Four U.S. Air Force personnel and an Iraqi pilot were killed Monday when a single-engine Iraqi military propeller plane crashed during a training mission in eastern Diyala province, about 80 miles northeast of Baghdad, Air Force officials said yesterday.

One of the four, Maj. William B. Downs, 40, spent several years in Winchester, Va.; he and the three others were stationed at Hurlburt Field, Fla.

Downs's family, reached in Shalimar, Fla., declined to comment.

A former neighbor in Winchester, Gail Miller, said that Downs and his wife had three children when they lived there and that he had been a commercial airline pilot as well. They left Winchester in 2001, she said.

The crash is under investigation, said Capt. Thomas Knowles, a spokesman for Hurlburt Field, where Downs was assigned to the 6th Special Operations Squadron, a combat aviation advisory unit whose mission is to assess, train and advise foreign air forces.

The plane was an Aerocomp Comp Air 7SL that had been donated to the nascent Iraqi air force by the United Arab Emirates, Knowles said. It crashed in the morning, local time. No other information was available yesterday.

Downs had written an article in the spring issue of the Air Force's Air & Space Power Journal, in which he outlined a "doctrine of unconventional airpower" for counterterrorism and counterinsurgency missions. The Air Force, he wrote, "must remain globally aware."

"That is, we need intimate knowledge of the people, languages, and cultures of the countries in which we operate; at the same time, we must understand how our actions in a particular area will affect others on the planet."

Downs went on to write that air attacks would be more effective politically if they were carried out by local forces, and suggested various types of aircraft that might be useful in covert missions while being affordable for poor governments. The ideal aircraft should be not be fancy and high-tech, but inexpensive, simple to maintain and operate yet equipped with reconnaissance capability, he wrote.

"The war on terror and our efforts against insurgents will take a long time," he concluded. "The U.S. Air Force must adapt itself for the fight."

A memorial service is being planned tomorrow at Hurlburt Field.

Air Force Maj. William B. Downs, 40, was in special operations.