What happened
On September 13, 2016, at 14:20 UTC, a D7 Straton Mini TR1 ultralight aircraft, registration OK-BUO 01, crashed into a forested area near the village of Choce and Dvořisko, Czech Republic. The pilot had spent the day performing maintenance on the aircraft, including work on the cockpit and wingtips. After engine start, the pilot taxied to runway 15 at LKCO and took off into the wind.
Following takeoff, the aircraft climbed slightly but maintained an unusually low altitude. While flying southeast toward the Babka hill, the aircraft encountered trees. The right wing struck the treetops, causing the aircraft to roll approximately 200 degrees and plunge into the ground. The impact destroyed the aircraft. Despite resuscitation efforts by emergency medical personnel, the pilot was pronounced dead at the scene.
The investigation
The ÚZPLN investigation focused on the aircraft's technical condition and the pilot's flight profile. Investigators examined the wreckage and found that while the engine was functional until the moment of impact, the airspeed indicator was completely inoperative. Detailed testing revealed that seven of the eight screws securing the instrument's glass frame had become loose, likely due to recent maintenance work performed by the pilot. This mechanical failure rendered the instrument unable to provide accurate readings.
Furthermore, the investigation looked into the pilot's medical status. While the pilot held a valid license, it was discovered that he had failed to disclose the use of prescribed antidepressants to his medical examiner, meaning he was flying without valid medical certification.
Findings
- The primary cause of the accident was the gradual loss of control over the aircraft due to a non-functional airspeed indicator while flying at low altitude through unstable air near an obstacle.
- The pilot was flying at an unusually low altitude and failed to utilize an available field for an emergency landing.
- The aircraft encountered turbulent airflow caused by the terrain and trees, which the pilot could not manage without accurate airspeed information.
- The airspeed indicator was non-functional due to improper handling during recent maintenance.
- The pilot was flying without valid medical certification because he had not disclosed his use of medication to his AME.