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.
John Hannon
The National Transportation Safety Board traveled to the scene of this accident.
Additional Participating Entities:
Federal Aviation Administration / Flight Standards District Office; Saddlebrook, New Jersey
Textron Aviation; Wichita, Kansas
Lycoming Engines; Williamsport, Pennsylvania
Hartzell Engine Technologies; Piqua, Ohio
Aviation Accident Factual Report - National Transportation Safety Board: https://app.ntsb.gov/pdf
Investigation Docket - National Transportation Safety Board: https://dms.ntsb.gov/pubdms
http://registry.faa.gov/N63TV
NTSB Identification: ERA15FA312
14 CFR Part 91: General Aviation
Accident occurred Saturday, August 15, 2015 in West Caldwell, NJ
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.
HISTORY OF FLIGHT
On August 15, 2015, at 1002 eastern daylight time, a Cessna T206H, N63TV, impacted trees and terrain after a loss of engine power during initial climb at Essex County Airport (CDW), Caldwell, New Jersey. The commercial pilot was fatally injured, and the airplane was destroyed. The airplane was registered to Stalactite, LLC, and operated by the pilot under the provisions of 14 Code of Federal Regulations Part 91. Visual meteorological conditions prevailed, and no flight plan was filed for the positioning flight, destined for Teterboro Airport (TEB), Teterboro, New Jersey.
According to a friend of the pilot, the pilot planned to fly to TEB, pick up the owner of the airplane and fly with him to South Hampton, where the owner had a residence. The friend owned a Cessna 182 and was interested in purchasing a Cessna 206 like the one the pilot was flying, so the pilot invited him to come to CDW before the flight and see the airplane.
The friend arrived at the airport about 0930 and noticed that the pilot had already completed the preflight inspection of the airplane. The pilot appeared to be "fine, his usual self, and doing good that morning," The pilot's friend was in the fixed base operator's (FBO) lobby when he heard the airplane's engine start. The airplane stayed on the ramp for a few minutes and then taxied out. About 10 minutes later, the pilot's friend saw the airplane as it passed by a window in the FBO. The airplane seemed quieter than it should have to him, and he thought that it did not seem to be moving very fast. About 10 minutes later, a line service agent entered the FBO and said that there had been an airplane accident.
According to information provided by the Federal Aviation Administration (FAA), the pilot contacted the CDW air traffic control tower, requested to taxi, and advised the controller that he had the current weather that was being transmitted by CDW's automatic terminal information service. The controller subsequently instructed the pilot to taxi to runway 22 and to hold short of the runway at intersection "November," which was normally used for airplanes departing on runway 22. The airplane taxied to the designated location and remained there for about 5 minutes. According to FAA inspectors, during the time that the airplane remained stationary, a student pilot heard the airplane's engine go from near idle to full power about five times and reported that the engine did not "sound right."
The air traffic controller cleared the pilot for takeoff with a left turnout. Shortly after becoming airborne, the pilot 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 pilot.
Review of security camera video revealed that, during the takeoff, the airplane appeared to accelerate slowly and rotated about 1,800 ft. after the pilot initiated the takeoff roll." Once airborne, the airplane began to pitch slightly up and down while remaining in ground effect and then slowly climbed. The airplane momentarily reached an altitude that was just above the trees that surrounded the airport, then began to lose altitude, and turned left about 90°. The airplane disappeared from view of the camera, and a smoke cloud then rose from behind a tree line.
According to witnesses who saw the airplane just before impact, the airplane was at the same height as the trees and appeared to be gliding toward the ground. One witness stated that the airplane appeared to be "in slow motion;" it then banked sharply to the left and pitched steeply down. Another witness reported that the airplane made "a hard-left turn, went into a nose dive, and exploded when it hit the ground." Three additional witnesses reported similar observations. The witnesses heard no noise coming from the airplane before the impact.
PERSONNEL INFORMATION
According to FAA and pilot records, the pilot held a commercial pilot certificate with ratings for airplane single-engine land and instrument airplane, a flight instructor certificate with a rating for airplane single-engine, and a ground instructor certificate with an advanced ground instructor rating. His most recent FAA third-class medical certificate was issued on March 30, 2015. He had accrued about 1,941 total hours of flight experience, 16 hours of which were in the accident airplane make and model.
AIRCRAFT INFORMATION
The airplane was a 6-place, single-engine, high-wing monoplane of conventional metal construction. It was equipped with fixed-tricycle-type landing gear and was powered by a turbocharged, 310-horsepower, Lycoming TIO-540-AJ1A engine, driving a three-blade, McCauley, controllable pitch propeller.
According to FAA and maintenance records, the airplane was manufactured in 2009. Its most recent annual inspection was completed on April 17, 2015. At the time of the inspection, the airplane and engine had accrued 1,155.4 total hours of operation.
According to the maintenance provider who had maintained the airplane since December 2011, anything that bothered the owner about the airplane would get fixed. Most of the items that were addressed by the maintenance provider were cosmetic or routine maintenance, such as oil and filter changes, gauges, starter replacement, lights, accessories, battery replacement, and compliance with airworthiness directives and service bulletins. The maintenance provider reported that the owner's landings could be a little rough, so they had also replaced some tires as he had experienced a few flat tires, and, as a result, the owner would keep a spare set in the airplane in case he blew a tire on landing.
Review of maintenance records revealed that the airplane's engine had been receiving regular oil changes since new as well as spectrometric oil analysis. Review of oil analysis reports provided by the maintenance repair organization indicated that a sample of the engine's oil that was taken on March 5, 2012, contained elevated levels of iron, nickel and chromium. Another sample taken on December 19, 2013, contained elevated levels of aluminum, chromium, iron, and nickel. In a report dated March 9, 2015, the laboratory commented about an oil sample that had been taken on March 4, 2015, stating that:
"These numbers are a lot easier to take than the high aluminum, chrome, iron, and nickel we saw last time. The shorter oil run obviously helped, but most of the metals are lower on a ppm/hour basis too, meaning that the engine really did wear better. If anything, nickel could still stand to be lower. 13 ppm is almost high enough to get a mark, so that's one we'll be monitoring next time. There's a trace of fuel to report this time, but that's not anything to worry about. It's likely just from normal use. Much better at 1,151.6 hours S[ince ]New."
In a report dated August 12, 2015, for an oil sample that was taken on August 4, 2015 (11 days before the accident), the laboratory commented that:
"Steady as she goes for this sample out of N63TV. If we're being picky you could say that iron should have come down as a result of the shorter oil run, but 39 ppm isn't bad at all for one of these engines after 20 hours on the oil. Everything else is in good shape, so we'd be surprised if the extra iron on a per-hour basis turned out to be an issue. No problems with the oil itself were found, making for a very nice report overall."
Maintenance records indicated that two repairs requiring replacement of major components of the engine had been accomplished. The first repair followed a report from the owner that the engine was experiencing high oil consumption. According to a maintenance entry dated January 21, 2013, and the associated work order, this resulted in the maintenance provider inspecting for the cause of the oil leaks by first washing down the engine, and then after a test flight, tightening loose rocker box return line coupling clamps, replacing a cracked air/oil separator, replacing leaking oil dipstick gaskets, and replacing a leaking fitting on the turbocharger wastegate actuator. During this inspection and maintenance action, maintenance personnel noticed oil on the inlet scroll of the turbocharger and oil on the belly of the airplane, so they replaced 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. According to a maintenance entry dated May 22, 2013, and the associated work order, this resulted in the maintenance provider checking the compressions and borescoping the cylinders.
During this inspection and maintenance action, maintenance personnel found pooled oil in the Nos.3, 5, and 6 cylinders. Per guidance from a Lycoming representative, they attached an airspeed indicator to a modified oil dipstick cap and then ran the engine. No excessive crankcase pressure was found. Next, they ran the engine to get the temperature up and shut down the engine at 1,300 rpm. Then they borescoped the cylinders again and found that all of the pistons were damp, all of the spark plugs were dry, and there was pooled oil in the Nos. 3, 5, and 6 cylinders. After these tests, maintenance personnel removed the Nos. 3, 5, and 6 cylinders and found the oil control rings stuck in the pistons. They installed new Nos. 3, 5, and 6, cylinder assemblies.
The maintenance records did not indicate that the check valve on the turbocharger oil supply line was cleaned or replaced following either of these engine repairs.
Turbocharger System Information
The airplane was equipped with a turbocharging system manufactured by Hartzell Engine Technologies (HET) that forced air into the engine's combustion chamber, allowing the engine to maintain sea-level manifold pressure as altitude increased. The turbocharging system consisted of a turbocharger, controller, wastegate, and pressure relief valve.
The turbocharger converted wasted energy, in the form of hot exhaust gases from the engine exhaust, into increased manifold pressure to increase power available from the engine. After air and fuel were burned in the cylinders, the exhaust gases from combustion were used to spin a turbine wheel at high speeds. The turbine wheel was connected to a compressor wheel that compressed induction air supplied through an opening in the lower cowl, that was ducted through a filter and into the compressor, increasing its density. The pressurized induction air would then pass through the throttle body and induction manifold into the engine cylinders, completing the cycle.
The controller sensed manifold pressure to maintain sea level horsepower at altitude, without over-speeding the turbocharger or over-boosting the aircraft's engine. It did this by controlling pressurized engine oil to hydraulically actuate the wastegate. The wastegate (exhaust bypass valve), used speed or compressor discharge pressure (boost) during certain conditions of a flight. Managed through the controller, the wastegate opened to allow exhaust gas to bypass the turbocharger, limiting speed and boost.
The pressure relief valve acted as a supplementary safety device in the airplane turbocharger system. The valve was set to open at a pressure slightly above the maximum turbocharger discharge pressure, should the controller or wastegate not adequately limit the boost pressure.
According to HET, the turbocharger operates at speeds over 100,000 rpm and at temperatures exceeding 1,650ºF, and oil is required at the correct flow rate and pressure to lubricate the bearings, stabilize the rotating shaft and bearings, and act as a coolant. The system's lubricating oil comes directly from the engine's oil system, so shutting down the engine immediately stops the flow of oil to the turbocharger. If the turbocharger is still turning at a high rate of speed when oil flow is cut off, the turbocharger bearings can be damaged. In addition, any stagnant oil remaining around the extremely hot turbine shaft will overheat and "coke" or burn.
The controller and the wastegate also use engine oil and pressure for operation and control of the turbocharger. If either one is contaminated by oil, does not receive the correct oil flow rate, or lacks sufficient oil pressure to function, system performance is compromised. In the event of malfunction of a turbocharged engine, HETs experience is that maintenance personnel assume that the turbocharger is at fault and replace it. Frequently the replacement unit fails, which prompts an investigation into the real cause of the initial failure. According to HET, the major cause of turbocharger failures is faulty lubrication systems.
The accident airplane was equipped with a check valve on the turbocharger oil supply line, which was located upstream from the turbocharger and regulated the supply of oil that it received. HET does not require the use of check valves, and the check valve installed on the airplane was supplied by the engine manufacturer. The check valve was used to prevent oil from draining into the turbocharger after shutdown and pooling in the turbocharger body. According to HET, this pooling can result in stagnant oil remaining around the extremally hot turbine shaft and coking or burning. Along with coking, bearing damage can occur that causes the bearings to orbit instead of spin, which can lead to turbine and/or compressor rub, wear, and failure.
If a check valve sticks in an open or partially open position, this allows the turbocharger's center body to fill with oil; the oil then leaks past the seals because the oil cannot drain and is not being scavenged. The absence of turbo air pressure (both in the compressor and turbine housings) also does not assist in preventing oil leakage past the piston rings, which can result in the presence of oil in the compressor/induction system (evidence of oil in the combustion chambers) and/or the turbine/exhaust system (resulting in smoking during engine start).
METEOROLOGICAL INFORMATION
The recorded weather at CDW, at 1012, about 10 minutes after the accident, included: variable winds at 3 knots, 10 miles visibility, clear skies, temperature 28°C, dew point -17°C, and an altimeter setting of 30.13inches of mercury.
AIRPORT INFORMATION
CDW was owned by the Essex County Improvement Authority and was located 2 miles north of Caldwell, New Jersey. It was classified by the FAA as a publicly owned, tower controlled, public use airport.
The airport elevation was 172 ft above mean sea level and was oriented in a 10/28 and 4/22 runway configuration. Runway 22 was asphalt, in good condition, and measured 4,552 ft long by 80 ft wide with a 0.2% gradient. The threshold was displaced 134 ft. The runway was equipped with high intensity runway edge lights and runway end identifier lights and was marked with nonprecision markings in good condition.
WRECKAGE AND IMPACT INFORMATION
The accident site was located in a wooded area about 0.3 nautical mile from the departure end of runway 22 on a magnetic heading of 156°. Examination of the accident site revealed that the airplane impacted terrain on a 20° magnetic heading after striking several trees. Further examination revealed that the airplane impacted in a nose-down, inverted attitude. During the impact sequence, the engine separated from its mounting location. The empennage was displaced about 20° to the left of the fuselage centerline and was partially separated from the aft fuselage. The wings were separated from their mounting locations. The fuselage came to rest upright on a 100° magnetic heading against the base of a tree. The majority of the fuselage was consumed by a postimpact fire.
The wing flaps were found in the up position. The elevator trim was near neutral. The fuel selector valve was in the "BOTH" position, and there was no evidence of fuel blockage. Control continuity was established from the ailerons, elevator, and rudder to the flight controls in the cockpit. There was no evidence of any inflight structural failure.
Examination of the propeller revealed that one of the three blades separated during the impact sequence and came to rest about 30 ft from the rest of the propeller assembly. The propeller blades did not display evidence of propeller rotation during the impact sequence.
Examination of the engine revealed that the rear of the engine had been heavily damaged by the postcrash fire, and the magnesium oil sump was destroyed by fire.
The engine's fuel system was heavily damaged by the postcrash fire. The engine-driven fuel pump was destroyed by the postcrash fire. The fuel servo inlet fuel screen was free of contaminants, and the diaphragm displayed thermal damage. The fuel flow divider was thermally damaged.
The left magneto's internal windings were found in the molten metal beneath the engine. The right magneto was found loosely attached to the rear accessory housing and was thermally damaged.
Attempts to rotate the engine drive train by hand were unsuccessful. There was no evidence of any type of blockage in the intake or exhaust systems. The spark plug electrodes displayed evidence of black sooty deposits indicative of carbon fouling. A portion of the No. 3 piston's skirt was missing; metal fragments were present in the crankcase, and metal was found extruded from the edges of the No. 3 main engine bearing.
The turbocharger system was partially destroyed by the postimpact fire; a majority of the damage was to the compressor housing and compressor wheel. The turbine housing exhaust port did not display evidence of turbine wheel rotation during the impact sequence. The turbocharger was secured to its mount with the exhaust pipes separated from the exhaust bypass valve on both ends. The slope controller and the pressure relief valve were destroyed by the post impact fire, and the exhaust bypass valve was partially destroyed but remained attached to the turbocharger.
MEDICAL AND PATHOLOGICAL INFORMATION
The Office of the State Medical Examiner, State of New Jersey, performed an autopsy on the pilot. The listed cause of death was blunt impact injuries.
The FAA Bioaeronautical Sciences Research Laboratory, Oklahoma City, Oklahoma conducted toxicological testing of the pilot. The specimens were negative for carbon monoxide.
Carvedilol, which is used to treat high blood pressure, was detected in urine and blood, and
quinapril, which is used to treat hypertension, was detected in urine. Use of these two non-impairing drugs was previously reported by the pilot to the FAA. Salicylate (aspirin) was detected in urine.
Review of FAA medical certificates and supporting documentation indicated that the pilot had a history of high blood pressure and a myocardial infarction with stent placement in 2007. Based on clinical reports, his conditions were stable, and no significant conditions were identified during his FAA physical examinations.
TESTS AND RESEARCH
At the request of the NTSB, Lycoming analyzed the metal fragments found in the engine crankcase and the metal extruded from the No. 3 main bearing. Lycoming determined that the metal fragments found in the engine crankcase were cast aluminum material. Chips recovered from the sludge in the crankcase were also made of the same material. The material was not from the No.3 piston and was most likely from the crankcase or other housing. The metal that was bulged or extruded out from the edges of the No. 3 main bearing (both halves) was made primarily of lead, with some tin and copper, indicating that it came from the bearing overlay material. It also indicated that the bearings experienced some localized melting and flow of the overlay material from the postcrash fire.
The turbocharger and wastegate were examined at Lycoming Engines by HET under the supervision of the NTSB. Examination of the turbocharger revealed that the compressor housing and mounting surfaces had been consumed by fire. The compressor wheel had been heavily damaged by fire. The compressor wheel nut was tight, and the compressor oil film journal bearing's radial holes were clear.
The compressor thrust collar radial holes were clear; there was no evidence of scratches, scoring, or galling of the end surfaces and no evidence of rubbing on the compressor backplate seal bore. There was no scoring or worn face areas on the compressor inboard thrust bearing.
The compressor back plate was corroded from heat and water exposure. No damage was observed to the attachment surfaces, and the seal bore inside diameter spacer was not damaged or scored. The compressor back plate oil squirt holes were also clear.
The turbocharger's turbine wheel could not be turned by hand. The turbine oil film journal bearing's radial holes were clear. No evidence of turbine wheel rub was present, and clearance existed between the turbine wheel blades and the turbine housing. The turbine wheel did not display evidence of foreign object damage or bent blades.
Examination of the center bearing housing revealed that there was no evidence of residual oil, and extreme corrosion was present. The oil squirt holes were clear, and no evidence of the outlet port being restricted by coking was discovered. The outlet and inlet gaskets were heat damaged.
The anti-rotation pins were of the split type, and they were secure and properly oriented.
The wastegate valve was free and could move through its full range of motion. The wastegate actuator body had been completely consumed by the postcrash fire; only the valve housing assembly, actuator shaft assembly, springs and retainer remained
At the request of the NTSB, Lycoming radiographically inspected the oil supply line check valve, which was located upstream from the turbocharger and regulated the supply of oil that it received. Review of the low-resolution x-ray images by Lycoming personnel indicated that the internal components appeared to be in sound condition, there was no obvious foreign object damage, and the ball was resting on the seat. The x-ray film also showed that the internal spring was slightly cocked about 5°.
The check valve assembly was then tested by installing it in a flow testing fixture, and the oil pressure was monitored while observing the check valve for flow. The engineering drawing specified the performance as follows: "No leakage allowed below 8 [pounds per square inch] psi; and check valve must open at 13 psi ±2 psi oil pressure". Leakage was observed from the check valve exit hole before 1 psi of pressure was reached. The oil stream flowing from the check valve steadily increased, and the vertical level of the stream rose higher until about 5 to 6 psi pressure was reached. At that point, the stream was nearly a straight jet of oil.
The turbocharger and oil supply line check valve were submitted to the NTSB Materials Laboratory for further examination. Examination of the turbocharger components revealed that they exhibited surface oxidation (rusting) and evidence of coking with soot residue. These conditions were consistent with exposure to fire, as well as exposure to water. The center bearing housing of the turbocharger had rusted to a degree that the iron oxide was starting to spall. No other visible damage, such as distortion, wear, or cracking, was present on the component exterior. The center housing was radiographed and inspected using computed tomography (CT) scanning. There were no discernable features noted on the center housing using these techniques.
The center housing was sectioned using a band saw with a water-based emulsion-coolant. The location of the sectioning was along the position of the turbine wheel. The housing bearing on the turbine side exhibited longitudinal score marks that were consistent with removal of the shaft, which had partially fused to the bearing. It also displayed circumferential wear, with relatively less rust and other surface contamination compared to the bearing on the compressor side. Gouging was also present on the interior surface of the turbine side bearing. There was no evidence of damage to, or blockage of, the oil holes.
The center housing bearing on the compressor side exhibited primarily circumferential wear. The longitudinal marks on the bearing were consistent with machine marks or sliding. There was internal surface rusting on this bearing. There was no evidence of blockage or damage to the oil holes or channels in this section of the housing. No other indications of internal mechanical malfunctions were found inside the center housing.
The turbine wheel blade fins did not exhibit any mechanical damage consistent with foreign object impacts, overheating, or distortion. There was no chipping or cracking observed.
The tapered stub shaft of the compressor side had fractured away from the threaded portions of the shaft during removal for examination. The features on the fracture surface had been entirely obliterated by smearing, consistent with post-fracture damage, and the area adjacent to fracture exhibited a jog on one side, with a general flat surface. This pattern was consistent with overstress failure in shear of a ductile material.
Gouge marks were present on the hexagonal cap on the turbine side of the wheel and most probably occurred during removal. Theses marks were consistent with an impact with an adjacent component or tool, in a clockwise rotation. The turbine side bearing surface of the turbine wheel also exhibited longitudinal gouging marks, in addition to the circumferential wear marks. These gouge marks matched those of the bearing surface of the sectioned center housing. These marks were consistent with the wheel assembly shifting forward while positioned in the housing.
The turbocharger oil supply line check valve and an exemplar check valve were inspected by radiography and CT scanning. The accident check valve exhibited a small gap between the ball and the internal channel along the neck. The spring that held the ball was angled. Neither the ball nor the spring in the exemplar check valve exhibited the features noted in the accident valve.
Sectioning of the accident check valve revealed 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. Fourier transform infrared spectroscopy revealed that the spectra of the foreign material was similar to lubricating oil.
ADDITIONAL INFORMATION
Lycoming Maintenance Guidance
A review of Lycoming's maintenance guidance revealed that the direct drive engine overhaul manual did not explicitly address the turbocharger system, nor was there guidance for checking or replacing the check valve, flushing of any reused oil lines, or flushing of other components such as the turbocharger, controller, wastegate, or air-oil separator. Further review also revealed that for maintenance personnel to maintain, repair, or replace the turbocharging system on the TIO-540-AJ1A model engine, a mechanic would have to rely on multiple documents including the Illustrated Parts Manual for the parts needed, the Service Table of Limits for applicable torques, and Service Bulletins, Service Letters, and Service Instructions applicable to that model or individual component for replacement.
Pilot Operating Handbook
Review of the Cessna T206H Pilot Operating Handbook (POH) short field takeoff performance charts revealed that when configured to a 20-degree flap setting, and assuming a 30° C temperature at sea level, the airplane's expected ground roll would be between 670 and 1015 feet, at a gross weight of 3,000 and 3,600 pounds respectively. The short field landing distance performance chart shoed that under similar conditions, and a gross weight of 3,600 pounds, the airplane's expected ground roll was 775 feet.
Further review of the POH also revealed that it did not list emergency procedures for turbocharger failures, under "ENGINE FAILURES," in Section 3 (Emergency Procedures). Under "ENGINE FAILURE DURING FLIGHT (Restart Procedures), in the POH, it also called for advancing the mixture control to the rich position if restart does not occur.
Cessna's "Pilot Safety and Warning Supplements," which was reissued in 1998 to incorporate turbocharger failures, stated, in part: "A failure of the turbocharger system will cause either an overboost condition or some degree of power loss. An overboost can be determined on the manifold pressure instrument and can be controlled by a throttle reduction. If turbocharger failure results in power loss, it may be further complicated by an overly rich mixture. This rich mixture condition may be so severe as to cause a total power failure. Leaning the mixture may restore partial power. Partial or total power loss could also be caused by an exhaust leak. A landing should be made a soon as practical for either an overboost or partial/total power loss."
Continental TSIO-520-C Engine
Some earlier models of the Cessna 206 were equipped with a turbocharged Continental TSIO-520-C engine, which was rated at 300 horsepower. Both the Continental TSIO-520-C and the Lycoming TSIO-540-AJ1A engines use turbochargers manufactured by HET. Review of system information for the Continental TSIO-520-C revealed that it also used a spring-loaded check valve to control oil flow through the turbocharging system and prevent oil flow from the engine oil cooler to the turbocharger when the engine was shut down.
Published guidance was issued by Continental Motors in a service bulletin (Service Bulletin SB16-3), which advised that if the check valve did not close properly or became blocked with foreign matter, the check valve may remain open, allowing oil to continuously flow to the turbocharger (after the engine is shut down and the oil scavenge pump is no longer actively returning oil to the engine oil sump).
The service bulletin also advised that characteristic symptoms associated with a blocked check valve are turbocharger oil leakage and oil leakage through the tailpipe or induction system.
It also included the following statement: "NOTE: Do not assume an oil leak from the turbocharger is simply an incorrectly operating check valve – thoroughly troubleshoot for causes of all turbocharger oil leaks."
The service bulletin also required that the check valve be checked:
- At each 50-hour inspection.
- Whenever a turbocharger oil leak was detected.
- Immediately following an engine test run after cylinder(s) replacement.
- After replacing lubrication system components.
NTSB Recommendation A-94-81
On April 11, 1994, the NTSB issued Safety Recommendation A-94-81 as a result of its investigation of a January 13, 1992, accident (NTSB Case No. LAX92FA092) involving a Cessna T210L, N22592, that occurred at the Temple Bar Airport, Temple Bar, Arizona, as the pilot attempted to execute an emergency landing. Two of the five persons aboard were killed, and three were seriously injured when the airplane struck the ground short of the runway. The pilot reported that the airplane had sustained a partial loss of engine power during cruise, but that he could not determine the nature of the problem. While descending to the airport, he turned the fuel boost pump on, and the engine lost additional power. Just before arriving over the airport, the cockpit and cabin areas filled with smoke, and the pilot secured the engine.
The NTSB determined that the probable causes of this accident were fatigue failure of the turbocharger's turbine shaft due to inadequate maintenance and the pilot's improper in-flight planning/decision after experiencing a turbocharger failure. Additionally, the lack of written instructions or an emergency procedure in the Cessna T210L Pilot's Operating Handbook (POH) relating to turbocharger malfunctions or failures contributed to the accident.
The NTSB's safety recommendation letter stated, in part:
From January 1, 1988, to May 4, 1993, there were 88 accidents and incidents involving aircraft engine turbochargers, resulting in 6 fatalities and 35 injuries. Many of these occurrences, in both single and twin-engine airplanes, involved loss of engine power, fire in flight, or smoke in the cockpit. Moreover, from January 1, 1986, to May 4, 1993, the Federal Aviation Administration (FAA) received 580 Service Difficulty Reports (SDRs) regarding aircraft turbocharging systems. The reports contained detailed system malfunctions that, in many cases, were attributed to inadequate installation, inspection, maintenance, service, or overhaul. The Safety Board noted, in connection with a significant number of the accidents, that improper pilot remedial actions following the turbocharger malfunction or failure may have contributed to these occurrences. For example, because compressed air to the engine normally produced by the turbocharger was no longer available, use of the boost pump, as evidenced in the accident with N22592, aggravated an already overly rich fuel mixture condition. This resulted in a further reduction in engine power and subsequent inability to sustain flight. Other inappropriate pilot actions or responses cited in accident reports that may also have exacerbated the loss of engine power or caused an in-flight fire because of turbocharger failure include the following: use of an inadequate emergency procedure, improper adjustment of the fuel mixture, improper use of the throttle control, and operating with known deficiencies in equipment."
Safety Recommendation A-94-81 asked the FAA to "require the amendment of pilot operating handbooks and airplane flight manuals applicable to aircraft equipped with engine turbochargers by including in the "Emergency Procedures" section information regarding turbocharger failure. The information should include procedures to minimize potential hazards relating to fire in flight and/or loss of engine power."
In a July 3, 1995, response, the FAA stated that it agreed with the intent of Safety Recommendation A-94-81 but did not believe that there was sufficient basis to issue an airworthiness directive applicable to all aircraft flight manuals (AFMs) or POHs with turbocharger installations. The FAA indicated, however, that it would take the following actions: 1) revise the AFM policy regarding minimum safe operating procedures following turbocharger failures during the next revision of Advisory Circular (AC) 23-8A "Flight Test Guide for Certification of Part 23 Airplanes;" 2) provide copies of Safety Recommendation A-94-81 to all aircraft certification offices and direct each office to provide the recommendation to each holder of a type certificate or supplemental type certificate having a turbocharged engine installation; 3) request type certificate or supplemental type certificate holders to revise their AFMs, POHs, or AFM supplements, as appropriate, to comply with Safety Recommendation A-94-81; and 4) provide the Safety Board a copy of the revised General Aviation Manufacturers Association (GAMA) Specification No. 1, "Specification for Pilots Operating Handbook," to address safe operating procedures following turbocharger failures.
Until the next revision to AC 23-8A was accomplished, the FAA issued a policy letter dated February 16, 1995, which added turbocharger failure procedures to the established list of systems that should be considered when evaluating the emergency procedures section of the AFM. In an August 15, 1997, response, the NTSB classified Safety Recommendation A-94-81 "Closed—Acceptable Alternate Action" based on the FAA's issuance of the policy letter, as well as the FAA's agreement to revise AC 23-8A.
NTSB Recommendation A-08-21
On May 13, 2008, the NTSB issued Safety Recommendation A-08-21 as a result of its investigation of a May 28, 2004, accident (NTSB Case No. CHI04GA130) involving a Cessna T206H, N9548D, that impacted terrain following a loss of engine power during cruise flight near Homer Glen, Illinois. The pilot was fatally injured, and the airplane was destroyed. Witnesses reported that they heard several attempted engine restarts as the airplane descended, and a witness reported that black smoke emanated from the airplane during each start attempt. The black smoke was indicative of a mixture that was too rich. Postcrash examination revealed that the turbocharger had seized. The oil supply line check valve was tested, and it would not hold 8 psi of oil pressure. Oil and debris were seen being expelled from the check valve assembly when it was placed under oil pressure. Examination of the airplane's POH revealed that the in-flight emergency procedures lacked information to assess the difference between an engine and a turbocharger failure and did not provide any clear guidance or instructions on how to handle a turbocharger failure once a pilot identified the problem.
The NTSB determined that the probable causes of this accident were:
The seized turbocharger, the altitude/clearance not maintained/obtained during approach to a forced landing on an agricultural field, and the unsuitable landing area encountered by the pilot. Contributing factors were the inadequate emergency procedures by the manufacturer, the trees, and the residential area.
The NTSB's safety recommendation letter stated, in part:
The Safety Board notes, however, that the intent of Safety Recommendation A-94-81 has still not been fully realized. In connection with its investigation of the May 28, 2004, accident in Homer Glen, Illinois, the Safety Board also reviewed a representative sampling of POHs for other airplane makes and models and determined that procedures addressing turbocharger failures have either not been incorporated in the emergency procedures section or, if included, are incomplete, potentially leading to an incorrect identification and response to a turbocharger failure that could result in a total loss of engine power. A query of the Safety Board's accident database revealed that from May 1, 1993, to the present, 23 accident/incidents have occurred involving aircraft engine turbochargers, resulting in 23 fatalities and 3 injuries; 15 of these accidents/incidents have occurred (resulting in 9 fatalities) since 1997, when Safety Recommendation A-94-81 was closed.
Safety Recommendation A-08-21 asked the FAA to "require manufacturers of aircraft equipped with engine turbochargers to amend their pilot operating handbooks and airplane flight manuals to include in the "Emergency Procedures" section information regarding turbocharger failure and, specifically, procedures to minimize potential hazards relating to fire in flight and/or loss of engine power."
On June 11, 2012, the NTSB classified Safety Recommendation A-08-21 "Closed—Unacceptable Action" based on the FAA's decision not to take the recommended action. In its classification letter, the NTSB stated it "remains concerned that, without the establishment of an FAA requirement, manufacturers of aircraft equipped with turbochargers still have not voluntarily included emergency procedures for turbocharger failures, and as a result, accidents and incidents continue to occur."
