Created Friday, Jan 6th 2023 18:14Z, last updated Wednesday, Jul 19th 2023 18:05Z
A Srilankan Airlines Airbus A320-200, registration 4R-ABN performing flight
UL-707 from Colombo (Sri Lanka) to Seychelles (Seychelles), landed on Seychelles's runway 31 at 05:10L (01:10Z), but drifted to the right hand side and went around. The aircraft landed on runway 31 about 15 minutes after the balked landing.
Sri Lanka's AIB rated the occurrence an incident and opened an investigation stating the aircraft had drifted to the right hand side of the runway and rating the occurrence a runway excursion.
On Jul 19th 2023 the AIB released their final report concluding the probable causes of the occurrence rated an incident were:
Before touchdown, a commanded right roll angle maintained for ~21s led to a deviation of the aircraft toward the right of the runway centerline.
The pitch-up order applied by the flight crew at ~110ft RA led the aircraft to float above the runway at ~50ft RA and thus exposed the aircraft to the lateral wind. The left crosswind component contributed to increase the deviation of the aircraft to the right of the runway centerline.
On ground, in spite of a leftward rudder pedal application, the aircraft skidded toward the right of the runway. This tendency to skid was a consequence of the aircraft dynamics (right roll + crosswind) and the reported weather conditions that led to a wet runway.
Additional contributors which may have perturbed approach and landing were:
- After a go-around, second approach was performed during the night with gusty wind conditions.
- Runway was most probably wet, as “rainy conditions” was reported in incident statement of the PIC and confirmed by METAR (heavy rain showers).
The AIB analysed amongst other details:
After touchdown the leftward rudder pedal orders, applied prior to touchdown, continued to be applied up to full deflection leading the heading to decrease to 301° and the drift angle to increase up to +7.5°.
In spite of this leftward rudder pedal application, the localizer deviation reached around -4/5DOT to the right of the localizer before starting to decrease: the aircraft skidded toward the right of the runway.
At maximal lateral deviation, the LOC antenna was ~0.5m on the runway shoulder, and with the high left drift angle (+7.5°) the right main landing gear was ~6m on the shoulder.
During the lateral runway deviation, MAX REV thrust was applied by the flight crew for ~17s.
As recommended in the following FCTM extract, in case of lateral control problem, the flight crew should consider to set the reverse thrust to REV IDLE instead of MAX REV, as the reversers have a destabilizing effect on the airflow around the rudder and thus decrease the efficiency of the rudder. Furthermore they create a side force, in case of a remaining crab angle, which increases the lateral skidding tendency of the aircraft.
Due to the leftward rudder application, the lateral deviation started to reduce: the aircraft stopped skidding toward the right of the runway.
Around 01:24:02 UTC, the runway was recovered around 1300m after a threshold at a ground speed of ~109kt.
Then the aircraft progressively re-aligned with the runway heading (310°).
After the incident, the aircraft stopped on the runway approx. 6 minutes and the flight crew had waited for aircraft inspection/runway inspection.
