# NTSB SEA93LA188: Cessna A188B, N21861, Three Forks, MT, September 2, 1993

- Type: NTSB accident investigation
- Classification: Accident · Serious injuries · Limited investigation · Final report
- Date: September 2, 1993, 15:12 local (22:12 UTC)
- Place: Three Forks, MT
- Coordinates: 45.909938, -111.430335 (estimated)
- Nearby events: https://openairdocs.org/map.md?lat=45.9099&lon=-111.4303&mi=10
- Phase of flight: [Maneuvering](https://openairdocs.org/ntsb-phases/450) (OpenAirDocs' grouping)
- Highest injury: Serious injuries
- Injuries: 1 serious
- Status: Completed, report August 1, 1994
- Report: Approved by Office Director
- NTSB case key (mKey): 41757
- NTSB case page: https://web.ntsb.gov/investigations/?ntsbnumber=SEA93LA188
- NTSB report (PDF, downloads): https://data.ntsb.gov/carol-repgen/api/Aviation/ReportMain/GenerateNewestReport/41757/pdf
- Page: https://openairdocs.org/ntsb/SEA93LA188

## Probable cause

THE PILOT'S FAILURE TO MAINTAIN FLYING SPEED RESULTING IN A STALL/MUSH. THE HIGH DENSITY ALTITUDE AND THE PILOT'S FAILURE TO COMPLETELY JETTISON HIS LOAD WERE FACTORS.

## Sequence of events

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

- Loss of control - in flight, maneuvering
  - weather condition - high density altitude (contributing factor)
  - load jettison - inadequate, pilot in command (contributing factor)
  - airspeed - not maintained, pilot in command (cause)
  - stall/mush - inadvertent, pilot in command

## Analysis

WHILE MANEUVERING IN PREPARATION FOR A SPRAY RUN THE AIRCRAFT BEGAN TO SETTLE. THE PILOT APPLIED FULL POWER BUT JETTISONED ONLY 30 TO 40 OF THE REMAINING 100 TO 110 GALLONS OF HIS CHEMICAL LOAD. A DENSITY ALTITUDE OF APPROXIMATELY 6000 FEET EXISTED AT THE TIME. THE PILOT REPORTED NO MECHANICAL MALFUNCTION WITH THE AIRCRAFT AT THE TIME OF THE EVENT.

## Factual narrative

On September 2, 1993, at approximately 1512 hours mountain daylight time (MDT), a Cessna A188B "AgWagon," N21861, registered to Agwagons, Inc., and being operated and flown by William R. Ferguson, a certificated commercial pilot, collided with terrain while applying Roundup over an agricultural field. The aircraft was destroyed and the pilot suffered serious injuries. Visual meteorological conditions existed at the time and no flight plan had been filed. The aerial application flight was to have been operated in accordance with the requirements set forth in 14CFR137 and had departed a field near the accident site at approximately 1503 hours. The aircraft departed with 20 to 25 gallons of fuel and 140 gallons of chemical.

The pilot reported that while maneuvering in preparation for a spray run "an area of down air was encountered." He stated that he increased propeller RPM to maximum and "the throttle was brought up." The pilot reported that 100 to 110 gallons of chemical remained at the time of the event and that he dumped approximately 30 to 40 additional gallons.

The pilot reported that "before anymore load could be dumped, the ground was impacted in a flat, level attitude."

During an interview with an FAA Inspector, the pilot stated that "he dumped part of his load, applied full power, but the aircraft continued to mush out." Additionally, he reported that there was no indication of any malfunction with the aircraft (refer to attached FAA Form 1360-33).

## Aircraft

- Registration: [N21861](https://openairdocs.org/aircraft/N21861), registered now, S/N 18801082 (OpenAirDocs)
- Reported make and model: CESSNA A188B
- Registry model: [Cessna A188B](https://openairdocs.org/model/cessna-a188b) (registry code 2073005) (OpenAirDocs)
- Registry engine: [Continental IO-520 series](https://openairdocs.org/engine/continental-io-520-series) (registry code 17032, reciprocating) (OpenAirDocs)
- Category: Airplane
- Serial number: 18801082
- Airframe hours: 4056
- Engines: CONTINENTAL IO-520D 300 horsepower reciprocating
- Damage: Destroyed
- Flight: Aerial application, Part 137
- Operator: Ferguson, William R.
- Registered owner: Agwagons, Inc.
- Airworthiness certificate: Special, Restricted (Special)
- Last inspection: 100 hour, July 26, 1993, 84 hours before

## Flight crew

As NTSB recorded them. NTSB leaves out names.

- Pilot; age 44; airline transport, flight instructor; airplane ratings: single-engine land, multi-engine land; instrument ratings: airplane; medical: class 2, valid medical--w/ waivers/lim; seat: front; flight hours: 9,934 total, 3,550 in this make and model, 9,735 as pilot in command, 173 in the last 90 days, 75 in the last 30 days, 6 in the last 24 hours

## Weather

- Conditions: Visual (VMC), Day
- Wind: 330° at 5 knots
- Visibility: 30 statute miles
- Lowest ceiling: none
- Temperature: 66 °F, dew point 46 °F
- Altimeter: 30.00 inHg
- Observed at: BZN, 11 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 19930902032839A](https://openairdocs.org/incident/19930902032839A), Sep 2, 1993: Cessna A188B, Three Forks, MT, Destroyed. Preparing to begin a spray run. Aircraft settled. Dumped small amount of load. Impacted. Density altitude a factor.

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.