N342J

On June 21, 2020, about 1330 Pacific daylight time, an Aerospatiale SA-342J helicopter, N342J, was destroyed when it was involved in an accident at Minden-Tahoe Airport (MEV), Minden, Nevada. The pilot and passenger sustained minor injuries. The helicopter was operated as a Title 14 Code of Federal Regulations Part 91 personal flight.

According to the pilot, he added 66 gallons of fuel to fill the helicopter’s tank; departed from MEV; and flew to Carson City Airport (CXP), Carson City, Nevada. He made one flight while at CPX and then returned to MEV. The total time for the three flights was about 1 hour 15 minutes. During the approach to land at MEV, while about 25 ft above ground level (agl) the pilot lowered the collective to descend near his intended landing spot. At that time, the helicopter’s speed was 10 to 15 knots. Immediately after the pilot lowered the collective, the engine lost total power. The pilot lowered the collective further to enter an autorotational descent. When the helicopter was about 15 ft above ground level, he increased the collective to try to cushion the landing. The helicopter struck the ground hard, and a postcrash fire ensued. The occupants egressed the helicopter unassisted. The pilot recalled that the rotors and the engine speed reduced to zero rapidly and estimated that the entire event took about 7 seconds. The pilot also recalled that, before the accident, the engine had been running at 500°C instead of its usual temperature of 450°C; other than that, the helicopter had been running “flawlessly.”

A witness who was at the airfield outside of his hangar stated that he noticed the helicopter depart from MEV. About 2 hours later, he heard the helicopter approaching the airport and saw what appeared to be a normal approach profile. The witness then heard “three or four pops occurring in rapid succession” followed by a “louder, deeper sound.” He then heard a sound consistent with the helicopter hitting the ground “very hard” and observed the helicopter on the ground and on fire.

The helicopter came to rest upright in a level field covered in short vegetation. The postcrash fire consumed all the airframe except for the fenestron, engine, transmission, and main rotor assembly. Examination of the crash site revealed that the fenestron and a small section of the tailboom separated from the helicopter. The three main rotors remained intact and attached to the hub. All three main rotor blades were thermally damaged near the blade roots and exhibited low-energy rotational damage, including minor chordwise and spanwise bending. The tips of the main rotor blades had minor damage. The transmission remained within the remnants of the fuselage. The engine separated from the fuselage.

Postaccident examination of the engine revealed that it sustained thermal and impact damage. The compressor would not manually turn, but the engine had a large dent in the turbine case that possibly caused interference. A borescope inspection was performed on the turbine wheels, and no physical or thermal damage was observed. The fuel control and the compressor bleed valve were removed for examination, which revealed no mechanical malfunctions or failures that would have precluded normal operation. A teardown examination of the main gearbox transmission revealed no evidence of seizure.

The pilot purchased the helicopter in 2009 and registered it as a normal category helicopter. According to a mechanic who maintained the helicopter for the pilot, he received checklists with notes about maintaining the helicopter from a representative of the previous owner. A review of the checklists revealed that the information was consistent with the engine manufacturer’s prescribed maintenance schedule. The mechanic placed the helicopter under an annual maintenance program, which, according to the mechanic, was similar to the manufacturer’s periodic program. The mechanic also stated that some maintenance was conducted sooner than what was called for in the manufacturer’s periodic schedule.

A review of the maintenance logbooks revealed that the Turbomeca Astazou XIVH turboshaft engine had 5,274.5 hours total time and 1030.5 hours’ time since overhaul. The engine logbook documented annual inspections from 2011 to 2019 and recorded a total of 167.8 hours during that time. According to the mechanic, the owner had operated the helicopter for a total of about 245 hours as of the date of the accident.

The mechanic reported that he conducted an engine compressor wash as part of each annual inspection, the last of which occurred in July 2019. He conducted the compressor wash on his own and rotated the engine, sprayed a cleaner/alcohol mix into the compressor while it ran down, and rinsed the engine compressor in the same manner. The mechanic reported using water that was not demineralized and used Rustlick detergent until he ran out then switched to a light detergent. The mechanic did not run the engine after the compressor rinse. According to the engine manufacturer, “not running and drying the engine could be detrimental because moisture finds its way into everything including the oil. If it is not run afterwards, it will not be eliminated.” A list of approved engine wash detergents did not include Rustlick.

The engine manufacturer identified the compressor wash requirement as a 50-hour engine cleaning (a daily rinsing, a weekly/25-hour washing, and a monthly/50-hour cleaning in a sandy atmosphere). Additional data provided by the engine manufacturer stated, “When engine operates in corrosive environment or a rinsing with non-de-mineralized water is carried out, there is pollution of the hot section parts of the engine. This causes a decrease of the pressure in the combustion chamber and of the HP turbine performance. The result of this issues is an increase in the T45 measure and therefore a decrease of the T4 margin.”

According to the engine manufacturer’s maintenance manual,

Engine performance degradation generally results from the compressor fouling and/or corrosion. The operator may prevent this deterioration by applying the compressor field cleaning procedure.

The compressor cleaning must be carried out often to be effective, because if applied to late, the coat of dirt is fixed, and it becomes very difficult to clean it without dismantling the engine.

Other reasons for engine performance degradation are:

Erosion of the air ducts

Ingestion of foreign objects

Vibrations with rubs leading to an abnormal increase of functional clearances

Unbalance caused by the accumulation of foreign objects.

Additionally, the manufacturer stated that, “the absence of engine washes effect is hard to quantify; however, it may lead to a dirty engine (in a salty environment can even lead to mechanical damage). Dirt has an impact on engine performance, which lead to an increase in T4 [exhaust gas temperature] to be compensated.”

The helicopter manufacturer published Service Letter No. 628-77-84, dated September 20, 1984, with the subject line “Helicopters SA 342-K-L-J Engine Condition Check: Ageing follow-up, which provided “further information about the engine ageing follow-up method; this letter does not modify the procedure described in the Flight Manual but provides details applicable to the various cases met in operation.” According to the mechanic, the owner had performed at least two of the engine aging follow-up checks listed in the service letter, but there was no documentation of the results of the checks.

The height/velocity diagram for the AS342J helicopter indicated that, while at a height of 25 feet above the ground and an airspeed of 15 to 20 knots, the helicopter would be operating inside the “avoid continuous operation” region.

The Federal Aviation Administration’s Helicopter Flying Handbook (FAA-H-8083-21B) states in part, “by carefully studying the height/velocity diagram, a pilot is able to avoid the combinations of altitude and airspeed that may not allow sufficient time or altitude to enter a stabilized autorotative descent.”