A story last Saturday reported that jetliners no longer would be allowed to wait on runways for nighttime takeoffs. Further interpretation of the Federal Aviation Administration ruling indicates that the ban will apply only at points runways intersect taxiways. At runway thresholds -- the ends of runways -- the practice still will be allowed. (Published 2/21/91)

The Federal Aviation Administration yesterday issued a nighttime ban on the common practice of allowing jetliners to wait on runways before being cleared for takeoff, a major factor in the Feb. 1 collision of two airliners at Los Angeles International Airport.

The restriction is one of several FAA moves following the accident on the Los Angeles runway and a Dec. 3, 1990, runway collision between two Northwest jetliners in Detroit. As part of its response, the agency has accelerated a plan to require standard runway and taxiway signs and lights and sped up new radar technology for avoiding incidents on the ground.

The new rule, which applies to night operations and daytime periods of reduced visibility, means that jetliners will be held on taxiways until cleared for takeoffs. The Air Transport Association, which represents major carriers, said the rule change should not increase flight delays. "It doesn't appear to present any real capacity or delay problems," ATA spokesman William E. Jackman said.

The practice of allowing planes to wait on runways became popular with controllers over the years because it allowed them to squeeze in more takeoffs and landings. But some pilots have criticized the custom as dangerous, especially at night when lights of an aircraft on the ground tend to blend into runway and taxiway lights.

The rule change, effective at 7 a.m. today, tells controllers that from sunset to sunrise "do not authorize aircraft to taxi into position and hold at an intersection. Additionally, do not authorize an aircraft to taxi into position and hold at any time when the intersection is not visible from the tower."

In the recent Los Angeles collision, a SkyWest Fairchild Metroliner was allowed to "taxi into position and hold" on Runway 24L at night by a controller who then became confused about its location and cleared a USAir Boeing 737 to land on the same runway. The crash killed 34, including all 12 on the smaller twin-prop plane. Sixty-seven people aboard the USAir jet survived.

The USAir first officer told the National Transportation Safety Board that he did not see the smaller plane, which was sitting about 2,400 feet down the runway, until after his jet touched down. The SkyWest plane had its navigation lights, rotating red beacon and taxi lights on, but not its strobe light.

One of the major factors the safety board is investigating is why the crew of the approaching jet could not see the smaller plane, whose array of lights met FAA and SkyWest regulations. It would not have been possible for the SkyWest crew to see the landing lights of the jet, which was approaching from its rear, because cockpits are not configured to allow crews to look backward and planes do not have rear-view mirrors.

Board investigators ran a test Monday night at Los Angeles in which they placed a Metroliner on Runway 24L with the same lights illuminated as the night of the crash, and approached it along the 737's flight path in a helicopter. Results of the test were not available yesterday.

However, pilots who have frequently flown into Los Angeles said they can easily understand why the pilots did not see the smaller plane, partly because the Metroliner's lights would blend into the runway and partly because the plane was sitting 2,400 feet down the runway, not at the end of the runway where the pilots' vision would be directed.

"That dinky white tail light is obliterated by the center-line lights, and the rotating beacon tends to get lost," a Boeing 727 captain said. "Things are so camouflaged. You're looking at points of light."

A 737 captain with hundreds of landings at Los Angeles said there is another problem at the time of day the crash occurred, as an airliner heads due west into a bright sun, then descends to a runway that is in the dark.

"At about 18,000 feet, the crew was flying into the sun," he said. "The sun was still hitting them in the face. And then there's still a relatively bright horizon directly in front of them. And then they drop down below the sand dunes and their eyesight has not totally recovered at that point, so it's making it difficult to differentiate those lights in front of them."