Accident Overview
On September 9, 2022, at 1314 Pacific daylight time, a Gates Lear Jet Corp. 36, registration N26FN, was substantially damaged when it overran runway 36 at North Island Naval Air Station (Halsey Field) Airport (NZY), San Diego, California. The two pilots aboard sustained minor injuries. The flight was conducted as a Title 14 Code of Federal Regulations public use flight supporting United States Navy training.
Flight Details
The flight originated from NZY to support Navy training off the coast of San Diego. The crew reported that the flight was uneventful until it was ended early due to icing conditions. During the return, the crew planned an instrument approach. Air traffic control advised that the airport was reporting VFR and offered a visual approach. The flight crew noted a staggered cloud base and maneuvered to maintain visual contact with the airport. The pilot in command (PIC) assumed calm wind based on departure conditions, as the tower did not provide updated wind information.
The crew calculated Vref as 140 knots indicated airspeed (KIAS) for the landing weight of 14,900 lbs with 20° of flaps. Due to underwing-mounted external storage, maximum flap extension was limited to 20°. The calculated landing distance was approximately 4,200 ft, accounting for 20° flaps and wet runway conditions. Runway 36 at NZY is 8,001 ft long, with an arresting gear located about 1,700 ft from the threshold.
Landing and Overrun
The PIC, who was pilot flying, reported that the approach speed and altitude were nominal, and the airplane touched down within about 200 ft of the arresting gear as planned. The second in command (SIC) stated that the PIC deployed spoilers and brakes, then announced the airplane was not slowing down. The PIC reported that the airplane did not decelerate normally, the brake anti-skid system was active, and it seemed to be hydroplaning. Cycling the brakes had no effect. At the 1,000 ft remaining sign, the SIC called out 100 knots. The PIC determined insufficient runway remained and the airplane overran the runway, continuing over the sea wall. After coming to rest, the crew assessed their injuries and secured the aircraft.
Recorded ADS-B data showed that on final approach, about 1,600 ft from the runway end, the airplane had a ground speed of 182 knots at 116 ft mean sea level (msl). At about 120 ft from the approach end and 50 ft above ground level, ground speed was about 175 knots. Touchdown occurred near the arresting cable at a ground speed of about 171 knots. About 38 seconds after touchdown, the airplane overran the end of the runway at a ground speed of 63 knots.
Meteorological Conditions
At 1255, a convective SIGMET was active for the area, advising embedded thunderstorms associated with Tropical Storm Kay. The ASOS at the airport reported, about 9 minutes before the accident, wind from 200° at 6 knots, visibility 2.5 statute miles, heavy rain, mist, broken ceiling at 3,300 ft, broken layer at 4,500 ft, overcast at 5,500 ft, temperature 25°C, dewpoint 23°C, and altimeter 29.51 inHg. Remarks indicated 0.06 inches of precipitation since 1252. Airport system reports showed 0.31 inches of precipitation between 0852 and 1305. The TAF for NZY forecasted wind from 290° at 7 knots, visibility 5 miles, light rain, and temporary conditions of wind from 230° at 12 knots with moderate rain showers. The flight crew reported that ATIS and tower did not report standing water on the runway, nor did they observe any.
Postaccident Examination
Postaccident examination revealed the airplane exited the departure end of the runway, breached the sea wall barrier, and came to rest about 460 ft from the end of the runway overrun. The airplane remained intact but the nose cone was crushed and pushed aft, crushing the forward pressure bulkhead. Prior to recovery, the airplane was submerged in salt water overnight, allowing water into the cockpit and cabin. The braking system could not be functionally tested due to saltwater immersion. Flat spots were identified on both left and right tires.
Landing Performance Study
A landing performance study conducted by the airplane manufacturer modeled various landing scenarios using factual data including ADS-B data and manufacturer performance data. The study considered effects of wet/dry runway, contaminated runway, full/intermittent hydroplaning, localized tailwind (not present in weather data), and inboard brake failure. The model that best fit the available data showed that the airplane touched down with a ground speed well in excess of the 140 knots reported by the crew, and subsequent to touchdown encountered full hydroplaning at speeds above 104 knots. The study produced a profile consistent with the factual data when significant hydroplaning was assumed, likely due to recent heavy rain and continued precipitation on the runway surface combined with high aircraft ground speed. The model indicated it was unlikely the high ground speed was due to a severe tailwind, and all aircraft brakes were likely operational.