California-based jets behind sonic booms

Cathy Scott

Friday, March 28, 1997 | 11:59 a.m.

Mystery solved.

Three times faster than the speed of sound -- that's how Tech. Sgt. Randy Mitchell described Beale Air Force Base's Blackbird jet that flew over Southern Nevada this week, setting off sonic booms heard across the Las Vegas Valley.

When an SR-71 flew over the Mojave Desert Wednesday night and turned around 70,000 feet above Lake Mead to return to California, it triggered a sonic boom that reached a radius of 100 miles, said Mitchell, a public affairs officer with Beale AFB's 9th Reconnaissance Wing.

Four times this week, pilots flew across Nevada in an SR-71, the world's most advanced strategic reconnaissance aircraft.

The SR-71 "flies at Mach3-plus or 2,400 mph-plus, three times the speed of sound, or faster than a .30-06 rifle bullet," Mitchell said.

"I talked to one of the pilots who was flying a mission," he said. "He said when they flew over Lake Mead, they did a slight turn. That's what caused the boom to come back toward Henderson."

Henderson Police got about 200 complaints from residents wondering why their homes were shaking.

"We've had calls from people wondering what is was," said Sgt. Gary Smith, who said dispatchers told residents they believed it was a plane from Nellis flying over Henderson.

For an SR-71 to make a turn, "it takes almost the entire state" because of its speed, Mitchell said in a telephone interview from Beale, about 40 miles south of Sacramento. The pilots turned the jet around over the lake "so they could return to Fort Irwin. They were going out across Nevada to turn around, then cross (the state) again."

With the last flight about 11 p.m. Wednesday, the pilots "won't be flying this route anytime soon," Mitchell said.

Sgt. James Brooks of Nellis Air Force Base's public affairs office said residents called the base with noise complaints, thinking the jet originated there. But Brooks said they learned later it was from Beale.

"They fly routes through Southern Nevada quite often," Brooks said. "Usually they put out a schedule to announce these things."

This time they didn't. Mitchell said the training mission was an exercise called Advanced Warfighter Experiment, a joint exercise with the army in Fort Irwin near Barstow, Calif.

Sonic booms, with noise similar to thunder, are caused when an object moves faster than the speed of sound -- about 750 mph at sea level. An aircraft traveling through the atmosphere produces air-pressure waves similar to water waves caused by a ship's bow. When the plane exceeds the speed of sound, the pressure waves combine and form shock waves.

If the plane makes a sharp turn or pulls up, the boom will hit the ground in front of the aircraft.

That's the sound Las Vegas residents heard on Tuesday and Wednesday nights, Mitchell said.

Ken Synnott, who lives in the southeast valley near Sam's Town, said the boom Wednesday night nearly knocked him out of his chair.

"My wife was going to bed and I was watching TV," Synnott said. "The chandeliers were shaking. It sounded like something was blowing up outside. It went 'baboom, baboom.' It was like a bomb had gone off.

"I was concerned. People were outside walking around, looking around, wondering what happened."

The SR-71, built in 1964, stopped flying in 1990. In 1994, it was put back into service. The Air Force has conducted faster-than-sound test flights since 1947 and today most Air force fighter aircraft are capable of supersonic speed.

Since February, the SR-71 has flown 13 Green Flag missions from Nellis, which were completed this month.

Pilots are limited as to where they can fly the jet, Mitchell said.

"We can't fly over any area that's populated more than 100,000 peope and we can't fly over any national parks," Mitchell said.