The aircraft involved was an Airbus A320-232, registration SU-GCC, MSN 2088. It made its first flight on 25 July 2003, and was delivered to EgyptAir on 3 November 2003. The aircraft was powered by two IAE V2527-A5 engines.
The flight was the aircraft's fifth that day, having flown from Asmara International Airport, Eritrea, to Cairo; then from Cairo to Tunis–Carthage International Airport, Tunisia, and back. The final completed flight of the aircraft before the crash was Flight MS803 to Paris.
The aircraft departed for Cairo International Airport from Charles de Gaulle Airport on 18 May at 23:09 (all times refer to UTC+2, used in France and Egypt at the time). It disappeared from radar while flying at flight level 370 (about 37,000 ft (11,300 m) in altitude) in clear weather, 280 km (170 mi; 150 nmi) north of the Egyptian coast, and about the same distance from Kastellorizo, over the eastern Mediterranean on 19 May at 02:30. The aircraft was lost 3 hours 25 minutes into the flight.
The aircraft was due to land at 03:05. It was originally reported that a distress signal from emergency devices was detected by the Egyptian military at 04:26, two hours after the last radar contact; officials later retracted this statement.
On the day of the crash Panos Kammenos, the Greek defence minister, noted the aircraft changed heading 90 degrees to the left, then turned 360 degrees to the right while it dropped from Flight Level 370 to 15,000 feet (4,600 m). This information was rejected on 23 May by an Egyptian official from the National Air Navigation Services Company, who stated that there was no change in altitude and no unusual movement before the aircraft disappeared from radar. It is possible that Egyptian radars were unable to track the aircraft as accurately as Greek radars due to their distance from the aircraft. On 14 June, Egyptian authorities confirmed the statements made by Greek officials. According to a former investigator, the initial left turn could have exceeded computer-controlled flight protections, and might also have come close to or exceeded the structural design limits of the aircraft.
Fifty-six passengers from twelve different countries were on board. Three passengers were reported to be children, including two infants. Some of the passengers held multiple citizenship.
The crew of ten consisted of two pilots, five flight attendants, and three security personnel. According to EgyptAir, captain Mohammed Shoqeir had 6,275 hours of flying experience, including 2,101 hours on the A320, while first officer Mohamed Assem had 2,766 hours.
The Egyptian Civil Aviation Ministry confirmed that search and rescue teams were deployed to look for the missing aircraft. Search efforts were carried out in coordination with Greek authorities. A spokesman for the Egyptian Civil Aviation Agency stated that the aircraft most likely crashed into the sea. Greece and France sent aircraft and naval ships to the area to participate in search and rescue efforts. The United Kingdom sent a naval ship, while the United States sent a naval aircraft.
On 20 May, units of the Egyptian Navy and Air Force discovered debris, body parts, passengers' belongings, luggage, and aircraft seats at the crash site, 290 km (180 mi; 160 nmi) off the coast of Alexandria, Egypt. Two fields of debris were spotted from the air between 20 May at dusk and 23 May at dawn; one of them was 3 nmi (3.5 mi; 5.6 km) in radius. At this time, the searched area measured nearly 14,000 km2 (5,400 sq mi), with the sea being 2,440 to 3,050 metres (8,000 to 10,000 ft) deep there.
The European Space Agency (ESA) announced on 20 May that it had possibly detected a 2 km-long fuel slick at 33°32′N 29°13′E, about 40 kilometres (25 mi) southeast of the last known location of Flight 804, on imagery captured by its Sentinel-1A satellite at 16:00 UTC on 19 May.
On 26 May, it was reported that signals from the aircraft's emergency locator transmitter had been detected by satellite, which narrowed the area where the main wreckage was likely to be located on the seabed to within a radius of 5 kilometres (3 mi). An emergency locator transmitter usually activates at impact to send a radio distress signal; this is not the signal from an underwater locator beacon (ULB) attached to a flight recorder, which is an ultrasonic pulse. The U.S. National Oceanic and Atmospheric Administration confirmed that the emergency locator transmitter signal was received by satellites minutes after the airliner disappeared from radar. A "distress signal" received two hours after the disappearance of the aircraft, possibly originating from the emergency locator transmitter, had been reported already on 19 May; this report was denied by EgyptAir.
At the beginning of June, after ultrasonic pulses from a ULB of one of the flight recorders had been detected, a "priority search area" 2 kilometres (1 mi) in radius was established.
The John Lethbridge, a vessel belonging to Deep Ocean Search, equipped with a remotely operated underwater vehicle that can detect signals in depths of up to 6,000 metres (20,000 ft), and map the seabed, was contracted by Egyptian authorities. Capable of retrieving the flight recorders from the seabed, it left the Irish Sea on 28 May and, at that time, it was expected to arrive at the search area around 9 June, after stopping in the Egyptian Port of Alexandria to board Egyptian and French investigators. The vessel was delayed, arriving in Alexandria on 9 June and at the search area some time on or before 13 June. On 15 June, Egyptian authorities announced that searchers on board the John Lethbridge had identified several main sections of wreckage on the seabed. On 9 July, the Egyptian government reported it was extending the John Lethbridge's stay at the crash site, to 18 July. The John Lethbridge concluded its mission to recover human remains and returned to the port of Alexandria on 16 July. On arrival, the recovered remains were transferred from the John Lethbridge to Egypt's Department of Forensic Medicine in Cairo for DNA analysis and processing.
On 22 May, an Egyptian remotely operated underwater vehicle (ROV), owned by the country's Oil Ministry, was deployed to join the search for the missing aircraft. President Abdel Fattah el-Sisi stated that the ROV can operate at a depth of 3,000 metres (9,840 ft). According to Egypt's chief investigator with the Civil Aviation Ministry, Ayman al-Moqadem, the ROV cannot detect signals from flight recorders.
A French Navy D'Estienne d'Orves-class aviso ship, the Enseigne de vaisseau Jacoubet, equipped with sonar able to detect the underwater "pings" emitted by the ULBs of the flight recorders, arrived at the possible crash site on 23 May. The French ship can deploy an ROV that can dive up to 1,000 metres (3,300 ft) and which is able to detect signals from ULBs but with limited depth range.
On 26 May, Italian and French companies capable of executing deep-sea searches, including ALSEAMAR and the Mauritius-based Deep Ocean Search, were asked by Egypt to help locate the flight recorders.
A more specialized French Navy ship, the oceanographic research ship Laplace, left the Corsican port of Porto-Vecchio for the search area on 27 May, according to French aircraft accident investigation body the Bureau d'Enquêtes et d'Analyses pour la Sécurité de l'Aviation Civile (BEA). The vessel can deploy three towed Alseamar hydrophone arrays that are designed to detect a ULB from a distance of up to nearly 4 kilometres (2 mi). On 1 June, the Egyptian Civil Aviation Ministry reported that "pings" from a ULB of one of the flight recorders had been detected by the Laplace. This was confirmed by the BEA whose spokesperson announced the establishment of a "priority search area".
The survey ship John Lethbridge was at the search area by 13 June. The ULBs, which were activated on 19 May, are designed to last for at least 30 days; the Egyptian board of inquiry said the signals would continue until 24 June. On 16 June, Egyptian authorities announced that the searchers on the John Lethbridge had found the cockpit voice recorder (CVR), damaged, at a depth of 13,000 feet (4,000 m). The memory unit was retrieved intact and sent to Cairo for investigation, following the transfer of the CVR to Egyptian civil aviation officials in Alexandria. The next day it was announced that the John Lethbridge had been used to retrieve, in several pieces, the second flight recorder—the flight data recorder (FDR). The memory unit was recovered from the damaged flight data recorder but an Egyptian official stated that the flight recorders require extensive repair before they could be properly analyzed and accessed.
On 19 June, Egypt's Aircraft Accident Investigation Committee announced that they, with the assistance of the Egyptian Armed Forces, had completed the drying procedure of the intact memory modules and started electrical testing of the memory modules from both the cockpit voice recorder and the flight data recorder.
On 21 June, officials involved in the investigation disclosed that the memory chips from both recorders were damaged. After the initial attempts to download data from both recorders failed, the Egyptian investigative committee announced on 23 June that both recorders would be sent to France's BEA to have salt deposits from the memory chips removed; the recorders would then be returned to Egypt for analysis.
On 27 June, the BEA announced that the FDR had been repaired and sent back to Cairo for data analysis by civil aviation safety authorities. A spokeswoman from the Paris prosecutor's office informed the Associated Press that a preliminary investigation into the accident would begin, since no evidence of any act of terrorism had been found. It was further announced that the office had opened a manslaughter investigation instead.
Initially, the disappearance and crash of Flight 804 was assumed to be linked to terrorism and insurgency in the region. Thus, for instance, the Egyptian Civil Aviation Ministry stated on 19 May that Flight 804 was probably attacked. Two US officials believed the aircraft was downed by a bomb, and a senior official said that monitoring equipment focused on the area at the time detected evidence of an explosion on board the aircraft; other officials from multiple US agencies said they had seen no evidence of an explosion in satellite imagery and another two intelligence officials stated there is nothing yet to indicate foul play.
According to Greek military radar data, Flight 804 veered off course shortly after entering the Egyptian flight information region. At Flight Level 370 (about 37,000 ft (11,300 m) in altitude), the aircraft made a 90-degree left turn, followed by a 360-degree right turn, and then began to descend sharply. Radar contact was lost at an altitude of about 10,000 ft (3,000 m). This information was later denied on 23 May by an Egyptian official from the National Air Navigation Services Company, who stated there was no change in altitude and no unusual movement before the aircraft disappeared from radar. On 14 June, Egyptian authorities confirmed the statements made by Greek officials.
On 19 May, Greece's Ministry of National Defence reported that it was investigating the report of a merchant ship captain who claimed to have seen a "fire in the sky" 240 km (150 mi; 130 nmi) south of the island of Karpathos.
Shortly after the disappearance, the French government began to investigate whether there had been a security breach at Paris Charles de Gaulle Airport.
Seven messages sent via the Aircraft Communications Addressing and Reporting System (ACARS) had been received from the aircraft between 02:26 and 02:29; contact was lost four minutes later at 02:33. The data, confirmed by France's Bureau of Investigations and Analysis, indicates that smoke may have been detected in the front of the airliner—in the front lavatory and the avionics bay beneath the cockpit. Smoke detectors of the type installed on the aircraft can also be triggered by the condensation of water vapour, producing fog, in the event of a sudden loss of pressure inside the cabin. The aircraft's optical smoke detectors have been deemed more reliable than older models on Airbus aircraft, as they produced fewer false warnings, but were sensitive to dust and some aerosols. The three windows mentioned in the data are cockpit windows. The flight control unit (FCU) is a cockpit-fitted unit that the pilot uses to enter instructions into the on-board flight computer. The spoiler elevator computer number 3 (SEC 3) is one of the three computers that controls the spoilers and elevator actuators. Two pilots—one interviewed by The Daily Telegraph, the other writing for The Australian—interpreted the data as possible evidence of a bomb.
At 02:36, seven minutes after the last ACARS message and the last ADS-B transmission, two transmissions from the aircraft’s Emergency Locator Transmitter (ELT) were received by the international Cospas-Sarsat system. These transmissions indicated that they were initiated in “test” mode, suggesting either an unusual manipulation of the cockpit ELT switch, or an electrical fault in the switch’s circuit. The transmissions were received by Cospas-Sarsat’s then-experimental MEOSAR system, and subsequent data collection and analyses by the Cospas-Sarsat Secretariat and engineers at France’s Centre national d'études spatiales (CNES) were successfully used to calculate the likely point of impact of the flight in the Mediterranean Sea.
Aviation expert David Learmount of Flight International suggested that an electrical fire could have started in the aircraft's avionics compartment and that the aircrew may have been too distracted to communicate their distress to air traffic control.
On 22 May, the French television station M6 reported that, contrary to official statements, one of the pilots told Cairo air traffic control about smoke in the cabin, and decided to make an emergency descent. Later that day, the report was dismissed as false by the Egyptian Civil Aviation Ministry.
On 24 May, a forensics official from Egypt's investigative team said that the remains of the victims indicated an explosion on board. The head of forensics denied the claim.
At the beginning of June, France 3 and Le Parisien reported that the aircraft had performed three emergency landings in the hours before the crash—at Asmara, Tunis, and Cairo—followed by technical inspections, after ACARS messages "signalled anomalies on board shortly after takeoff from three airports". On 2 June, Safwat Musallam, EgyptAir's chairman, denied the report.
With investigations into the crash ongoing, Egyptian officials announced on 29 June that data recovered from the flight data recorder, as well as recovered wreckage from the plane, indicated that smoke had occurred on the aircraft, which matches previous information relayed by the plane's automated systems (ACARS). Egyptian Civil Aviation Ministry experts have suggested that wreckage from the front section indicates high temperature combustion. Also, the data showed that the flight data recorder recorded the smoke and fault alarms at the same moment that the aircraft's ACARS relayed messages about them to the ground station, and that the data recorder stopped recording at an altitude of 37,000 ft (11,300 m) above sea level. Media reported that data from the cockpit voice recorder indicated one of the pilots had tried to extinguish the fire in the cockpit before the airplane crashed. However, after these reports were released, the Egyptian Civil Aviation Authority urged "media to be cautious while issuing press releases about the accident and to only rely on official reports issued by the committee itself." Later, on 16 July, the committee confirmed that the cockpit voice recording mentioned "the existence of a fire".
On 17 September 2016, Reuters relayed a Sept 16 report from the French news outlet Le Figaro that French forensic investigators visiting Cairo noted traces of the explosive TNT on the aircraft debris. According to Le Figaro's source, Egypt proposed a joint report with France announcing the discovery of evidence of an explosive, but France declined, alleging that Egyptian judicial authorities did not allow the French investigators "to carry out an adequate inspection to determine how the traces could have got there".
On 15 December 2016 Egyptian investigators announced that traces of explosives had been found on the victims, although a source close to the French investigation expressed doubts about Egypt's latest findings. On 13 January 2017, French newspaper Le Parisien published an article claiming that unspecified "French authorities" believed the aircraft might have have been brought down by a cockpit fire caused by an overheating phone battery; it noted parallels between the position where the co-pilot had stowed his iPad and iPhone 6S and data which suggested an accidental fire on the right-hand side of the flight deck, next to the co-pilot.
EgyptAir retired the Flight 804 (MS804) flight number and replaced it with Flight 802 (MS802) for inbound flights from Paris to Cairo, while the outbound flight number was changed from Flight 803 (MS803) to Flight 801 (MS801).