Pascal Mercier and his family were originally booked on the flight; Mercier later re-booked to a different flight since he had young children and therefore did not wish to fly on a late night flight with them. After the crash hotel staff members checked rooms of passengers booked on Flight 604; the hotel crew found Mercier and his family in the room. Mercier reported that 82 people who had stayed in the same hotel had boarded Flight 604.
Charles de Gaulle Airport initially indicated the Flash Airlines flight as delayed; authorities began notifying relatives and friends of the deaths of the passengers two hours after the scheduled arrival time. Authorities took relatives and friends to a hotel, where they received a list of passengers confirmed to be on the flight.
Marc Chernet, president of the victims' families association of Flight 604, described the disaster as the "biggest air disaster involving French nationals" in civil aviation.
Most of the passengers were French tourists who originated from the Paris area. A January 5, 2004 provisional passenger list stated that twelve entire French families had boarded the flight. Members of seventeen families appeared at Charles de Gaulle Airport to take passengers on the flight; this fact gave the airport staff indication that entire families died on Flight 604.
|Final tally of passenger nationalities|
|, , and||0||1||1|
The American National Transportation Safety Board (NTSB) and the French Bureau d'Enquêtes et d'Analyses pour la sécurité de l'Aviation Civile (BEA) investigated and concluded that the pilot suffered spatial disorientation, and the copilot was unwilling to challenge his more experienced superior. Furthermore, according to the NTSB and BEA, both officers were insufficiently trained. The NTSB stated that the cockpit voice recorder showed that 24 seconds passed after the airliner banked before the pilot began correcting maneuvers. Egyptian authorities disagree with this assessment, as does the Egyptian public, who both tend to attribute the cause to mechanical issues. Shaker Kelada, the lead Egyptian investigator, said that if Hamid, who had more experience than the copilot, detected any problems with the flight, he would have raised objections. Some media reports suggest that the plane crashed due to technical problems, possibly a result of the apparently questionable safety record of the airline. This attitude was shown in a press briefing given by the BEA chief, who was berated by the first officer's mother during a press conference, and demanded that the crew be absolved of fault prior to the completion of the investigation. Two months after the crash Flash Airlines went bankrupt.