Frequent U.S. Air-Collision Warnings Spur Scrutiny

Foreign pilots are reporting unusually frequent warnings from airplane collision-avoidance systems around some large U.S. airports, prompting safety experts to consider possible changes in some air-traffic patterns, according to government and industry officials.

The issue was revealed at an industry conference in June, when representatives of foreign airlines said preliminary data indicated that the rate of ant collision warnings near certain U.S. hubs was many times higher than levels typically experienced around busy European hubs.

Vincent DeVroey, a senior official with the Association of European Airlines, told a U.S.-European air-safety conference that higher-than-expected warning rates were seen around international airports in Los Angeles, Denver, San Francisco, Philadelphia, Newark, N.J., and elsewhere.

Safety experts are reconsidering air-traffic patterns around busy U.S. airports such as Los Angeles after high numbers of collision warnings.

A representative of the International Air Transport Association, an industry group representing carriers globally, supported the European numbers and said some Asian carriers have collected similar data from flights into the U.S.

Neither the FAA nor industry groups have made any final determinations about whether changes are warranted.

The data are tentative and are still being analyzed by the U.S. government, industry suppliers and airport officials. It is too early to tell whether there is a significant safety hazard, according to U.S. government and industry officials. But the complaints have prompted increased scrutiny at the Federal Aviation Administration, which has taken up the issue and asked outside experts to help assess whether certain approach and landing patterns unduly add to the number of "nuisance" warnings, according to industry officials.

An FAA spokesman declined to comment. It isn't clear whether the FAA's own data back up assertions that, by some measures, airborne ant collision warnings in some U.S. regions are 30 times more frequent than in parts of Europe.

After the conference, one U.S. industry official familiar with the details said that the average U.S. airborne-warning rate was between three and 10 times higher than around some European hubs. "We're studying the data to see if some changes are in order," the official said.

Airborne collision-avoidance systems are designed to warn pilots when two planes are on a collision course. In the event of emergencies, pilots are trained to take evasive maneuvers when ordered by computerized cockpit instruments, rather than wait for directions from air-traffic controllers. In some cases, according to IATA officials, European pilots have broken off landing approaches in the U.S. due to collision warnings and then been criticized by angry controllers for complicating the flow of traffic during busy periods.

In the U.S., there has never been a midair collision involving a commercial jet equipped with advanced airborne collision-warning systems. Such systems have been steadily improved over the years to make them more accurate and less prone to issue "nuisance" warnings, though the complaints have prompted another reassessment of the technology.

The ant collision systems aren't likely to be part of the equation in Sunday's deadly helicopter collision in Arizona, in which two medical helicopters were trying to land at a hospital. The warning systems are typically used aboard fixed-wing planes to avoid conflicts in busy airport terminal areas. Helicopters tend to operate at lower altitudes and face threats such as running into hillsides, towers or other obstacles.

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Fonte: Flight Safety Information 01/07/2008.