Amateur-built RV-4 accident near Yellowstonepark, Wyoming, July 4, 1991
On July 4, 1991 at about 3:00 pm local time, a amateur-built RV-4, registered N44AZ, was substantially damaged in an accident near Yellowstonepark, Wyoming. It was a personal flight under general aviation rules (Part 91). 1 person was killed and 1 person had minor injuries. The weather was visual conditions (good weather).
The NTSB's probable cause their words, unchanged
A COLLAPSED INDUCTION AIR DUCT. FACTORS INCLUDE INADEQUATE DESIGN BY THE MANUFACTURER/BUILDER, AND A MISJUDGED RATE OF DESCENT BY THE PILOT.
Source: NTSB aviation accident database, copy made October 5, 2026. Docket and reports at the NTSB.
What the record shows
- Date
- July 4, 1991 · about 3:00 pm local time
- Place
- Yellowstonepark, Wyoming · map
- Type
- Accident
- Injuries
- 1 person was killed and 1 person had minor injuries.
- Weather
- visual conditions (good weather)
- Aircraft
- Amateur-built RV-4
- Registration
- N44AZ · registry record · serial 1
- Damage
- Substantial damage
- Flight
- Personal flight · general aviation rules (Part 91)
The NTSB's narrative final · quoted from the NTSB record
THE PILOT OF THE RV-4 EXPERIMENTAL AIRCRAFT EXPERIENCED A PARTIAL POWER LOSS, AND RECEIVED FATAL INJURIES WHEN THE AIRCRAFT IMPACTED THE WATER, DURING AN ATTEMPTED EMERGENCY LANDING, NEAR THE SHORELINE OF A LAKE. LATER INSPECTION OF THE ENGINE FOUND THAT THE SCAT TUBING WHICH RAN FROM THE AIR INTAKE FILTER TO THE FUEL INJECTOR BODY, WAS ROUTED IN A MANNER THAT CAUSED THE INTERNAL WIRE SUPPORT TO BE DISPLACED, ALLOWING THE TUBING WALLS TO COLLAPSE. THIS CONDITION REDUCED THE INDUCTION AIRFLOW TO THE ENGINE.
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: multi-engine land; single-engine land
- Flight time: 450 hours in all
- Medical certificate: Class 2 (valid medical--w/ waivers/lim.)
- Seat: unk
The aircraft
- Last inspection: inspection type not recorded; 0 hours since
- Maximum gross weight: 1,500 lb
- Seats: 2
- Landing gear: fixed
- Engine: Lycoming IO-320-E3D (piston); 0 hours total
The flight
- Departed from: WYS Westyellowstone WY at 2:30 pm
- Destination: CPR Casper WY
- Flight plan: none
- Runway 0
Weather at the time
- Light: daylight
- Visibility: 20 statute miles
- Sky: clear
- Temperature: 0°F (-18°C), dew point 0°F (-18°C)
Injuries
| Fatal | Serious | Minor | None | |
|---|---|---|---|---|
| Crew | 1 | |||
| Passengers | 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 N44AZ 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.