Bell 47-GB31 accident near Olathe, Colorado, July 17, 1998
On July 17, 1998 at about 6:30 pm local time, a Bell 47-GB31 (helicopter), registered N92HA, was substantially damaged in an accident near Olathe, Colorado (Clifford Field). It was an aerial application (crop spraying) flight under agricultural flying rules (Part 137). No one was hurt; 1 person was on board or involved. The weather was visual conditions (good weather).
The NTSB's probable cause their words, unchanged
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.
Source: NTSB aviation accident database, copy made October 5, 2026. Docket and reports at the NTSB.
What the record shows
- Date
- July 17, 1998 · about 6:30 pm local time
- Place
- Olathe, Colorado · Clifford Field · map
- Type
- Accident
- Injuries
- No one was hurt; 1 person was on board or involved.
- Weather
- visual conditions (good weather)
- Aircraft
- Bell 47-GB31 · all 47-GB31s on the register
- Registration
- N92HA · no longer on the register · serial 3696
- Damage
- Substantial damage
- Flight
- Aerial application (crop spraying) flight · agricultural flying rules (Part 137)
The NTSB's narrative final · quoted from the NTSB record
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.
The complete narrative as the NTSB published it. The NTSB's docket holds the report as a PDF and any photographs, statements and other documents from the investigation.
The factual record from the NTSB's investigation tables, in plain English
Pilot
- Certificate: commercial pilot
- Ratings: single-engine land; rotorcraft: helicopter
- Flight time: 20,245 hours in all; 351 in this make and model; 334 in the last 90 days; 87 in the last 30 days
- Medical certificate: Class 2 (valid medical--w/ waivers/lim.)
- Seat: left
The aircraft
- Airframe total time: 6,260 hours
- Last inspection: annual inspection, January 29, 1998; 35 hours since
- Maximum gross weight: 2,950 lb
- Seats: 3
- Landing gear: fixed
- Engine: Lycoming TVO-435-B1A (piston); 0 hours total
The flight
- Departed from: 1C04
- Flight plan: none
- Runway 17, 4,000 ft by 100 ft
Weather at the time
- Light: daylight
- Wind: from 350° at 8 knots
- Visibility: 10 statute miles
- Sky: clear
- Temperature: 88°F (31°C), dew point 45°F (7°C)
- Altimeter: 30.00 inHg
- Observation at 6:53 pm from MTJ, 30 miles away
Injuries
| Fatal | Serious | Minor | None | |
|---|---|---|---|---|
| Crew | 1 |
Documents from the investigation the NTSB's docket: the evidence folder behind the report
The docket, the folder of records gathered during an investigation (maintenance records, photographs, witness statements, examinations), has not been read from the NTSB for this case yet; the list appears here once it has. Open the docket at the NTSB.
Other NTSB records under N92HA the same tail number, which may have belonged to a different aircraft at the time
Everything on this page comes from the NTSB's public records. The narrative, probable cause and findings are the NTSB's own words; the coded tables behind the report are written out in plain English, with pilots' ages, home towns and medical details left out. The documents and photographs are the NTSB's docket, shown as the NTSB released them. This site's own text never names anyone involved. A preliminary report can change; the final report usually follows one to two years later, and the page is refreshed when it does.