A small plane bursts into flames on a runway at Dulles International Airport, forcing a Boeing 767 to veer off course and into a fuel truck. Dozens are injured. Hospitals are put on alert.

On Saturday, more than 100 firefighters, medical personnel and others from across the region will respond to these events as they unfold at Dulles — part of elaborate training exercise designed to give first responders and other personnel in the region real-time experience dealing with an airport emergency.

As part of the event, participants will battle a fire. Others will rescue, treat and transport injured passengers, while another group works to clean up and contain a fuel spill on the runway. Inside the terminal at Dulles, airline personnel will manage a crowd of volunteers pretending to be friends and relatives of passengers aboard the planes.

“We try and make it as realistic as possible,” said Matthew Crosman, a senior operations official at the Metropolitan Washington Airports Authority.

In other words, chaotic, but controlled.

The Federal Aviation Administration requires airports across the country to hold such exercises every three years to test emergency readiness and response. MWAA, which manages Dulles as well as Reagan National Airport, is overseeing the exercise, which took six months to plan.

Mass casualty events are very rare, said Kevin Stiles, a battalion chief at the Loudoun County fire and rescue department. “On a daily basis, we don’t use these skills very much. However, when it does happen, you have to be prepared to respond.”

Fatal crashes involving U.S. airliners are even rarer. No U.S. airline crash has killed more than 50 people since 2001. The last major accidental air crash in the D.C. region occurred in 1982, when an Air Florida plane crashed into the Potomac River, killing 74 passengers and crew members.

But Crosman said it’s important to stay current because new scenarios and vulnerabilities are always emerging.

The recent problems involving Boeing’s new 787 Dreamliner, for example, have been closely watched by airport safety officials. The jets were grounded after battery fires aboard two of the jets, including one in Boston.

The mandatory exercise Saturday at Dulles will be the first taking place on an actual runway. In past years, officials have used an area that connects the airport to the National Air and Space Museum’s Steven F. Udvar-Hazy Center. And also for the first time, the exercise will use a wide-body jet, courtesy of United Airlines, which is providing a Boeing 767.

“That’s absolute gold, as far as training is concerned,” Crosman said of the aircraft.

More than 20 agencies will participate, including fire and rescue workers from MWAA, Loudoun, Fairfax and Fort Belvoir.

The first responders know little more than that they will be dealing with an airport emergency. Hospitals, including Reston Hospital Center, also will be on alert. As part of the exercise, “patients” will be brought to the hospital for treatment.

“It allows us to implement our emergency preparedness procedures and practice and also learn and figure out how we can adjust and adapt as needed,” said Melissa Ozmar, spokeswoman for Reston Hospital.

MWAA Deputy Fire Chief Tom Kenney said the Boston Marathon bombing underscores the importance of preparation.

“These are low-frequency but high-hazard events, but when they occur, it’s going to be bad,” he said.

Saturday’s exercise is expected to last three hours. Airport officials caution that people near the area should not panic if they see smoke and hear sirens.

Crosman said the exercise is also an opportunity for officials to test new emergency medical procedures.

For example, officials will be trying out a new system for tracking patients. Each will receive a wristband with a bar code that will be linked to a master list. Each time a patient is moved, the bar code will be scanned, which is intended to make tracking easier.

Kenney said that in reviewing previous exercises, officials determined it was taking too long to transport patients to hospitals. So this year, instead of evaluating critical patients at a succession of triage stations, the focus will be on getting them into ambulances.

“We’re going to get patients, treat them and get them on the road quickly,” Kenney said.