They had been working on a radio mast in the Hoher Meissner hills when the accident happened, 30km (18 miles) south-east of Kassel.
The transmitter belongs to regional public broadcaster Hessischer Rundfunk (HR), which said it was upset by the news.
In a tweet, it said its thoughts were with the workers' families.
The Hoher Meissner transmitter has three radio masts that are up to 220m in height and HR said initial reports indicated the accident happened on the tallest of the three.
According to the broadcaster, the three engineers on the platform were winched up a diagonal cable towards the mast but at a height of 50m they got into difficulty.
They tried to pull themselves up using cables, but when the cables sagged the platform fell to the ground on to an asphalt surface. The men died at the scene.
The broadcaster said it would do its utmost to find out what had caused the accident.