What happened
On December 2, 1998, a Cessna 152 was conducting a private round-trip flight from Finow to Flensburg and back. During the return leg, the aircraft's flight path became erratic north of Krakower See, deviating significantly from its intended course. By 16:08, the aircraft was observed circling near Blankenförde.
At 16:37, the pilot contacted Finow via radio with a distressed message, stating that the windshield had shattered, the cockpit was fogging up, and all instruments, including the GPS, were obscured. The pilot reported that they could no longer see anything and were unsure of their position. Shortly after a final, unanswered radio attempt, the aircraft collided with trees in a forested area near Großzerlang. Both occupants sustained fatal injuries.
The investigation
The BFU examined the wreckage, including fragments of the aircraft's windshield. Laboratory analysis of the Plexiglas (PMMA) pieces revealed that the thicker fragments, likely from the windshield, exhibited significantly lower viscosity than the thinner side or rear window fragments. Microscopic examination showed macro- and micro-cracks in the windshield frame area that existed prior to the accident.
Investigators also analyzed a spray cleaner concentrate used by the operator to clean the windows. The study found that this cleaner acted as a stress-cracking agent. Additionally, the investigation noted that the windshield thickness was inconsistent with manufacturer specifications. Meteorological data confirmed that the flight occurred in deteriorating conditions, with low visibility (2–4 km) and low cloud ceilings (as low as 400 ft AGL) during the onset of darkness.
Findings
- The pilot continued the flight into increasing darkness despite encountering very low visibility and low cloud ceilings.
- The pilot had very limited experience in night VFR operations.
- The sudden failure of the windshield was a significant contributing factor.
- The use of a specific spray cleaner concentrate likely promoted stress-cracking in the windshield.
- Pre-existing cracks were visible in the windshield frame, which could have been detected through a visual inspection.