CNN) -- An investigation is under way into a previously unrevealed incident last week in which two jetliners nearly collided over Hong Kong, aviation authorities said Tuesday.The September 18 incident reportedly did not come to light publicly until an article revealing it was published Tuesday in the English-language newspaper The Standard of Hong Kong.
The two jets, carrying more than 600 passengers and crew members, came within seconds of colliding, the newspaper reported, citing a former Hong Kong aviation official.
According to a statement issued by Hong Kong's Civil Aviation Department, a Cathay Pacific Airways flight that was bound for Hong Kong International Airport came within 1 nautical mile (2 km) of a Dragonair A330 airplane that was in a holding pattern for landing.
The international standard for separation between aircraft is 5 nautical miles (9.26 kilometers) horizontally or 1,000 feet (304) meters vertically), the department said.
The incident happened during a stormy afternoon when aircraft were stacked up for landing over Hong Kong, the department said. An air traffic controller was trying to shuffle waiting aircraft around so that the Cathay Pacific flight, which was low on fuel, could land more quickly. That's when controllers noticed the flights were too close.
The pilots of both aircraft failed to respond to commands to change course at one point or another during the incident, the department said. Collision avoidance systems on both aircraft activated after the crew of the Cathay Pacific flight failed to respond to a command to climb to a higher altitude.
Cathay Pacific said in a statement that "both Cathay Pacific and Dragonair pilots had taken appropriate actions under the circumstances to re-establish standard separation between the two aircraft."
The pilots could see each other's planes during the incident and there was no risk of collision, the department and Cathay Pacific said.
But The Standard quoted Hong Kong's former civil aviation chief Albert Lam Kwong-yu as saying that, based on normal speeds of the airliners involved, they were about six seconds from colliding.
"The chance of a crash is absolutely high," the paper quoted Lam as saying. "The passengers really came back from hell."
The flights involved were Cathay 841 from New York to Hong Kong, and Dragonair 433 from Kaoshiung, Taiwan, to Hong Kong. The Cathay jet had 317 people aboard and the Dragonair jet had 296 aboard, according to aviation officials.
Investigators have ruled out air traffic controller fatigue as a cause of the near-collision, the department said. The air controller in charge of the flights was appropriately rested and has since returned to work, the agency said.
Investigators will examine air traffic procedures, staffing levels and flight crew operations, the department said.
Hong Kong has been the site of four other near-collision incidents in the last 11 years.
-- In September 2010, a Cathay Pacific plane taking off for London after midnight had to deviate from the runway center line at high speed because the tail of another plane was too close to its path.
-- In July 2006, a Dragonair Airbus and a Northwest Airlines Boeing -- both heading for Tokyo -- were reported to be just 100 meters apart vertically while 80 nautical miles east of the Hong Kong airport.
-- In September 2004, a China Southern Airlines plane leaving Hong Kong and an incoming Malaysia Airlines cargo plane came within 304 meters of each other 55 nautical miles south of the airport.
-- In June 2001, a Dragonair Airbus to Shanghai and a Cathay Pacific flight arriving from Seoul were reported 210 meters apart 110 nautical miles east of Hong Kong.
