Bloomington-Monroe County

The pilot had received an outlook briefing during the morning hours before the accident. The briefing included information regarding widely scattered thunderstorms and rain showers along portions of the pilot's planned route of flight. At the time of the accident, a convective weather significant to the safety of all aircraft (convective SIGMET) was in effect for the pilot's route of flight, and the information about the convective SIGMET was broadcast to the pilot by air traffic control (ATC). Several airplanes in the vicinity of the accident airplane were deviating around weather. Conversations between the accident pilot and the ATC controller were consistent with the accident airplane's weather radar functioning, and the possibility that the accident airplane's weather radar was providing more information than the ATC weather radar. Although the pilot initially declined a deviation query by ATC, he later accepted one. Shortly after, the pilot was unable to maintain his assigned altitude of 28,000 feet msl (FL 280), and the airplane impacted terrain consistent with a vertical descent. At the time of the accident, at FL 280, weak to moderate weather radar echoes existed. Very strong to intense weather radar echoes were seen about FL 200. The ATC facility was equipped with NEXRAD derived weather displays. The weather displays had four settings: below FL 240, between FL 240 and FL 330, above FL 330, and from sea level to FL 600. At the time of the accident, the ATC controller's weather display indicated weak to moderate echoes above FL240. Very strong to intense weather radar echoes existed about FL200; however, the ATC controller did not have his weather display set to that altitude as he was not controlling traffic at that altitude. The investigation could not determine if the pilot was aware of the stronger intensity echoes below his altitude, or if the airplane's weather radar was depicting the stronger echoes. Examination of the wreckage did not reveal any preimpact mechanical malfunctions.

The pilot reported that while on final approach to runway 35, the aircraft encountered 'extreme windshift' and was blown about 550 feet right of course with a 30 knot loss of airspeed (from 130 to 100 knots). He stated the aircraft lost about 300 feet, then was blown back on course with an additional loss of altitude. Subsequently, the aircraft touched down hard on the approach end of the runway. During touchdown, the right main tire blew out, the right propeller struck the runway 9 times and the right wing was damaged. The surface wind was reported to be from 240° at 10 knots with no gusts. All four occupants escaped uninjured.

During an ILS to runway 35, the approach was normal until the aircraft was approximately 100 feet above the decision height, except there was condensation on the windshield. Touchdown was hard. A witness said the aircraft landed approximately 1/3 of the way down the 5,200 feet runway. After landing, with the props in 'ground fine,' braking action was ineffective on the wet runway. The aircraft was not equipped with an anti-skid braking system. Subsequently, the aircraft continued off the runway and went down an embankment into a field. Scrub marks on the runway and reverted rubber on the tires indicated the aircraft was hydroplaning. According to the flight manual, 4,500 feet (plus a 10% factor for no anti-skid) would have been required to stop on a dry runway in the prevailing weather conditions, which included a slight tailwind. Two pax, acting as flight attendants (f/a's), assisted the other pax in evacuating. An investigation revealed the f/a's were not properly trained; the pax were not completely briefed before the flight; and the passenger briefing cards were inadequate. The aircraft was on a business flight to transport an entertainment troupe.