Accident Summary
On September 4, 2020, about 2002 central daylight time, a Swearingen SA227-AC airplane, registration N362AE, was substantially damaged during a landing at San Antonio International Airport (SAT), San Antonio, Texas. The pilot was not injured. The airplane was operating as a Title 14 Code of Federal Regulations Part 135 cargo flight.
According to the pilot, while on a ¾-mile final approach to runway 13L, the airplane yawed right. He regained control with left rudder and continued the approach. The airplane remained wings level with the nose aligned to the runway until crossing the threshold. Shortly after reducing engine power for the flare, the airplane entered a right roll, which became more pronounced. The pilot was unable to regain control before the airplane landed hard on the right main landing gear with a 20° right-wing-down roll. The airplane departed the right side of the runway, where the nose landing gear collapsed. The pilot postulated that the right roll was due to a right engine malfunction.
Flight Path Analysis
Automatic dependent surveillance-broadcast (ADS-B) data provided the airplane's flight path and parameters. At 2001:07, the airplane crossed perpendicular over runway 13L at 2,677 ft mean sea level (msl) and 182 knots calibrated airspeed (KCAS). It then entered a left turn to join the downwind leg for runway 13L. By 2001:38, the airplane was abeam the threshold on a 1 nautical mile (nm) wide left downwind at 2,629 ft msl, 138 KCAS, descending at 702 feet per minute (fpm). About 10 seconds later, it was in a left turn toward base leg descending at 1,976 fpm and 135 KCAS.
The operator's general operations manual defined a stabilized approach: wings level on final at 300 ft above touchdown zone elevation, airspeed within 10 knots of approach speed (130 knots) and not less than required, descent rate not exceeding 1,000 fpm, and only small heading and pitch changes. The reference airspeed (Vref) for the landing weight of 12,000 lbs was 106 knots. A go-around was required if not stabilized at 1,000 ft or if destabilized.
ADS-B data showed that at 2002:08, the airplane was 1,000 ft above the runway 13L threshold while descending at 2,055 fpm and 125 KCAS—more than double the allowed descent rate and 5 knots below the specified approach speed. At 2002:17, the airplane was descending at 2,929 fpm at 134 KCAS, still in a left turn with a 31° left-wing-down roll, nearly three times the descent rate limitation.
At 2002:28, 300 ft above the threshold, the airplane had a 16° left-wing-down bank, 135 KCAS, and 1,376 fpm descent. At 2002:36, it was established on the extended centerline at 120 KCAS and 1,250 fpm descent, about 0.14 nm from the threshold. At 2002:41, the airplane crossed the threshold at 43 ft above ground level, 111 KCAS (Vref+5 knots), and 1,015 fpm descent. Three seconds later, at touchdown, the airplane was 36 ft right of centerline with a ground track 1.5° right of the runway course, airspeed 104 KCAS, descent rate 733 fpm, flight path angle -3.9°, and roll angle 3.7° right-wing-down. The airplane came to rest in the grass infield between runway 13L and taxiway M, about 525 ft south-southeast from the final ADS-B track point.
Aircraft Examination
Postaccident examination revealed substantial damage to the fuselage, right engine nacelle structure, right-wing main spar, and forward pressure bulkhead. Flight control continuity was confirmed from control surfaces to cockpit controls, and measured range-of-travel for aileron, elevator, and rudder were within maintenance manual limits. No discrepancies were noted with the stabilizer trim control system; its full travel time was within limits. Borescope inspection of both engines did not reveal any evidence of internal gas path component failure. The turbines rotated freely. No airfoil damage or debris was observed. Both fuel control unit filter bowls contained fuel. Both propellers exhibited impact-related damage.