On November 14, 2022, about 1134 eastern standard time, a Piper PA-18-150, N9858P, was substantially damaged when it was involved in an accident near St. Augustine, Florida. The pilot was not injured. The airplane was operated as a Title 14 Code of Federal Regulations Part 91 aerial observation flight. The purpose of the flight was to map erosion from a hurricane that had passed through the area. The pilot departed Daytona Beach International Airport (DAB), Daytona Beach, Florida, at 0910, destined for Northeast Florida Regional Airport (SGJ), St. Augustine, Florida. According to the pilot, before departure he performed his normal preflight inspection of the airplane, during which he checked the flight controls, oil level, and fuel level. He also checked the fuel quality by sampling the fuel tanks and gascolator (fuel strainer). The fuel tanks had been topped off with fuel the previous day per the operator’s normal procedures. After takeoff from DAB, the pilot flew north and began mapping the coastline from around Palm Coast, Florida, to St. Augustine, Florida. He contacted the SGJ air traffic control tower and stayed on frequency for traffic advisories as he was flying a north-south grid and entered and exited the airspace surrounding SGJ. About 1130, the engine “sputtered” for 30 to 60 seconds twice, and then sputtered a third time before it lost power completely. The pilot established the airplane in a glide configuration between the St. Augustine inlet to the north and the St. Augustine beach pier to the south. The pilot elected to land to the north, which was the direction of the headwind and where he had observed fewer people walking along the beach. The pilot began his “troubleshoot checklist,” followed by the “shutdown checklist,” as he spiraled the airplane down over St. Augustine beach. In the process of his final spiraling maneuver, as he was heading south, the airplane began sinking rapidly and faster than he had anticipated. He immediately leveled the wings and pitched the airplane’s nose farther down to keep the airplane gliding to the south. On short approach to the beach, he began to see people on the beach and decided to land the airplane into the shore break to avoid them. During the landing roll, as the weight fully transferred to the main landing gear, the main landing gear dug into the sand, and the airplane nosed over and came to rest inverted. The pilot then unlatched his seatbelt and egressed. The pilot stated that bystanders ran up to assist and several mentioned that they could smell fuel leaking out of the back of the wings. He also smelled “avgas.” During the recovery of the wreckage, the pilot observed that both the left and right fuel tank caps were missing. About two weeks after the accident, the pilot advised that a person with a metal detector had located the missing fuel caps, which were buried in the sand on the beach in the vicinity of where the airplane had come to rest. Postaccident examination of the airplane revealed that the engine mounts, vertical stabilizer, and rudder were substantially damaged during the accident sequence. The engine was examined after it was recovered from the accident site and thumb compression was attained on all four cylinders when the crankshaft was manually rotated. All of the exhaust and intake valves were functional, and all of the top sparkplug electrodes were normal gray in color. Internal examination of the cylinders by borescope did not reveal any anomalies. Both magnetos produced spark at all towers, oil was in the rocker boxes and galleries, and drivetrain continuity was confirmed from the propeller flange to the rear accessory gears. Examination of the fuel system revealed only trace amounts of fuel in the system. Testing with water-finding paste did not indicate the presence of water. The gascolator displayed a small amount of debris in the bottom of the bowl (external to the screen). The carburetor float bowl was clean and was devoid of fuel; the float valve and accelerator pump were both functional, and the floats did not exhibit any indications of leakage. Further examination of the fuel system did not reveal any indication of pull-out or impact damage to the tops of the filler necks or fuel cap locking slots. At 1643, the weather reported at SGJ, about 7 nautical miles northwest of the accident site, included a temperature of 21°C and a dew point 19°C. The calculated relative humidity at this temperature and dewpoint was 88%. Review of the icing probability chart contained within Federal Aviation Administration Special Airworthiness Information Bulletin CE-09-35 revealed the atmospheric conditions at the time of the accident were "conducive to serious icing at glide [idle] power."