Pilot error, compounded by weather-related icing conditions, caused the plane crash that killed two medical transport workers almost two years ago.

Flight nurse Diane Efaw and pilot Maureen McGee, both 47, were killed instantly Dec. 26, 2006, when the Cessna 414 nose-dived onto the infield at John Murtha Johnstown-Cambria County Airport.

A final report by National Transportation Safety Board investigators says McGee failed to fully lower the single-engine plane’s landing gear and then tried to fly the damaged aircraft after bouncing off the runway.

“The pilot’s decision to abort the landing with a damaged aircraft” is listed as the probable cause. Icing and the pilot’s failure to lower the landing gear are included as contributing factors.

McGee was coming into the Johnstown airport because of icing conditions, the report notes. Often a factor in air crashes, the buildup of ice on aircraft wings, tail and fuselage impairs handling, airport manager Scott Voelker said.

“Can icing cause a change of flight characteristics? Absolutely,” Voelker said.

Ice buildup changes the shape of the wing, reducing the lifting power, veteran Johnstown pilot Barney Custer said. Pilots often must increase speed to compensate.

“Icing on the tail can really be bad for control purposes, near the ground,” Custer said.

The Flight Source LLC medical flight was traveling from company headquarters at Morgantown, W.Va., to pick up a patient at Teterboro Airport in New Jersey when McGee called Cleveland Center air traffic controllers to report icing.

She asked to climb from 9,000 feet to 13,000 feet to get above the mixed precipitation. Controllers cleared her for the new altitude, but McGee soon radioed back to say the plane could not climb any higher because of the accumulated ice. She asked to descend to 7,000 feet, and later to 3,000 feet.

“We are barely keeping up with it,” McGee radioed, according to the investigators’ report.

Controllers responded they could not approve a 3,000-foot flight because of the region’s terrain. Johnstown’s runways are more than 2,200 feet above sea level and area ridges approach 3,000 feet and higher.

Then McGee was approved to approach for landing at Johnstown as an attempt to melt off some ice at the lower altitude. A controller in the Johnstown tower asked if she intended to land or “execute a missed approach,” or fly-by.

“It depends if my ice comes off or not,” McGee responded. “If the ice does not come off, we’re gonna land.”

It was the last radio call from the ill-fated plane.

Watching the plane approach through binoculars, Johnstown tower personnel noticed the wheels were not down and called to remind the pilot seconds before ordering “go around, go around, go around.”

Controllers then saw the plane hit the ground hard, “like a Navy carrier landing,” about 2,000 feet along the 7,000-foot runway, and then appeared to take off again “almost perfectly,” the report said.

About 2,000 to 3,000 feet later, the plane turned hard to the right, crashed into the grass and burst into flames.

Those first on the scene reported ice chunks scattered along the otherwise-dry runway from the point of initial impact to the final crash site.

Investigators painstakingly measured grass and runway gouges, paint scrapings and skid marks indicating the plane’s propellers, engine mounts and a wing tip hit the ground during the aborted landing. The space between the tire marks showed the wheels were about 45 inches closer together than the landing gear’s “fully-down” position.

Markings from the initial “hard” landing stretched about 400 feet along the runway and nearby grass.

The distraction of trying to handle the ice-caked plane may have caused McGee to forget about the landing gear, Voelker said, noting he witnessed similar incidents during his 30-year Air Force career.

“It happens where planes have landed with the gear up,” Voelker said. “It’s not common.”

The investigators’ report shows McGee had over 3,500 hours of flight time, including 68 in the 30 days prior to the wreck.

“That’s a lot of time in 30 days,” Voelker said. “She was an experienced pilot.”

“Even the most experience pilot can make bad judgments,” Custer said. Flying over Pennsylvania’s mountains in bad weather and choosing Johnstown’s hilltop airfield may have been the first bad judgments, he suggested.

“But it’s really hard to second guess,” Custer said.

Flight Source has not changed any of its procedures in the aftermath of the crash, co-owner Mark Shipley said.