On June 25, 1993, a Mooney M20K, N5655M, registered to Ronald E. Venema of Crown Point, Indiana, and piloted by an instrument rated private pilot, disappeared during a flight over Lake Michigan. The airplane departed in what a witness described as a light mist which had followed a heavy rain shower. Visual meteorological conditions prevailed at the time of departure. The 14 CFR Part 91 flight was not operating under a flight plan. The pilot is presumed to have received fatal injuries. The flight originated from Hobart, Indiana, at 1215 central daylight time. Witnesses who observed N5655M depart stated that fog was approaching the airport from the Lake Michigan shoreline which is approximately five miles north. Both witnesses stated the airplane departed to the south after takeoff. One of the witnesses stated a thunderstorm had passed over the airport shortly before the departure. He said the thunderstorm had been moving southeast and was still visible when N5655M departed. The Federal Aviation Administration Flight Service Station (FSS) located at Terre Haute, Indiana, stated that no weather briefing service was provided to N5655M. The FSS checked with other FSS facilities in states bordering Indiana regarding a possible weather briefing by the pilot of N5655M. The other FSS's responded negatively. The Civil Air Patrol, a United States Air Force Auxiliary, conducted an air and ground search for the missing airplane with negative results. The search included the southern section of Lake Michigan. The U.S. Coast Guard conducted a search of the southern section of Lake Michigan with negative results. The flight instructor who had flown with the missing pilot stated he had done so at the pilot's request for insurance purposes. The instructor was asked to appraise the pilot's flying habits and ability. He stated the pilot lacked discipline to do the appropriate pre- flight planning. He stated it was his opinion the pilot knew how to do it, but did not want to do it because it would take too much time. He said the pilot's basic flying skills were above average. A family member stated the pilot had been talking of having a GPS radio navigation aid installed. She stated he may have been going to do that. A check of the avionics shops located within a 100 NM radius of Hobart, Indiana, revealed the pilot had not made arrangements with any of the shops for radio work on N5655M. An interview with the pilot's son-in-law revealed he had flown with the pilot approximately one week prior to the missing flight's takeoff. He stated that the vacuum pump had failed during the flight that was conducted under night instrument meteorological conditions. According to the person contacted by the missing pilot regarding the failed vacuum pump the pilot told him the airplane was a "...handful when flying without the gyros." It has not been determined if a new pump had been installed on N5655M prior to June 25, 1993, departure. An interview was conducted with an Airframe and Powerplant mechanic who had been employed by the pilot's business. He stated he had been asked by the pilot to change the pump on the airplane because his instruments were not working. The mechanic stated the pump had approximately 30 hours on it at the time of failure. He stated he was told by the Hobart Airport manager that he could not do maintenance on the airplane. The mechanic stated he did not remove the pump; he replaced the cowl and left the airport after talking with the manager. According to the mechanic, the pilot removed the pump at some point in time after his experience with the airport manager. He stated the pilot had told him that the person who sold him the airplane advised him to take the pump to a facility located near Hobart, Indiana. This facility was to give the pilot a new pump according to the mechanic. He stated he could not recall the facility's name or location. The mechanic confirmed the son-in- law's statement regarding the night flight in instrument meteorological conditions when the vacuum pump had failed. Components of an airplane, believed to be N5655M have been found along the Lake Michigan shoreline between Michigan City, Indiana, and New Buffalo, Michigan. These components are: An oxygen bottle with the airplane's registration number hand printed on its exterior, a front seat with fabric matching that of N5655M's interior, sheet metal colored as N5655M that was identified as a portion of a Mooney aileron main spar, a section of the wing rib assembly, and a portion of the right hand aileron's top skin. The wing rib section and aileron skin were identified as Mooney airplane components. A briefcase containing the missing pilot's personal affects was found north of Michigan City, Indiana, along Lake Michigan's shore.