The A320's engines had operated normally throughout most of the flight, reported Egypt's state newspaper. But the aircraft's final electronic messages reveal an unexpected change prior to vanishing from radar.
Egypt's state-owned al-Ahram newspaper on Tuesday reported that EgyptAir flight MS804 pilot Mohammed Shoukair signed off on the aircraft's technical condition before departing Charles de Gaulle Airport in Paris, France.
The aircraft transmitted 11 electronic messages from when its engines started on Wednesday evening until it disappeared on Thursday. The first two messages showed the engines operating normally.
However, a message at 0026 UTC indicated a change in the temperature of the co-pilot's cockpit window, according to al-Ahram.
The aircraft continued to transmit messages for three minutes until it vanished from radar with 66 people on board, including 56 passengers, seven crew members and three security personnel.
The report comes as the head of Egypt's forensic teams on Tuesday downplayed the theory that an explosion brought down EgyptAir flight MS804.
The A320 aircraft lost contact with air traffic controllers last week shortly after entering Egyptian airspace.
The following day, an Egypt-led search and rescue operation "found personal belongings of passengers and parts of the wreckage 290 kilometers (180 miles) north of Alexandria," according to an Egyptian army spokesman.
Egypt and French authorities have yet to discover the cause behind the aircraft's tragic end, although technical failure and terrorism have not been ruled out.
Investigators hope that the black boxes will shed light on flight MS804's last moments before vanishing from radar.
Over the past year, Egypt has suffered a series of aviation disasters. In March, a man hijacked a domestic Cairo-bound EgyptAir flight and forced the pilot to divert the aircraft to Cyprus. The man claimed to have a suicide belt strapped to his body.
In October, a Russian passenger plane was downed over the Sinai Peninsula minutes after departing from the Red Sea resort town of Sharm el-Sheikh.
All 224 people on board died in the aviation tragedy. The "Islamic State" militant group's Sinai affiliate claimed responsibility for the attack shortly afterwards.