They fix planes and load and unload heavy bags in sweltering heat and frigid cold. For many passengers, they are invisible, though they toil right underfoot. Airport ground workers do their jobs amid the deafening roar of aircraft engines and the arrival and departure of tanker-size jetliners. They must avoid stepping in oil slicks and watch out for baggage carts whizzing by.

Now the ground workers' tough conditions are coming under closer scrutiny. For the first time, airlines and the Federal Aviation Administration will co-host a three-day symposium focused on improving safety on the tarmac at the nation's airports. Participants in the gathering, which begins Sept. 6, will analyze data on accidents to help airlines identify dangers and adopt strategies for reducing risks.

"It's next in line to be dealt with," said Basil J. Barimo, vice president of operations and safety for the Air Transport Association, a trade group that represents major U.S. airlines.

While serious injuries and death occur, the most common injuries among ground workers result from heavy lifting, in many cases causing severe back strain. According to figures from the Bureau of Labor Statistics, there were 4.53 injuries and fatalities per 100 airport ground workers in 2004, the latest year for which data are available. By comparison, coal miners had a rate of 6.58 injuries and fatalities per 100 workers; in construction, the rate was 5.77.

So far this year, four ground workers have been killed or seriously injured, according to data collected by The Washington Post. In one incident, a mechanic died in January when he was sucked into the engine of a Continental Airlines aircraft at El Paso International Airport. A month later, a baggage handler for Comair, a Delta Air Lines regional carrier, was killed when he was struck by a baggage cart at the Detroit airport. Three serious or deadly accidents occurred in 2005 and two in 2004.

Through the busy summer season, ground workers have been under increased pressure to load and unload bags swiftly and to ensure that the aircraft are prepared for safe travel. Many financially strapped carriers have reduced their staffs, leaving more work for the remaining employees. Some airlines have been hiring ground workers at lower wages to cut costs.

Several airlines said training and supervision of workers remained as much a priority as passenger safety. "As a company committed to the highest standard of safety, Northwest will continue to seek and promote the practices, procedures and processes necessary to assure safe working conditions for our employees and business partners," said Dean Breest, a spokesman for the airline.

At US Airways, ground workers go through a three-week training program on procedures, including one-on-one instruction on the tarmac. "We're very heavily focused on safety," said Anthony Mulé, senior vice president for customer service.

Mulé acknowledged that crowded planes put more pressure on ground workers. "We are asking people to work harder to accommodate the increased traffic, but we are not asking more of this group than we are of other work groups," Mulé said.

Many workers and their families say more needs to be done to ensure a safer environment, and they urge more oversight. FAA officials said that the agency reviews each airline's safety guidelines for the workers but that it was up to the individual carriers to enforce those rules.

Jim Ballough, director of the FAA's flight standards service, said the agency sends inspectors to airports to assess flight preparations and safety on the ground. But some airline officials said those random inspections focus more on air-flight matters than on ground safety. The officials added that more safeguards are needed to protect workers.

Southwest Airlines is in "constant dialogue" with the FAA about employee safety, said Barry Brown, vice president of safety and security for the airline. But, he added, the FAA was "more aggressive" about ensuring the safety of the passengers.

Workers complain that oversight tends to shift among agencies. After an accident occurs, the government agency that leads the investigation varies depending on the type of incident. Further, no one entity -- not the FAA, the National Transportation Safety Board, Occupational Safety and Health Administration, the Bureau of Labor Statistics, the airline association or unions -- keeps comprehensive records of injuries and fatalities among ground workers. The involvement of multiple agencies hinders record-keeping and can keep some cases from getting the attention they need, industry experts say.

Paul Kempinski, director of ground safety for the International Association of Machinists & Aerospace Workers District 141, said unions have urged government agencies to more rigorously monitor ground operations. OSHA "only comes out when something happens," said Kempinski, who represents baggage handlers at United and Aloha airlines and US Airways. "Something needs to be done sooner. Someone needs to be in charge of oversight."

Several high-risk industries have special federal agencies that oversee working conditions. For example, the Labor Department created the Mine Safety and Health Administration in 1978 to oversee mine safety. This year, there have been 34 miner fatalities out of 108,734 workers.

That no one entity oversees workplace injuries within airlines does not surprise those who study such accidents. Kenneth Rosenman, a physician and professor at Michigan State University who in May published a three-year investigation on workplace injuries and illnesses in Michigan, said only about 40 percent of job injuries or fatalities are reported. He said employees and companies think there's little incentive to report accidents to federal authorities.

"Our national system of counting injuries and illness is inadequate and misses over half of the injuries and illness in the workplace," Rosenman said.

Safety oversight has become more critical, workers say, because airlines are hiring less experienced -- and lower paid -- workers to replace ones who were let go under restructuring.

US Airways pared baggage handlers to 158 from 229 between September 2001 and its merger with America West in September 2005, according to union figures. The reductions mirrored an industry-wide trend. U.S. airlines employed 91,323 airport ground workers in 2005, down from 140,120 in 2000, according to the latest numbers available from the Bureau of Transportation Statistics. Jobs in this category include aircraft mechanics, workers who load and unload bags, and those who clean and fuel the planes.

With the hard work and low pay, airlines struggle to fill ground worker jobs. And that means longer waits for travelers when retrieving their checked bags on arrival, especially now that passengers are required to check more items under heightened security rules.

US Airways, for example, is seeking to hire more baggage handlers at its Philadelphia hub. The airline had a job fair in the spring, but many workers hired then have already quit. To lure more candidates and retain workers, US Airways has offered such incentives as iPods and television sets.

Yolanda Corbett, 32, was attracted to a subsidiary of the airline during an earlier hiring fare in 2005. She liked the free travel offered to employees and a chance to take her two young daughters to Disney World. The pay, about $9.75 an hour, was low, but it represented steady work for the single mother who had held such odd jobs as babysitting after being laid off from an accounting position at a local Welfare to Work office.

For two weeks, US Airways baggage handlers instructed the D.C. resident on the proper way to lift bags and navigate the busy runways of Reagan National Airport in a baggage-loading cart. She received a 100 percent accuracy rating in her training tests. In her third week on the job, Corbett was killed when she lost control of a baggage cart, which rammed the side of a regional jet, pinning her under the aircraft and severing her spine.

The NTSB attributed the accident to Corbett's inexperience with driving the cart.

Corbett's mother, Mary, said her daughter was trained to operate the baggage cart, but the day she was killed was the first time she had driven it by herself. "She wasn't trained properly. She wasn't ready to drive that vehicle. It just wasn't safe," she said.

US Airways officials have declined to comment on training and safety incidents prior to the merger, citing the company's new management team.

Though fatal and serious injuries among ground workers are less numerous than those in some other industries, Rosenman, the Michigan State professor, said the incidence could be lower if injuries were tracked and investigated. Labor experts said the lack of stringent reporting and record-keeping highlights the invisible nature of the ground worker.

"They're the forgotten worker," said Peg Seminario, safety and health director for the AFL-CIO. "They fall through the cracks."