Two aircraft came within a vertical separation height of 800 feet, 200 feet less than what is supposed to be, towards the west of Mumbai airspace on Thursday night.

The incident occurred about 100 nautical miles west of Mumbai. It was noticed when the Traffic Collision Avoidance System (TCAS) of the Gulf Air flight GF 064 headed towards Mumbai informed the pilot of an intruding aircraft — Flight SV 601 of Saudi Airlines.

An Air Traffic Control official, however, said though an aircraft intruding into the vertical separation height was an air safety issue, it was not alarming as there were safety features in an aircraft to take care of intrusions up to 300 feet.

The Gulf Air flight was on its way to land at the Mumbai airport with 180 passengers from Bahrain while the Saudi Airlines aircraft was flying over the Mumbai airspace to Riyadh from Dhaka. The Saudi Airlines flight had about 377 passengers on board. “The Saudi Aircraft had climbed 200 feet without permission from the ATC. The pilot of the Gulf Air aircraft had spotted another aircraft climbing into its airspace on his warning system,” an airport official said.

However, soon ATC officials intervened and asked the Saudi Airlines pilot to maintain its given altitude.

The digital radar at the ATC also spotted the Saudi aircraft moving up in height. “Earlier we could not have spotted the aircraft exceeding its altitude as the radars were analogue, but now we have digital radars that can trace the exact height of the aircraft,” the official said.