Amateur-built RF5B SPERBER N66GL accident near Lookout Pass, Montana

Probable cause

The pilot’s improper decision to continue flight toward rising terrain after the engine overheated, which necessitated a precautionary landing when the motorglider could not maintain altitude in downdrafts.

NTSB analysis

The airline transport pilot reported that, during a cross-country flight and while climbing toward a mountain pass, the experimental, amateur-built motorglider's engine began to overheat. The pilot delayed the climb to allow the engine to cool down and continued toward the pass, which resulted in reduced terrain clearance. As the motorglider approached the pass, it encountered a downdraft, and the engine was unable to produce enough power to stop the descent. Due to the reduced altitude, the pilot realized that he would be unable to safely turn the glider around, so he executed a precautionary landing on a freeway. During the landing, the glider struck a freeway barrier.

The pilot reported that, other than the engine overheating, there was no evidence of any preimpact mechanical anomalies with the glider that would have precluded normal operation.

Text from the NTSB. Open the NTSB docket for WPR18LA145 for the full record.