A routine Air Canada flight from Toronto Pearson Airport to London, England, declared an emergency on Thursday at the tail end of its journey across the Atlantic Ocean. 

According to Aviation Source News, flight AC858 was travelling over the Atlantic Ocean near Northern Ireland when the emergency declaration was made. 

The aircraft reportedly had less than an hour of its journey remaining when the emergency call came in. The aviation news website notes that the emergency was serious enough to prompt the use of a Squawk Code 7700, indicating a serious issue onboard the aircraft. 

The code can be inputted by the aircraft's pilots or instructed by air traffic control (ATC) and alerts the ground crew to prepare for the flight's arrival. 

Medical emergency @RadarBoxCom https://t.co/KmUVRYkEk0

— Flight Emergency (@FlightEmergency) April 18, 2024

Initially, it was unclear what the nature of the emergency was, but later, Aviation Source News determined that it was a medical emergency. 

Pilots eventually changed the squawk code from 7700 to 5170, indicating that the emergency onboard was under control, and that the flight did not need to be diverted to a nearby airport. 

The flight landed safely at Heathrow Airport at 3:14 p.m. local time without further incident.