SAN ANTONIO -- National Transportation Safety Board investigators spent Monday going through the wreckage of a plane that crashed in Comal County.

The plane went down Sunday morning in bad weather at a private ranch off of Ahern Creek in Spring Branch, just north of Bulverde.

Dylan Lord, 13, Brendon Lord, 12, and their grandfather, Carlos McKinney, 60, were flying back home to Pearland, outside of Houston when the single-engine craft crashed.

McKinney was piloting the Beechraft Bonanza.

On Monday, the FAA and NTSB investigators looked through the wreckage, which was spread over 1,000 feet.

"They were in cruise instrumental flight, or IFR flight at 9000 feet," said Tom Latson, NTSB Air Safety Investigator.

"The pilot asked for a deviation around the weather and was given permission to deviate around the weather. The plane descended to 8,300 feet, after that it disappeared off the radar," Latson said.

Latson told KSAT Monday that it will take some time to figure out exactly what went wrong, but investigators do know the plane was in an area of severe weather and that there was an "in-flight break-up" before it hit the ground.

On Tuesday, crews will move the wreckage to a secure storage facility near Dallas where they will examine the engine, the propeller and the other parts of the aircraft.

Investigators expect a preliminary report within a week, but a full detailed report into the cause of the crash may take as long as a year.

Grief counselors at the boys' schools at the Pearland Independent School District were on staff Monday morning to help classmates cope with the tragedy.

"They were both very well loved, popular students," said Pearland Independent School District spokesperson Renea Ivey-Sims.