Fort Meade, MD, USA
N6116L
AMERICAN AA-1
The commercial pilot reported that, during the 4 months before the accident, the airplane had experienced ongoing engine issues, including engine roughness. Maintenance personnel were informed about the engine roughness, and a mechanic attributed the problem to the ignition system and subsequently replaced components of the system. The pilot reported that the purpose of the flight was to verify that the previous repairs made to eliminate the engine roughness had resolved the problem. The pilot performed a thorough preflight inspection and a full-power engine run-up and noted no discrepancies. During the initial climb, when the airplane was about 250 ft above ground level, the engine rpm decreased from 2,500 to 1,500 and then increased to 1,900. The pilot's attempts to restore engine power were unsuccessful. The airplane impacted treetops and then came to rest on the ground inverted. Postaccident examination of the engine revealed that all of the dry valve tappet clearances were less than prescribed by indications on the engine data plate. The reported loss of engine power and engine roughness was consistent with the valve clearances being incorrectly adjusted. The engine operator's manual and a nonmandatory service instruction (SI) referenced in the manual specify that the tappet clearances should be checked every 100 hours of operation. A review of the maintenance logbooks revealed that the last check of the tappet clearances was performed in accordance with the SI about 224 hours, or about 7 years 7 months, before the accident by the same mechanic who had been troubleshooting the recent engine issues. If the mechanic had checked the dry tappet clearances while troubleshooting the ongoing engine issues, it is likely that he would have detected the incorrect dry tappet clearances and properly resolved the ongoing engine issues.
***This report was modified on March 7, 2016. Please see the docket for this accident to view the original report.*** On February 8, 2015, about 1407 eastern standard time, an American AA-1, N6116L, collided with trees then the ground during a forced landing shortly after takeoff near Fort Meade, Maryland. The commercial-rated pilot and one passenger sustained serious injuries and the airplane was substantially damaged. The airplane was co-owned by three private individuals and was operated under the provisions of 14 Code of Federal Regulations (CFR) Part 91 as a personal, local flight. Visual meteorological conditions prevailed at the time and a Washington, D.C., SFRA flight plan was filed. The flight was originating at the time of the occurrence. The pilot stated that the purpose was to perform touch-and-go landings to verify that previous repairs related to engine roughness eliminated the problem. He performed a preflight inspection of the airplane, and reported that no contamination was noted in the fuel sample from each tank that had 3/4 capacity. After engine start he taxied to runway 28, and performed a full power engine run-up that lasted between 2.0 and 2.5 minutes; the magneto drops were equally 75 rpm, and no engine roughness was noted. With no flaps extended, the auxiliary fuel pump on, and the fuel selector on the right tank, he initiated takeoff from runway 28. He reported that during the takeoff roll when at 60 to 70 miles-per-hour (mph), he noted full dynamic red line rpm of 2,500. The airplane became airborne about midpoint of the runway (normal), and he began climbing at 80 mph, which is Vx. About 30 to 40 seconds after full power application, while at about 250 feet above ground level, he noted an abrupt partial loss of engine power. He reported that the engine rpm dropped from 2,500 to 1,500 then went to 1,900. He cycled the magneto switch from both to right, back to both, then to right, and back to both thinking the issue was specified to 1 magneto. Switching of the magnetos had no effect. He applied carburetor heat, and then turned off the auxiliary fuel pump, but those actions did not restore engine power. He indicated he did not have any more time for troubleshooting, and he did not move the fuel selector valve. While flying between 62 and 65 mph, he flared at the tree top height. He did not lose consciousness, but did not recall unfastening his lapbelt. He got out of the inverted airplane from the right side. Following recovery of the airplane, inspection of the Lycoming O-235-L2C engine, S/N L-9916-15, was performed by a representative of the engine manufacturer with oversight by representatives of the Federal Aviation Administration (FAA). The engine was equipped with solid tappets. Inspection of the engine data plate revealed ".005" was stamped next to the original ".010" stamp pertaining to tappet clearance. Crankshaft, camshaft, and valve train continuity was confirmed during hand rotation of the propeller, and thumb suction and compression was noted in each cylinder. Steel pushrods were installed at all cylinders. Dry tappet clearance was checked using a feeler gauge, and the smallest thickness gauge 0.002 inch could not be inserted at any of the valves. A smaller feeler gauge was not available; therefore, the actual dry tappet clearance value for each valve was not determined. Borescope inspection of all cylinders revealed pitting and scuffing of the No. 3 cylinder. Removal of the No. 3 cylinder revealed scuffing of the piston side. Inspection of the fuel metering, ignition, and exhaust system components revealed no evidence of preimpact failure or malfunction. The report from the engine manufacturer representative is contained in the NTSB public docket. According to the engine manufacturer's Operator's Manual, the Lycoming O-235 series engines which have solid tappets requires manual adjustment by an adjusting screw located in the valve rocker cover to maintain tappet clearance. Further review of the operator's manual revealed that at each 100 hours the tappet clearance is to be checked. The trouble shooting section indicates one cause for low power and uneven running to be incorrect tappet clearance. Excerpts from the Lycoming Operator's Manual are contained in the NTSB public docket. A review of Lycoming Service Instruction (SI) No. 1480 associated with the accident make and model engine indicates that with steel pushrods installed, the dry tappet clearance for all cylinders should be set to 0.002 to 0.008 inch. The instructions also indicates to mark the engine data plate with ".005" as the new dry tappet clearance near the original value, and references Lycoming Service Instruction No. 1068. The service instruction is contained in the NTSB public docket. Lycoming SI No. 1068A associated with the accident make and model engine specifies the procedures to adjust the tappet clearance, and also specifies that the tappet clearance be checked after each 100 hours of operation. It also indicates that when only 1 cylinder is being replaced, to set the tappet clearance for that cylinder, and then run the engine and recheck the tappet clearance. The service instruction which is not mandatory is contained in the NTSB public docket. The pilot, who is a part owner of the airplane, reported that about the end of September, during a flight in the traffic pattern at traffic pattern altitude, an engine roughness was felt. The airplane was landed, and maintenance personnel were informed of the rough running engine. The mechanic indicated at that time that the spark plugs should have been changed at the annual inspection but he tried to save the owners some money. The spark plugs were changed and the airplane was flown again. During that flight, the engine again began to run rough intermittently. The mechanic was informed and he checked the fuel system and no discrepancies were noted. The cylinders were also borescoped, and the mechanic believed the issue was related to the ignition system. As such, the ignition harness was replaced. After replacing the ignition harness, in an attempt to duplicate the aircraft's attitude, the airplane was placed in a tail low attitude, simulating a climb attitude, and the engine was started and operated to full power. The engine roughness was not evident during the engine run. About 1 or 2 weeks later, the engine began to run rough about 2.0 to 2.5 minutes into a full power engine run-up in advance of an intended flight. The flight was aborted and the airplane was taxied to the ramp. The mechanic was informed, and the magnetos were replaced (the engine logbook indicates that on January 9, 2015, internal components of both magnetos were removed and replaced including the distributor block and gear, contact points, capacitor, and rotor gear. The magnetos were reinstalled and timed to the engine and the airplane was approved for return to service). This was believed to solve the rough running engine issue. Review of copies of the engine logbook revealed the engine was signed off as being overhauled on June 21, 1999, at engine total time 2,082.2 hours. The engine was installed in the airplane on July 10, 2000, and there was no record that the engine had been removed since being installed after overhaul. Further review of the maintenance records revealed only 1 entry in which the adjustment of the tappet clearance was performed in accordance with Lycoming Service Instruction 1068A. The entry was dated July 20, 2007, at engine time since major overhaul of 136.2 hours. The tappet clearance adjustment was performed by the same mechanic who was troubleshooting the recent engine issues. An entry dated July 16, 2014, indicates the No.3 cylinder removed due to no compression and then reinstalled after it was repaired. The engine time since major overhaul at the time of the accident was approximately 360 hours, or approximately 224 hours since the valve clearance was last checked and adjusted in accordance with Lycoming Service Instruction No. 1068A. Excerpts of the engine maintenance records are contained in the NTSB public docket.
The mechanic’s failure to detect the incorrect dry valve tappet clearances while troubleshooting ongoing engine issues, which resulted in partial loss of engine power during takeoff. Contributing to the partial loss of engine power was the mechanic's failure to inspect the dry tappet clearances in accordance with the engine operator's manual and a referenced service instruction.
Source: NTSB Aviation Accident Database
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