Philip J. Klass, 85, an aviation journalist who investigated UFO sightings and wrote books debunking reports of visits from outer space, died Aug. 9 at a nursing facility in Cocoa, Fla. He had cancer.

Mr. Klass lived in Washington for more than 50 years before moving to Merritt Island, Fla., in 2003.

He had retired as senior avionics editor of Aviation Week & Space Technology in 1986 but continued to contribute to the magazine for a number of years. He is credited with coining the term "avionics," a blending of aviation and electronics. His work, which included one of the first books about spy satellite technology, "Secret Sentries in Space" (1971), won him honors in the field of aeronautical journalism and engineering.

He was more widely recognized as an authority on unidentified flying objects. He was reviled as a "disinformer" by believers in alien beings, particularly those who insisted they had been abducted for scientific testing.

Mr. Klass, an electrical engineer by training, said he based his assessments on methodical research and visits to the field.

"While some people gaze at the sky and see flying saucers or bright balls of light," one biographer observed, "Klass sees atmospheric phenomena, celestial bodies and airplanes trailing advertising banners."

In a 1993 debate on "Larry King Live" with David Jacobs, a Temple University professor who wrote a book suggesting that more than 1 million Americans had been abducted and taken aboard UFOs for study, Mr. Klass observed:

"If aliens are invading our bedrooms, impregnating our teenage girls; if they're abducting little children, cutting flesh samples out without even putting Band-Aids on; if you're not safe anywhere on the face of the Earth -- then it is something that this nation needs to mobilize."

His first investigation, in 1966, was of a sighting two years earlier near Socorro, N.M. He found that it had been a hoax perpetrated in an attempt to bring tourism to the economically depressed town.

Mr. Klass went on to write seven books, including the well-regarded "UFOs Explained" (1975). He was interviewed on news broadcasts that included the "CBS Evening News" and for television programs devoted to space phenomena.

"In nearly 30 years of searching, investigating famous cases, I have yet to find one that cannot be explained in down-to-earth prosaic terms," Mr. Klass told interviewers for the PBS program "NOVA."

"Therefore, if somebody says to me, 'I have been abducted by strange-looking creatures that do these dreadful things to me,' I'm quite confident that they could not possibly be extraterrestrials. . . . I am quite confident that there is no scientific, credible evidence to show that we've had alien visitors, let alone that they're doing these dreadful things."

Mr. Klass wrote about extraterrestrial issues in his own Skeptics UFO Newsletter and appeared on talk shows and lectured widely. His investigative findings were routinely criticized by people and organizations who took seriously UFOs and alien abductions.

He once told an interviewer: "I've found that roughly 97, 98 percent of the people who report seeing UFOs are fundamentally intelligent, honest people who have seen something -- usually at night, in darkness -- that is unfamiliar, that they cannot explain."

He said the sightings were often of objects such as reentering satellites, meteor fireballs and hot-air balloons.

His books included "UFO Abductions: a Dangerous Game" (1988) and "The Real Roswell Crashed-Saucer Coverup" (1997). In the first, he promised $10,000 to any victim whose abduction by aliens could be confirmed by the FBI. No one ever collected.

Mr. Klass was born in Des Moines and raised in Cedar Rapids, Iowa. After graduating from Iowa State University, he worked for a decade at General Electric as an electrical engineer. He joined Aviation Week in 1952 and later wrote extensively about surveillance satellites for that industry publication.

He was a fellow of the Institute of Electrical and Electronics Engineers and a founder of the Committee for the Scientific Investigation of Claims of the Paranormal. He was awarded top honors of the Aviation/Space Writers Association, the Lauren D. Lyman Award of the Royal Aeronautical Society and the Boeing Decade of Excellence Award for lifetime achievement.

His investigative papers form the Philip Klass Collection of the American Philosophical Society. An asteroid discovered in 1983 was named in his honor.

Before he took on UFO debunking as a full-time avocation, Mr. Klass was a Civil War buff. He designed and built animated electronic battle displays used by the National Park Service at the Gettysburg and Antietam battlefields. His other interests included skiing and sailing.

He was a member of the National Press Club and the National Aviation Club.

Survivors include his wife of 25 years, Nadya Ganev Klass of Merritt Island; two stepchildren, Anton Ganev of Olney and Diana Dryden, both of Merritt Island; a sister, Rosanne Klass of New York; and three grandchildren.