What happened
On 7 March 2006, a Boeing 737-76N, registration G-STRH, was operating a passenger flight from Manchester to Banjul, Gambia, via Bristol. While establishing on the ILS approach for Runway 09 at Bristol International Airport, the flight crew initiated a visual orbit to reduce their altitude. The aircraft was being manually flown by the first officer, who had deactivated the flight director commands.
During this maneuver, a powerful southerly wind caused the aircraft to roll out with significant localiser deflection, positioning it north of the ILS centerline. The aircraft descended to 1,500 feet, which was approximately 800 feet below the glidepath and below the minimum radar vectoring altitude. As the aircraft approached the runway threshold at 3 nm, the tower controller observed the aircraft was not re-establishing on the localiser and instructed a go-around. The crew executed the maneuver, and the aircraft subsequently landed safely following a further radar-vectored approach.
The investigation
An investigation by the AAIB utilized data from the aircraft's Quick Access Recorder to reconstruct the flight path. The investigation examined the impact of meteorological conditions, noting that while the airfield reported visibility in light rain, the area where the orbit occurred was subject to much stronger winds, estimated at 35-40 knots from 190 degrees.
Investigators also reviewed air traffic control procedures and company manuals. It was noted that while the crew was in visual contact with the ground, the tower controller's decision to limit the aircraft's descent to 1,500 feet was intended to maintain safety, though the aircraft's progress toward the localiser was insufficient to avoid the go-around instruction.
Findings
- The flight crew's decision to use a visual orbit to lose height, rather than accepting radar vectors, contributed to the difficulty in re-establishing the approach.
- The first officer's decision to fly without flight director assistance removed critical vertical and lateral steering guidance, making the aircraft more susceptible to wind drift.
- A strong southerly crosswind caused the aircraft to drift north of the localiser centerline.
- The aircraft descended below the minimum radar vectoring altitude and the ILS glidepath.
- The crew's awareness of the wind conditions during the orbit was insufficient to prevent the deviation.