Twice in the last two days, an airliner has set the hijack code. On Tuesday a Corendon 737 squawked 7500 on its way to Nuremberg and two German Eurofighters were sitting off its wings before it landed. On Wednesday an Air India 787 did the same over India and was diverted to Jaipur.

Both incidents ended harmlessly. But they offer a rare look at a system that most people never see: Quick Reaction Alert, the armed fighters that every NATO country keeps ready around the clock for exactly this moment. Here is how it works, from the first warning on a radar screen to the moment a fighter pilot pulls up alongside an airliner's cockpit.

Step One: Something Is Wrong

Every QRA launch starts with a mismatch. An aircraft stops answering air traffic control, flies off its route, enters airspace without permission, or, as on Tuesday, transmits squawk 7500, the code for unlawful interference. Civil controllers pass the problem to the military, which watches the same airspace through its own radar network.

Across Europe, NATO's air operations centres monitor up to 30,000 air movements a day, according to the Alliance. The centre at Uedem in Germany covers the airspace north of the Alps, Torrejón in Spain the south, and Bodø in Norway the Nordic region and the Arctic. Their job is to decide, quickly, which air base should launch. That is why the Corendon jet was first watched by a Croatian fighter, according to regional reports, and then handed over to Germany's.

Step Two: The Scramble

In Britain, the process has been described in detail by Forces News. Air operations officers at the Control and Reporting Centre at RAF Boulmer spot the problem and share the picture with the National Air and Space Operations Centre at High Wycombe. The centre decides whether a launch is justified. If it is, the order goes back to Boulmer and on to the pilots at RAF Lossiemouth o RAF Coningsby, who sit in a crew room next to sheds holding two armed tifones.

The jets are airborne within minutes. A Voyager tanker at RAF Brize Norton can be put on standby so the fighters can refuel in the air. If the threat is urgent, the jets can be cleared to fly supersonic, which is why some QRA launches over the UK are followed by reports of loud bangs. In Germany, the equivalent pair is called the Alarmrotte: two armed Eurofighters at Wittmund in the north and Neuburg in the south, the jets that met the Corendon 737.

A pair of RAF Typhoons launching on a QRA training scramble at RAF Coningsby.

Step Three: The Intercept

Once the fighters find their target, the first job is simply to look. Is the cockpit occupied? Are the pilots conscious? Is there any sign of a struggle? Fighter pilots stay where the crew can see them and use internationally agreed visual signals, such as rocking their wings, to tell an aircraft with no radio to follow them.

Most intercepts end peacefully, as they did over Bavaria this week. A crew whose radio has failed sees the fighter, follows its instructions and lands. In the UK, aircraft that need to be escorted to the ground are normally taken to Stansted, which is designated for handling threat aircraft. In Germany, the Corendon jet was simply escorted to its planned destination, which was closed while police checked it.

NATO explains what happens during an air interception, from detection to escort.

Switzerland: From Office Hours to Around the Clock

Not every country has always flown QRA around the clock. For years, air policing by the Swiss Air Force was largely limited to office hours. That changed on 31 December 2020. Since then, two armed F/A-18 Hornets have been ready 24 hours a day, seven days a week, at Payerne, able to be airborne within 15 minutes.

The Swiss distinguish between hot missions, emergency launches against aircraft that violate Swiss airspace or seriously break air traffic rules, and live missions, routine checks on foreign state aircraft flying through with a diplomatic clearance. In 2020 alone, before the 24/7 service began, the air force counted 15 hot missions and 290 live missions. In May 2025, it tested doubling the alert force to four F/A-18s for two weeks.

Why It Has to Assume the Worst

The uncomfortable truth of QRA is that almost every alert turns out to be harmless: a faulty radio, a wrong frequency, a mistyped code. But the system cannot know that in advance. As the Nuremberg police spokesman put it after Tuesday's alert, because nobody could reach the cockpit, the authorities had to take the situation very seriously from the start.

That is the whole philosophy in one sentence. QRA exists for the one day in thousands when the worst case is real. On every other day, it costs a few hours of fuel and some nervous passengers. Most people think that is a fair price.

Sky News was given access to the RAF pilots on Quick Reaction Alert, who explain how they would deal with a hostile aircraft.

Sources: NATO (Air Policing / Air Defence); Wikipedia (Quick Reaction Alert); Forces News; Moneycab / Swiss Federal Department of Defence; blue News; t-online; inFranken.de.