Beech C23 accident near Boulder, Colorado, May 18, 1991
On May 18, 1991 at about 4:50 pm local time, a Beech C23, registered N6AL, was substantially damaged in an accident near Boulder, Colorado (Boulder Municipal airport). It was a business flight under general aviation rules (Part 91). 2 people were seriously injured and 1 person had minor injuries. The weather was visual conditions (good weather).
The NTSB's probable cause their words, unchanged
INADVERTENT STALL/MUSH DUE TO THE PASSENGERS'S DELAY IN RELINQUISHING AIRCRAFT CONTROL, AND INADEQUATE SUPERVISION OF THE FLIGHT BY THE PILOT IN COMMAND. FACTORS WERE: MIXTURE NOT LEANED, AND A HIGH DENSITY ALTITUDE TAKEOFF WITH A SLIGHT QUARTERING TAILWIND.
Source: NTSB aviation accident database, copy made October 5, 2026. Docket and reports at the NTSB.
What the record shows
- Date
- May 18, 1991 · about 4:50 pm local time
- Place
- Boulder, Colorado · Boulder Municipal · map
- Type
- Accident
- Injuries
- 2 people were seriously injured and 1 person had minor injuries.
- Weather
- visual conditions (good weather)
- Aircraft
- Beech C23 · all C23s on the register
- Registration
- N6AL · registry record · serial M-1421
- Damage
- Substantial damage
- Flight
- Business flight · general aviation rules (Part 91)
The NTSB's narrative final · quoted from the NTSB record
THE REAR SEAT PASSENGER SAID THE INSTRUCTOR LET THE FRONT SEAT PASSENGER MAKE THE TAKEOFF AND 'TALKED' HIM THROUGH THE PROCEDURE. SHORTLY AFTER LIFT OFF, BOTH PASSENGERS HEARD A 'WARNING BUZZER' SOUND THAT CONTINUED UNTIL GROUND IMPACT. THE INSTRUCTOR WAS SERIOUSLY INJURED AND COULD NOT RECALL ANY DETAILS OF THE ACCIDENT.
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: flight instructor, commercial pilot
- Ratings: multi-engine land; single-engine land; instructor: airplane single-engine; instructor: instrument airplane; instrument: airplane
- Flight time: 767 hours in all; 2 in this make and model; 61 in the last 90 days; 20 in the last 30 days; 682 as pilot in command; 368 on instruments
- Medical certificate: Class 2 (valid medical--no waivers/lim.)
- Seat: left
The aircraft
- Airframe total time: 2,756 hours
- Last inspection: annual inspection, March 7, 1991; 68 hours since
- Maximum gross weight: 2,450 lb
- Seats: 4
- Landing gear: fixed
- Engine: Lycoming O-360-A4G (piston); 0 hours total
- Operator: Dakota Ridge Aviation, INC.
The flight
- Flight plan: none
- Runway 26, 4,100 ft by 75 ft
Weather at the time
- Light: daylight
- Wind: from 130° at 7 knots
- Visibility: 25 statute miles
- Sky: broken clouds at 1,200 ft; clear
- Temperature: 63°F (17°C), dew point 45°F (7°C)
- Altimeter: 30.00 inHg
Injuries
| Fatal | Serious | Minor | None | |
|---|---|---|---|---|
| Crew | 1 | |||
| Passengers | 1 | 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.
About this page
Everything above comes from the NTSB's public accident database: the narrative, probable cause and findings are the NTSB's own words, and the coded tables behind its report (pilot, aircraft, flight, weather, injuries, sequence of events) are written out in plain English. Pilots' ages, home towns and medical details are left out on purpose. The documents and photographs are the NTSB's docket, the folder of records gathered during the investigation, shown as the NTSB released them (the NTSB redacts some personal details first) and listed under the NTSB's own titles. This site's own text never names pilots, passengers or anyone else involved. A preliminary report describes what is known soon after the event and can change; the final report, with the probable cause, usually follows one to two years later and this page is refreshed when it does. Case number DEN91FA072.