The airline transport pilot and non-instrument-rated private pilot were conducting a three-leg Civil Air Patrol (CAP) "compassion flight" to transport a passenger from Florida to Louisiana. The pilots departed the CAP squadron's home base in Alabama and flew to Florida, where they encountered a 2 1/2-hour delay while waiting for the passenger to arrive. After picking up the passenger, they subsequently transported her to her destination in Louisiana. The pilots then departed on the 1-hour return flight in dark night conditions to their home base, where a squadron meeting was scheduled for that evening. All three flights were conducted under instrument flight rules (IFR).During the accident flight, the weather at the destination airport deteriorated from visual meteorological conditions to instrument meteorological conditions, with low cloud ceilings, reduced visibility, and fog; these conditions had been forecasted to develop. The mission pilot should have been aware of both the forecast and actual weather conditions, as he had received an electronic weather briefing, filed an IFR flight plan, and had filed an alternate destination in the event of poor weather at the intended destination. However, the airport the pilot selected as an alternate was located only 10 nautical miles northwest of the destination airport and was affected by the same weather conditions; both airports reported 1/2 statute miles visibility and vertical visibility about 200 ft about the time of the accident.As the flight approached the destination, the pilot elected to divert to the alternate airport and received vectors for an instrument landing system (ILS) precision approach. The investigation was unable to determine why the pilot chose to divert. About 300 ft agl (100 ft above the decision height where the runway environment must be visible), the pilot initiated a missed approach procedure. Radar data showed that, rather than completing the prescribed climb to 2,000 ft on runway heading, the airplane entered a shallow right turn and continued to descend until radar contact was lost. The airplane impacted trees and terrain and was destroyed by a postcrash fire. Examination of the airplane and its systems identified no engine, airframe, or avionics anomalies that would have precluded normal operation. Additionally, no medical factors were identified that could explain the sequence of events.CAP required that all flight activities obtain a flight release before departure. As part of the flight release Page 2 of 19 ERA16FA100process, pilots were required to consult with a flight release officer (FRO), who in part ensured the pilot was qualified in the airplane and met currency requirements and input the route of flight into an electronic log system. A CAP member could become qualified as an FRO by completing a one-time online course; they were not required to be rated pilots, FROs were not required to flight follow a flight, and were not responsible for the actual conduct of the flight. The FRO who released the accident flight had a phone conversation with the pilot before the first leg of the trip to cover all three legs. They discussed the pilot's health and readiness to fly, the clouds at altitude that would require the pilot to file an IFR flight plan on each leg and assessed that the operational risk management for the flights was low.While the risk assessment completed on the morning of the accident may have been accurate at that time, the delay encountered in picking up the passenger resulted in a significant change in the circumstances of the flight, introducing the risk factors of deteriorating weather conditions at the destination, a longer duty day, and the pressure to return in time for the squadron meeting. It could not be determined whether the pilot completed a risk assessment specifically for the accident flight taking these factors into account, but even if he had, he was not required to discuss the risk assessment with the FRO or otherwise obtain explicit approval to depart on the accident flight.The pilot's alternate airport choice was likely one of convenience rather than one that was chosen with operational considerations in mind. Additionally, the selected alternate did not meet the legal minimum weather requirements to be filed as an alternate. At the time of departure, the airplane had about 5 hours of fuel onboard, well in excess of IFR-required fuel reserves. This gave the pilot the flexibility of selecting other alternate airports that may have been farther away but were experiencing better weather conditions. A witness at the departure airport stated that, although the pilots had expressed some concern about the weather conditions before departing, they indicated that they wanted to return before conditions deteriorated and so that they could attend their squadron meeting. It is likely that the pilot was affected by "get-there-itis" as he made the decision to continue to his planned destination even though there were choices available that were significantly less risky, such as staying overnight and completing the flight the next morning or diverting to an airport that was not affected by the widespread coastal fog at the destination and alternate airports.The pilot's logbooks were not recovered and his total instrument experience, recency of experience, and experience in the accident airplane could not be determined.. The pilot's failure to climb the airplane during the missed approach procedure is consistent with the effects of spatial disorientation in the form of a somatogravic illusion. During this illusion, the vestibular system indicates a climb even though, in fact, the airplane is level. The sensation typically occurs when there are few visual cues (flying away from an airport at night in poor weather) and the airplane is accelerating, such as during a missed approach. Because a somatogravic illusion occurs within the vestibular system and antihistamines may affect the functioning of the vestibular system, it is possible that the pilot's use of doxylamine contributed to the illusion; however, without a blood level to indicate the amount of the drug remaining in the pilot's system, whether it contributed to the accident could not be determined.