ELFRIDA, AZ, USA
N761KC
Cessna T210M
The aircraft collided with ground obstructions and nosed over during a night forced landing on a dirt road following a catastrophic engine failure during cruise. A large hole was found in the engine case on each side of the upper spine between the numbers 1 and 2 cylinders. FAA AD 99-09-17 was issued on April 22, 1999, and mandated compliance with Continental Mandatory Service Bulletin (MSB) 99-3, which required visual and ultrasonic inspections of the crankshaft for cracks; these inspections had to be done by Continental factory service representatives. The inspection was performed on May 4, 1999, 220 hours prior to the accident. To perform the inspection, cylinders 1 and 3, and all 4 counterweights on the crankshaft had to be removed. This engine's crankshaft has 4 counterweights, which are installed on hangar blades extending out on each side of the Nos. 2 and 5 crank cheeks (CC). The weights are retained on the blades by pins, which are held in the bores by pin retaining plates on each side of the weight. These plates are slightly elliptical on one edge of the circumference, which forms an ear that results in an interference fit within the bores of each weight. The plates are held in place by snap rings that fit into separate grooves machined into the weight bores. Three versions of MSB 99-3 were eventually issued. 99-3A was issued on April 22, 1999, and was current when the compliance inspection was performed. Versions 99-3B and 99-3C were issued on July 6 and 27, 1999, respectively, and superceded 99-3A and each other in sequential order. An additional Service Bulletin, SB 00-3, was issued on February 2, 2000 (13 days prior to the accident and 9 months after the crankshaft inspection was performed), and provided detailed and specific procedures for the reinstallation of crankshaft counterweights, including the correct orientation and installation of the counterweight pins, retainer plates, and snap rings. The principal difference between MSB 99-3A, and versions 99-3B and 99-3C, is that versions B and C incorporate the guidance on counterweight pin retainer plate and snap ring installation found in SB 00-3. Versions 99-3B and 99-3C specifically emphasize a dimensional measurement between snap ring ears as a means to determine that they are fully seated in their grooves. SB 00-3 and versions B and C of SB 99-3 specify that the pin retainer plates and snap rings must be installed in specific orientations within the weight bores. Review of the precursor service bulletins to SB 00-3 disclosed that it was the first one to detail and emphasize the criticality of the retainer plate and snap ring orientations within the bores, and provide a measurement between the snap ring ears when the ring is fully seated within the weight bore. The engine overhaul manual does not go into specific detail regarding the orientation of the pin retainer plates and snap rings, nor does it provide a measurement of the snap ring ears to verify full seating of the ring. All other references that would have been available to the mechanic at the time of the inspection did not address the criticality of the correct counterweight retainer plate and snap ring installation. During the inspection process on May 4, 1999, the operator's mechanic prepared the engine by removing cylinders 1 and 3 and the associated connecting rods. When the factory representative arrived to perform the visual and ultrasonic inspections of CC2 and CC5, the mechanic removed the counterweights. Following the inspection, the mechanic reinstalled the weights, connecting rods, and cylinders. The mechanic would have had to perform all the work through the 5.5-inch cylinder base openings in the crankcase, and the weight bores, including the positions of the retaining plate snap rings, would have been perpendicular to the opening. According to the mechanic who performed the job, the work was inspected by a company inspector at each stage and signed off on the work order. The oil pan was removed from the engine and the sump contents were in part identified as follows: 1. A crankshaft counterweight (in pieces) identified as having been mounted on crank cheek 2 as the leading weight. 2. 2 Crankshaft counterweight pins. By part number, one pin was for the No. 2 leading weight and one was from the No. 3 trailing weight. 3. 4 Counterweight pin retaining plates 4. 5 counterweight retaining plate snap rings Of the four recovered counterweight pin retaining plates from the oil sump pan, two were bent and distorted and two were not damaged or distorted. For the recovered pin retaining plate snap rings, three were distorted and two were not; the undistorted snap rings were of the correct diameter. During disassembly of the engine, the condition of the three remaining counterweight assemblies were documented as follows: The No. 1 trailing weight on crank cheek 2 remained attached to the blade, with the pin retainer plates and snap rings correctly installed. The No. 3 trailing weight on crank cheek 5 was partially retained on the hangar blade by only the forward pin. The aft pin, and, the retainer plate and snap ring from one side of the weight were missing; these parts were found in the oil sump. The forward pin was in place and retained by its associated retainer plates and snap rings. One snap ring was installed correctly and one was not. The No. 4 leading weight on crank cheek 5 remained on its hangar blade. All snap rings and retainer plates were intact and installed correctly. Examination of the engine found no evidence of oil starvation or exhaustion, or any other internal anomaly beyond the separation of the No. 2 leading counterweight that would have led to the catastrophic destruction of the engine.
HISTORY OF FLIGHT On February 15, 2000, at 2024 hours mountain standard time, a Cessna T210M, N761KC, collided with ground obstructions and nosed over during a forced landing near Elfrida, Arizona. The forced landing was precipitated by a catastrophic engine failure during cruise. The airplane was operated by the Department of the Treasury, U.S. Customs Service, as a public-use airplane under 14 CFR Part 91 of the Federal Aviation Regulations. The airplane sustained substantial damage. The two pilots, the sole occupants, were not injured. Visual meteorological conditions prevailed and a company visual flight rules flight plan was filed. The flight originated from Davis-Monthan Air Force Base, Tucson, Arizona, at 1940 as a training flight. According to information provided by the U.S. Customs Service and the pilots, the flight left the US Customs Tucson Air Operations base at Davis-Monthan AFB for a training flight in the Douglas, Arizona, area. No discrepancies were noted with the run-up at Davis-Monthan AFB or until the engine problem happened. The pilot said he was at 5,100 feet msl and using a power setting of 30 inches of manifold pressure and 2,600 rpm. Both pilots heard a loud bang, like a hammer hitting the inside of the engine, which was followed by severe vibrations and sparks emanating from the front of the airplane. According to both crewmembers, the vibrations were constant; however, when the pilot powered back the vibrations seemed to intensify. The pilot reported that from the sparks he thought they might have lost a portion of a propeller blade and began looking for a place to land. They were over a highway running through a built up area, but the pilot considered that there was a likelihood of power lines over and around the highway. They saw a dirt road reflecting in the moon light and set up for a landing there. On short final to the road, the pilot had to maneuver to the left in order to miss a large tree on the right-hand side of the road. As the pilot maneuvered back to the center of the road, the right wing began to contact trees on the roads right shoulder, which slued the airplane into a drainage ditch. It contacted a barbed wire fence and several other trees, and then nosed over. Ground witnesses reported observing sparks emanating from the cowl area as the airplane descended toward the road. Gross external visual assessment of the engine disclosed a large hole in the engine case on each side of the upper spine between the numbers 1 and 2 cylinders and a quantity of oil on the fuselage from the firewall aft to the tail. PERSONNEL INFORMATION The pilot holds a commercial pilot certificate with airplane ratings for single engine land, multiengine land, and instruments, and also ratings for rotorcraft helicopters and instrument helicopter. In addition, his certificate is endorsed for private privileges in gliders limited to aero tow only. The most recent issuance of the certificate was August 8, 1998. The most recent second-class medical certificate was issued on October 11, 1999, without limitations. He is employed by US Customs as a pilot and flies both fixed wing and helicopters for the service. The pilot's total time was 4,151 hours, of which 3,395 were accrued in helicopters, with 22 hours in the Cessna T210. His total night experience was 722 hours. According to US Customs records, he completed a standardization check ride on October 23, 1999, which also covered the requirements of a biennial flight review. In addition, he completed an instrument competency check and a check out in the Cessna T210 on February 3, 2000. The second pilot is also employed by US Customs as a fixed wing and rotorcraft pilot, and holds an Airline Transport Pilot certificate with an airplane multiengine land rating and type ratings for the Beech 200 and Cessna 500. In addition, his certificate is endorsed for commercial privileges in single engine land airplanes, rotorcraft helicopters and instrument helicopters. His most recent first-class medical certificate was issued without limitations on May 13, 1999. According to Customs records, he has accrued a total time of 1,950 hours, of which 550 were in helicopters, with 18 in the Cessna T210. His most recent US Customs standardization check ride was accomplished on August 30, 1999, in a Cessna 550. Both pilots were wearing shoulder harnesses; however, they did not have helmets. AIRCRAFT INFORMATION The Cessna T210M aircraft, serial number 21062308, was operated by US Customs and maintained on an annual/100-hour inspection program. A contractor, Raytheon Aerospace Company, a Federal Aviation Administration (FAA) certificated Repair Station, performed the maintenance on the aircraft and engine at the Tucson Air Branch base, and at a facility in Phoenix, Arizona. The maintenance records were reviewed. At the time of the accident, the airframe had accumulated a total time in service of 5,579 hours. The airplane flew approximately 30 hours per month on a historical average. A 100-hour inspection was completed on the morning of the accident at the Phoenix maintenance facility. The aircraft was then ferried down to the Tucson base and was dispatched on the accident flight. The records disclosed that there were no unresolved maintenance discrepancies or open items at the time of departure. The airplane was refueled prior to departure on the accident flight from a USAF truck with 100LL aviation gasoline. Fuel samples were taken from the refueling truck and from the aircraft, and sent to the USAF laboratories at Wright Patterson AFB for analysis. The sample from the truck met specification ATSM D-910 for 100LL aviation gasoline. The sample from the aircraft wing tank met all specifications except for sulfur content, which exceeded the maximum allowable percent/mass by 0.14. The historical maintenance and rebuild records for the engine were examined. The Teledyne Continental TSIO-520-R engine, serial number 293964-R, was rebuilt by the Continental factory to zero time tolerances on March 20, 1998. The engine was then shipped to Raytheon Aerospace Services and installed in N761KC on May 15, 1998, at an airframe total time of 5,106 hours. A 100-hour inspection was completed on the engine on the morning of the accident. FAA Priority Letter Airworthiness Directive (AD) 99-09-17 was issued on April 22, 1999, and mandated compliance with Teledyne Continental Motors Mandatory Service Bulletin (MSB) 99-3 for specific engines identified by serial number. The accident engine was subject to both the AD and the MSB. AD 99-09-17 was subsequently superceded by AD 99-19-01 on September 30, 1999; however, the applicability provisions remained the same. The AD and the MSB were issued due to a history of 8 crankshaft failures (the 8 fractured crankshafts were as of July 27, 1999), which were traced to a Teledyne Continental factory manufacturing process involving the installation of crankshaft counterweight bushings on the crankshaft counterweight hangar blade. According to the MSB, the manufacturing process discrepancy produced a condition, which induced a crack and catastrophic fracture of one or more crankshaft cheeks. The AD and MSB required visual and ultrasonic inspections of the identified crankshafts for cracks. The AD and MSB mandated that these inspections be accomplished by Teledyne Continental factory service representatives. Three versions of MSB 99-3 were eventually issued: 99-3A was issued on April 22, 1999; 99-3B superceded 99-3A and was issued on July 6, 1999; 99-3C was issued on July 27, 1999, and superceded 99-3B. All three versions of MSB 99-3, and AD's 99-09-17 and 99-19-01, are appended to this report for reference. An additional Teledyne Continental Service Bulletin, SB 00-3, and pertinent pages from the TSIO-520 overhaul manual are also appended to provide the reader with illustrations of the parts and components referenced herein for clarity. Continental SB 00-3, which was issued on February 2, 2000, provided detailed and specific procedures for the reinstallation of crankshaft counterweights, including the correct orientation and installation of the counterweight pins, retainer plates, and snap rings. In pertinent part, the TSIO-520 crankshaft is designed to incorporate four counterweights, which are installed on hangar blades extending out on each side of the numbers 2 and 5 crank cheeks (CC). The number 2 crank cheek is between the number 1 and 2 rod journals (RJ) at the rear of the crankshaft. The number 5 crank cheek is located between the number 3 and 4 rod journals. The hangar blades are on each side of the designated crank cheeks. With the number 1 rod journal at the 12 o'clock position and looking forward from the rear of the crankshaft, the hangar blade nomenclature is as follows: 1) the blade on the right side of CC2 is the number 2 leading blade and the counterweight is the number 2 leading weight; 2) The blade on the left side of CC2 is the number 1 trailing blade and weight; 3) The blade on the upper side of CC5 (CC5 is nearly horizontal with the No. 1 RJ at 12 o'clock) is the number 4 leading blade and weight; and 4) the blade on the lower side of CC5 is the number 3 trailing blade and weight. The crankshaft counterweight hangar blades have two holes bored, and bushings are pressed into these bores. The weights have corresponding holes bored with bushings pressed into them and are retained on the blades by pins, which extend through the blade bushing and into the weight bore bushings. The pins are held in the bores by counterweight pin retaining plates placed in the bores on each side of the weight. These plates are slightly elliptical on one edge of the circumference, which forms an ear that results in an interference fit within the bores of each weight. The plates are held in place by snap rings that fit into separate grooves machined into the weight bores. The weights attached at each blade are specific part numbers for that position, and each weight requires specific part numbered pins for that particular weight. The weights must be installed on opposing blades as a matched set of equal weight and with the same part number. Continental SB 00-3 specifies that the pin retainer plates and snap rings must be installed in specific orientations within the bores; the plate ears must point outward away from the crankshaft centerline and the snap ring ears must face inward toward the crankshaft. One side of the snap ring has a sharp beveled edge, which must point away from the weight. For the snap ring to be fully seated in the groove, a minimum dimension of 0.179 inches must separate the snap ring ears. Review of the precursor service bulletins to SB 00-3 disclosed that it was the first one to detail and emphasize the criticality of the retainer plate and snap ring orientations within the bores, and provide a measurement between the snap ring ears when the ring is fully seated within the weight bore. The engine overhaul manual does not go into specific detail regarding the orientation of the pin retainer plates and snap rings within the counterweight bores, nor does it provide a measurement of the snap ring ears to verify full seating of the ring. All three versions of MSB 99-3 require that cylinders 1 and 3, and their associated connecting rods, be removed to facilitate the visual and ultrasonic inspection of the crankshaft cheeks Nos. 5 and 2 associated with the counterweight hangar blades on those cheeks. Following the cylinder and connecting rod removal, all four crankshaft counterweights must be removed to fully expose the area to be inspected. The principal difference between MSB 99-3A, and versions 99-3B and 99-3C, is that versions B and C incorporate the guidance on counterweight pin retainer plate and snap ring installation found in SB 00-3. Versions 99-3B and 99-3C specifically emphasize the 0.179-inch dimension between snap ring ears when the rings are fully seated in their grooves. Review of the maintenance records and Raytheon work orders disclosed that AD 99-09-17 and MSB 99-3A were complied with on this engine on May 4, 1999, 220 hours prior to the accident, at the Raytheon maintenance facility in Phoenix. Recall that revision "B" of MSB 99-3 was not issued until July 6, 1999. A Raytheon mechanic prepared the engine by removing cylinders 1 and 3 and the associated connecting rods. When the Teledyne Continental representative arrived to perform the visual and ultrasonic inspections of CC2 and CC5, the mechanic removed the counterweights. Following the inspection, the mechanic reinstalled the weights, connecting rods, and cylinders. According to the mechanic who performed the job, the work was inspected by a Raytheon inspector at each stage and signed off on the work order. Investigators noted during teardown of the engine that all the work related to the removal and reinstallation of the weights on the crankshaft blades would have to have been accomplished through the 5.5-inch diameter cylinder base openings for the Nos. 1 and 3 cylinders in the crankcase. The weight bores and the retaining plate snap rings would be perpendicular to the openings and only clearly visible with the aid of inspection mirrors. The crankshaft counterweights are not typically removed or reinstalled in the field, and this work is usually performed in overhaul facilities with the crankshaft out of the engine. The mechanic, the inspector, and the Teledyne Continental service representative were interviewed, and they also submitted written statements. In addition, the Raytheon Chief Quality Control Inspector at the Tucson maintenance base was interviewed. The chief quality control inspector said that as part of his duties he maintains the various maintenance documents for the aircraft maintained at the facility. When Airworthiness Directives or Manufacturers Service Bulletins are received, he determines applicability and schedules the work to be done. When AD 99-9-17 and Continental Mandatory Service Bulletin 99-3 came, he determined that it was applicable to N761KC by engine serial number. Coordination was done to schedule the crankshaft inspection with Continental. He prepared the work order package for the Phoenix facility. The package would have consisted of a work order (subsequently identified as Work Order 990768, which is appended to this report) specifying the work to be performed, copies of the AD, MSB, and all other relevant references, plus a kit of parts anticipated for the work. By checking the maintenance document revision log, he determined that version 99-3A of the Continental Mandatory Service Bulletin would have been sent in the package. The mechanic who performed the work in Phoenix holds a FAA Airframe and Powerplant Technician certificate and a FAA Inspection Authorization. He is also a designated inspector for Raytheon Aerospace. The mechanic recalled doing the work specified in the work order concerning the crankshaft inspection. He stated that prior to the Continental representative arriving, he prepped the engine by removing cylinders one and three, including the pistons and connecting rods, in order to gain access to the affected counterweights. When the Continental representative arrived, the snap rings and retainer plates holding the counterweight pins were removed with the aid of snap ring pliers and a small hook end scribe. The counterweight pins and the weights were then removed. The Continental representative performed the ultrasonic inspection of the crankshaft. As each throw of the crankshaft was inspected, he put the weights and pins back on the weight blades. He stated that the snap rings and pin end retainer plates were new parts supplied in the inspection kit and he installed them with the Continental representative watching his actions. He said that at each step of the counterweight reinstallation, he had the Continental technical representative verify that the installation was complete and correct. He specifically asserted that he installed the snap rings with the sharp edge out and had the Continental representative verify that the snap rings were correctly installed. When the inspection was completed and th
The company mechanic's failure to correctly install one or more of the crankshaft counterweight pin retaining plate snap rings, specifically ensuring that the snap rings were fully seated in their grooves. This led to the complete separation of the No. 2 leading counterweight and the partial separation of the No. 3 trailing weight from the crankshaft and a resulting internal catastrophic engine failure. A factor in the accident was the lack of definitive procedural guidance in any of the engine manufacturer's reference material, available at the time, on the correct installation of these components.
Source: NTSB Aviation Accident Database
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