Background
Prior to departure from Lambert Field/St. Louis International Airport, the pilot contacted the operations manager at M. Graham Clark Airport, Point Lookout, Missouri, to inquire about current weather conditions. The operations manager reported that the weather was "pretty poor."
Flight Sequence
The aircraft departed St. Louis at 1411 central standard time. At 1447, the pilot checked in with Springfield Approach Control and was initially instructed to expect an ILS approach to runway 2 at Springfield-Branson Regional Airport. At 1501, the pilot requested to proceed to Point Lookout and execute the GPS approach to runway 11. Springfield Approach cleared the pilot to descend to 3,000 feet mean sea level (msl) and cleared the aircraft for the approach. Radar data showed the aircraft crossing the initial waypoint at 3,000 feet msl at 1507:08, then turning to a heading of 116 degrees. At 1507:17, the aircraft descended to 2,500 feet msl. At 1508:51, Springfield Approach instructed the pilot to switch to the advisory frequency and to call back with a cancellation or missed approach. The pilot acknowledged, stating they were "RAWBE inbound" on the GPS 11 approach and would call on the miss or cancellation. The operations manager at M. Graham Clark Airport heard the pilot on the common frequency state, "Citation 525KL is RAWBE inbound on the GPS 11 approach." At 1509:01, radar showed the aircraft beginning a descent from 2,500 feet msl. The last radar contact was at 1509:48, when the aircraft was five nautical miles from the airport on a 296-degree radial at 2,100 feet msl. At 1530, the operations manager heard Springfield Approach attempting to contact the aircraft and initiated a search.
Weather Conditions
The weather observation at M. Graham Clark Airport at 1430 central standard time reported 300 feet overcast, rain and mist, visibility 3/4 mile, temperature 53°F, winds variable at 3 knots, and altimeter 29.92 inches of mercury. The minimum weather requirements for the GPS runway 11 straight-in approach for a Category B aircraft are a ceiling of 600 feet and visibility of 1 mile.
Toxicology
Examination of the aircraft wreckage revealed no anomalies. The Federal Aviation Administration's toxicology testing of pilot specimens detected the presence of Doxepin in the kidney and liver. According to the Physicians' Desk Reference, drowsiness may occur with use of this drug, and patients should be warned against driving or operating dangerous machinery. The prescribing physician stated the Doxepin was used to treat the pilot's irritable bowel condition. The pilot's wife reported that he had not slept well for several nights prior to the accident due to problems with the FAA. A friend who spoke with the pilot just before the flight confirmed the pilot saying, "I haven't slept for three days," and noted that the pilot "wasn't himself that day."
Probable Cause
The probable cause of the accident, as determined by the official investigation, is that the pilot descended below the minimum altitude for the segment of the GPS approach. Factors relating to the accident were low ceilings, rain, and pilot fatigue.