APACHE JUNCTION Federal authorities are trying to determine why a small plane crashed into a mountain in central Arizona, killing both people aboard.

The single-engine aircraft took off from Falcon Field Airport in Mesa and went down around 8 a.m. Saturday in the Superstition Mountains area east of Apache Junction, about 50 miles east of downtown Phoenix.

The National Transportation Safety Board said the Socata TB 30 Epsilon plane was operating as part of a flight of three airplanes.

They said the plane was headed to Payson in north-central Arizona and crashed in extremely vertical and rocky terrain.

Pinal County Sheriffs officials said they were still working to positively identify the two people killed in the crash.

National Transportation Safety Board officials say investigators would be documenting the crash site and collecting any flight track or radar data that may be available.

A preliminary report detailing the facts and circumstances of the fatal crash is expected in two to three weeks.

The final report, including the probable cause and any contributing factors, is expected in 12 to 24 months.

The Federal Aviation Administration and Pinal County Sheriffs Office also are investigating the fatal crash.