Avoiding Plane Crashes By Crunching Numbers

But finding them, even with all the data, isn't easy.

Robert Sumwalt, vice chairman of the National Transportation Safety Board and a strong advocate of data monitoring, likened the hunt for precursors to "reading tea leaves" because it can require imagination to tie together incidents that don't seem hazardous at first blush.

The first U.S. carriers adopted the data-monitoring measures in the mid-1990s, decades after foreign airlines implemented similar programs. They have only recently expanded across the domestic industry; 11 of the 17 U.S. carriers with such programs have started them since 2000. The growth has been fueled by the decreasing cost and increasing computing power.

Regulators and investigators, including those with the NTSB, have pushed for adoption of the initiatives. Pilot unions have eased their resistance to such projects. They play a critical role in analyzing the data, which is not supposed to be used to punish pilots for mistakes. Carriers have also realized economic benefits beyond preventing crashes: The information has helped many to reduce fuel consumption and improve maintenance reliability.

Although data monitoring is a hot topic inside the industry, some airlines have been reluctant to talk about their programs. Executives worry that they might scare passengers if they discuss potential problems, no matter how rare, or may encounter pushback from pilots unions. Representatives at United, American and Alaska airlines all declined to comment.

Southwest Airlines, which started its program in 2003, said it has mined data on more than 1 million flights to help the FAA and air traffic controllers to better understand pilot workloads at certain airports. It has even used the data to pinpoint where planes experience turbulence. The carrier hopes that this information will reduce injuries to passengers and flight attendants who get jolted in the bouncy air.

Southwest executives said one of their biggest challenges is finding ways to use the database.

"We are always asking ourselves, 'What should we be asking this data that we haven't thought of yet?' " said Don Carter, senior manager of the carrier's flight safety program.

US Airways, which was reeling from several crashes in the early 1990s, was one of the first airlines to use data to improve safety. The safety issues uncovered by the airline, which is expected to join the FAA initiative by year's end, are similar to those exposed by other airlines using the same data-monitoring techniques, according to pilot groups, regulators and airline representatives.

Just over half of US Airways' 356 jets carry recording devices that compile data from thousands of flights a week. Analysts and members of the Air Line Pilots Association at the carrier then sift through the data for a minuscule number of potential precursors.

In mid-2006, for example, US Airways' computers alerted the company to what executives and pilots considered a high rate of "unstabilized" approaches -- incidents in which planes come in too fast or sink too quickly during the final phases of landing. Such approaches are usually not dangerous unless other complications arise, such as trying to land on a short, slick runway.

Working with the pilots union and instructors, the carrier changed its landing checklists to allow better communication by pilots and co-pilots about whether the plane was stable as it neared the ground. If the plane was not stable by 500 feet, the pilots are instructed to abandon the landing attempt.