# NTSB CHI94IA017: Piper PA-24-250, N6846P, Thief Rvr Falls, MN, October 14, 1993

- Type: NTSB incident investigation
- Classification: Incident · No injuries · Incident investigation · Final report
- Date: October 13, 1993, 19:45 local (Oct 14, 1993, 00:45 UTC)
- Place: Thief Rvr Falls, MN
- Coordinates: 48.110267, -96.170959 (estimated)
- Nearby events: https://openairdocs.org/map.md?lat=48.1103&lon=-96.1710&mi=10
- Phase of flight: [Enroute](https://openairdocs.org/ntsb-phases/400) (OpenAirDocs' grouping)
- Highest injury: No injuries
- Injuries: 1 uninjured
- Status: Completed, report August 30, 1994
- Report: Approved by Office Director
- NTSB case key (mKey): 9397
- NTSB case page: https://web.ntsb.gov/investigations/?ntsbnumber=CHI94IA017
- NTSB report (PDF, downloads): https://data.ntsb.gov/carol-repgen/api/Aviation/ReportMain/GenerateNewestReport/9397/pdf
- Page: https://openairdocs.org/ntsb/CHI94IA017

## Probable cause

FATIGUE FAILURE OF THE PROPELLER BLADE, ORIGINATING FROM A CORROSION PIT.

## Sequence of events

In NTSB's coding before 2008 (https://www.ntsb.gov/GILS/Documents/codman.pdf).

- Airframe/component/system failure/malfunction, cruise - normal
  - propeller system/accessories,blade - fatigue (cause)
- Forced landing, descent - emergency

## Analysis

IN CRUISE FLIGHT AT 8500 FEET MSL, THERE WAS A SEPARATION OF APPROXIMATELY ONE FOOT OF THE OUTBOARD PORTION OF ONE PROPELLER BLADE.  THE PILOT SHUT DOWN THE ENGINE AND MADE AN UNEVENTFUL LANDING IN A SUNFLOWER FIELD.  EXAMINATION OF THE FAILED PROPELLER BLADE REVEALED IT HAD FAILED DUE TO FATIGUE. THE ORIGIN OF THE FATIGUE FRACTURE WAS AT A CORROSION PIT ON THE CAMBER SURFACE OF THE BLADE MEASURING 0.012 INCH WIDE AND 0.0014 INCH DEEP.

## Factual narrative

On October 13, 1993, at 1945 central daylight time, a Piper PA-24-250, N6846P, experienced a separation of approximately one foot of the outboard portion of one propeller blade while in cruise flight at 8,500 feet mean sea level.  The private pilot made an uneventful forced landing near Thief River Falls, Minnesota.  There was no damage to the airplane.  The personal flight originated at Warroad, Minnesota, at 1900, with an intended destination of Arthur, North Dakota.  No flight plan was filed, and visual meteorological conditions prevailed at the time.

The engine logbook indicated the propeller had been overhauled and reinstalled on April 1, 1986 at airframe total time of 2,942 hours.  There were four annual inspection logbook entries stating the propeller had been "dressed and painted."  The last inspection was an annual inspection completed on December 1, 1992.  The airplane had flown 88 hours since inspection.  The total time accumulated since the propeller had been overhauled was 1,000 hours.

The remaining portion of the failed propeller blade was sent to the National Transportation Safety Board Materials Laboratory, Washington D.C., for examination.  The metallurgical report stated the fracture was typical of a fatigue separation.  The fatigue origin was a corrosion pit on the camber surface of the blade measuring 0.012 inches wide and 0.0014 inches deep.

## Aircraft

- Registration: [N6846P](https://openairdocs.org/deregistered/N6846P-1994-09-28), registration cancelled 1994-09-28, S/N 241979 (OpenAirDocs)
- Reported make and model: PIPER PA-24-250
- Registry model: [Piper PA-24](https://openairdocs.org/model/piper-pa-24) (registry code 7102402) (OpenAirDocs)
- Category: Airplane
- Serial number: 24-1979
- Airframe hours: 3942
- Engines: LYCOMING O-540-A1A5 250 horsepower reciprocating
- Damage: No damage
- Flight: Personal, Part 91
- Registered owner: Jeffrey J. Peltier
- Airworthiness certificate: Standard, Normal
- Last inspection: Annual, December 1, 1992, 88 hours before
- Departed: RAD, WARROAD, MN
- Destination: ND03, ARTHUR, ND

## Flight crew

As NTSB recorded them. NTSB leaves out names.

- Pilot; age 38; private; airplane ratings: single-engine land; instrument ratings: airplane; medical: class 3, valid medical--no waivers/lim.; seat: left; flight hours: 1,968 total, 1,500 in this make and model, 41 in the last 90 days, 18 in the last 30 days, 4 in the last 24 hours

## Weather

- Conditions: Visual (VMC), Day
- Wind: 170° at 7 knots
- Visibility: 10 statute miles
- Lowest ceiling: none
- Temperature: 45 °F, dew point 30 °F
- Altimeter: 29.00 inHg
- Observed at: TVF, 6 nm away

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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