Two passenger airplanes had a close shave over Bengaluru’s airspace on July 10, triggering anti-collision alarms and an inquiry by the Director General of Civil Aviation (DGCA).
Indigo operates both the aircraft. In a press statement on Thursday, Indigo said their Traffic Collision Avoidance System (TCAS) resolution advisory system was triggered when a plane operating on the Coimbatore-Hyderabad route came close to another on the Bengaluru-Kochi sector.
According to sources, the airplanes came within 4 nautical miles (around 7.4 km) of each other, with a vertical separation of just 200 feet. Considering the low vertical separation between the aircraft, and that on average an aircraft cruises at over 900 kilometres per hour, it could have been a matter of a few seconds before the two planes came face-to-face.
More than 300 passengers were seated in the two Airbus 320 aircraft.
Bengaluru’s airspace divided between the Kempegowda International Airport, Yelahanka Air Force base and HAL airport. Sources in the know said the incident happened over HAL’s airspace.
Around 11 p.m., 6E 779 (Coimbatore-Hyderabad) was traversing over the city. The aircraft was directed by HAL’s Air Traffic Controller (ATC) to climb to 36,000 feet.
Meanwhile, 6E 6505 (Bengaluru-Kochi) had just departed the city. The aircraft was directed to ascend to 28,000 feet.
During this period, they came ‘close’ (in aviation terms) to each other.
The TCASs, which is mandatory for major civil airplanes carrying more than 19 passengers, were triggered, when the planes were within 4 nautical miles (NM) of each other.
According to sources aware of the matter, while the safe limit varies (from just 3 NM near BIAL’s runway to more than 10 NM away from the city), for HAL, it is less than 5 NM.
“Pilots on board both aircraft were alerted to the presence of the other by on-board systems,” said Bangalore International Airport Limited in a statement about the incident.
Indigo has said they ‘followed normal procedure’ and reported the incident to a regulator.
HAL has confirmed that the incident occurred over their airspace and have sent details to the DGCA.
A DGCA officer said, in the normal course of action, the air traffic controller is taken off duty, the recordings sealed and details sent to DGCA, which conducts a preliminary inquiry into the possible lapses.
If termed serious, the investigation is handed over to the Aircraft Accidents Investigation Bureau.