A British Airways plane was intercepted by fighter jets over Hungary after it lost contact with air traffic controllers.
The Boeing 777 was reportedly escorted by two Hungarian Air Force Gripens scrambled to identify the aircraft after it passed over its border unannounced on Saturday afternoon.
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According to air safety protocols pilots must make contact with air traffic controllers on the ground when passing from one country's airspace to another.
When the BA jet failed to do so Hungarian authorities reportedly issued their highest alert and the pair of fighter jets were sent to identify the aircraft and ensure it was making safe progress.
The Gripens reportedly took off at 12.55pm before the BA flight made contact with ground control. The jets returned to their base at 13.21pm.
A BA spokesman said: "Communication was quickly restored with air traffic control and the flight landed normally at Heathrow."
There have been several similar incidents in the recent past where civilian commercial flights have inadvertently triggered high-level security alerts.
In October, passengers on board a Monarch airlines flight from Madeira to Birmingham spotted fighter jets in close proximity to the plane after it lost communication over French airspace.