Initial attempts to download information from the flight data and voice recorders of an EgyptAir plane that crashed into the Mediterranean last month have failed, and key parts of the recorders are being sent to France for repairs, according to Egyptian and US officials.

The “electronic boards” of the recorders will be flown next week to the offices of the French aviation accident investigation bureau near Paris, authorities said. After the boards are repaired and salt removed, they will be sent back to Cairo for data analysis, Egypt’s investigation committee said in a statement late on Thursday.

The recorders, also known as black boxes, were extensively damaged when EgyptAir flight 804 travelling from Paris to Cairo plunged into the sea on 19 May, killing all 66 people on board.

French and US investigators have overseen the effort to extract information from the recorders. The recorders were made by Honeywell, a US company. The plane, an A320, is made by Airbus, which is based in France.

The black box memory units typically provide investigators with critical data, including the pilots’ conversations, details about how the plane’s engines, navigation systems, and auto-pilot were working, and even information about smoke alarms.

The pilots made no distress call before the crash, and no group has claimed to have brought down the aircraft.

Radar data showed the aircraft had made violent moves after cruising normally in clear skies, plummeting from 38,000ft (11,582 metres) to 15,000ft (4,572 metres). It disappeared when it was at an altitude of about 10,000ft (3,048 metres).

Leaked flight data indicated a sensor had detected smoke in a lavatory and a fault in two of the plane’s cockpit windows in the final moments of the flight. Egypt’s civil aviation minister, Sherif Fathi, has said terrorism was a more probable cause than equipment failure or some other catastrophic event.