HISTORY OF FLIGHTOn June 26, 2019, about 2037 Pacific daylight time, a Cessna 172S, N3504A, departed Watsonville, California, for an unknown destination. Since that time, neither the airplane nor the person presumed to be the pilot has been located. The airplane is presumed to have been destroyed by impact in the Pacific Ocean, and the pilot is presumed to have received fatal injuries. The airplane was operated as a Title 14 Code of Federal Regulations Part 91 personal flight. Federal Aviation Administration (FAA) ground-based radar tracking data for June 26 revealed a series of transponder code 1200 returns from an aircraft that appeared to have departed from Watsonville Municipal airport (WVI) starting at 2038:34. The first radar data return indicated an altitude of 200 ft mean sea level (msl), and the track was consistent with a departure from runway 20. The airplane flew a course to the southwest in a constant climb until it reached an indicated altitude of 4,500 ft. At that point, it was about 5 nautical miles (nm) offshore, which was about 8 nm from WVI. The airplane then began a turn to the west-northwest and climbed to a maximum altitude of 4,900 ft msl. It continued about 10 nm in that direction, during which it descended to an altitude of about 1,000 ft msl. The airplane then turned northwest and began to fly parallel to the coastline about 3 nm offshore. That track extended about 16 nm, and the latter portion was flown at altitudes that varied between 700 and 400 ft msl. The airplane turned to the west, then entered a left descending circle about 1 nm in diameter. The final radar return was recorded at 2102:18, near the completion of the circle. That evening, a group of campers were at a campground about 30 miles west-northwest of WVI, about 1 mile inland from and with a direct view of the Pacific Ocean. They reported that, about 2100, while facing approximately west, they observed a "blinking white and green light," which they perceived to be a helicopter, flying roughly northbound over the ocean. They then saw it descend "straight down" to the water and observed a "large splash." They reported the event to local law enforcement, and two San Mateo County Sheriff's Office (SMCSO) officers responded to the campsite within the hour. The SMCSO communicated with the United States Coast Guard (USCG) and other agencies that evening and determined that no aircraft had been reported as being in distress or missing. About 2300, the USCG advised SMCSO that the "circumstances did not meet the criteria to initiate a search," and that the USCG would not be responding to the event. The following day, a Santa Cruz Flying Club (SCFC) pilot who had scheduled the accident airplane for that day discovered that the airplane was not in its tiedown location and could not be located at the airport. SCFC used a self-dispatch system for its pilots and airplanes. Follow-up investigation by the SCFC president was unable to account for the airplane and one of the SCFC member pilots. The next day, the SCFC president notified the Watsonville Police Department and WVI management that the airplane was missing. Review of WVI surveillance video depicted an airplane similar in appearance to the accident airplane taxiing across a ramp at nightfall on June 26. The airplane registration number was not discernible in the image, and no further images of that airplane were captured. The SCFC president reported that this operation of the airplane was not scheduled or authorized. The last radar return was located about 31 nm northwest of WVI, about 3.2 miles off the California coast at a transponder-indicated altitude of 0 ft and about 3.8 miles southwest of the land-based eyewitnesses. In response to the radar data findings, additional land and ocean searches were conducted on June 29 and 30. The USCG conducted a search in the region of the final radar return. No wreckage or other indications of the airplane were observed. A ramp check of Half Moon Bay Airport (HAF), Half Moon Bay, California, the next-closest airport to the final radar return, did not locate the airplane. A search of WVI located the pilot's vehicle with his mobile telephone inside. Law enforcement personnel did not locate the pilot at his residence, and communications with the pilot's next-of-kin also failed to locate him. PERSONNEL INFORMATIONThe pilot's personal flight records were not recovered. The SCFC president reported that the pilot's most recent flight review was completed on July 10, 2017, and that the pilot then flew solo twice in SCFC airplanes, in July and October of 2017. The October 2017 flight was the pilot's last contact with SCFC until he returned in May 2019 in order to regain his flight currency. The pilot flew an SCFC airplane with an SCFC flight instructor twice, on May 29 and June 7, 2019. The instructor did not sign the pilot off to fly SCFC airplanes solo, and the pilot had scheduled several more sessions with SCFC airplanes. However, he did not conduct any additional flights in SCFC airplanes until the accident flight. In his written statement to the NTSB, the instructor who flew with the pilot in 2019 did not cite any concerns about the pilot's behavior or attitude. According to his FAA medical certificate applications, the pilot had at least three prior convictions for driving under the influence of alcohol, but was granted an eligibility letter to obtain an FAA medical certificate by the FAA Aerospace Medical Certification Division (AMCD) in June 2004; the letter required the continued abstinence from alcohol. The pilot had a family history of bipolar disease and major depression. In 2007, the AMCD determined that the pilot had no substance abuse or dependence, but he was found by AMCD to have "Adjustment Disorders with Depressed Mood." AMCD granted an eligibility letter on 05/24/2007, but that issuance did not require any FAA follow-up action with or by the pilot. METEOROLOGICAL INFORMATIONThe 2100 WVI automated weather observation included wind from 320° at 8 knots, visibility 10 miles, an overcast ceiling at 700 ft agl, temperature 14°C, dew point 13°C, and an altimeter setting of 30.06 inches of mercury. Local sunset occurred at 2030, and twilight ended at 2101. COMMUNICATIONSThe WVI common traffic advisory frequency (CTAF) that was used for pilot self-reporting communications was not recorded by the airport. A review of a commercially available recording of the WVI CTAF for the relevant time period did not reveal any communications from any aircraft identified as N3504A. There were no known communications between the missing airplane and any air traffic control facilities during the accident flight.