His proton torpedo run in the Death Star trench unsuccessful, and with no surviving wingmen to protect him, Red Leader soon finds himself at the end of Darth Vader's targeting computer. Initiating Luke into action for his attack run, the brave leader's starboard engine damage suffers further attack from the lethal and merciless TIE pilot, sending him crashing down to the surface of the planet killer...
Filming Red Leader's demise at ILM: https://starwarsaficionado.blogspot.co.uk/2017/10/star-wars-at-40-death-star-surface.html
UPDATE: From the Revised Fourth Draft script of 19th April, 1976, Red Ten (played onscreen by Robert O'Mahoney) died in space, following Red Leader out from the torpedo surface detonation. It's quite possible that Mahoney filmed his death scene in the cockpit at Elstree against a star background rather than blue screen (as both options were used in studio), hence in the finished film, when his character's demise was instead changed to the inside of the Death Star trench, a substitute pilot's death - Red Twelve - was used instead (noticeable for his different helmet, if you pause the moment).