What happened
On November 5, 2005, a Schleicher ASK-13 glider, registration PH-405, departed from Hilversum aerodrome for a local flight. The crew consisted of a pilot and a passenger, who was an instructor in training. During the initial tow, the pilot noted that the low position of the sun necessitated using one hand to shield his eyes to maintain visibility of the tow plane and the airfield obstacles.
After releasing from the tow approximately 2 kilometers southeast of the field, the flight proceeded through a series of maneuvers. At the request of the passenger, the pilot decided to perform a slip landing. During the approach, the pilot initiated a slip with the right wing down. To increase the effectiveness of the maneuver, the pilot fully opened the airbrakes at an altitude of approximately 100 meters. However, the low sun continued to shine directly into the pilot's eyes, significantly hindering his ability to accurately judge altitude and descent rate.
As the aircraft approached the tree line at a high rate of descent, the passenger noted the danger but was unable to intervene immediately as his hands were not on the controls. The pilot eventually closed the airbrakes and ended the slip, but the aircraft struck the ground with a high forward speed of approximately 90 km/h. The impact occurred in a shallow depression in the field, resulting in a heavy landing.
The investigation
The investigation focused on the pilot's decision-making and the environmental factors present during the approach. Investigators reviewed the pilot's statements regarding the visibility issues and the execution of the slip maneuver. The investigation also noted that the airfield's ground services had attempted to contact the aircraft via radio but were unsuccessful, likely due to the onboard radio volume being set too low.
Findings
- The primary cause of the accident was a pilot error in judgment regarding the decision to perform a complex slip landing during periods of poor visibility caused by the low sun.
- The hard landing was directly caused by the pilot terminating the slip maneuver too late, leading to an excessive descent rate.
- The low angle of the sun hindered the pilot's ability to accurately estimate altitude and descent speed.
- The structural integrity of the PH-405 was compromised, with broken tubes in the cockpit framework and damage to the landing gear.
Safety action
- The investigation noted that the airfield's ground services had already planned to change the landing runway due to the poor visibility conditions experienced by other pilots.