Incident Overview
The flight crew was supporting a United States Navy training mission and ended the flight early due to icing conditions. They calculated a landing reference speed (Vref) of 140 knots indicated airspeed and a landing distance required of 4,200 ft for a wet runway with a flap setting of 20°. Due to underwing-mounted external storage, the maximum flap extension was limited to 20°. The aircraft was configured with 20° flaps and touched down at 140 kts.
Runway and Weather Conditions
The runway was 8,001 ft long, but an arresting cable located 1,701 ft from the threshold reduced the available runway distance to about 6,300 ft. The airport weather observation system recorded 0.06 inches of liquid equivalent precipitation between 18 and 9 minutes before the accident, and 0.31 inches in the preceding 4 hours.
Landing and Overrun
After touchdown, the second in command reported that the pilot-in-command deployed the spoilers and brakes, then announced that the aircraft was not slowing down. The PIC stated that the aircraft did not decelerate normally, the brake anti-skid system was active, and the airplane seemed to be hydroplaning. Cycling the brakes had no effect. The aircraft overran the departure end of the runway, breached an ocean sea wall, and came to rest nose-down on a sandbar.
Investigation and Performance Study
A landing performance study by the aircraft manufacturer modeled various scenarios using ADS-B data and manufacturer-provided performance data. The study considered wet and dry runways, contaminated runways, full and intermittent hydroplaning, a localized tailwind (not present in weather data), and an inboard brake failure. The most likely scenario, based on the data, was a touchdown ground speed well in excess of the 140 kts Vref, followed by full hydroplaning at speeds above 104 kts. The aircraft remained on the sandbar overnight and was submerged in saltwater, preventing functional testing of the braking system. Physical evidence and modeling did not indicate a brake failure, and ADS-B data did not support a localized tailwind. It is likely that the flight crew landed too fast and encountered hydroplaning due to a recent heavy rain shower, diminishing the calculated stopping distance.