Hong Kong aviation authorities have launched an investigation after a collision alert was triggered when two cargo planes took off at the same time from the airport and have removed the air traffic control staff involved from frontline duty.
The Civil Aviation Department (CAD) said on Friday the staff might have failed to follow take-off protocols.
"The CAD is highly concerned about the incident and has immediately initiated an investigation and follow-up actions according to procedures," a spokesman said.
"Preliminary information indicates that the incident may involve non-compliance by ATC [air traffic control] personnel with established procedures for arranging aircraft for take-off. The relevant ATC personnel have been temporarily removed from frontline ATC duties."
Secretary for Transport and Logistics Mable Chan said on Friday her bureau paid great attention to aviation safety.
She has ordered the department to submit a report on the incident as soon as possible.
An MNG Airlines Airbus A330 and a Silk Way West Airlines Boeing 777 were both cleared for take off at around 7am (5am Thai time) on Thursday by air traffic control from the central and southern runways at Hong Kong International Airport.
The Airbus plane was bound for Turkmenistan, while the Boeing aircraft was heading to Baku, Azerbaijan.
According to the department, one of the cargo planes was instructed by air traffic control to climb to 5,000 feet, while the other was told to reach 3,000 feet to maintain separation.
But the climb rates of the planes did not match what air traffic staff had expected, leading to the planes failing to achieve the "desired vertical separation".
Authorities said the Silk Way West Airlines plane issued an anti-collision warning to its crew and descended to 2,500 feet when it was about seven nautical miles northeast of the airport.
The two aircraft carried on to their destinations afterwards, the department said.
