LOS ANGELES (AP) — Eight people aboard a B-52 bomber that crashed shortly after takeoff Monday morning at a U.S. Air Force base in Southern California's Mojave Desert are believed to be dead, according to the Air Force.

"Initial indications are that the crash was not survivable," the Edwards Air Force Base, north of Los Angeles, posted on social media. The cause of the crash is under investigation, officials said.

Educate your inbox

Subscribe to Here’s the Deal, our politics newsletter for analysis you won’t find anywhere else.

There was no information yet on the crew, however aerial footage showed virtually nothing left of an aircraft. Emergency crews responded after the aircraft went down around 11:20 a.m. Black smoke rose from a large swath of charred desert at Edwards Air Force Base near what appeared to be a runway, with emergency vehicles nearby. The military hasn't said whether the bomber was armed.

The Boeing B-52 Stratofortress is a long-range bomber that entered service in 1955. Designed to carry both conventional and nuclear weapons, it has been used in conflicts involving the U.S. military from Vietnam to Iran.

By Monday afternoon, the airfield remained closed and all inbound aircraft were being diverted. Non-commercial visitor passes for the base were suspended "to allow the installation to focus entirely on emergency response operations," officials said in a statement.

Edwards Air Force Base is home to a large portion of the U.S. Air Force's aircraft test and development efforts and is about 100 miles (161 km) north of Los Angeles. The 412th Test Wing, which runs the base, also conducts developmental testing of all Air Force aircraft, weapons systems, software and components before purchase by the service as well as throughout their lifespan.

The vast desert base is also where Air Force test pilot Chuck Yeager reached a speed of Mach 1.05 and broke the sound barrier in 1947.

The way the B-52 crashed so quickly after takeoff without getting very high or going far makes aviation safety expert Jeff Guzzetti suspect some kind of flight control malfunction. But it's too soon to say what might have caused the control problem.

It's possible the controls were rigged wrong after maintenance, he said, or a catastrophic engine problem or a failure of a piece of equipment that was being tested.

"I think it was definitely a controllability issue. Now, whether that was tied to an engine failure, a flight control failure, or some new testing device failure, I'm not sure," said Guzzetti, who used to investigate crashes for both the Federal Aviation Administration and the National Transportation Safety Board.

Although the Air Force has been flying B-52 bombers for more than 70 years, testing out new equipment on a plane can create new challenges.

"A flight test is always riskier than normal operations, so that's why you have specially trained test pilots, and you should have other safety protocols," Guzzetti said.

Toropin reported from Washington D.C. AP Transportation Writer Josh Funk contributed to this story from Omaha, Nebraska.