The wing centre section alone weighs 115 kg (254 lb), requiring a large crew in order to rig it for flight.

The wing features six flaps, with the outer pair moving at a 2:1 differential ratio with the ailerons.

[1][2][3] The 604 prototype, flown by Walter Neubert, came in sixth in the 1970 World Gliding Championships held at Marfa, Texas, even though the pilot was lost overnight after a land-out during the competition and missed the following day.

[1][2] In 1981, Marion Griffith Jr. flew a 604 for 645 mi (1,038 km) from Refugio, Texas to Liberal, Kansas to win the Barringer Trophy, while also setting a US distance to a goal record.

[4] In July 2011, five of the eleven 604s built were located in the United States and registered with the Federal Aviation Administration in the Experimental - Racing/Exhibition category.