What happened
On 18 June 2021, a Boeing 737-436, registration G-POWS, was performing a cargo flight at London Southend Airport. After landing, the crew was instructed by Air Traffic Control to taxi via Taxiways A and Z to hold short of Runway 05. The route was unfamiliar to the commander.
While executing a 90-degree turn from Taxiway Z onto Taxiway B, the right main landing gear left the paved surface. The commander, attempting to prevent the aircraft from becoming stuck in the soft ground, applied a high power setting of approximately 86% N1. However, the aircraft lost momentum and came to a stop on the grass. The excursion resulted in damage to the stalks and couplings of two taxiway edge lights and some cable ducting.
The investigation
The AAIB investigation examined several factors, including the accuracy of ground charts and the crew's perception of the taxiway width. The investigation also looked into the operator's handling of the cockpit voice recorder (CVR) following the event. It was found that the operator had accessed the CVR despite the existence of a state safety investigation, which is prohibited under international and UK regulations. Additionally, the investigation found that the operator's communications to the crew had incorrectly implied they were acting on behalf of the AAIB.
Findings
- The primary cause was the crew's incorrect belief that they were turning onto a wider taxiway.
- Inaccurate ground charts and a misleading company briefing sheet contributed to the error.
- Visual illusions, potentially caused by the contrasting colors of the taxiway surfaces, influenced the pilots' perception of the pavement width.
- The crew's unfamiliarity with the specific taxi routing played a role in the excursion.
- The use of high engine thrust during the excursion posed a potential risk of jet blast to nearby personnel or equipment.