# NTSB ERA12LA191: Cessna 172N, N4737D, Flat Rock, VA, February 17, 2012

- Type: NTSB accident investigation
- Classification: Accident · No injuries · Limited investigation · Final report
- Date: February 17, 2012, 16:52 local (21:52 UTC)
- Place: Flat Rock, VA
- Coordinates: 37.520278, -77.820274 (estimated)
- Nearby events: https://openairdocs.org/map.md?lat=37.5203&lon=-77.8203&mi=10
- Phase of flight: [Enroute](https://openairdocs.org/ntsb-phases/400) (OpenAirDocs' grouping)
- Defining event: [Enroute-cruise: Loss of engine power (partial)](https://openairdocs.org/ntsb-events/342)
- Highest injury: No injuries
- Injuries: 1 uninjured
- Status: Completed, report September 5, 2013
- Report: Approved by Office Director
- NTSB office: Eastern Region Aviation
- Parties: FAA/FSDO
- ADs cited in the narratives: [AD 80-04-03 R2](https://openairdocs.org/ad/80-04-03-R2) (OpenAirDocs)
- NTSB case key (mKey): 82953
- NTSB case page: https://web.ntsb.gov/investigations/?ntsbnumber=ERA12LA191
- NTSB report (PDF, downloads): https://data.ntsb.gov/carol-repgen/api/Aviation/ReportMain/GenerateNewestReport/82953/pdf
- NTSB docket: https://data.ntsb.gov/Docket?ProjectID=82953
- Page: https://openairdocs.org/ntsb/ERA12LA191

## Probable cause

The partial loss of engine power due to the failure of the exhaust valve spring seat for reasons that could not be determined.

## Findings

NTSB's coded findings; those marked are part of the probable cause.

- [Not determined](https://openairdocs.org/ntsb-findings/05000000): Not determined › Not determined · Unknown/Not determined (probable cause); cases with it: [Cessna 172N, 24 cases](https://openairdocs.org/ntsb-findings/05000000/cases.md?model=2072434), [All aircraft, 2,247 cases](https://openairdocs.org/ntsb-findings/05000000/cases.md)

## Sequence of events

The events NTSB coded, in order, by phase of flight. The defining event best describes what happened.

- [Enroute-cruise: Loss of engine power (partial)](https://openairdocs.org/ntsb-events/342) (defining event); cases with it: [Cessna 172N, 23 cases](https://openairdocs.org/ntsb-events/342/sequence.md?model=2072434), [All aircraft, 1,858 cases](https://openairdocs.org/ntsb-events/342/sequence.md)
- [Emergency descent: Off-field or emergency landing](https://openairdocs.org/ntsb-events/440); cases with it: [Cessna 172N, 31 cases](https://openairdocs.org/ntsb-events/440/sequence.md?model=2072434), [All aircraft, 3,365 cases](https://openairdocs.org/ntsb-events/440/sequence.md)
- [Landing-landing roll: Collision during takeoff/land](https://openairdocs.org/ntsb-events/490); cases with it: [Cessna 172N, 18 cases](https://openairdocs.org/ntsb-events/490/sequence.md?model=2072434), [All aircraft, 1,309 cases](https://openairdocs.org/ntsb-events/490/sequence.md)

## Analysis

According to the pilot, while in cruise flight, the engine began to lose power. He noticed a vibration in the throttle control and an “oily” smell. Engine power decreased to 1,500 rpm. The airplane was unable to maintain altitude, and the pilot elected to make an emergency landing in a field. During the landing roll, the airplane collided with an embankment and sustained substantial damage to the fuselage. An examination of the engine revealed that the No. 4 valve spring seat had broken. A review of the maintenance records revealed that the engine had accumulated 1865.34 hours since the last overhaul 6.5 years before the accident. According to Lycoming Service Instruction 1009AU, the recommended time between overhaul is 2,000 hours or 12 years, whichever occurs first. Further review of the maintenance records revealed compliance with Airworthiness Directive 80-04-03 R2, which covers the replacement of the upper exhaust valve spring seats and the exhaust hydraulic lifters. The exhaust valve seat failed 134.66 hours before the next recommended overhaul. The investigation was unable to determine the reason for the valve seat failure.

## Factual narrative

On February 17, 2012, about 1652 eastern standard time, a Cessna 172N, N4737D, made a force land following a partial loss of engine power near Flat Rock, Virginia. The airplane sustained substantial damaged and the private pilot was not injured. The airplane was registered to Green Hat Aviation LLC, and operated by an individual under the provisions of 14 Code of Federal Regulations Part 91 as a personal flight. Visual meteorological conditions prevailed and no flight plan was filed. The flight originated from Manassas Regional Airport/Harry P. Davis Field (HEF), Manassas, Virginia at 1549. According to the pilot, he was at an altitude of 4,500 feet when the engine began losing power. He noticed a strong vibration in the throttle control and began to notice an "oily smell." The engine power decreased to 1,500 rpm but continued to run. The pilot contacted the air traffic controller (ATC) and declared an emergency. He advised ATC of his intention to land in a field, and ATC suggested a private grass strip. The pilot advised ATC that he did not have enough altitude to make it to the strip and continued towards the field. The pilot made a forced landing in the field, and during the landing roll the airplane collided with an embankment. Examination of the airplane by a Federal Aviation Administration inspector confirmed structural damage to the firewall, fuselage and both wings. During an examination of the engine, it was noted that the No. 4 cylinder exhaust valve spring seat had broken. As a result of the broken valve spring seat, the push rod became dislodged. A review of the maintenance records revealed that airworthiness directive (AD 80-04-03 R2) was performed, which instructs the replacement of the upper exhaust valve spring seats and the exhaust hydraulic lifters. According to the Lycoming Service Instruction 1009AU, the recommended time between overhaul (TBO) periods is 2,000 hours or 12 years, whichever comes first. The last engine overhaul was conducted on August 29, 2005, and 134.66 hours remained on the engine before the next recommended overhaul.

## Aircraft

- Registration: [N4737D](https://openairdocs.org/deregistered/N4737D-2018-01-24), registration cancelled 2018-01-24, S/N 17272345, built 1979 (OpenAirDocs)
- Reported make and model: CESSNA 172N
- Registry model: [Cessna 172N](https://openairdocs.org/model/cessna-172n) (registry code 2072434) (OpenAirDocs)
- Registry engine: [Lycoming 0-320 series](https://openairdocs.org/engine/lycoming-0-320-series) (registry code 41508, reciprocating) (OpenAirDocs)
- Category: Airplane
- Serial number: 17272345
- Airframe hours: 1557
- Engines: LYCOMING 0-320 SERIES 180 horsepower reciprocating
- Damage: Substantial damage
- Flight: Personal, Part 91
- Airworthiness certificate: Standard, Normal
- Last inspection: Annual, June 20, 2011, 11 hours before
- Departed: HEF, Manassas, VA
- Destination: FAY, Fayetteville, NC

## Flight crew

As NTSB recorded them. NTSB leaves out names.

- Pilot; age 42; injuries: none; private; airplane ratings: single-engine land; instrument ratings: airplane; medical: class 3, without waivers/limitations; seat: left; flight hours: 783 total, 767 in this make and model, 669 as pilot in command, 20 in the last 90 days, 1 in the last 30 days, 1 in the last 24 hours

## Weather

- Conditions: Visual (VMC), Day
- Wind: 150° at 3 knots
- Visibility: 4 statute miles
- Lowest ceiling: 9,000 ft broken
- Temperature: 45 °F, dew point 43 °F
- Altimeter: 30.06 inHg
- Observed at: OFP, 24 nm away

## 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 20120217001819A](https://openairdocs.org/incident/20120217001819A), Feb 17, 2012: Cessna 172N, Powhatan, VA, Substantial damage. While cruising at 4,500 feet, PIC lost RPM from 2500 to 1500 RPM with a strong vibration. Pilot located a field, accomplished an emergency landing checklist…

## Docket (10 files)

The files NTSB released with the investigation on July 16, 2013, on NTSB's docket system: https://data.ntsb.gov/Docket?ProjectID=82953. 9.2 MB in all.

- Pilot/Operator Aircraft Accident Report, NTSB Form 6120.1 (item 1, .PDF, 605 KB): https://data.ntsb.gov/Docket/Document/docBLOB?ID=40377349&FileExtension=.PDF&FileName=Pilot%2FOperator%20Aircraft%20Accident%20Report,%20NTSB%20Form%206120.1-Redacted.PDF
- Maintenance record pages-engine overhaul (item 2, .PDF, 189 KB): https://data.ntsb.gov/Docket/Document/docBLOB?ID=40377132&FileExtension=.PDF&FileName=Maintenance%20record%20pages-engine%20overhaul-Redacted.PDF
- Maintenance record entries for annual inspection (item 3, .PDF, 1.0 MB): https://data.ntsb.gov/Docket/Document/docBLOB?ID=40377133&FileExtension=.PDF&FileName=Maintenance%20record%20entries%20for%20annual%20inspection-Redacted.PDF
- TACH and Engine Record (item 4, .PDF, 738 KB): https://data.ntsb.gov/Docket/Document/docBLOB?ID=40377134&FileExtension=.PDF&FileName=TACH%20and%20Engine%20Record-Redacted.PDF
- Lycoming service instruction SI1009AU (item 5, .PDF, 45 KB): https://data.ntsb.gov/Docket/Document/docBLOB?ID=40377135&FileExtension=.PDF&FileName=Lycoming%20service%20instruction%20SI1009AU-Master.PDF
- Airworthiness Directive-AD 80-04-03 R2 (item 6, .PDF, 1.2 MB): https://data.ntsb.gov/Docket/Document/docBLOB?ID=40377136&FileExtension=.PDF&FileName=Airworthiness%20Directive-AD%2080-04-03%20R2-Master.PDF
- Photo 1-FAA photo-buckled firewall (item 7, .PDF, 2.1 MB): https://data.ntsb.gov/Docket/Document/docBLOB?ID=40377139&FileExtension=.PDF&FileName=Photo%201-FAA%20photo-buckled%20firewall-Master.PDF
- Photo 2-FAA photo-buckled right wing (item 8, .PDF, 1.1 MB): https://data.ntsb.gov/Docket/Document/docBLOB?ID=40377140&FileExtension=.PDF&FileName=Photo%202-FAA%20photo-buckled%20right%20wing-Master.PDF
- Photo 3-FAA photo-Broken valve spring retainer top view (item 9, .PDF, 984 KB): https://data.ntsb.gov/Docket/Document/docBLOB?ID=40377141&FileExtension=.PDF&FileName=Photo%203-FAA%20photo-Broken%20valve%20spring%20retainer%20top%20view-Master.PDF
- Photo 4-FAA photo-Broken valve spring retainer bottom view (item 10, .PDF, 1.2 MB): https://data.ntsb.gov/Docket/Document/docBLOB?ID=40377142&FileExtension=.PDF&FileName=Photo%204-FAA%20photo-Broken%20valve%20spring%20retainer%20bottom%20view-Master.PDF

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.

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