Two pilots and an engineer were among eight airmen and civilians killed when a B-52 bomber crashed at a US Air Force base.

The 90-ton 'Stratofortress' went down just outside of Los Angeles about 11.20am on Monday just after taking off from Edwards Air Force Base.

Civilian engineer Jeromy Douglas Smith was a Defense Department contractor on board the plane alongside military members and government employees.

Smith celebrated the birth of his second child, a baby boy, just four months ago, and his eldest son is just two-and-a-half years old.

He recently bought a home with his wife Lauren Smith, whom her family said would struggle to pay for the property by herself.

Smith's father Jason called him a 'dedicated American' as he announced his death on Tuesday morning.

'You are gone, but will live in our hearts forever. Working for the DOD and giving back to his country was a big part of what Jeromy loved about life,' he wrote.

'I know you are in Heaven, you reached the top doing what you always loved to do. Goodbye, son.'

Lauren's sister Lindsey appealed for donations to help pay for the family's expenses without Smith's salary to support them.

'Our hearts are absolutely shattered. You hear tragedies everyday, but never feel the magnitude until it hits close to your own heart,' she wrote.

'She is left to navigate being a newly single mom, while also having to grieve the love of her life.

'Our entire family is devastated by this great loss. My brother-in-law was an incredible husband and an amazing father to their boys.'

Lauren is an elementary school teacher at Muroc Joint Unified School District near the Edwards base.

'The sudden loss has left Lauren facing unimaginable grief and uncertainty, as she tries to navigate life for herself and her children,' her friend Heidie Suprenant said.

'The family had just purchased their home together, and now Lauren is left to manage everything on her own, while caring for her two young boys.'

Another on board the plane was a military pilot named Greg, who was mourned online by his friend and fellow airman Mathew Landry's father.

'Please pray for Mathew's friend Greg that died in the B-52 Today in CA. Eight people died in the crash,' Michael Landry wrote, sharing photos of Greg.

'Mathew was scheduled to go this Friday at Edwards Air Force Base to do some flying before this accident. 

'It was a test plane with some new updated equipment and advanced technology. The runway is the longest (3 miles long) in the desert, and no birds in the area. 

'Weather was good. The plane had the top notch pilots for the test run.'

Photos Michael Landry shared showed the pilot in his flight suit and at a formal event that may have been his academy graduation. 

Decorated test pilot Lieutenant Colonel Miles Middleton was the highest ranking airman known to be on board, and was also killed.

Middleton commanded the 419th Flight Test Squadron at Edwards base from 2016 to 2018, which the doomed test flight was part of.

His family released a photo of him being passed the squadron guidon by his predecessor, Colonel Scott Cain, at a ceremony in 2016.

The 419th Squadron oversees the Global Power Bomber Combined Test Force, which tests some of the air force's most powerful aircraft. 

Family friend Melissa Lynch appealed for help for Middleton's widow Pam to support their family without him.

'With Miles gone, Pam is now responsible for supporting her family on her own,' she wrote.

The military has not yet named any of the crash victims and the other five are yet to be publicly identified.

Colonel James Hayes, deputy commander of the 412th Test Wing at Edwards, said the cause of the crash was being investigated.

'Initial indications are that the crash was not survivable,' he said.

Hayes said the 'routine test flight' was assessing Radar Modernization Program upgrades, which were installed starting in December.

The upgrade was part of a program to extend the life of the decades-old B-52 long-range bombers to the 2050s.

An anonymous air force member posted on a military social media group claiming maintenance crews were under 'intense pressure' to upgrade the planes faster 'at all costs'.

'Once a month they grill the Wing Commanders and entire B-52 sustainment enterprise for hours questioning why they have not yet achieved the target MC rate and what steps we are taking at the unit level to make it happen,' they wrote.

'My heart goes out to all those affected by today's crash. I hope the culture in the command soon shifts from chasing unrealistic MC targets to focusing on safety and compliance for both our maintenance and flying operations.' 

Hayes said it would take at least six months before a report on the causes of the crash would be released.

'Right now, we're going to set up an interim safety board to do the initial gathering of facts, and that will then lead to a safety investigation board, which will look into those root causes,' he said. 

Hayes said that process would take about 30 days, and the results would be sent to an accident investigation board and released to the public.

The crash left plumes of thick black smoke covering the area in the Mojave Desert.

The runway was also left with a large char mark on the sandy runway in the aftermath, leaving it unusable for routine trips on Tuesday.

The airfield was then closed and all inbound flights were temporarily diverted.

The Boeing B-52 Stratofortress is one of the oldest aircraft in the US Air Force's fleet, first entering service in 1955. 

It has a wingspan of 185ft, which is almost twice the length of a standard NBA basketball court.

The aircraft, which is often referred to as 'the Buff' or 'Bug Ugly Fat', can carry up to 70,000lb of bombs and other military weapons. 

The plane typically carries a crew of five and can fly up to 50,000 feet and refuel mid-air.  

The B-52H, the current version of the bomber plane, was used during missions in the conflict between the US and Iran. 

That specific version can also hold nuclear-armed cruise missiles and nuclear bombs.