# NTSB ANC08LA060: Piper PA-34, N11HR, Ocala, FL, June 14, 2008 - Type: NTSB accident investigation - Classification: Accident · No injuries · Limited investigation · Final report - Date: June 14, 2008, 12:15 local (16:15 UTC) - Place: Ocala, FL - Coordinates: 29.170278, -82.221107 - Nearby events: https://openairdocs.org/map.md?lat=29.1703&lon=-82.2211&mi=10 - Phase of flight: [Landing](https://openairdocs.org/ntsb-phases/550) (OpenAirDocs' grouping) - Defining event: [Landing-flare/touchdown: Powerplant sys/comp malf/fail](https://openairdocs.org/ntsb-events/340) - Highest injury: No injuries - Injuries: 4 uninjured - Status: Completed, report April 15, 2009 - Report: Approved by Office Director - NTSB office: Alaska Regional Office - Parties: Jacksonville, FL FSDO-15 - NTSB case key (mKey): 67951 - NTSB case page: https://web.ntsb.gov/investigations/?ntsbnumber=ANC08LA060 - NTSB report (PDF, downloads): https://data.ntsb.gov/carol-repgen/api/Aviation/ReportMain/GenerateNewestReport/67951/pdf - Page: https://openairdocs.org/ntsb/ANC08LA060 ## Probable cause The pilot's continued operation of the airplane with a known mechanical deficiency--a propeller that would feather at low power. Contributing to the accident was the uncommanded feathering of the propeller. ## Findings NTSB's coded findings; those marked are part of the probable cause. - [Propeller system: propeller controlling system](https://openairdocs.org/ntsb-findings/01046120): Aircraft › Aircraft propeller/rotor · Malfunction (probable cause); cases with it: [Piper PA-34-200T, 1 case](https://openairdocs.org/ntsb-findings/01046120/cases.md?model=7103406), [All aircraft, 25 cases](https://openairdocs.org/ntsb-findings/01046120/cases.md) - [Info processing/decision: decision making/judgment](https://openairdocs.org/ntsb-findings/02041520): Personnel issues › Action/decision · Pilot (probable cause); cases with it: [Piper PA-34-200T, 6 cases](https://openairdocs.org/ntsb-findings/02041520/cases.md?model=7103406), [All aircraft, 3,098 cases](https://openairdocs.org/ntsb-findings/02041520/cases.md) ## Sequence of events The events NTSB coded, in order, by phase of flight. The defining event best describes what happened. - [Landing-flare/touchdown: Powerplant sys/comp malf/fail](https://openairdocs.org/ntsb-events/340) (defining event); cases with it: [Piper PA-34-200T, 1 case](https://openairdocs.org/ntsb-events/340/sequence.md?model=7103406), [All aircraft, 820 cases](https://openairdocs.org/ntsb-events/340/sequence.md) - [Landing-flare/touchdown: Hard landing](https://openairdocs.org/ntsb-events/092); cases with it: [Piper PA-34-200T, 7 cases](https://openairdocs.org/ntsb-events/092/sequence.md?model=7103406), [All aircraft, 2,102 cases](https://openairdocs.org/ntsb-events/092/sequence.md) ## Analysis According to the private pilot, who was on a personal cross-country flight, he was about 6-10 feet above the landing runway when the left engine's propeller feathered. He said that the airplane dropped hard onto the runway, collapsing the nose landing gear and driving it through the top of the fuselage. The pilot reported that during the past several months the left propeller would feather uncommanded when taxiing from landing. He said that on the advice of his mechanic he had the propeller overhauled, and then replaced the engine--neither of which fixed the problem. The pilot, in consultation with his mechanic, determined that the propeller would probably not feather in flight. The pilot said that he planned to land with extra power during the accident flight, but found himself high and long on final approach, and when he reduced engine rpm to idle, about 6-10 feet above the runway, the left propeller feathered. ## Factual narrative On June 14, 2008, about 1215 eastern daylight time, a twin-engine Piper PA-34 airplane, N11HR, sustained substantial damage during a hard landing when the left propeller feathered on short final, at Ocala International Airport-Jim Taylor Field, Ocala, Florida. The airplane was being operated by the pilot as a instrument flight rules (IFR) personal cross-country flight under Title 14, CFR Part 91, when the accident occurred. The private certificated pilot and the three passengers were not injured. Visual meteorological conditions prevailed during the final approach, and an instrument flight plan was filed. The airplane departed Houston, Texas, about 0630. During a telephone conversation with the National Transportation Safety Board (NTSB) investigator-in-charge (IIC) on June 18, the pilot said about 6-10 feet above the runway during landing, the left engine's propeller went to the feathered position uncommanded. He said the airplane dropped hard onto the runway, collapsing the nose landing gear. The pilot reported that during the past several months the left propeller would feather uncommanded when taxiing from landing. He said that on the advice of his mechanic, he had the propeller overhauled, which did not fix the problem, and then replaced the engine. The pilot discussed the continuing problem with his mechanic, and determined that the propeller would probably not feather uncommanded in-flight. For the accident flight, the pilot said he planned to land with extra power, but found himself high and long on final approach. He said when he reduced engine rpm to idle, about 6-10 feet above the runway, the left propeller feathered. He reported that the airplane struck the runway hard, driving the nose landing gear through the top of the airplane's nose, and breaking the windshield. On June 20, the propeller and propeller governor were removed and taken to an FAA certified propeller repair station. An examination of the propeller and governor found no evidence of mechanical failure or anomaly. Additional Information/Research During a discussion with a certificated propeller shop owner in Tucson, AZ, he said the problem of propellers feathering uncommanded on light twin-engine airplanes was quite common in their area. He said the local college aeronautical training center had the same problem with the Beech 76 Duchess' used for training. Their investigation, in conjunction with the FAA, revealed that the problem was that of engine oil viscosity. He said the problem only occurs during the summer months when temperatures are high. He said there are numerous contributing factors. 1. Ambient temperature in conjunction with engine operating temperature 2. Oil viscosity/grade i.e. 15w50 vs. 5w40 3. Oil cooler size/capacity 4. Engine wear/tolerances 5. Propeller governor volume 6. Propeller cylinder spring pressure According to the propeller shop owner, depending on circumstances, one or more of the above may cause or contribute to the problem. He said there are several fixes, and that any one or a combination of the following could potentially solve the problem, depending on the combination of factors creating the problem for the specific engine and propeller. 1. Use a higher oil viscosity/grade of oil to raise the viscosity at higher temperature. 2. Larger oil cooler 3. Replace/rebuild the engine 4. Change propeller governor to a higher volume governor 5. Reduce the propeller cylinder spring pressure In the college aeronautical training center case, the propeller manufacturer authorized the reduction of the propeller cylinder operating pressure through the use of lighter springs, and reduced the pressure from 41 psi to 22 psi, and eliminated the problem. The propeller manufacturer maintains a list of airplanes approved for the reduced operating pressures. According to the propeller shop, there are no ill effects due to the reduced operating pressure, however the manufacturer does not include an airplane on the list unless a problem is reported for the specific make and model. A canvas of east coast and west coast propeller shops by the IIC revealed that during summer months the shops receive complaints of propellers going into feather during shutdown. They attributed this to low oil viscosity also, and advise pilots to shutdown at a lower rpm so the mechanical stops will engage before the oil pressure bleeds off and the propeller feathers. The east, west, and central US propeller shops contacted were not aware of each other's findings, and according to propeller shop managers, mechanics are not familiar with the issues associated with oil viscosity either. All the shops reported mechanics sending airworthy propellers and governors in for unnecessary repairs. ## Aircraft - Registration: [N11HR](https://openairdocs.org/aircraft/N11HR), registered now, S/N 34-7970233, built 1979 (OpenAirDocs) - Reported make and model: PIPER PA-34 - Registry model: [Piper PA-34-200T](https://openairdocs.org/model/piper-pa-34-200t) (registry code 7103406) (OpenAirDocs) - Registry engine: [Continental TSIO-360 series](https://openairdocs.org/engine/continental-tsio-360-series) (registry code 17019, reciprocating) (OpenAirDocs) - Category: Airplane - Serial number: 34-7970232 - Airframe hours: 1567 - Engines: Continental IO-360 200 horsepower reciprocating - Damage: Substantial damage - Flight: Personal, Part 91 - Registered owner: Louis Farbre - Airworthiness certificate: Standard, Normal - Last inspection: Annual, May 1, 2008 - Departed: KAXH, Houston, TX - Destination: KOCF, Ocala, FL - Flight plan: IFR - Airport: KOCF, Ocala International Airport, runway 36, 6,907 × 150 ft, asphalt ## Flight crew As NTSB recorded them. NTSB leaves out names. - Pilot; age 66; injuries: none; private; airplane ratings: single-engine land, multi-engine land; instrument ratings: airplane; medical: class 3, with waivers/limitations; last flight review March 1, 2008; seat: left; flight hours: 5,250 total, 1,655 in this make and model, 5,149 as pilot in command, 23 in the last 90 days, 8 in the last 30 days, 5 in the last 24 hours ## Weather - Conditions: Visual (VMC), Day - Wind: 300° at 3 knots - Visibility: 10 statute miles - Lowest ceiling: 7,500 ft broken - Temperature: 30 °F, dew point 21 °F - Altimeter: 29.95 inHg - Observed at: KOCF ## 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 20080614849659A](https://openairdocs.org/incident/20080614849659A), Jun 14, 2008: Piper PA34200T, Ocala, FL, Substantial damage. (-23) On June 14, 2008 when Piper seneca N11HR was on short final over the runway at an estimated ten to twelve feet of altitude the left engine went into… 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.