Disturbing Questions

For a long time federal investigators won’t know for sure what caused the fiery crash that killed 133 persons at the Dallas-Fort Worth Airport. But the available evidence raises disturbing questions about whether passenger safety has a high enough priority with Washington budget managers.

So far, the presence of a wind shear--violent downdrafts or sudden changes in wind direction that are extremely dangerous when encountered at low altitudes--has not been confirmed. But aviation specialists strongly suspect that such a shear was the culprit.

According to on-the-scene accounts, a localized thunderstorm producing heavy rains, lightning and winds gusting to 80 m.p.h. was in the vicinity of the airport at the time of the accident. Yet the automatic weather advisory service at the airport was reporting relatively modest winds of 6 m.p.h. to 18 m.p.h.

Investigators for the National Transportation Safety Board say that it is difficult to pin down just what conditions existed where at the precise time of the accident. They say that a heavy “rain cell” was in the area, but will not say for sure that it was a thunderstorm. In fact, board spokesmen say that weather around the airport was “mostly benign,” and that airliners land every day in conditions appearing to be worse. The cockpit recorder apparently shows that the crew, until the last minute, did not realize that anything was amiss.

Radar on airliners can’t see wind shears, but can detect thunderstorms, which often produce wind shears. Did the onboard radar fail to signal the danger ahead, or did the Delta pilots ignore the evidence at hand? Testimony from other pilots flying in the area should provide some clues.

Moments before the crash, the controller had ordered the Delta jet to sharply reduce its speed to avoid overtaking a Learjet landing ahead of it. At only 172 m.p.h. the airliner did not have the extra margin over stalling speed that is advisable for landings where extreme turbulence is present--and survivors say that the air was rough. So why didn’t the controller advise one plane or the other to pull up and make another landing approach? Why didn’t the Delta pilot abort the landing on his own?

The Dallas-Fort Worth airport, like many others, is equipped with a wind-shear alarm system, but it is notoriously unreliable. The system reported a wind shear a few minutes after the accident, but none before.

A vastly improved wind-shear alarm system has been tested successfully at Denver’s Stapleton Airport, but the federal budget office has not approved funds for buying and installing the system at major airports around the country.

Experts believe that wind shears--or microbursts, as the violent-downdraft variety is sometimes called--have been responsible for 28 air accidents killing 491 people since 1964. The worst accident attributed to a wind shear was the crash of a Pan American jet near New Orleans three years ago that killed all 145 people aboard.

The case for high-priority action is indisputable. The federal government should get on with the business of installing the new alarm system at major airports without further foot-dragging.