# NTSB FTW98LA315: Bell 47-GB31, N92HA, Olathe, CO, July 17, 1998

- Type: NTSB accident investigation
- Classification: Accident · No injuries · Limited investigation · Final report
- Date: July 17, 1998, 12:30 local (18:30 UTC)
- Place: Olathe, CO
- Coordinates: 38.600212, -107.979423 (estimated)
- Nearby events: https://openairdocs.org/map.md?lat=38.6002&lon=-107.9794&mi=10
- Phase of flight: [Maneuvering](https://openairdocs.org/ntsb-phases/450) (OpenAirDocs' grouping)
- Highest injury: No injuries
- Injuries: 1 uninjured
- Status: Completed, report September 28, 1999
- Report: Approved by Office Director
- NTSB case key (mKey): 43169
- NTSB case page: https://web.ntsb.gov/investigations/?ntsbnumber=FTW98LA315
- NTSB report (PDF, downloads): https://data.ntsb.gov/carol-repgen/api/Aviation/ReportMain/GenerateNewestReport/43169/pdf
- Page: https://openairdocs.org/ntsb/FTW98LA315

## Probable cause

The pilot's inadequate in-flight planning which resulted in an encounter with his own wake turbulence.  Related factors were high density altitude and wake turbulence.

## Sequence of events

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

- Loss of control - in flight, maneuvering - aerial application
  - in-flight planning/decision - inadequate, pilot in command (cause)
  - weather condition - high density altitude (contributing factor)
  - weather condition - turbulence (contributing factor)
  - wake turbulence - inadvertent, pilot in command (cause)
  - aircraft control - not maintained, pilot in command (cause)
- In flight collision with terrain/water, descent - uncontrolled
  - terrain condition - open field

## Analysis

While on its third aerial application pass, to dispense a rinse load, the helicopter flew into its own wake turbulence and had insufficient power to overcome the settling which ensued.   The helicopter struck the ground in a nose low attitude and the main rotor blades severed the tail boom.  Density altitude at the time was computed to be approximately  8,900 feet.

## Factual narrative

On July 17, 1998, at 1230 mountain daylight time, a Bell 47-GB31 helicopter, N92HA, settled to a hard landing while maneuvering near Olathe, Colorado, during an aerial application flight.  The commercial pilot and sole occupant was not injured and the helicopter sustained substantial damage.  The flight was being operated as an aerial application flight under Title 14 CFR Part 137, and no flight plan was filed.  Visual meteorological conditions prevailed.

According to the pilot, he was dispensing a rinse load and had made three passes over the same path.  He said the wind came up as he turned the helicopter for another pass and he flew into his own wake turbulence.  The pilot said he had insufficient power to overcome the ensuing descent and the helicopter settled onto the ground in a nose low attitude.  This caused the main rotor blades to strike the tail boom and sever it from the aircraft.

Density altitude at the time was computed to be approximately 8,900 feet.

## Aircraft

- Registration: N92HA (not matched to a registry record)
- Reported make and model: Bell 47-GB31
- Category: Helicopter
- Serial number: 3696
- Airframe hours: 6260
- Engines: Lycoming TVO-435-B1A 260 horsepower reciprocating
- Damage: Substantial damage
- Flight: Aerial application, Part 137
- Registered owner: Olathe Spray Service, Inc.
- Airworthiness certificate: Special, Restricted (Special)
- Last inspection: Annual, January 29, 1998, 35 hours before
- Departed: 1C04
- Airport: ICO4, Clifford Field, runway 17, 4,000 × 100 ft, dirt

## Flight crew

As NTSB recorded them. NTSB leaves out names.

- Pilot; age 52; commercial; airplane ratings: single-engine land; medical: class 2, valid medical--w/ waivers/lim; seat: left; flight hours: 20,245 total, 351 in this make and model, 334 in the last 90 days, 87 in the last 30 days, 6 in the last 24 hours

## Weather

- Conditions: Visual (VMC), Day
- Wind: 350° at 8 knots
- Visibility: 10 statute miles
- Lowest ceiling: none
- Temperature: 88 °F, dew point 45 °F
- Altimeter: 30.00 inHg
- Observed at: MTJ, 30 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 19980717027069A](https://openairdocs.org/incident/19980717027069A), Jul 17, 1998: Bell 47G3B1, Olathe, CO, Substantial damage. (-23)Despending rinse load asjacent to runway. Made 3 consecutive passes over same path. Wind came up 7-8 mph, turned into preceding passes wake. Started to…

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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