The U.S. National Transportation Safety Board is sending four investigators to Afghanistan to help with the probe of the April 29 crash of a National Airlines Boeing 747-428 freighter on departure from Bagram Airfield.

All seven crewmembers on board, who were Americans, were killed in the 11:20 a.m. crash. The GE CF6-80C2B1F-powered aircraft, one of three in Michigan-based National Airlines’ fleet, was destroyed.

According to National Airlines, Flight NCR102 — registration N949CA — was a “purely cargo flight” with no passengers aboard. The carrier says the 747 was carrying “vehicles and routine general cargo.”

A video that emerged on LiveLeaks shows the 747 at a very high angle of attack over the airfield after takeoff, followed by a roll to the left and a rollover to the right. The aircraft hit the ground with the wings level in a slightly nose-low attitude but with a very high vertical descent rate.

The investigation is under the control of the Afghanistan Ministry of Transportation and Commercial Aviation.