LOCKHART, Texas — It appears a hot air balloon made contact with high-tension power lines before crashing into a pasture in Central Texas, killing all 16 on board, according to federal authorities who are investigating the worst such disaster in U.S. history.

A power line was tripped at 7:42 a.m. Saturday, and the first call to 911 came a minute later, National Transportation Safety Board member Robert Sumwalt said during a news conference. The crash site was near a row of high-tension power lines, and aerial photos showed an area of scorched land underneath. One witness described seeing a “fireball” near the power lines.

The NTSB will look at all factors that might have played a role, including weather, but is concentrating on gathering “perishable evidence, the evidence that goes away with the passage of time,” Sumwalt said, noting some of that is witness statements whose accuracy can fade with time.

“This wreckage will not be here more than another day or so,” he added.

The pilot was Skip Nichols, 49, said Alan Lirette, who identified Nichols as his best friend, roommate and boss. Lirette said he helped launch the balloon, which was carrying a total of 16 people, none of them children. The NTSB has not yet publicly identified the pilot or the passengers.

The NTSB said the balloon was run by Heart of Texas Hot Air Balloon Rides. Nichols’ Facebook page identifies himself as the chief pilot of that business, which does not appear to be registered with the state of Texas.

The passengers met the balloon operator in the San Marcos Wal-Mart parking lot at about 5:45 a.m. Saturday, and traveled to Fentress Texas Airpark. Ground crew members told the NTSB that they launched the balloon about 20 minutes after the expected 6:45 a.m. time and communicated with it by cellphone, and the pilot navigated with an iPad.

The balloon traveled about 8 miles from takeoff to crash, and the basket was found about three-quarters of a mile from the balloon material itself.

Caldwell County Sheriff Daniel Law and the Texas Department of Public Safety said in a statement that NTSB and medical professionals have said identification of the victims will be “a long process.”

Lirette said Nichols was “a great pilot.”

“There’s going to be all kinds of reports out in the press and I want a positive image there too.”

Philip Bryant of Ballooning Adventures of Texas in Richmond, which also does inspections and maintenance for other operators, said the balloon had “very good equipment, very new equipment.” Bryant said the manufacturer of Nichols’ balloon mandates an annual inspection, adding that he couldn’t do it this year but believes Nichols took it to another inspector.