The sole written account of this deed is in William of Malmesbury's history Gesta Regum Anglorum (Deeds of the English Kings), written in 1120. This account is, however, usually considered to be historically believable.
According to William, Eilmer had observed the flight of birds and concluded that with the proper apparatus, a human being might glide rather than fall from a height. He constructed wings, affixed them to his arms and legs, and leaped from a tower. After gliding for a furlong (roughly 200 meters), he crash landed and broke both legs. Undaunted, he believed that he could have made a more controllable landing had he constructed a tail for his gliding apparatus, and was preparing for a second flight when the abbot of Malmesbury Abbey forbade him from risking his life in any further experiments.