Accident Sequence
The pilot executed an instrument approach and landing in heavy rain. The airplane touched down near the displaced runway threshold at about 128 knots, approximately 21 knots above the landing reference speed, indicating an unstabilized approach. Both wing ground spoilers automatically deployed upon touchdown. The pilot reported a "solid" touchdown and promptly initiated braking, but the airplane did not decelerate. The main wheels initially spun up, but both wheel speeds subsequently decayed, consistent with hydroplaning in the heavy rain. When wheel speeds did not recover, the brake control unit alerted the flight crew to an anti-skid failure; the pilot recalled an anti-skid CAS message displayed during the landing. The pilot then activated the emergency brake system, after which wheel speeds decayed. The airplane overran the departure end of the runway at about 60 knots, crossed an airport perimeter road, and encountered a small creek before coming to rest. The wings separated from the fuselage and were immediately adjacent to it.
Weather Conditions
The pilot reported light to moderate rain beginning on final approach. Weather data and surveillance images indicated heavy rain and limited visibility at the airport during the landing. Thunderstorms were active in the vicinity, with a rainfall rate between 4.2 and 6.0 inches per hour at the time of the accident. Approximately four minutes before the accident, a surface observation recorded visibility as 3 miles; three minutes later, visibility decreased to 3/8 mile. The pilot was using the multifunction display and a tablet for weather radar, which showed green and yellow returns (light to moderate rain). He chose not to activate the airplane's onboard weather radar because the other two sources did not indicate severe weather.
Brake System and Hydroplaning
The runway exhibited skid marks beginning about 1,500 feet from the departure end. Each main tire had one patch of reverted rubber wear consistent with reverted rubber hydroplaning. The main landing gear remained extended, both tires pressurized. The tire pressures corresponded to a minimum dynamic hydroplaning speed of about 115 knots. The airplane flight manual stated that in the event of an anti-skid failure, main brakes should be applied progressively and brake pressure modulated as required. The emergency brake is intended for brake failure; however, the pilot activated the emergency brake while the main brakes still functioned, though without anti-skid protection.
Pilot Actions and ATC Communications
About four minutes before the accident, the tower controller advised the pilot of changing wind conditions and better weather west of the airport, but did not update the pilot regarding visibility along the final approach course or precipitation at the airport. The pilot stated that the rain started 2 to 3 minutes before landing, commenting it was not the heaviest rain he had ever landed in. He did not request visibility updates from ATC.
Probable Cause
The probable cause, as stated in official findings, was the airplane's hydroplaning during the landing roll, which resulted in a runway excursion. Contributing to the accident was the pilot's continuation of an unstabilized approach, his decision to land in heavy rain conditions, and his improper use of the main and emergency brake systems. Also contributing was the air traffic controller's failure to disseminate current airport weather conditions to the flight crew in a timely manner.