The Australian Transport Safety Bureau (ATSB) has released its final report into a loss of separation incident at Sydney Airport in January. Two aircraft saw their separation reduced to 60 meters and 1.3 horizontal nautical miles. It was close enough for the ATSB to classify the incident as serious and open an investigation.
United Airlines Boeing 777 gets close to a Virgin Australia ATR
The incident occurred on January 22 and was reported in Simple Flying. A United Airlines Boeing 777-300 was departing for San Francisco, operating a scheduled service. Inbound was a Virgin Australia ATR 72 from Tamworth, a regional city in New South Wales.
According to the ATSB report, the United Airlines flight was taking off from runway 34L. The aircraft was to stay on runway heading (335º) until reaching 1,500 ft. At this point, it was to turn left and track left towards Richmond on Sydney’s metropolitan fringes.
But the United Airlines flight stayed on its initial heading until it reached 2,120 feet. At this point, the aircraft turned right about 45º from the required heading, and the loss of separation incident occurred.
Sydney ATC detected the loss of separation and issued instructions to increase separation. Both flights continued without incident.
The ATSB report indicates that when the incident occurred, the Boeing 777 and ATR 72 had a vertical separation of 60 meters and a lateral separation of 1,843 meters (about 1.0 nautical miles). At the time, early afternoon, weather conditions in and around Sydney were excellent.
ATSB zeros in on United pilots
There were four pilots on the United Airlines flight, a captain and three first officers. During take-off, all were in the cockpit, with two of the first officers in observer seats. The captain was familiar with Sydney Airport and its take-off procedures.
The ATSB investigation found the United Airlines captain configured the flight management computer for a standard instrument departure based on expectations from prior experience. The configuring followed receipt of ATIS but before receiving their pre-departure clearance.
When Sydney ATC did provide pre-departure clearance, the information differed from the pilot’s previous experience. The message to United’s pilots from ATC was;
“United eight seventy (UA870), delivery, cleared to San Francisco via DIPSO, flight planned route, runway three-four left (34L), Richmond five departure, radar transition, climb via SID to five thousand (5,000)…”
The first officer read back the clearance information, omitting the radar transition component.
The United Airlines crew then checked the Richmond five standard instrument departure (SID) chart. It stated;
“Parallel runway operations – DO NOT TURN RIGHT. Track 335⁰. At 1500 [ft] turn LEFT, track direct RIC NDB [Richmond], then follow transition instruction.”
In addition to commercial traffic in the area, there is a large air force base at Richmond and substantial air force traffic.
Miscommunication a key factor
The United captain then re-programmed the flight management computer, replacing the SYD1 procedure with the RIC5. The pilot was unsure about the specific coding for two transition options (radar or Richmond) provided by the flight management computer.
The radar transition option in the flight management computer included what the ATSB termed “a deliberate discontinuity (gap) in the waypoint sequence (coding).”
The captain removed the discontinuity, effectively canceling the pre-programmed radar transition procedure. The captain said he reported removing the discontinuity to the first pilot, but there was no acknowledgment.
As the United Airlines flight was climbing through 2,120 feet, Sydney ATC saw the plane was turning right and issued instructions to turn left. At this point, the Virgin Australia aircraft was sighted visually and also via the traffic alert and collision avoidance system.
What the final ATSB report found
Yesterday’s report by the ATSB found the contributing factors were;
- The United Airlines pilot flying incorrectly amended the flight management computer for the cleared departure; and
- The amended flight management computer setup was probably not effectively communicated to the crew or effectively cross-checked by the pilot monitoring or relief pilots.
The report also found;
- The United Airlines pilot monitoring did not complete a full readback of the radar transition component of the pre-departure clearance, nor did the Sydney clearance delivery controller insist on a full readback; and
- The Sydney departures controller observed the United Airlines aircraft turning right and towards the Virgin Australia plane and quickly issued unambiguous and immediate instructions to both aircraft to rectify the situation and re-establish the required separation.