Police say the man, who's not yet been named, died at around 6.40pm on 18 September.
Police say the 66-year-old died in a single vehicle accident on the track to Fort Clonque, at Alderney's south-western tip.
They say as investigations are carried out there will be a police presence in the area and ask people to stay away.


Iran effect looming in Guernsey's latest inflation figures
Alderney to explore data centre hosting
Prime Guernsey seafront location for sale
Woman (20) arrested on suspicion of attempted murder in Guernsey
Last day to register for Guernsey's upcoming by election
New citizen science project observing Guernsey dragonflies and damselflies
Channel Islands music school to hit global stage with Dubai launch
67,000 sickness days across the States of Guernsey last year