A flight crew elected to perform an air turnback to their departure station after noticing a 'Fueling' light had illuminated on their Master Warning Panel along with a Master Caution chime and a quick shudder of their Dassault Falcon-50 aircraft.

Narrative

After fueling the aircraft both pilots conducted separate visual inspections of the aircraft. All doors appeared to be closed. After leveling off at 17;000 FT the 'Fueling' light illuminated on the Master Warning Panel along with the Master Caution chime. While the pilot not flying was checking the QRH for the indicated caution; a quick shudder of the airplane was felt. Per the checklist and what was felt in flight; we elected to return to our departure airport. Upon landing; we could see that the fueling panel door came off the aircraft in flight.A mod was completed on this aircraft which makes the fueling door and latches sturdier. Unfortunately; it is also possible for the panel latches to catch between the frame and the aircraft skin; which provides very little strength. When the fueler closed the fueling panel; two of the latches were not secured behind the frame. The panel appeared closed visually but two of the latches did not catch where they were supposed to. A flight crew member should always double check the security of panels/doors by closing it themselves. A visual inspection can be misleading.