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Aviation Accident

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NTSB Identification: ERA15FA312
14 CFR Part 91: General Aviation
Accident occurred Saturday, August 15, 2015 in West Caldwell, NJ
Probable Cause Approval Date: 09/18/2017
Aircraft: CESSNA T206H, registration: N63TV
Injuries: 1 Fatal.

NTSB investigators either traveled in support of this investigation or conducted a significant amount of investigative work without any travel, and used data obtained from various sources to prepare this aircraft accident report.

The commercial pilot was departing in the turbocharged airplane to go to another airport and pick up the owner of the airplane. He contacted the air traffic control tower and received instructions from the controller to taxi to the active runway and hold short. The airplane taxied to the designated location and remained there for about 5 minutes. During this time, a student pilot heard the airplane's engine cycle from near idle to full power about five times and reported that the engine did not "sound right." The pilot requested and received clearance to takeoff, and, shortly after becoming airborne, advised that he had a "problem," declared an emergency, and requested to "return to the field immediately." The controller cleared the pilot to land on any runway, and the pilot reported that he was unable to maintain engine power. There were no other communications from the airplane.

Review of security camera video revealed that the airplane was slow to accelerate and did not rotate until about 1,800 ft down the 4,552-foot-long runway from the point where the pilot initiated the takeoff roll. Once airborne, the airplane began to pitch slightly up and down while remaining in ground effect. Considering that the pilot was the only occupant of the six-seat airplane, the airplane should have become airborne much sooner. Further, there was adequate runway remaining at the point of rotation for the pilot to abort the takeoff and stop on the remaining runway. However, the pilot elected to continue the takeoff.

The airplane climbed slowly, momentarily reaching an altitude that was just above the trees that surrounded the airport, then began to lose altitude, and turned left about 90°. The airplane then disappeared from view of the camera, and a smoke cloud was observed to rise from behind a tree line. Witnesses who observed the airplane just before impact saw the airplane gliding toward the ground "in slow motion" and heard no noise coming from the airplane. The witnesses reported that the airplane then rolled into a steep left bank, entered a nose dive, and exploded when it hit the ground. The witness observations were consistent with the pilot failing to maintain adequate airspeed, resulting in the airplane exceeding its critical angle of attack and an aerodynamic stall.

Examination of the wreckage revealed signatures indicating that the propeller and the turbocharger's turbine wheel were not rotating during the impact sequence, which is indicative of a loss of engine power. The spark plug electrodes displayed evidence of black sooty deposits indicative of carbon fouling. The carbon fouling could have been the result of failure of the turbocharging system, which can result in an overly rich mixture condition so severe as to cause a total power failure.

Examination of the turbocharging system revealed that it had been heavily damaged by the postcrash fire, and only the turbocharger and wastegate were recovered. Examination of the turbocharger revealed that the turbine and compressor wheels, which were interconnected by a shaft, could not be rotated by hand as the shaft had partially fused to the bearings likely as a result of exposure to the postcrash fire. The bearing radial holes were clear, and there were no excessive or abnormal scoring marks on the bearings as would be expected if they were contaminated, distressed, or subject to prolonged oil starvation. There was also no coking of oil in the turbocharger body that would have prevented lubrication of the bearings, and no definitive rotational rub marks that would have suggested excessive bearing wear or imbalance. Examination of the wastegate also did not reveal any anomalies, and the wastegate valve was free and could move through its full range of motion. The wastegate actuator body had been mostly consumed by the postcrash fire; only the valve housing assembly, actuator shaft assembly, springs, and retainer remained.

X-ray examination of the oil supply line check valve, which was located upstream from the turbocharger and regulated the supply of oil that it received, showed that instead of being straight, the internal spring was slightly cocked about 5°. Review of the manufacturer's specifications revealed that no check valve leakage was allowed below 8 psi of oil pressure. However, flow testing of the check valve revealed that oil leaked from the check valve exit hole before 1 psi of pressure was reached, which indicated that the check valve was likely not preventing oil from draining into the turbocharger after shutdown and was pooling in the turbocharger body. During further examination of the check valve using computed tomography scanning and radiography, a small gap was found between the ball and the internal channel along the neck. Sectioning of the check valve revealed that the angled spring and the small gap between the ball and the internal channel were due to the presence of contamination in the internal channel on the upstream (inlet) side of the check valve and the presence of foreign material between the ball and the internal channel along the neck. The presence of contamination in the check valve indicated that contamination was likely present in other components of the turbocharging system. Because the controller and the wastegate use engine oil and pressure for operation and control of the turbocharger, if either one is contaminated, system performance can be compromised.

Maintenance records indicated that two repairs requiring replacement of major components of the engine took place about 2 years before the accident. The first repair occurred following a report by the owner of high oil consumption, and it entailed replacing a cracked air/oil separator, leaking oil dipstick gaskets, a leaking fitting on the turbocharger wastegate actuator, and the turbocharger "due to oil leaking past shaft seal intake system." The second repair occurred about 4 months later, when the owner again reported high oil consumption. This resulted in replacement of the Nos. 3, 5, and 6 cylinders because the oil control rings stuck in the pistons of these cylinders, which indicated debris had been deposited in the ring grooves. Although these repairs provided evidence that suggested the oil system was contaminated, the maintenance records did not show that any reused oil lines, the turbocharger oil supply line check valve, or turbocharger system components such as the controller and wastegate were flushed. Further, review of the engine manufacturer's guidance revealed that it did not include instructions for checking or replacing the check valve during inspections, flushing of any reused oil lines, the check valve, and components such as the turbocharger, controller, and wastegate whenever a turbocharger leak was detected, following an engine test run after cylinder replacement, after replacing lubrication system components, or when doing any type of maintenance where contamination or foreign debris could be introduced into the system. If the engine manufacturer had included these instructions and the mechanics had performed actions such as flushing the check valve and turbocharger system components following either of the two engine repairs, it is likely the contamination found in the check valve (and likely present in other components of the turbocharging system) would have been removed. The presence of contamination in the check valve, the airplane's maintenance history, and the carbon fouling of the spark plugs, strongly suggest that the engine lost power due to contaminated oil compromising the performance of the turbocharger system.

The National Transportation Safety Board asked the Federal Aviation Administration in 2008 to require manufacturers to amend their pilot operating handbooks (POHs) to include emergency procedures for turbocharger failures (Safety Recommendation A-08-21). However, the FAA did not take this action, and review of the POH for the airplane revealed that it did not include an emergency procedure for turbocharger failure. Under the emergency procedure for an engine failure, the POH called for advancing the mixture control to the rich position if restart does not occur, but review of the airplane manufacturer's supplementary information revealed that a failure of the turbocharger system would cause either an overboost condition or some degree of power loss and that, if a turbocharger system failure resulted in power loss, it may be further complicated by an overly rich mixture. According to the supplementary information, this rich mixture condition may be so severe as to cause a total power failure. It could not be determined whether the total loss of engine power in this case was due solely to failure of the turbocharger system or whether it was the result of a partial loss of power due to failure of the turbocharger system that was exacerbated by an overly rich mixture.

The National Transportation Safety Board determines the probable cause(s) of this accident as follows:
  • A loss of engine power due to a malfunction of the turbocharging system likely due to contaminated oil. Also causal were the pilot's decision to continue the takeoff although the airplane was not performing normally and his failure to maintain adequate airspeed following the loss of engine power, which resulted in the airplane exceeding its critical angle of attack and an aerodynamic stall. Contributing to the accident was the engine manufacturer's inadequate guidance regarding inspection and maintenance of its turbocharged engines.