid, avoid, avoid." That is, learn to recognize the conditions that lead to wind shear, and if you see them, don't try to take off or land.

Basically, the manual says do not take off or land if the intended flight path has localized heavy winds or heavy precipitation, and consider holding back if facing moderate or greater turbulence, a rain shower, lightning or virga, which is rain that evaporates before it hits the ground.

"Avoidance is what we teach our people," said Perkins, now head of United's 747 training program, "and we give them every tool we can."