Cessna 421C accident near Longmont, Colorado, July 10, 2021
On July 10, 2021 at about 2:45 pm local time, a 1978 Cessna 421C, registered N66NC, was substantially damaged in an accident during takeoff near Longmont, Colorado (Vance Brand Airport). It was a personal flight under general aviation rules (Part 91). 4 people had minor injuries. The weather was visual conditions (good weather).
The NTSB's probable cause their words, unchanged
The loss of performance for reasons that could not be determined.
Source: NTSB aviation accident database, copy made October 5, 2026. Docket and reports at the NTSB.
What the record shows
- Date
- July 10, 2021 · about 2:45 pm local time
- Place
- Longmont, Colorado · Vance Brand Airport · map
- Type
- Accident
- Injuries
- 4 people had minor injuries.
- Weather
- visual conditions (good weather)
- Aircraft
- Cessna 421C, built 1978 · all 421Cs on the register
- Registration
- N66NC · no longer on the register · serial 421C0519
- Damage
- Substantial damage
- Flight
- Personal flight · general aviation rules (Part 91)
The NTSB's narrative final · quoted from the NTSB record
The pilot reported that he performed the “before starting engine” and “starting engine” checklists and everything was normal before taking off in the twin-engine airplane. He performed an engine runup and then started his takeoff roll. The pilot reported that about halfway down the runway the airplane was not accelerating as fast as it should. He attempted to rotate the airplane; however, “the airplane mushed off the runway.” The airplane settled back onto the runway, then exited the departure end of the runway, where it sustained substantial damage to the wings and fuselage. The airplane engine monitor data indicated the airplane’s engines were operating consistent with each other at takeoff power at the time of the accident. Density altitude at the time of the accident was 7,170 ft and according to performance charts, there was adequate runway for takeoff. The reason for the loss of performance could not be determined.
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
What happened, in order
- Miscellaneous/other during takeoff
- Runway excursion during takeoff (rejected takeoff)
- Loss of control in flight during takeoff defining event
The NTSB's findings
- Personnel issues › Action/decision › Info processing/decision › Decision making/judgment › Pilot
- Aircraft › Aircraft oper/perf/capability › Performance/control parameters › Climb rate › Attain/maintain not possible
- Environmental issues › Conditions/weather/phenomena › Temp/humidity/pressure › High density altitude › Effect on equipment
- Personnel issues › Task performance › Use of equip/info › Aircraft control › Pilot
Pilot
- Certificate: commercial pilot
- Ratings: multi-engine land; single-engine land; instructor: airplane single-engine; instructor: instrument airplane; instrument: airplane
- Flight time: 2,801 hours in all; 169 in this make and model; 32 in the last 90 days; 26 in the last 30 days; 2,584 as pilot in command; 1,550 on instruments
- Last flight review: June 12, 2021
- Medical certificate: Class 2 (with waivers/limitations)
- Seat: left
- Injury: minor injuries
The aircraft
- Airframe total time: 5,476 hours
- Last inspection: annual inspection, August 18, 2020
- Seats: 8
- Landing gear: retractable
- Engine 1: Continental GTSIO-520 (piston); 0 hours total
- Engine 2: Continental GTSIO-520 (piston); 0 hours total
- Fire on the ground
The flight
- Destination: KASE Aspen CO
- Flight plan: none
- Runway 29, 4,799 ft by 75 ft
Weather at the time
- Light: daylight
- Wind: from 140° at 3 knots
- Visibility: 10 statute miles
- Sky: clear
- Temperature: 79°F (26°C), dew point 48°F (9°C)
- Altimeter: 30.31 inHg
- Observation at 9:15 am from KLMO
Weather report (METAR): METAR KLMO 101515Z AUTO 14003KT 10SM CLR 26/09 A3031 RMK AO2 T02570094
Injuries
| Fatal | Serious | Minor | None | |
|---|---|---|---|---|
| Flight crew | 1 | |||
| Passengers | 3 |
Documents from the investigation the NTSB's docket: the evidence folder behind the report
9 documents, released by the NTSB on September 14, 2023. View them here, or download them; the NTSB redacts some personal details before release, and this site shows the NTSB's own titles rather than its file names.
| # | Document | What it is | |
|---|---|---|---|
| 1 | Pilot/operator Aircraft Accident Report, NTSB Form 6120.1 | PDF, 11 pages | View Download |
| 2 | Photographs | PDF, 2 pages | View Download |
| 3 | Engine Monitor Report | PDF, 2 pages | View Download |
| 4 | Jpi Readings | PDF, 2 pages | View Download |
| 5 | Jpi Raw Data | data file | Download |
| 6 | E-mail, Continental Motors Review of Engine Monitor Data | PDF, 3 pages | View Download |
| 7 | Cessna 421C Takeoff and Climb Performance Charts | PDF, 3 pages | View Download |
| 8 | Density Altitude Calculator | PDF, 3 pages | View Download |
| 9 | Vance Brand Airport Information | PDF, 4 pages | View Download |
The same docket at the NTSB · documents without a copy here are fetched from the NTSB when you open them.
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.