What happened
On 12 November 1996, a Boeing 727-251, registered N-263US, was operating a scheduled cargo flight from Stockholm/Arlanda to Örebro Airport. During the approach to runway 19, the crew encountered heavy snowfall and low visibility. Although the landing itself appeared normal, the aircraft touched down approximately 250 meters beyond the standard touchdown zone, aided by a tailwind.
Following the landing, the captain utilized reverse thrust and wheel braking to decelerate. As the aircraft reached a lower speed, the captain unreversed the engines and released the brakes with the intention of taxiing to the end of the runway to perform a turnaround. However, the aircraft failed to stop within the runway limits, sliding off the end of the pavement and coming to a rest 7/6 meters into the leveled area beyond the threshold. There were no injuries to the crew, and the aircraft sustained only minor ground damage.
The investigation
The Swedish Board of Accident Investigation (SHK) examined the flight and sound recorders, as well as the runway conditions at the time of the incident. The investigation focused on the accuracy of the friction reports provided to the crew and the pilot's decision-making during the landing roll.
Investigators found that the friction values reported to the crew—which indicated "good" to "medium" braking action—were inaccurate. A test performed 21 minutes prior to landing had been conducted in a single direction and at a speed below the recommended 95 km/h, making the results less reliable. Furthermore, the investigation revealed that the computer used for the friction test had been incorrectly programmed, erroneously attributing the results to runway 01 instead of runway 19. Subsequent testing conducted after the incident confirmed that the actual friction on the runway was significantly lower than what had been communicated to the flight crew.
Findings
- The pilot touched down significantly past the intended touchdown zone.
- The captain released the brakes and engine reverse thrust too early, underestimating the aircraft's actual ground speed.
- Visual perception of the aircraft's speed may have been skewed by snowflakes moving in the same direction as the tailwind.
- The actual runway friction was lower than the reported values due to ongoing snowfall and improper testing procedures.
- There were significant deficiencies in how runway conditions and friction values were measured, reported, and maintained at the airport.
Safety action
The investigation highlighted a lack of strict regulations regarding the maintenance and calibration of friction-measuring equipment. The SHK recommended that the Swedish Civil Aviation Administration establish formal requirements for the calibration of this equipment, similar to the standards used for aircraft maintenance. Additionally, the Board suggested that the individuals performing friction tests should sign their recording slips to increase accountability and responsibility for the accuracy of the reported data.