What happened
On February 10, 1999, an Israel Aircraft Industries ASTRA operating a commercial passenger flight from Granada, Spain, to Braunschweig, Germany, veered off the runway during its landing roll. After touching down on runway 26, the aircraft utilized reverse thrust until approximately 80 knots. However, the crew experienced unexpectedly low braking effectiveness from the wheel brakes. As the aircraft reached the end of the runway, its speed remained too high, causing it to slide laterally off the pavement and onto taxiway "CHARLIE." The aircraft came to a stop on soft ground, causing a runway edge light to be destroyed. All 9 occupants, including 2 crew members and 7 passengers, were uninjured, and no damage to the aircraft was found.
The investigation
The BFU investigation examined the runway conditions, radar data, and pilot reports. While the pilots initially reported the approach as normal and the runway as "dry," radar analysis and subsequent inspections revealed that light snowfall had begun approximately 20 minutes before the incident, significantly degrading the surface. Investigation of the runway surface showed that the western portion of the runway and the taxiway were covered in 1–2 cm of snow.
Investigators also reviewed the responsibilities of the airport's air traffic controllers and airfield supervisory staff. While a vehicle equipped with a Tapley meter had recently measured "good" braking action, the BFU noted that this method is outdated and failed to capture the localized degradation caused by the recent snowfall. Furthermore, the investigation noted a discrepancy between the PAPI (Precision Approach Path Indicator) placement and the recessed runway threshold, which could potentially lead to unsafe approach profiles.
Findings
- The primary cause of the excursion was the accumulation of snow on the western portion of runway 26 and the subsequent slippery condition of taxiway "CHARLIE."
- A contributing factor was the aircraft's excessive speed at the end of the runway, resulting from reduced braking effectiveness due to the runway surface condition.
- A contributing factor was the inaccurate assessment of the runway condition by airfield supervision and air traffic controllers, which led to a delay in necessary snow removal operations.