On September 5, 1995, a Let L-23 SUPER BLANIK (registration N99970) was involved in an aviation accident near White Bear Lake, MN. Investigators recorded the probable cause as: The pilot's failure to ensure the spoilers were fully retracted, which resulted in an excessive loss of altitude during the final approach. This summary draws on records from the U.S. National Transportation Safety Board (NTSB) historical archive.
A glider pilot experienced unexpected altitude loss on final approach, striking a power line with the landing gear before descending onto a road. No pre-impact mechanical malfunction was found.
What happened
The pilot reported that while on final approach for landing, the aircraft experienced a rapid and unexpected loss of altitude. During this descent, the landing gear made contact with a power line, causing the wire to break. Despite the impact, the glider continued its trajectory and eventually descended onto a nearby road.
The investigation
A thorough examination of the accident site and the aircraft was conducted to determine the cause of the incident. Investigators found no evidence of any pre-impact mechanical malfunction or failure within the aircraft systems that could account for the altitude loss.
Findings
The pilot later provided a written statement questioning whether the spoilers had been fully retracted before landing. This uncertainty suggests that inadvertent spoiler deployment may have contributed to the excessive sink rate and subsequent altitude loss during the final phase of flight.
Probable cause
The pilot's failure to ensure the spoilers were fully retracted, which resulted in an excessive loss of altitude during the final approach.