Incident Overview
On 6 December 2007, an Airbus A319 aircraft, registration 9V-SBE, departed from Singapore Changi Airport bound for Yangon, Myanmar. The aircraft was initially cleared to climb to 6,000 ft and turn left to 090 degrees. About two minutes later, the crew requested a heading of 050 degrees to avoid weather. The approach controller initially did not approve but shortly after, at 1515:13 hrs, cleared the A319 to turn onto the requested heading and climb to 10,000 ft. At approximately 1515:50 hrs, while climbing through 8,500 ft, the A319 came within 0.67 NM horizontal separation of a Boeing 737, registration PK-GGN, which was level at 9,000 ft. The minimum required separation was either 1,000 ft vertical or 3 NM horizontal.
The B737 was approaching from the south at 11,000 ft at 1512:50 hrs. It was cleared to descend to 9,000 ft at 1514:15 hrs and instructed to turn onto a heading of 360 degrees at 1515:06 hrs. The loss of separation occurred while the B737 was in straight and level flight. Both aircraft had Traffic Advisory (TA) indications from their TCAS systems, but no Resolution Advisory (RA) was generated. The A319 crew reduced their rate of climb slightly upon seeing the B737, and the B737 crew remarked they were too close to traffic based on the TA. The B737 crew reported operating in Instrument Meteorological Conditions (IMC) and did not see the other aircraft.
Controller Actions
The approach controller, on the third day of a three-day 0800-1600 hrs shift, was managing six aircraft, considered moderate traffic, but weather made the situation complex. At 1514:10 hrs, she cleared the A319 to climb from 6,000 ft to 8,000 ft, and at 1514:15 hrs, she cleared the B737 to descend from 10,000 ft to 9,000 ft. Her plan was to expedite lateral separation by turning the A319 to 050 degrees and the B737 to 360 degrees, then climb the A319 above 8,000 ft and descend the B737 after they passed. However, at 1515:13 hrs, five seconds after turning the A319 to 050 degrees, she cleared it to climb from 8,000 ft to 10,000 ft, through the B737's altitude, while the aircraft were still converging. She could not explain why she did so. She noticed the loss of separation on radar at 1515:47 hrs and instructed the A319 to maintain 8,000 ft, but did not inform either crew of the conflict.
Weather and Conditions
The weather at the time was poor with widespread intermittent moderate to heavy rain in Singapore and the southern South China Sea. The METAR at 1500 hrs reported rain, with cloud layers at various heights. The radar display showed extensive weather in the Changi Control Zone.
Aftermath
The A319 crew did not submit a report to Singapore ATC. The B737 crew attempted to contact Changi Tower but were unsuccessful; they submitted an Air Safety Report to their airline. The approach controller verbally reported the incident to the Watch Manager at the end of her shift at 1545 hrs, but did not write an incident report or submit to a medical examination as required. She stated she was uncertain whether she had given a wrong instruction or the pilot had erred. The incident was confirmed after review of recordings.
Medical and Personnel
The approach controller, aged 39 with 12 years' experience, was medically examined after the incident and no abnormality was found. She reported feeling tired during the last hour of her shift but could not quantify her fatigue. The ATS provider had no tool to gauge controller fatigue.