58-20-02 de HAVILLAND: Applies to All Model 104 "Dove" Aircraft.
Compliance required by January 1, 1959.
In an emergency such as a wheels up landing, the placing of the ground/flight switch on the "Ground" position to minimize fire risk would isolate the fire extinguisher system.
Dove Modification 655 has therefore been introduced which provides an electrical supply to the fire extinguisher circuit from the battery side of the ground/flight switch, even when the switch is in the "Ground" position, thus ensuring that the fire extinguisher system is operative at all times.
The British Air Registration Board considers this mandatory. The FAA concurs with this action and considers compliance therewith mandatory.
(de Havilland TNS CT (104) No. 153 covers the same subject.)