Accident Overview
On April 17, 2021, at about 1715 eastern daylight time, a Cessna 172 airplane, registration N60457, was substantially damaged when it was involved in an accident near Venice Municipal Airport (VNC), Venice, Florida. The flight instructor and the private pilot receiving instruction were not injured. The airplane was operated by Florida Flight Training Center as an instructional flight under Title 14 Code of Federal Regulations Part 91.
Flight Sequence
According to the flight instructor, the private pilot receiving instruction had not completed a flight review since 2008. The accident flight was the second flight toward a flight review signoff. The airplane departed with full fuel and maneuvers were completed in the local area before returning to VNC for touch-and-go landings. The flight instructor demonstrated the first touch-and-go, which was uneventful. The student then took the flight controls for the second touch-and-go. While on downwind in the traffic pattern, abeam the runway numbers, the student pilot intended to reduce engine power to 1,700 rpm, but the rpm dropped to 1,000. The instructor observed the student attempt to increase power with no change in rpm.
The flight instructor immediately took the controls and attempted to troubleshoot the engine issue, but the engine only produced two “weak vibrations” and could not be restarted. The instructor determined that the glide path would not allow reaching the runway, so he turned right to land on a golf course fairway and pond. Subsequently, the left wing contacted trees and the airplane came to rest partially submerged in a pond, where both pilots safely egressed. The fuselage, wings, and empennage sustained substantial damage.
Engine Examination
The engine remained submerged in water for about 18 hours before recovery. During recovery, the wings were removed and about 35 gallons of fuel was recovered. A sample of that fuel was blue and absent of debris or water. On May 10, 2021, the engine was examined by a National Transportation Safety Board investigator. Visual examination revealed all major accessories, fuel lines, and control cables were intact and secure. Additional fuel samples from the belly sumps and firewall fuel filter were blue and absent of debris and water.
When the bottom spark plugs were removed, dark water was observed draining from three of the four cylinders. The spark plugs were dark in color, and three of the plugs exhibited corrosion and debris from water exposure. The valve covers and ignition leads for both magnetos were removed, and the propeller was manually rotated. Valvetrain continuity was established on each cylinder, and the impulse couplings for both magnetos were heard clicking. However, spark was only observed on two of the left magneto’s ignition leads as the propeller was rotated. The top plugs were dark and also exhibited corrosion and debris.
The spark plugs were cleaned, and a small gas tank was plumbed into the right-wing fuel port. Several attempts to start the engine were unsuccessful. The magneto caps were removed, revealing corrosion in the cap and interior housing of both magnetos. An attempt to dry the right magneto and remove visible corrosion did not allow the engine to start. A brand-new right magneto was installed and timed, after which the engine started immediately and ran without interruption through its full power range.
Maintenance Records
Review of maintenance records found that the most recent 100-hour inspection was completed on March 25, 2021. The inspection documented routine maintenance actions, and the airplane had flown about 40 hours since that inspection. An attempt to retrieve data from the primary and multi-function display systems was made, but the SD cards contained no data.