What happened
During a night approach to runway 01 under instrument meteorological conditions, the flightcrew was executing an ILS approach amidst drizzle and a wet runway surface. Wind conditions were reported as 110 degrees at 14 knots, with gusts up to 18 knots. The crew had established an approach speed (Vapp) of 128 knots and a landing speed (Vref) of 122 knots.
Flight data indicates the aircraft was initially flying via autopilot as it passed the middle marker at 200 feet AGL. Shortly after the first officer identified the runway, the captain disconnected the autopilot at a radio altitude of 132 feet. Following this disconnection, the aircraft experienced increasing glideslope and localizer deviations. Approximately five seconds before the aircraft reached the ground, it underwent a series of lateral rolls. The Saab aircraft crossed the runway threshold at 130 knots and 35 feet altitude.
The aircraft touched down 2,802 feet from the approach end of the 5,495-foot runway. The landing roll continued for 2,693 feet, during which the aircraft failed to stop before the pavement ended. The aircraft subsequently exited the runway and struck a drainage ditch located 175 feet beyond the departure end of the runway. There were no fatalities or injuries reported in the accident.
Findings
Investigation of the site revealed that the runway safety area (RSA) was inadequate, as a previous proposal to extend the runway had been approved despite concerns regarding the reduction of the RSA. A drainage ditch had been installed in this area. While the aircraft's performance was analyzed, calculations suggested that on a wet runway, the aircraft required 1,989 feet from the moment braking was initiated to reach a full stop. The disconnection of the autopilot during the final stages of the approach contributed to the loss of stabilized flight parameters. Post-accident inspections of the ILS equipment confirmed all components were functioning correctly, and no mechanical failures were found on the aircraft that would have prevented normal operation.