# NTSB CEN14LA439: Air Tractor AT-401, N4542W, Wray, CO, August 19, 2014

- Type: NTSB accident investigation
- Classification: Accident · Minor injuries · Limited investigation · Final report
- Date: August 19, 2014, 07:40 local (13:40 UTC)
- Place: Wray, CO
- Coordinates: 40.100276, -102.240837 (estimated)
- Nearby events: https://openairdocs.org/map.md?lat=40.1003&lon=-102.2408&mi=10
- Phase of flight: [Initial climb](https://openairdocs.org/ntsb-phases/350) (OpenAirDocs' grouping)
- Defining event: [Initial climb: Loss of engine power (total)](https://openairdocs.org/ntsb-events/341)
- Highest injury: Minor injuries
- Injuries: 1 minor
- Status: Completed, report February 11, 2015
- Report: Approved by Office Director
- NTSB office: Central Region
- Parties: FAA Flight Standards District Office
- NTSB case key (mKey): 89906
- NTSB case page: https://web.ntsb.gov/investigations/?ntsbnumber=CEN14LA439
- NTSB report (PDF, downloads): https://data.ntsb.gov/carol-repgen/api/Aviation/ReportMain/GenerateNewestReport/89906/pdf
- NTSB docket: https://data.ntsb.gov/Docket?ProjectID=89906
- Page: https://openairdocs.org/ntsb/CEN14LA439

## Probable cause

A loss of the No. 1 cylinder’s compression due to a stuck exhaust valve caused by a lack of sufficient valve clearance, which resulted in a loss of engine power and a forced landing. Contributing to the loss of engine power were the worn intake and exhaust valves in cylinders No. 3 and 4.

## Findings

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

- [Engine (reciprocating): recip engine power section](https://openairdocs.org/ntsb-findings/01058520): Aircraft › Aircraft power plant · Malfunction (probable cause); cases with it: [Air Tractor AT-401, 2 cases](https://openairdocs.org/ntsb-findings/01058520/cases.md?model=0390204), [All aircraft, 233 cases](https://openairdocs.org/ntsb-findings/01058520/cases.md)
- [Engine (reciprocating): recip engine power section](https://openairdocs.org/ntsb-findings/01058520): Aircraft › Aircraft power plant · Damaged/degraded (probable cause); cases with it: [Air Tractor AT-401, 2 cases](https://openairdocs.org/ntsb-findings/01058520/cases.md?model=0390204), [All aircraft, 233 cases](https://openairdocs.org/ntsb-findings/01058520/cases.md)

## Sequence of events

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

- [Initial climb: Loss of engine power (total)](https://openairdocs.org/ntsb-events/341) (defining event); cases with it: [Air Tractor AT-401, 6 cases](https://openairdocs.org/ntsb-events/341/sequence.md?model=0390204), [All aircraft, 3,820 cases](https://openairdocs.org/ntsb-events/341/sequence.md)
- [Emergency descent: Off-field or emergency landing](https://openairdocs.org/ntsb-events/440); cases with it: [Air Tractor AT-401, 3 cases](https://openairdocs.org/ntsb-events/440/sequence.md?model=0390204), [All aircraft, 3,365 cases](https://openairdocs.org/ntsb-events/440/sequence.md)
- [Landing-landing roll: Nose over/nose down](https://openairdocs.org/ntsb-events/096); cases with it: [Air Tractor AT-401, 2 cases](https://openairdocs.org/ntsb-events/096/sequence.md?model=0390204), [All aircraft, 2,287 cases](https://openairdocs.org/ntsb-events/096/sequence.md)

## Analysis

During initial climb, the pilot felt a subtle vibration from the engine and noticed the manifold pressure dropping rapidly. When he attempted to increase manifold pressure by opening the throttle, the engine began to vibrate violently and lost all power. The pilot made a downwind forced landing, and the airplane nosed over. The engine was later partially disassembled and examined. A small amount of aluminum and steel filings were recovered from oil drained from the rocker arm sump. A cylinder compression check revealed that the Nos. 1 and 3 cylinders were non-functioning and that the No. 4 cylinder exhibited weak compression. The intake valve in the No. 3 cylinder was found to have a ridge worn on its face, and the valve seat was worn excessively. The No. 1 cylinder's exhaust valve was stuck open and was binding in the valve guide. The exhaust valve clearances for the cylinders were then checked and found to be less than the Pratt and Whitney overhaul limits of 0.003" to 0.0055", with a maximum wear limit of 0.010". Most likely, the engine lost power due to the stuck exhaust valve.

## Factual narrative

On August 19, 2014, about 0740 mountain daylight time, the pilot of an Air Tractor AT-401, N4542W, made a forced landing in a field near Wray, Colorado. The pilot, the sole occupant on board, sustained a minor injury. The airplane was substantially damaged. The airplane was being operated by Tri-County Ag of Wray, Colorado, under the provisions of 14 Code of Federal Regulations Part 137 as an aerial application flight. Visual meteorological conditions prevailed at the time of the accident, and no flight plan had been filed. The local flight originated from Wray Municipal Airport (2V5), Wray, Colorado, approximately 0700.According to the pilot's accident report, he had just finished spraying a field and was climbing out to return to his home base when he felt a subtle vibration from the engine and noticed manifold pressure dropping rapidly. When he attempted to increase manifold pressure by opening the throttle, the engine began to vibrate violently and lost all power. The pilot made a downwind forced landing. To avoid a drainage ditch and power lines ahead, the pilot applied heavy braking and the airplane nosed over. The vertical stabilizer and rudder, cockpit, and left wing sustained crushing damage. On October 14 and 15, the engine was partially disassembled and examined. Engine oil was drained from the rocker arm sump. In addition to carbon, a small amount of aluminum and steel filings were recovered. A compression check of all the cylinders was made with the following results: Cylinder 1 0/80 Cylinder 2 50/80 Cylinder 3 0/80 Cylinder 4 20/80 Cylinder 5 25/80 Cylinder 6 75/80 Cylinder 7 65/80 Cylinder 8 55/80 Cylinder 9 55/80 Cylinders 1, 3, and 4 were removed and examined. The intake valve in the number 3 cylinder had a ridge worn of its face, and the valve seat was worn excessively. The exhaust valve in the number 1 cylinder was stuck open and was found to be binding in the valve guide. It was removed with extreme difficulty. The exhaust valve clearances were then checked and found to be less than the Pratt and Whitney overhaul limits of .003" - .0055", with a maximum wear limit of .010", to wit: Cylinder 1 Clearance .002" Stem size .610" Guide size .613" Cylinder 3 Clearance .0022" Stem size .611" Guide size .6132" Cylinder 4 Clearance .0022" Stem size .611" Guide size .6132"

## Aircraft

- Registration: [N4542W](https://openairdocs.org/deregistered/N4542W-2020-07-10), registration cancelled 2020-07-10, S/N 401-0767 (OpenAirDocs)
- Reported make and model: AIR TRACTOR AT-401
- Registry model: [Air Tractor AT-401](https://openairdocs.org/model/air-tractor-at-401) (registry code 0390204) (OpenAirDocs)
- Registry engine: [Pratt & Whitney R1340 series](https://openairdocs.org/engine/pratt-whitney-r1340-series) (registry code 52016, reciprocating) (OpenAirDocs)
- Category: Airplane
- Serial number: 401-0767
- Year built: 1989
- Airframe hours: 7969
- Engines: Pratt & Whitney R-1340-S3H1G 600 horsepower reciprocating
- Damage: Substantial damage
- Flight: Aerial application, Part 137
- Operator: Aurora Cooperative, doing business as Tri-County Ag
- Registered owner: Wilmington Trust Company, Trustee
- Airworthiness certificate: Special, Restricted (Special)
- Last inspection: 100 hour, August 8, 2014, 30 hours before
- Departed: 2V5, Wray, CO
- Destination: 2V5, Wray, CO
- Equipment: Stall warning system

## Flight crew

As NTSB recorded them. NTSB leaves out names.

- Pilot; age 22; injuries: minor; commercial; airplane ratings: single-engine land; medical: class 2, without waivers/limitations; seat: single; restraint: 4-point; flight hours: 750 total, 400 in this make and model, 625 as pilot in command, 250 in the last 90 days, 170 in the last 30 days, 4 in the last 24 hours

## Weather

- Conditions: Visual (VMC), Day
- Wind: calm
- Visibility: 10 statute miles
- Lowest ceiling: none
- Temperature: 61 °F, dew point 55 °F
- Altimeter: 29.95 inHg
- Observed at: 2V5

## 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 20140819015309A](https://openairdocs.org/incident/20140819015309A), Aug 19, 2014: Air Tractor Inc AT-401, Wray, CO, Substantial damage. On 08/19/2014 at 0745 MDT, N4542W, an Air tractor AG-401 restricted airworthiness airplane flipped on landing in a field after power loss. The sole commercial…

## Docket (11 files)

The files NTSB released with the investigation on October 30, 2014, on NTSB's docket system: https://data.ntsb.gov/Docket?ProjectID=89906. 12.4 MB in all.

- Pilot/Operator Aircraft Accident Report, NTSB Form 6120.1 (item 1, .PDF, 731 KB): https://data.ntsb.gov/Docket/Document/docBLOB?ID=40418359&FileExtension=.PDF&FileName=Pilot%2FOperator%20Aircraft%20Accident%20Report,%20NTSB%20Form%206120.1-Redacted.PDF
- Engine Teardown Report (item 2, .PDF, 339 KB): https://data.ntsb.gov/Docket/Document/docBLOB?ID=40418360&FileExtension=.PDF&FileName=Engine%20Teardown%20Report-Redacted.PDF
- Excerpts from Engine Maintenance Logbook (item 3, .PDF, 973 KB): https://data.ntsb.gov/Docket/Document/docBLOB?ID=40418361&FileExtension=.PDF&FileName=Excerpts%20from%20Engine%20Maintenance%20Logbook-Redacted.PDF
- Photo 1 - Oil From Rocker Arm Sump (item 4, .PDF, 788 KB): https://data.ntsb.gov/Docket/Document/docBLOB?ID=40418362&FileExtension=.PDF&FileName=Photo%201%20-%20Oil%20From%20Rocker%20Arm%20Sump-Master.PDF
- Photo 2 - Interior of Number 3 Cylinder (item 5, .PDF, 1.7 MB): https://data.ntsb.gov/Docket/Document/docBLOB?ID=40418363&FileExtension=.PDF&FileName=Photo%202%20-%20Interior%20of%20Number%203%20Cylinder-Master.PDF
- Photo 3 - Number 3 Cylinder Intake Valve (item 6, .PDF, 821 KB): https://data.ntsb.gov/Docket/Document/docBLOB?ID=40418364&FileExtension=.PDF&FileName=Photo%203%20-%20Number%203%20Cylinder%20Intake%20Valve-Master.PDF
- Photo 4 - Number 3 Cylinder Exhaust Valve (item 7, .PDF, 985 KB): https://data.ntsb.gov/Docket/Document/docBLOB?ID=40418365&FileExtension=.PDF&FileName=Photo%204%20-%20Number%203%20Cylinder%20Exhaust%20Valve-Master.PDF
- Photo 5 - Face of Number 3 Exhaust Valve (item 8, .PDF, 1.1 MB): https://data.ntsb.gov/Docket/Document/docBLOB?ID=40418366&FileExtension=.PDF&FileName=Photo%205%20-%20Face%20of%20Number%203%20Exhaust%20Valve-Master.PDF
- Photo 6 - Cylinder Number 1 Intake and Exhaust Valves (item 9, .PDF, 1.8 MB): https://data.ntsb.gov/Docket/Document/docBLOB?ID=40418367&FileExtension=.PDF&FileName=Photo%206%20-%20Cylinder%20Number%201%20Intake%20and%20Exhaust%20Valves-Master.PDF
- Photo 7 - 20-80 Compression on Cylinder Number 4 (item 10, .PDF, 1.8 MB): https://data.ntsb.gov/Docket/Document/docBLOB?ID=40418368&FileExtension=.PDF&FileName=Photo%207%20-%2020-80%20Compression%20on%20Cylinder%20Number%204-Master.PDF
- Photo 8 - Carburetor Heat Box Lock Wired in Cold Position (item 11, .PDF, 1.3 MB): https://data.ntsb.gov/Docket/Document/docBLOB?ID=40418369&FileExtension=.PDF&FileName=Photo%208%20-%20Carburetor%20Heat%20Box%20Lock%20Wired%20in%20Cold%20Position-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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