For about an hour on Wednesday morning, Israel thought it might have a hijacked airliner heading its way. flydubai flight FZ1073, a Boeing 737 MAX 8 from Dubai to Tel Aviv with around 174 people on board, suddenly switched its transponder to the emergency code 7700, and then, seven minutes later, to 7500: the code a crew uses to signal unlawful interference with an aircraft. In plain language, a hijacking.

The Israeli Air Force scrambled fighter jets. Prime Minister Benjamin Netanyahu and Defence Minister Israel Katz convened an urgent security meeting. The aircraft turned away from Israel, descended and landed at Tabuk in north-western Saudi Arabia.

Then the story changed. Israeli officials said it was not a hijacking at all. According to Israeli security sources quoted by Israeli media and CNN, the alarm was set off by a violent altercation between the two pilots in the cockpit.

How the morning unfolded

The flight took off from Dubai International at 03:05 UTC, just after 7 a.m. local time, and was due at Ben Gurion around 9:30 Israel time. Flightradar24’s tracking shows the squawk changing to 7700 at 05:31 UTC, about two and a half hours into the flight, and to 7500 at 05:38, while the jet was over Jordan and approaching Israeli airspace.

The aircraft then turned back towards Saudi Arabia, left ground-based tracking coverage and descended to around 15,000 feet. Israel’s security establishment went to full alert. Reports that the pilots had stopped communicating normally with Israeli controllers only added to the tension.

The jet landed safely at Tabuk shortly before 10 a.m. Israel time. Shortly afterwards, the prime minister’s office said the incident was not believed to be a hijacking.

What 7500 means, and why Israel reacted so fast

Every airliner carries a transponder that broadcasts a four-digit code to air traffic control. Three codes are reserved for trouble: 7700 for a general emergency, 7600 for a radio failure and 7500 for unlawful interference. A crew that dials 7500 is telling the ground, silently, that someone else may be in control of the aircraft. Controllers are trained to treat it as real until proven otherwise.

For Israel, which has lived with the threat of aircraft being used as weapons for half a century, a 7500 squawk on a flight approaching Tel Aviv is about as serious as a signal gets. Scrambling fighters to intercept and identify the aircraft is the standard response, and it is exactly what happened on Wednesday.

What happened in the cockpit

As more detail emerged during the day, the “fight between the pilots” turned out to be something far more serious. According to The Aviation Herald, the Boeing 737 MAX 8, registration A6-FKF, was cruising at 34,000 feet about 130 nautical miles north-east of Tabuk when it dropped to around 19,000 feet in roughly 90 seconds. That is an extraordinarily steep descent for an airliner, far beyond anything a crew would fly deliberately in normal operations.

Passengers described violent manoeuvring, a sudden dive and then chaos. Israeli media quoted passengers saying they heard screams as the aircraft dived. Several reported a physical fight in the cockpit and that one pilot had been attacked with a pocket knife. Video shared from the cabin shows a pilot with blood on his shirt being treated in the aisle and another man restrained on the floor, and a passenger can be heard calling for help and saying the attackers had been subdued.

According to an Israeli official, two airline pilots travelling off duty as passengers, one a South African citizen and one from New Zealand, got into the cockpit together with cabin crew and passengers and pinned the attacker to the floor. Control of the aircraft was regained, it levelled off at around 15,000 feet and flew on to land safely at Tabuk about 85 minutes after leaving cruise altitude. It is not yet officially confirmed who flew the aircraft for the landing.

Israel’s Air Defense Forces said the captain is a citizen of the United Arab Emirates and the first officer an Omani citizen, and Israeli authorities have opened an investigation into the first officer amid growing indications that he tried to take control of the aircraft to crash it. Tabuk Airport said both pilots were taken to hospital with injuries, the captain with serious stab wounds. Photos taken after landing appear to show damage to the aircraft’s rudder.

flydubai confirmed that the emergency had been triggered by a fight between the pilots, said it was investigating and had informed the Israeli authorities, and sent another aircraft to Tabuk to collect the 174 passengers, 27 of them children. In Israel, Transportation Minister Miri Regev demanded that flydubai flights be suspended, and according to Hebrew media asked the Civil Aviation Authority to check whether the UAE had breached its aviation agreement with Israel, which reportedly allows only pilots from countries with diplomatic relations with Israel to fly into the country. Israel has no diplomatic relations with Oman. Israeli broadcaster Kan reported that the Mossad, the Shin Bet, the Israel Defense Forces and the Transportation Ministry are all involved in the investigation.

What we still do not know

The most important question: why. No authority has published a motive, and early reports disagree on details, including which pilot attacked which and what exactly happened to the transponder codes. The first officer has not been charged, and investigators will now rely on the cockpit voice recorder, the flight data recorder, the pilots themselves and the many passenger videos.

If the suspicions are confirmed, FZ1073 would join a very short list of airliners a pilot tried to crash on purpose, alongside Germanwings 9525 in 2015, when the first officer locked the captain out of the cockpit. The difference this time is that the cockpit door did not keep help out. We will update this story as official findings emerge.

Sources: Flightradar24, Ynet, The Times of Israel, The Jerusalem Post, Reuters (via Cyprus Mail), CNN, Calcalist, The Aviation Herald, Tabuk Airport, flydubai