Three Mayday calls, 20 diversions to other airports and two packed Cathay Pacific and Dragonair passenger jets with more than 600 passengers and crew on board on a collision course: Were the extraordinary sequence events of Sept 18 in the skies around Hong Kong a freakish one-off or symptoms of deeper-rooted problems, asks Simon Parry.
It was a day when, with hindsight, anyone would have wanted to keep their feet firmly on the ground. For four nerve-jangling hours on Sept 18, a combination of treacherous weather and congested airspace set off a series of unprecedented events that made the sky a potentially dangerous place to be.
At the same time, five times below the planes that circled Hong Kong on that gloomy Sunday, one of the most stressful places on earth must have been the tower at Chek Lap Kok airport where air traffic controllers struggled under tremendous pressure to bring order to the chaotic events above them.
From 10 am until 2 pm, as a growing backlog of planescircled waiting to land in Hong Kong, three Cathay Pacific planes made requests for emergency landings as they began to run dangerously low on fuel, and around 20 planes from different carriers were diverted to airports in Macao, Chinese mainland and Taiwan.
Then, most dramatically of all, at around 1.13 pm, Traffic Collision Avoidance System (TCAS) cockpit alarms sounded on a Cathay Pacific Boeing 777 300-ER flying in from New York and a Dragonair Airbus A330 flying from Taiwan as they found themselves on a collision course.
Hurtling towards each other with a combined total of more than 600 passengers and crew, the planes were within 2,000 metres with the cockpit crew able to see each other when the Dragonair plane steered upwards and the Cathay plane dived to put a safe distance between them.
Even then, the drama was not over, according to reliable air traffic control sources who say the Dragonair flight was forced to change course for a second time to avoid another aircraft - also believed to be a Cathay Pacific flight - although an airline spokesman said later the planes involved in the second incident were never close enough trigger cockpit alarms.
The events in the skies around Hong Kong on September 18 are already the subject of an investigation by the Civil Aviation Department. But they have reopened a ferocious debate within Air Traffic Control (ATC) as to whether the manpower levels are adequate.
In May, a China Daily investigation revealed how some air traffic controllers were concerned about growing traffic volumes staffing levels and a stretched manpower along with a build-up of untaken leave that had seen some controllers accumulate more than 180 unclaimed days off.
Speaking to the newspaper on condition of anonymity, some air traffic controllers said fatigue was leading to an increase in mistakes by weary controllers and they warned flight safety was being compromised. "We need at least 10 or 15 more controllers to cope," one of them said, claiming many young controllers were "demoralized, unmotivated and numbed into submission".
The concerns culminated in a tense exchange of letters between the Civil Aviation Department and the Hong Kong Air Traffic Control Association, which represents 30 per cent of controllers, in which the association complained about fatigue and manpower levels.
Despite air traffic movements in Hong Kong rising this year to record levels of nearly 1,000 incoming and outgoing flights a day, CAD Director General Norman Lo claimed staffing levels have kept pace, insisting: "I am sure there is sufficient manpower."
Now - following the drama of Sept 18 - the arguments have resurfaced with worried air traffic controllers again contacting the China Daily to say they need more staff and that the events of that Sunday may only be a foretaste of something worse to come.
"The controllers involved are still a bit shell-shocked about how fast everything developed and how close we came to the worst possible scenario that day," said one controller, again speaking on condition of anonymity. "They feel frustration towards management."
For their part, the airlines involved in the drama and the CAD have issued jarring statements in which the CAD appears to blame the pilots for failing to respond to initial air traffic control instructions while Cathay Pacific and Dragonair insist cockpit crew responded correctly.
Confirming the loss of separation - the technical term for a near-miss - between the incoming Cathay Pacific flight from New York and the Dragonair flight from Kaohsiung, a spokeswoman for both airlines insisted: "There was no risk of collision and at no time was the safety of the flights compromised.
"At the closest, they were one nautical mile (2,000 meters) apart when abeam from each other with increasing vertical separation. Both aircraft's TCAS equipment generated appropriate alerts and the pilots took immediate action to maintain adequate separation."
The two flights had been put in a holding pattern around 40 nautical miles southwest of Chek Lap Kok at the time of the incident and the planes were "restricted to narrow tracks to avoid bad weather when descending from the holding area to land in (Hong Kong)", the spokeswoman said.
A CAD statement, however, focussing on the actions of the air traffic controller involved in the specific incident involving the Cathay Pacific Boeing and the Dragonair Airbus, said: "The A330 was holding at (position) FL220 together with five other aircraft at respective lower levels when the B777 was inbound to the same area for holding.
"The crew of the B777 reported having only 10 minutes holding fuel, a same company aircraft then offered to swap its landing slot.
"While attempting to rearrange the holding sequence, the controller detected the conflict of the A330 and B777 aircraft at the same level and immediately instructed both aircraft to turn when they were about 8.5 nautical miles apart and both crews of the A330 and the B777 were in visual contact with each other."
The statement continued: "The A330 crew did not accept the turn instruction.The controller then instructed the B777 to climb to a higher level for vertical separation but with no response from the crew.
"About 17 seconds later, the A330 reported 'TCAS climb' and the B777 reported 'TCAS descent'. They passed at 1 nautical mile (2 km) in diverging turns and increasing in vertical separation. The standard separation applicable is 5 nautical miles or 1,000 feet.
"The avoiding actions were executed in a controlled manner and as both pilots had the other aircraft in sight well in advance, there was no risk of collision."
It added: "The controller took appropriate corrective actions to ensure safe operations well before the separation was reduced to below the standard and in accordance with the laid down procedures.
"All actions by the controller were conducted in a calm and timely manner throughout the occurrence."
Responding to the claim that the pilots did not respond to the initial ATC directions, the airlines' spokeswoman said: "Both Cathay Pacific and Dragonair pilots took appropriate actions under the circumstances to re-establish standard separation between the two aircraft."
Giving an insight into the extent of the chaos on Sept 18, the airlines' spokeswoman confirmed that eight other Cathay Pacific planes had diverted to Taipei, Kaohsiung, Macau and Guangzhou, creating delays in arriving at Chek Lap Kok of two to three hours.
"In addition, two freighter services and a passenger flight from London CX256 also made a fuel emergency request for priority landing while at requested holding position," she added. "One freighter diverted to Macau, while the other two flights landed in Hong Kong. All landed without incident with sufficient spare fuel ranging from 30-50 minutes of flight."
The CAD in a detailed statement was categorical in dismissing suggestions that the events of September 18 raised questions about manpower and fatigue among controllers.
"The controller had three work shifts in the preceding seven days and had just returned from a day off," the statement said. "After finishing a one-hour break, the controller had worked for about 10 minutes before the occurrence. Therefore, fatigue or tiredness were not likely to be contributory".
The statement added: "On a normal day, there are typically eight controller working positions for the Approach Control Sectors. In anticipation of the difficult traffic due to bad weather, there was one additional working position opened up - a total of nine - on Sept 18, and 13 controllers were provided to man the 9 positions in managing the air traffic.
"The staffing provision was considered sufficient to meet the traffic level. Over the past five years, more than 40 new rated controllers have been added to the system, representing more than 25 percent increase in controller strength. The healthy staffing situation has been thoroughly discussed and shared with the controllers association in May."
However, the assurances from the CAD have been dismissed by some air traffic controllers who contacted the China Daily, one of whom described said colleagues on duty on September 18 viewed what happened as "a near collapse of an ATC system".
The controller said: "Although the weather was a contributing factor, the whole situation illustrated there was no contingency plan, no back up and supervisors responsible for a general overview of traffic werecovering traffic positions. Once again the staffing situation is glaringly obvious.
"Anyone who sees the radar recordings and listening to the tapes will see just how chaotic a situation it was. The controller involved got swamped.
"She should not be made responsible for a systematic failure. Perhaps an investigation by the Cathay or Dragon pilots union would result in a more balanced finding."
The controller said it was "very lucky indeed" that the two aircraft involved in the loss of separation had each other in sight and said there could have been a "very different result" if visibility had been poorer.
"It's all very well to say the controller involved had just had a day off but when was the last time the controller had a significant two or three week break away from work?" the controller asked.
"The CAD says there was sufficient staffing that day but no mention is made of three supervisors having to cover operational positions due to the traffic and thereby missing the overall position and the continuing inbound traffic."
Another air traffic controller said it was "absolute rubbish" to say that the staffing situation was healthy, pointing out that staff were being taken off regular duty to prepare for the opening of the new Air Traffic Control centre due to open at Chek Lap Kok next year.
"We are operationally understaffed as too many experienced controllers have been attached to the project team for the new center."
If the dispute that erupted in May can be taken as a guide, Norman Lo and his fellow executives can be expected to contest the claims of the air traffic controllers who voiced their concerns to theChina Daily.
CAD leaders have made it clear they see the alarmist talk as the grumblings of a minority who overestimate the difficulties of an admittedly tight but manageable manpower situation affecting all Hong Kong government departments.
For the air traffic controllers involved, however, the situation has become deeply disturbing and the events of Sept 18 have only reinforced their fears. "The alarm bells are getting louder and management can't afford to keep closing their ears to them," one of them said.