Firefighters were called to a road traffic collision on the M4 Spur Road, near Heathrow.
One man was out of his vehicle before the Brigade arrived and was assessed on scene by London Ambulance Service. Another man was sadly pronounced dead at the scene.
The Brigade was called to assist the Metropolitan Police Service at 1240 and the incident was over for firefighters by 1335. Fire crews from Heathrow, Hayes and Hillingdon fire stations attended the scene.
Anyone with further information should call the Metropolitan Police Service on 101.