# NTSB ANC96LA124: Piper PA-18, N7797B, Skwentna, AK, August 14, 1996 - Type: NTSB accident investigation - Classification: Accident · No injuries · Limited investigation · Final report - Date: August 13, 1996, 16:15 local (Aug 14, 1996, 00:15 UTC) - Place: Skwentna, AK - Coordinates: 61.929168, -151.730743 (estimated) - Nearby events: https://openairdocs.org/map.md?lat=61.9292&lon=-151.7307&mi=10 - Phase of flight: [Initial climb](https://openairdocs.org/ntsb-phases/350) (OpenAirDocs' grouping) - Highest injury: No injuries - Injuries: 2 uninjured - Status: Completed, report August 29, 1997 - Report: Approved by Office Director - NTSB office: Alaska Regional Office - NTSB case key (mKey): 2880 - NTSB case page: https://web.ntsb.gov/investigations/?ntsbnumber=ANC96LA124 - NTSB report (PDF, downloads): https://data.ntsb.gov/carol-repgen/api/Aviation/ReportMain/GenerateNewestReport/2880/pdf - Page: https://openairdocs.org/ntsb/ANC96LA124 ## Probable cause An engine failure due to an eroded engine piston. Factors in the accident were unsuitable terrain for a forced landing and improperly timed magnetos. ## Sequence of events In NTSB's coding before 2008 (https://www.ntsb.gov/GILS/Documents/codman.pdf). - Loss of engine power(total) - mech failure/malf, takeoff - initial climb - engine assembly,piston - eroded (cause) - ignition system,magneto - timing improper (contributing factor) - Forced landing, emergency descent/landing - In flight collision with terrain/water, emergency descent/landing - terrain condition - none suitable (contributing factor) ## Analysis The certificated private pilot and the sole passenger departed a remote lake in a float equipped airplane. About 3 minutes after departure, the engine began to run rough and then quit. The pilot turned back toward the lake, but was unable to glide to the lake and landed on the shoreline. Postaccident inspection of the engine revealed no compression in the number 4 cylinder. The top piston compression ring was frozen in its slot. The outer and upper edge of the top of the piston was eroded and scored. Tiny particles of the piston material were attached to the spark plugs. One magneto was timed 4 degrees before the recommended setting of 25 degrees. ## Factual narrative On August 13, 1996, about 1615 Alaska daylight time, a float equipped Piper PA-18, N7797B, crashed during a forced landing about 11 miles northeast of Skwentna, Alaska. The airplane was being operated as a visual flight rules (VFR) cross-country personal flight when the accident occurred. The airplane, registered to and operated by the pilot, sustained substantial damage. The certificated private pilot and the sole passenger were not injured. Visual meteorological conditions prevailed. The pilot reported that he departed a remote area known as Quiet Lake. About 3 to 4 minutes after departure at an altitude of 400 to 500 feet above the ground, the engine began to lose power. Emergency procedures failed to restore engine power and the pilot turned back toward the lake. The pilot made a "mayday" radio call and then the engine quit completely. The airplane touched down about 40 feet short of the lake shore and the front portion of the left float assembly dug into the ground. The airplane received damage to the fuselage and left wing. The pilot indicated that both he and his passenger were wearing helmets. On August 15, 1996, the National Transportation Safety Board (NTSB) investigator-in-charge (IIC) examined the airplane after it was recovered. The airframe gascolator contained a small amount of blue colored fuel and several large particles. The carburetor bowl contained a small amount of green colored fuel with several small particles. The exhaust tube from the number 4 cylinder was horizontally split, adjacent to the point where the tube is attached to the muffler. The number 4 cylinder push rod retainer tab was broken. A cylinder compression test revealed the number 1 cylinder was 75/80 PSI; the number 2 cylinder was 76/80 PSI; the number 3 cylinder was 74/80 PSI; the number 4 cylinder was zero. Examination of the bottom spark plug from the number 3 cylinder revealed the insulator was broken. The bottom number 4 cylinder spark plug was heavily fouled with metallic particles. The upper number 4 cylinder spark plug was fouled and the insulator was broken. On August 21, 1996, an engine examination was conducted at Alaska Engines, Anchorage, Alaska. The examination revealed the paint on the number 4 cylinder was discolored and darkened. The right magneto was timed to 21 degrees before top dead center (BTC). The left magneto was timed to 23 degrees BTC. The proper magneto timing is 25 degrees BTC. Removal of the number 4 cylinder and piston revealed the top piston compression ring was frozen in its slot. The outer and upper edge of the top of the number 4 piston was eroded and scored. Tiny particles of the piston material were attached to the spark plugs. Slivers of metal were located in the oil screen. The magnetos were removed and examined. The right magneto points were found to open 5 degrees late. The carburetor was removed and examined. All internal parts conformed to appropriate part numbers and all airworthiness directives had been applied. Sealant was found around the threads of the inlet fuel coupling. The pilot reported that he fueled the airplane from a portable tank that he owned. He last obtained fuel for the tank on August 8, 1996, with the purchase of 100 gallons of 100LL octane fuel. The pilot provided a sample of blue colored fuel from his portable tank and it was submitted for testing. The examination revealed the fuel sample met the specifications for aviation fuel. The lead content of the fuel was 1.63 milliliters per gallon. The maximum lead content for 100LL fuel is 2.00 milliliters per gallon. Examination of the airplane's maintenance records revealed the engine was converted from an O-320-A2B, 150 horsepower, to an O-320-B2B, 160 horsepower, under a supplemental type certificate (STC) on February 7, 1992. The engine was disassembled, inspected, and repaired on February 6, 1996, due a propeller strike. ## Aircraft - Registration: [N7797B](https://openairdocs.org/aircraft/N7797B), registered now, S/N 18-4449, built 1955 (OpenAirDocs) - Reported make and model: Piper PA-18 - Registry model: [Piper PA-18A](https://openairdocs.org/model/piper-pa-18a) (registry code 7101804) (OpenAirDocs) - Registry engine: [Lycoming O&VO-360 series](https://openairdocs.org/engine/lycoming-o-vo-360-series) (registry code 41514, reciprocating) (OpenAirDocs) - Category: Airplane - Serial number: 18-4449 - Airframe hours: 516 - Engines: Lycoming O-320-A2B 160 horsepower reciprocating - Damage: Substantial damage - Flight: Personal, Part 91 - Registered owner: Clayton R. Waggood - Airworthiness certificate: Standard, Normal - Last inspection: Annual, February 6, 1996, 212 hours before - Destination: BELUGA, AK ## Flight crew As NTSB recorded them. NTSB leaves out names. - Pilot; age 39; private; airplane ratings: single-engine land, single-engine sea; medical: class 3, valid medical--no waivers/lim.; seat: front; flight hours: 430 total, 285 in this make and model, 430 as pilot in command, 81 in the last 90 days, 33 in the last 30 days, 2 in the last 24 hours ## Weather - Conditions: Visual (VMC), Day - Wind: 180° at 5 knots - Visibility: 30 statute miles - Lowest ceiling: none - Temperature: 61 °F ## FAA reports on this event (1) The FAA's own accident and incident reports, matched to the aircraft by N-number and date (OpenAirDocs). - [Accident 19960813022559A](https://openairdocs.org/incident/19960813022559A), Aug 13, 1996: Piper PA18A, Skwenta, AK, Substantial damage. Floatplane departed a lake, lost power. Landed on shore. Engine bad shape. Timing plugs and broken righ nr cyl. ## Other investigations on N7797B (2) From the NTSB's public API. Aircraft are matched to registry aircraft by N-number and event date, checked against the reported serial number, make and model; the registry's history has gaps, so older matches can be wrong. Compare the reported make and model. - [NTSB ANC96LA170](https://openairdocs.org/ntsb/ANC96LA170), Jan 22, 1996: Piper PA-18 (N7797B), Skwentna, AK, substantial damage. Probable cause: The pilot's selection of an unsuitable site for landing. A factor associated with the accident is the snow-covered terrain. - [NTSB UNK64X2527](https://openairdocs.org/ntsb/UNK64X2527), Jun 27, 1964: Piper PA18A (N7797B), Sinton, TX, destroyed, 1 fatal From the NTSB's public API. Aircraft are matched to registry aircraft by N-number and event date, checked against the reported serial number, make and model; the registry's history has gaps, so older matches can be wrong. Compare the reported make and model. --- OpenAirDocs.org is an independent research project of [Contrail Labs](https://contraillabs.com/). It is not affiliated with the FAA or the NTSB. Source documents are U.S. government works in the public domain.