N26FNGates Lear Jet 36 · 1975

On September 9, 2022, at 1314 Pacific daylight time, a Gates Lear Jet Corp. 36, N26FN, was substantially damaged when it was involved in an accident near San Diego, California. The two pilots sustained minor injuries. The airplane was operated as a Title 14 Code of Federal Regulations public use flight.

The flight crew reported that the flight originated from North Island Naval Air Station (Halsey Field) Airport (NZY), San Diego, California, to support United States Navy training off the coast of San Diego. The flight was conducted as briefed with no abnormalities; however, the flight was ended early due to icing conditions.

During the return flight to NZY, the crew planned for an instrument approach. Air traffic control advised that the airport was reporting VFR and that a visual approach was available if the flight crew had the airport in sight. The flight crew noted a staggered cloud base and maneuvered to maintain visual contact with the airport. The pilot in command (PIC) reported that the tower did not provide the flight crew with updated wind information, and he assumed that the wind was calm, as it had been when the flight departed.

The flight crew calculated Vref (reference speed) as 140 knots indicated airspeed (KIAS) for the landing weight of 14,900 lbs with 20° of flaps. Due to underwing-mounted external storage, the landing flaps were limited to a maximum extension of 20°. The calculated landing distance was approximately 4,200 ft and included factors for 20° flaps and wet runway conditions. Runway 36 at NZY was 8,001 ft long; however, an arresting gear was located within the first portion of the runway (about 1,700 ft from the threshold).

The PIC, who was the pilot flying, reported that the approach speed and altitude were nominal, and that the airplane touched down within about 200 ft of the arresting gear as planned. The SIC reported that the PIC deployed the spoilers and brakes, then announced that the airplane was not slowing down. The PIC stated that the airplane did not decelerate normally, that the brake anti-skid system was active, and that the airplane seemed to be hydroplaning. He cycled the brakes, which had no effect. At the 1,000 ft remaining sign, the SIC called out, “100 knots.” The PIC stated that insufficient runway remained on which to stop, and the airplane overran the runway and continued over the sea wall. After the airplane came to rest, the flight crew assessed their injuries and the “aircraft switches were secured, and the engines were shut down.”

According to the flight crew, the automated terminal information service (ATIS) at the airport and the tower controller did not report standing water on the runway, nor did the pilots observe any.

Recorded ADS-B data showed that while on final approach to the runway, about 1,600 ft from the approach end runway, the airplane had a ground speed of 182 knots, at an altitude of 116 ft mean sea level (msl). The airplane had slowed to about 175 knots about 120 ft from the approach end of the runway, about 50 ft above ground level. The data showed that the airplane’s approximate touchdown point was near the arresting cable which was located about 1,700 ft from the approach end of the runway at a ground speed of about 171 knots. The data showed that about 38 seconds after the approximate touchdown, the airplane overran the end of the runway at a ground speed of 63 knots.

Postaccident examination revealed that the airplane had 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 with the nose cone crushed and pushed aft, which also crushed the forward pressure bulkhead. Prior to recovery, the airplane was submerged in salt water overnight, and water entered the cockpit and cabin areas. As a result of the saltwater immersion, the airplane’s braking system was not functionally tested. Flat spots on both the left and right tires were identified.

At 1255, the National Weather Service’s Aviation Weather Center issued a convective SIGMET that was active for the accident location and valid until 1455. The SIGMET advised an area of embedded thunderstorms associated with Tropical Storm Kay.

The ASOS located on the airport reported that, about 9 minutes before the accident, the wind was from 200° at 6 knots, visibility 2 1/2 statute miles, heavy rain, mist, broken ceiling at 3,300 ft above ground level (agl), a broken cloud layer at 4,500 ft agl, overcast clouds at 5,500 ft agl, temperature 25° Celsius (C), dewpoint 23°C, and altimeter setting of 29.51 inches of mercury. The ASOS remarks included that 0.06 inches of liquid equivalent precipitation fell since 1252. According to NZY system reports, the airport received 0.31 inches of liquid equivalent precipitation between 0852 and 1305.

The Geostationary Operational Environmental Satellite (GOES)-17 data depicted cloudy conditions over the accident region.

A Terminal Aerodrome Forecast (TAF) issued for NZY and valid for the accident time, forecasted wind from 290° at 7 knots, visibility 5 miles, light rain, few clouds at 2,000 ft agl, scattered clouds at 5,000 ft agl, ceiling overcast at 10,000 ft agl, with frequent to moderate turbulence in clouds from 1,000 to 10,000 ft, and an altimeter setting of 29.47 inches of mercury. Also forecasted were temporary conditions of wind from 230° at 12 knots, visibility of 6,000 meters and moderate rain showers.

Two Honeywell Aerospace Digital Electronic Engine Controls (N1 DEECs) were installed on the airplane, one per engine.

Incident recorder and data fault history from both N1 DEECs were successfully extracted, with data showing that both engines were operating and responding to power lever inputs throughout the approach and accident sequence. About 30 seconds after touchdown, the Power Lever Angle (PLA) increased with corresponding appropriate response of N1 and N2 speeds, along with interstage turbine temperature (ITT). At the end of the downloaded data, a simultaneous fault between the left and right N1 DEECs was recorded and was consistent with an electrical power loss to both units.

A landing performance study conducted by the airplane manufacturer modeled a variety of landing scenarios considered during the investigation. The modeling used factual information provided by the investigation, including ADS-B data, as well as manufacturer-provided airplane performance data specific to the airplane. The study considered the effect on landing distance of both a wet and dry runway, a contaminated runway, both full and intermittent hydroplaning, a localized tailwind (which was not present in the weather data), and an inboard brake failure.

The modeling in the study “produced a profile consistent with the factual data when significant hydroplaning was assumed, likely due to the recent heavy rain and continued precipitation on the runway surface combined with a high aircraft ground speed. The model indicated that it was unlikely the high ground speed was due to a severe tailwind, and it also showed that all aircraft brakes were likely operational.” The model that best fit the available data showed that the airplane touched down with a ground speed well in excess of the 140 kts reported by the crew and that, subsequent to the touchdown, encountered full hydroplaning at speeds above 104 kts (See figure, below).

Figure plotting speed with landing distance along with runway features. Note the incorporated ADS-B data of groundspeed and time.