Ayres S2RT34 and Schweizer G164B mid-air collision near Marysville, California, May 9, 1991
On May 9, 1991 at about 3:49 pm local time, 2 aircraft, Ayres S2RT34 (N3633Q) and Schweizer G164B (N4012Y), were involved in a mid-air collision near Marysville, California. 1 person was killed and 1 person was seriously injured. The weather was visual conditions (good weather).
The NTSB's probable cause their words, unchanged
THE PILOTS' INADEQUATE VISUAL LOOKOUT FOR OTHER AIR TRAFFIC.
THE PILOTS' INADEQUATE VISUAL LOOKOUT FOR OTHER AIR TRAFFIC.
Source: NTSB aviation accident database, copy made October 5, 2026. Docket and reports at the NTSB.
What the record shows
- Date
- May 9, 1991 · about 3:49 pm local time
- Place
- Marysville, California · map
- Type
- Accident · mid-air collision
- Injuries
- 1 person was killed and 1 person was seriously injured.
- Weather
- visual conditions (good weather)
- Aircraft 1
- Ayres S2RT34
- Registration
- N3633Q · no longer on the register · serial 60747
- Damage
- Destroyed
- Flight
- Aerial application (crop spraying) flight · agricultural flying rules (Part 137)
- Aircraft 2
- Schweizer G164B
- Registration
- N4012Y · no longer on the register · serial 777B
- Damage
- Destroyed
- Flight
- Aerial application (crop spraying) flight · agricultural flying rules (Part 137)
The NTSB's narrative for the Ayres S2RT34 final · quoted from the NTSB record
THE PILOT OF THE AYRES (THRUSH) WAS PERFORMING AN AERIAL APPLICATION FLIGHT OVER A FIELD ADJACENT TO AN AIRSTRIP FROM WHICH A SCHWEIZER (AG CAT) HAD JUST DEPARTED. THE SCHWEIZER WAS ENROUTE TO PERFORM AN AERIAL APPLICATION FLIGHT AT ANOTHER FIELD. AS THE AYRES PILOT WAS BEGINNING TO REVERSE COURSE TO MAKE ANOTHER APPLICATION RUN, THE SCHWEIZER, WHICH WAS ON INITIAL CLIMB, COMMENCED A RIGHT TURN, AND THE FLIGHT PATHS OF THE TWO AIRPLANES CONVERGED. AFTER THE NEARLY HEAD ON COLLISION, THE TWO AIRPLANES DESCENDED OUT OF CONTROL AND CRASHED INTO THE UNDERLYING FIELD.
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 NTSB's narrative for the Schweizer G164B final · quoted from the NTSB record
THE PILOT OF THE AYRES (THRUSH) WAS PERFORMING AN AERIAL APPLICATION FLIGHT OVER A FIELD ADJACENT TO AN AIRSTRIP FROM WHICH A SCHWEIZER (AG CAT) HAD JUST DEPARTED. THE SCHWEIZER WAS ENROUTE TO PERFORM AN AERIAL APPLICATION FLIGHT AT ANOTHER FIELD. AS THE AYRES PILOT WAS BEGINNING TO REVERSE COURSE TO MAKE ANOTHER APPLICATION RUN, THE SCHWEIZER, WHICH WAS ON INITIAL CLIMB, COMMENCED A RIGHT TURN, AND THE FLIGHT PATHS OF THE TWO AIRPLANES CONVERGED. AFTER THE NEARLY HEAD ON COLLISION, THE TWO AIRPLANES DESCENDED OUT OF CONTROL AND CRASHED INTO THE UNDERLYING FIELD.
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 for the Ayres S2RT34 from the NTSB's investigation tables, in plain English
Pilot
- Certificate: commercial pilot
- Ratings: multi-engine land; multi-engine sea; single-engine land; single-engine sea; rotorcraft: helicopter
- Flight time: 8,000 hours in all
- Medical certificate: Class 2 (valid medical--no waivers/lim.)
- Seat: unk
The aircraft
- Last inspection: inspection type not recorded, January 2, 2000
- Maximum gross weight: 6,000 lb
- Seats: 1
- Landing gear: fixed
- Engine: P&W PT6A-34AG (turboprop); 0 hours total
- Not recorded
The flight
- Departed from: NONE Marysville CA at 3:30 pm
- Flight plan: none
- Runway 0
Weather at the time
- Light: daylight
- Visibility: 5 statute miles
- Sky: clear
- Temperature: 0°F (-18°C), dew point 0°F (-18°C)
Injuries
| Fatal | Serious | Minor | None | |
|---|---|---|---|---|
| Crew | 1 |
The factual record for the Schweizer G164B from the NTSB's investigation tables, in plain English
Pilot
- Certificate: commercial pilot
- Ratings: single-engine land
- Flight time: 4,460 hours in all
- Medical certificate: Class 2 (valid medical--no waivers/lim.)
- Seat: unk
The aircraft
- Last inspection: inspection type not recorded, January 2, 2000
- Maximum gross weight: 5,200 lb
- Seats: 1
- Landing gear: fixed
- Engine: P&W R1340 (piston); 0 hours total
- Operator: Onstott Dusters, INC.
The flight
- Departed from: NONE Marysville CA at 3:48 pm
- Flight plan: none
- Runway 0
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 N3633Q 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.