The US National Transportation Safety Board (NTSB) is assisting the Afghanistan Ministry of Transportation and Commercial Aviation in the investigation of the crash of a National Airlines Boeing 747-400 freighter shortly after takeoff from Bagram Air Base in Afghanistan Monday.

NTSB said in a statement the cargo aircraft crashed just after takeoff from the US-operated air base at 11:20 a.m. local time April 29. All seven crewmembers onboard were killed and the aircraft was destroyed. The seven crewmembers were all American citizens. The accident site is within the perimeter of the air base.

The cargo flight was being operated on behalf of the US Air Force and was destined for Dubai’s Al Maktoum International Airport.

National Airlines said the flight, NCR102, was a purely cargo flight and that its load consisted of vehicles and routine general cargo.

“Safety is always our top priority at National Airlines,” National Airlines president Glen Joerger said. “This is a devastating loss for our family and we’ll work diligently with authorities to find the cause.”

NTSB senior air safety investigator Tim LeBaron is the US accredited representative for the investigation. He will lead a team of three additional investigators from the NTSB as well as representatives from FAA and Boeing.

National Airlines is based in Orlando, Fla., and is a wholly owned subsidiary of National Air Cargo Holdings. It operates scheduled and on-demand cargo service globally and charter passenger service in the Middle East.