Postaccident Inspection Of The Aircraft Revealed A Missing Cooling System Expansion Tank Cap And A Low Coolant Level

Location: Geyserville, California Accident Number: WPR25LA095
Date & Time: February 17, 2025, 12:20 Local Registration: N14QK
Aircraft: Quicksilver Aeronautics LLC L-S2S Aircraft Damage: Substantial
Defining Event: Loss of engine power (total) Injuries: 2 None
Flight Conducted Under: Part 91: General aviation - Personal

Analysis:: During cruise flight, the pilot reported that he noticed a temperature alarm, and a short time later, the engine sustained a complete loss of power. The pilot initiated a forced landing to a dirt road located in a vineyard. During the landing roll, the airplane veered to the right and struck a pole, which resulted in substantial damage to the right wing. A postaccident inspection of the aircraft revealed a missing cooling system expansion tank cap and a low coolant level. The piston faces also showed high heat signatures from red discoloration and scoring along the cylinder walls. The pilot reported that he removed the cooling system tank cap during the preflight inspection to check the water level and did not resecure it. During the flight, the engine likely lost cooling fluid and overheated, which resulted in a complete loss of engine power.

Probable Cause and Findings: The National Transportation Safety Board determines the probable cause(s) of this accident to be -- The pilot’s failure to secure the coolant cap during the preflight inspection, which resulted in a total loss of engine power due to overheating and a subsequent forced landing.

FMI: www.ntsb.gov