History of the Flight
The aircraft, a Boeing 737-76N registered G-STRH, was operating a public transport flight from Manchester to Banjul with a stop at Bristol Airport. On 7 March 2006 at 0945 UTC, the crew was vectored onto the ILS localiser for Runway 09 at Bristol. After being cleared to descend to 2,500 ft, the first officer, who was the handling pilot, requested an orbit to lose height while the aircraft was level at 2,800 ft, approximately 500 ft above the glidepath and 5 nm from the runway. The crew was cleared for the orbit, and the commander declined a controller's offer of radar vectors.
The first officer commenced a right descending turn and switched off the flight director because it was providing steering information toward the localiser. During the orbit, a strong southerly wind caused the aircraft to roll out north of the localiser centreline with full deflection. At that point, the aircraft was about 600 ft below the glidepath and below the minimum radar vectoring altitude, though the crew was visual with the ground. The tower controller instructed the aircraft to maintain 1,500 ft until established back on the ILS. When the range to the runway reached 3 nm and the aircraft had not re-established on the localiser, the tower controller instructed a go-around. The crew had been on the verge of initiating the go-around themselves. A subsequent radar-vectored ILS approach was flown without incident.
Flight Recorders
The Quick Access Recorder (QAR) provided data from the initial approach to landing. The Cockpit Voice Recorder recordings were overwritten due to late notification.
Meteorology
Met Office data indicated a south-westerly flow. Bristol Airport reported surface wind 130° at 16 kt, visibility 8,000 metres in light rain, scattered cloud at 700 ft, and broken cloud at 1,200 ft. The airfield is at about 600 ft elevation. The aftercast estimated wind at 2,000 ft from 190° at 35-40 kt. The crew reported good VMC during the orbit and were visual with the ground.
Air Traffic Control
The aircraft was in communication with Bristol Tower, but control remained with Bristol Radar. Both controllers approved the orbit, but the requirement to maintain 2,500 ft while orbiting was overlooked. The tower controller eventually limited the descent to 1,500 ft.
Discussion
According to the AAIB, the flight crew allowed the aircraft to descend significantly below the ILS glidepath, minimum sector altitude, and minimum radar vectoring altitude. This situation developed after arriving at the final approach fix approximately 500 ft above the glidepath. The orbit was considered a pragmatic option to lose height, but the strong crosswind was not adequately considered. Deselecting the flight director removed vertical steering information. The MCP altitude window remained set at 2,500 ft while the aircraft descended to and maintained 1,500 ft. The orbit resulted in a rollout with full localiser deflection, making re-establishment difficult and leading to the go-around.
Follow-up Action
The operating company reiterated requirements for visual approaches and issued a flight crew notice prohibiting orbits on or during final approach to self-position on the ILS. Bristol Air Traffic Services noted that orbits are permitted but not considered best practice.