Investigators examining the Boeing 767 crash at Miami International Airport over the weekend revealed that two key systems designed to slow the aircraft were not activated prior to the incident. The National Transportation Safety Board (NTSB) reported late Tuesday that the plane’s speed brakes and thrust reversers were not deployed before the jet ran off the runway and struck nearby vehicles.

During a briefing, NTSB lead investigator Chihoon Shin said data retrieved from one of the plane’s black boxes showed no evidence of the speed brakes—panels that increase aerodynamic drag—or thrust reversers, which help reduce speed during landing, being used. While the aircraft’s wheel brakes were applied 23 seconds before the end of the recording, the brakes were subsequently released, and the engine throttles were increased to power levels indicative of a go-around maneuver. Go-arounds are standard procedures pilots initiate to abort and retry a landing. After this, the throttles were reduced to idle and the brakes reapplied until the recording concluded.

NTSB Chairwoman Jennifer Homendy declined to offer conjecture on why these critical safety systems were not engaged. The crash on Sunday resulted in five fatalities and injuries to five others. The plane overran the runway and collided with vehicles near the airport. Most of the cargo aboard the aircraft consisted of contact lenses.

The flight was operated by cargo carrier 21 Air under an Amazon Air contract. Amazon stated it is cooperating fully with local officials and investigators, while 21 Air expressed devastation over the accident. The NTSB continues to investigate the circumstances surrounding the crash to determine contributing factors.