ERA10GA320

The total loss of engine power resulting from the fatigue failure of the engine's number 2 cylinder exhaust valve. The fatigue failure was due to valve guide wear that led to excessive clearance between the valve and valve guide. Contributing to the accident was the contract operator’s lack of compliance with its own maintenance procedures, which, if followed, would have prevented the accident.

The aerial observation flight was conducted by a 14 CFR Part 135 certificated on-demand air carrier under contract to the U.S. Forest Service. As the flight neared its destination airport, the pilot reported via the airport's common traffic advisory frequency his intent to land. Witnesses reported that, as the airplane overflew them on approach to the airport, it appeared to be in distress, trailing black smoke with the engine "sputtering." The airplane subsequently impacted a light stanchion about 1,300 feet short of the intended landing runway. Before coming to rest, the airplane struck a house and several parked cars, and it was nearly consumed during a post-impact fire. Postaccident examination revealed a catastrophic failure of the airplane's engine, which originated with a fatigue failure of the number 2 cylinder exhaust valve. The fatigue failure was likely due to abnormal loading associated with excessive valve-to-valve guide clearance resulting from valve guide wear. Typically, valve guide wear results from either overall elevated engine operating temperatures or individually elevated valve temperatures due to improper valve seating. The normal wear pattern observed on the number 2 exhaust valve seat suggested that improper valve seating was not an issue in this case. Significant exhaust valve guide wear was observed on all cylinders, with the valve guides of the generally cooler cylinders near the front of the engine showing less wear than those of the generally hotter cylinders near the rear of the engine. This overall pattern suggested a persistent elevated temperature problem, which could have resulted from either improper engine operation or an undiagnosed maintenance issue. The investigation revealed that, when performing engine cylinder differential pressure tests during required routine inspections of the airplane’s engine, the contract operator utilized gauges that had not been calibrated since their purchase and did not perform the tests in accordance with the engine manufacturer's recommendations. Also, the engine manufacturer recommended that cylinder borescope inspections be accomplished in conjunction with the differential pressure tests, and there were no notations in the engine maintenance records of any visual borescope inspections of the interior of the cylinders. Further, there was no notation in the records that the fuel injection system had been inspected and adjusted per the engine manufacturer’s recommendations. If properly performed, differential pressure tests and borescope inspections may have detected valve guide wear and prevented the exhaust valve failure, and fuel injection system inspections may have detected and corrected incorrect adjustment of the engine fuel system, which can result in elevated engine cylinder temperatures and lead to valve guide wear. These and other instances of non-compliance with manufacturer service recommendations discovered during the investigation indicated that the contract operator was not maintaining the airplane in a manner consistent with its "Operator's Manual," which dictated that inspections of time-limited components were to be conducted in accordance with the applicable manufacturers' recommendations.

HISTORY OF FLIGHT On June 21, 2010, at 1257 eastern daylight time, a Cessna T210L, N30266, registered to Sterling Airways, Inc., and operated under contract by the United States Department of Agriculture (USDA) Forest Service, was substantially damaged when it struck a light stanchion and collided with terrain while maneuvering for a forced landing following a total loss of engine power near William T. Piper Memorial Airport (LHV), Lock Haven, Pennsylvania. The certificated airline transport pilot and two USDA Forest Service mission specialists were fatally injured. Visual meteorological conditions prevailed, and a company visual flight rules (VFR) flight plan was filed for the public use aerial observation flight, which departed Clarion Country Airport (AXQ), Clarion, Pennsylvania, about 1035. According to a representative of USDA Forest Service, the purpose of the flight was to conduct an aerial survey of tree defoliation in southwestern Pennsylvania. A review of fueling records revealed that the pilot serviced the airplane with 49 gallons of fuel on the evening of June 20, 2010. Automated Flight Following (AFF) data provided by the USDA Forest Service indicated that, on the morning of the accident, the pilot repositioned the airplane from its base at Hornell Municipal Airport (4G6), Hornell, New York, to AQX where the two USDA Forest Service mission specialists boarded it about 1030. The flight from AQX was scheduled to arrive at LHV about 1300 to refuel the airplane, before continuing with the survey. About 1250, AFF data indicated that the airplane was about 14 miles west of LHV, at an altitude of 2,500 feet msl (about 1,000 feet agl). Subsequent data indicated that the airplane tracked generally northeast over the next 6 minutes, toward the town of Lock Haven. The airplane's final indicated position was about 3 miles west of the LHV runway 9 threshold, at an altitude of 1,519 feet msl (about 1,000 feet agl). According to a certificated flight instructor (CFI) who was flying in the traffic pattern at LHV for runway 27, he heard the accident pilot announce over the LHV Common Traffic Advisory Frequency (CTAF) that he was 8 miles southwest of the airport. The CFI also heard the accident pilot ask if fuel was available at the airport. About 2 minutes later, the CFI heard the accident pilot report that he was 5 miles southwest of the airport. The CFI heard no further transmissions by the accident pilot. The CFI also stated there was no tone of urgency in the accident pilot's voice nor did he declare an emergency at any point. A Piper PA-24 subsequently taxied onto runway 27, and the pilot announced his position via the CTAF before departing to the west. Shortly after that airplane departed, when the CFI had turned his airplane onto the base leg of the traffic pattern, an unknown person announced on the CTAF that there had been an explosion off the departure end of the runway, which the CFI later learned was the accident airplane. Two witnesses, who worked at Lock Haven University, about 1.5 nautical miles northwest of the accident site, observed the accident airplane as it overflew university property. Both of the witnesses stated that the airplane was flying lower when compared to the other airplanes that they would normally see landing at the airport. Shortly after first observing the airplane, it began trailing smoke. The smoke trail then stopped, and they both heard a loud noise, similar to a "gun blast." Both witnesses stated that after the initial loud noise, the engine ceased operating for several seconds, and then it started to "cough and sputter." Both of the witnesses reported hearing a second loud noise while the engine continued to sputter. Numerous other individuals witnessed the accident airplane as it approached LHV over the town of Lock Haven, and their statements were generally consistent. Six of the witnesses described that the airplane’s engine was "sputtering" as it flew over them, and several remarked about how loud the engine was. One witness commented that "it sounded like a connecting rod problem with the engine due to the noise it was making." Six of the witnesses also commented that the airplane appeared to be "struggling" to maintain altitude, or that it was lower than normal as it overflew them. Several witnesses commented that they thought it unusual that the airplane's landing gear was retracted as it overflew them. PERSONNEL INFORMATION The pilot, who was an employee of Sterling Airways Inc., held an airline transport pilot certificate with ratings for airplane single and multiengine land. He also held a flight instructor certificate with ratings for airplane single engine and instrument airplane. His most recent Federal Aviation Administration (FAA) second-class medical certificate was issued on December 29, 2009. The pilot’s logbooks were not recovered, but according to USDA Forest Service records, the pilot had logged 8,280 total hours of flight experience as of March 16, 2010, with 1,775 hours in the accident airplane make and model. AIRCRAFT INFORMATION According to FAA records, the airplane was manufactured in 1973. The airplane was equipped with a Teledyne Continental Motors TSIO-520-H engine. The most recent engine overhaul was completed by Sterling Airways Inc. on May 7, 2004, and on that date the airplane had accumulated 4,276 total hours of operation. According to maintenance records, the engine was "…overhauled [in accordance with] TSIO-520 sandcast series [overhaul manual]," and all hardware was replaced in accordance with Teledyne Continental Motors Service Bulletin (SB) SB97-6. All six cylinders and their respective exhaust and intake valves were replaced with new Teledyne Continental Motors parts. The following logbook entry documented a post-maintenance flight check conducted by the accident pilot. The pilot entered a remark of "fuel flow low," which was addressed in the following log entry, "Adjusted fuel flow pressure per overhaul manual. (Cessna) Ground run check good." An engine logbook entry dated June 7, 2007, at 4,710 total aircraft hours, documented an annual inspection. The entry also noted, "Removed #3 & 6 cyl for valve (exh) & valve guides both cyl. Cylinders re-installed with new gaskets." No additional details regarding the cylinder work performed during this inspection were documented in the engine maintenance log. An airframe maintenance logbook entry dated January 18, 2008, documented the completion of an annual inspection and the flight of the airplane for a period of about 6 hours under 14 CFR Part 91. The entry noted that airworthiness directives (ADs) were complied with prior to departure and that an airworthiness conforming validation check was performed during the annual inspection. All time limited components were checked, and the airplane was cleared to return to 14 CFR Part 135 service. No further entries removing or reinstating the airplane to 14 CFR Part 135 service were noted. The airplane's most recent annual inspection was completed on March 9, 2010, at 5,000 total aircraft hours. The engine logbook entry for the inspection noted a replacement of the engine oil and filter with an accompanying check of the oil and oil filter contents. The magnetos, timing, and compression checks were satisfactory, with a note describing the cylinder differential pressure test values as 75, 68, 72, 74, 77, and 70 psi for cylinders 1 through 6, respectively. The spark plugs were cleaned, gapped, tested, and reinstalled. The oil filter adapter was repositioned and the engine was washed. The entry noted that no applicable ADs were required to be complied with at the time, and a ground run of the engine was satisfactory. The airplane had accumulated about 45 additional hours of operation between the time of the annual inspection and the date of the accident flight. Detailed inspection of the airplane's maintenance records from the t