What happened
On April 24, 2003, at approximately 18:00 UTC, a PZL SWDNIK PW-5 glider, registration CS-PBN, was engaged in a recreational soaring flight near Covilhã, Portugal. While flying over a forested slope in the eastern Serra da Estrela region, the pilot attempted to execute a turn to the north to better utilize available rising air currents. During this maneuver, the aircraft encountered a sudden downdraft, leading to a rapid loss of altitude.
In an attempt to avoid terrain, the pilot reduced the angle of attack and turned the aircraft toward the east, heading for the Covilhã valley. However, the descent continued until the glider struck the treetops. Following the impact, the aircraft spun approximately 120 degrees and slid 30 meters down the slope before coming to a halt near a clearing. The pilot sustained light injuries, specifically a minor abrasion to the right eyebrow, and was able to exit the aircraft unassisted.
The investigation
The GPIAAF investigation focused on the atmospheric conditions and the pilot's maneuvers during the flight. Investigators established that the area was experiencing intense orographic, thermal, and wave activity, characterized by strong updrafts interrupted by sudden downdrafts. A mountain wave had established itself to the north of the site, with winds blowing from the northwest at 10 to 15 knots.
Technical analysis revealed that as the pilot turned north to position the glider against the wind, the combination of the turn and a tailwind component likely pushed the aircraft away from the mountain range and toward the Covilhã valley. In this specific area, the strong northwest winds were generating significant downdrafts. The investigation confirmed that the pilot recognized the rapid loss of altitude and attempted to maneuver toward the valley to maintain clearance from obstacles, but was unable to prevent the collision.
Findings
- The primary cause of the accident was the inability of the pilot to maintain altitude control while navigating intense orographic activity.
- The presence of a mountain wave to the north created highly unstable air characterized by sudden, sharp downdrafts.
- The aircraft's flight path during the turn placed it in a zone of descending air near the valley edge.