A single-engine airplane crashed while trying to land at the Montgomery County Airpark near Gaithersburg yesterday morning, exploding into flames and killing its two occupants.

The victims were indentified as Jacob and Mary Dickinson, both 57, of Topeka, Kan.

The couple had left Richmond yesterday morning and were in the area to visit relatives and conduct business, according to Montgomery County police spokeswoman Ann Evans.

Jacob Dickinson traveled throughout the country selling museum display cases.

Witnesses and a federal accident investigator said the plane apparently crashed because its landing gear was not deployed or did not deploy.

They said the plane touched down on its belly, bounced about 30 feet in the air and crashed nose-first beside the runway before catching fire.

The plane was piloted by Jacob Dickinson, investigators said, and he gave no indication of the landing gear problem before the crash.

"The consensus {of eyewitness accounts} is that the plane was coming in to land . . . and a landing gear was not fully in the down position," said Al Dickinson, an air safety investigator with the National Transportation Safety Board.

"There are different reports about how far down it was. Several pilots in the area radioed the pilot to try to warn him, but he never responded."

The plane, a single-engine Beechcraft, came to rest on a taxiway that parallels the runway's south side, and was quickly engulfed in flames, accordidng to authorities.

Although witnesses said the fire was extinguished in less than 15 minutes, the intense blaze destroyed the aircraft's exterior.

According to witnesses, the incident occurred about 10:15 a.m. The Montgomery County Airpark, which is near Gaithersburg off Route 124, has only one runway, and the plane was approaching the strip from the west.

Two other planes were sitting on the taxiway preparing to take off as the airborne plane approached, and both pilots on the ground saw that the incoming plane's landing gear was not locked in place.

Patrick Hart, of Manassas, was the first pilot to notice the problem. "He was about a quarter-mile out," Hart said. "I grabbed my radio and said, 'Landing gear up, landing gear up.' I assume he did not recognize the gear were not down."

The plane in line behind Hart was piloted by David Kicklighter, a flight instructor from Winchester, Va.

He said that the incoming pilot never acknowledged Hart's radio warning.

"The plane settled in on the runway and then started to veer left," Kicklighter said. "Then it went airborne again, up about 30 feet, I'd say. Then it cartwheeled and struck the ground nose-first."

John Everett, an off-duty Fairfax County firefighter who lives within sight of the airpark, was one of the first on the scene.

"The flames were as high as my head," Everett said. "One person had been thrown out of the wreckage; another firefighter and I dragged her about 25 feet away. We tried to look inside to see if there was anything we could do, but there wasn't."

Dickinson, the safety investigator, said yesterday that the aircraft probably was equipped with a warning light that should have alerted the pilot that his landing gear was not deployed.

He said investigators would attempt to determine whether there was a malfunction in the landing gear or the warning system, or whether the crash resulted from pilot error.

A final accident report is not expected for several weeks.