An aircraft tracking site Flightradar showed flight CA428 turning south towards Tai O village and the surrounding mountains at around 9.30pm, instead of continuing westwards along the normal route until it left the island.
According to South China Morning Post, an air control officer was forced to issue an immediate warning and set of directions to the pilot to correct the flight path.
The Airbus A320, with a seating capacity of 200, landed safely in China’s western city of Chengdu about two hours later.
It had been at 3,400 feet during the wrong turn. The peak nearby – the highest point on Lantau – is 3,066 feet. But according to Civic Party lawmaker Jeremy Tam Man-ho, a licensed pilot, the minimum safe altitude for that area is 4,300 feet.
“If the plane was carrying more cargo or passengers, or if the plane was a bigger one, it might not have achieved its altitude at that time,” Tam said. “If the plane turned towards the mountains at an even lower altitude, you could imagine what the consequence could have been.”
But he added that an anti-collision system on the plane would have directed it to climb up immediately before any mishap.
Air China said the flight crew had questions about the air traffic control officer’s directions but, due to a busy radio frequency, the pilot decided to turn first while still confirming the directions.
“Air China has been putting air safety as our top priority,” a spokesman said. “We will further strengthen our safety education.”
Tam suggested there was no reason why the pilot should have deviated from the normal route. Even if there was a radio failure, he should have stuck to the normal departure path, he said.
Tam earlier shared an audio recording of a conversation between the air traffic officer and the pilot, in which the officer is heard issuing repeated directions to “turn right immediately”, warning of “terrain ahead”. When the pilot does not turn, she can be heard warning of the mountains again and requesting he climb to 5,000 feet immediately.
After the pilot corrects the mistake, the officer tells him she will have to submit a report about the incident to authorities. The pilot can be heard apologising.