4 in Mid-Air Plane Crash Dead: 2 Other Planes Hit Building, Train Tracks (VIDEOS)

Four people in a mid-air plane crash over Anthem, Ariz. died Friday. Each small single engine plane was carrying two passengers, but all of them were pronounced dead at the scene by medical personnel.

The four people in the mid-air plane crash resulted in one of the planes hitting the ground mostly intact while the other burst into flames, nearly disintegrating much of the aircraft. Witnesses spotted the small airplanes crash into each other around 10 a.m. and called emergency services for help. The accident occurred about 20 miles north of Phoenix in Anthem, Ariz.

What has stumped Federal Aviation Administration officials investigating the incident is the reason for the crash. No malfunctions were reported, and none have been found so far.

"Both of them collided," Larry Nunez of the Phoenix Fire Department told ABC 15 news. "We don't know how or why, the skies are clear."

One of the planes has been identified as a Piper manufactured out of Norfolk, Mass. but the victims have not yet been identified. The plane was operated by the TransPac Aviation Academy, a flight school that operates out of Deer Valley airport about 15 miles southwest of the accident, which has given officials some theories as to the cause of the accident.

"I'm getting reports that they are possibly student pilots," Capt. Dave Wilson told The New York Times. The FAA and National Transportation Safety Board investigations are ongoing, he added.

There were also two other airplane crashes on Friday across the U.S.

The first occurred in Linden, N.J. when a small aircraft piloted by 58-year-old Craig Maccalum crashed into some train tracks. Both men in the plane were severely injured, but pulled from the wreckage in time.

A second plane crash occurred in Herndon, Va., when a light aircraft smashed into an apartment building, injuring three people. In that case, the plane had little fuel and was suffering from an electrical malfunction, according to NBC News.