N5251CCessna T310R · 1978

On July 18, 2023, about 0904 mountain daylight time, a Cessna T310R, N5251C, was destroyed when it was involved in an accident near Santa Fe, New Mexico. The pilot was fatally injured. The airplane was operated as a Title 14 Code of Federal Regulations Part 91 personal flight.

Air traffic control tower communications information revealed that the tower controller cleared the pilot for takeoff from runway 20 and reported that the wind was calm. The pilot acknowledged the clearance. ADS-B data showed that the airplane began the takeoff roll about 0901. About 0903, the pilot reported, “51C’s got an engine failure.” The tower controller asked the pilot to “say again,” and the pilot re-stated, “51C’s got an engine failure.” The tower controller cleared the pilot to make a left turn to runway 33, and the pilot acknowledged. About seven seconds later, the controller told the pilot that he was, cleared to land on any runway, to which the pilot stated that he was “going to get some altitude.” The controller acknowledged and asked the pilot to “confirm one engine.” The pilot replied, “one engine;” there were no other transmissions from the pilot.

ADS-B data revealed that after takeoff, the airplane drifted from over the runway to the left but generally maintained the runway heading. Most of the flight was over a neighborhood. Upon departure, the airplane generally maintained the runway heading for about 1 mile and climbed to a maximum altitude of about 6,425 ft mean sea level (msl), or about 200 ft above ground level (agl). After about 1 mile, the airplane turned slightly to the left and continued south for about 1 mile. The airplane maintained 6,425 ft until 0902:37, when it began a slow descent and maintained about 101 to 102 knots ground speed. Around 0902:56, the airplane began a left turn while descending at a greater rate. (See figure 1.)

Figure 1. Google Earth image showing the accident airplane’s flight path and altitude.

The last ADS-B data point, recorded at 0903:37, captured the airplane over a gulley at an undetermined altitude, at 86 knots, on a track of 044°, and about 150 ft southwest of the accident site. The airplane was aligned with an alley that was oriented 044° magnetic, as shown in figure 2.

Figure 2. Google Earth image showing the estimated last ADS-B data point location of the airplane (blue arrow) on the recorded magnetic heading of 044°, and the alley in front of the airplane. A gulley is outlined by dashed white lines, and power distribution lines are identified with a yellow dashed line.

Witnesses who were travelling in a car going westbound on Interstate 25, reported watching the airplane flying eastbound with a nose-up attitude, at a low altitude, with the left propeller not rotating and the landing gear up. The driver pulled over and stopped as the airplane passed the car. The witnesses reported that the airplane was in a left bank, then the wings leveled as it cleared a ravine. The left wing impacted a house and the airplane spun around. Another witness in the car reported there was a set of power distribution lines next to the frontage road, and that there was traffic on the freeway.

One witness, located next door to the house that the airplane impacted, stated that the airplane’s left wing and tail dropped but not more than 45° before the airplane struck the south side of the house.

A dashcam video, taken less than one half mile from the accident site, supported the ADS-B data and witness statements of the accident airplane at a low altitude, descending in a nose-high attitude heading south toward Interstate 25 and a frontage road, then turning about 90° to the left. The airplane’s wings leveled before exiting the view of the camera at an extremely low altitude.

The pilot’s personal logbooks were not recovered, and no details of his recent and past experience were available. Friends of the pilot described him as having excellent knowledge and experience with multi-engine airplanes including war birds, float planes, and helicopters. One friend described his management of the [airplane] engines as fantastic. Another described the accident pilot as one of the most qualified pilots that he has ever known.

On the day of the accident, the pilot requested that the airplane’s four tanks be topped off and purchased 60.6 gallons of 100 low lead fuel at SAF. The airplane had the optional 63-gallon auxiliary fuel tanks installed. All weight and balance information was reported to be in the airplane and lost in the postaccident fire.

Aircraft performance calculations revealed that, given the environmental conditions at the time of the accident, an empty weight of 3,942.8 lbs, 978 lbs of fuel (63-gallon auxiliary tanks), a 200-lb pilot, and 10 lbs of baggage, the airplane had a predicted one-engine inoperative climb rate of about 300 ft per minute at a gross weight of 5,130.8 lbs.

The SAF automated weather observation recorded about the time of the accident included variable wind, 10 statute miles visibility, clear sky conditions, temperature 26°C, dew point temperature 4°C, and a barometric pressure of 30.30 inches of mercury. The airport elevation was 6,349 ft msl. Density altitude was calculated to be 8,769 ft msl.

On the day of the accident, the pilot requested that the airplane’s four tanks be topped off and purchased 60.6 gallons of 100 low lead fuel at SAF. The airplane had the optional 63-gallon auxiliary fuel tanks installed. All weight and balance information was reported to be in the airplane and lost in the postaccident fire.

Aircraft performance calculations revealed that, given the environmental conditions at the time of the accident, an empty weight of 3,942.8 lbs, 978 lbs of fuel (63-gallon auxiliary tanks), a 200-lb pilot, and 10 lbs of baggage, the airplane had a predicted one-engine inoperative climb rate of about 300 ft per minute at a gross weight of 5,130.8 lbs.

The fuselage came to rest upright on the parking area of a private residence. The first point of impact was likely the southwest corner of a modular house, located at an elevation of 6,301 ft msl. Thermal damage to the house prevented determining the exact initial impact point. Most of the fuselage, including the cockpit, was consumed by a postaccident fire. The left side of the fuselage was intact up to about the middle of the fuselage. A visual examination of the left engine revealed multiple breaches to the engine case. The left propeller remained attached to the engine. Two of the blades appeared to be in the feather position and exhibited aft bending. The third blade appeared straight. The landing gear was found in the retracted position.

Examination of the left engine, model number TSIO-520-BB23B, serial number 287610-R, revealed a counterweight jammed next to cylinder No. 1. The oil sump was removed, and a significant amount of metal debris was observed in the sump. Among the debris were pieces of crankshaft counterweights, counterweight retaining rings, retainer plates, bushings, and a connecting rod cap, as shown in figure 3.

Figure 3. Photo of the oil sump with counterweight components identified.

The cylinders and the crankcase bolts were removed and the crankcase was split open. The two counterweight assemblies located between cylinder Nos. 3 and 4 were found separated from the crankshaft attachment flanges or “cheeks.” . One counterweight assembly, located between cylinder Nos. 1 and 2, remained attached; the other was partially separated from the crankshaft flange and was wedged against the crankcase between the crankshaft flange and valve lifters. (See figure 4.)

Figure 4. Left engine showing the counterweight cheeks, and the one attached counterweight.

Visual examination of the counterweight that remained attached to the crankshaft flange showed that the retaining ring ears on the aft side were facing approximately 180° from the crankshaft centerline, while the retaining rings on the forward-facing side were oriented toward the crankshaft centerline. (See figure 5).

Figure 5. Left engine counterweight showing the retaining rings on the aft-facing side (left photo) and the retaining rings on the forward-facing side (right photo).

One of the aft retaining rings was found installed with the sharp edge outboard, while the other was incorrectly installed “flipped over,” with the sharp edge facing inboard.

The retaining ring ear gaps were measured with a digital micrometer. The table below details the retainer ring ears’ gap measurements.

Table 1 . Left engine counterweight retaining clip gap measurements.

The right engine, model number TSIO-520-BB24B, serial number 287609-R, was examined and the Nos. 1 and 3 cylinders were removed. Examination of the counterweights revealed that the aft facing retaining rings were oriented facing 180° from the crankshaft centerline, and the forward-facing retaining rings were oriented facing toward the crankshaft centerline, as shown in figure 6. Examination of the right engine revealed no mechanical malfunctions or failures that would have precluded normal operation.

Figure 6. The right engine, showing the removal of the Nos. 1 and No. 3 cylinders, and the aft-facing retaining ring of one counterweight.

A review of engine maintenance logbooks revealed that both engines were overhauled in October 1998, and installed into the airplane on April 29, 1999. Logbook entries dated May 27, 1999, for both engines, indicated that, 1.1 hours since the major overhaul, the Nos. 1 and 3 cylinders were removed, and the dampers (counterweights) were removed to comply with Teledyne Continental Motors (TCM) AD 99-09-17, which was superseded by AD 99-19-01, dated September 15, 1999. On October 1, 2009, both engines underwent top overhauls that included the replacement of all cylinders, at 665.2 hours since the major overhaul. The time from the AD 99-09-17 maintenance to the last annual inspection, performed on July 13, 2023, was calculated to be 1,162.3 hours. Damage to the instruments precluded further calculations of the total engine hours beyond the last annual inspection.

Mandatory Service Bulletin MSB 99-3C, revised on July 27, 1999, issued by TCM, now Continental Aerospace Technologies, called for the removal of two cylinders, two connecting rods, and all counterweights to facilitate the visual and ultrasonic inspection of the Nos. 2 and 5 crankshaft cheeks. MSB 99-3C identified the accident engines, by serial number, as applicable to the MSB.

MSB 99-3C stated in part, “INSTALL SNAP RINGS TOWARD THE CRANKSHAFT CENTERLINE AS SHOWN.” and “INSTALL SNAP RINGS WITH SHARP EDGE (FLAT SURFACE) FACING OUTBOARD.” and “MINIMUM GAP BETWEEN SNAP RING EARS = 0.179 INCH.” (See figure 7.)

Figure 7. Excerpt from MSB 99-3C.

MSB 99-3C stated, in part,

10. Position the crankshaft so that the rearward [aft-facing] retaining rings and plates of a counterweight on the number two crankshaft cheek can be removed.

12. Using the procedure in steps 10 and 11 remove the remaining counterweight on the number two crankshaft cheek and remove the two counterweights on the number five crank cheek.

The FAA Airplane Flying Handbook (FAA-H-8083-3C) stated, in part,

The critical engine is the engine whose failure has the most adverse effect on directional control. On twins with each engine rotating in conventional, clockwise rotation as viewed from the pilot's seat, the critical engine will be the left engine.

An autopsy of the pilot was conducted by the Office of the Medical Investigator, University of New Mexico, Albuquerque, New Mexico. The cause of death was listed as blunt force injuries.