Cessna 172 accident near Skwentna, Alaska, July 16, 2021
On July 16, 2021 at about 8:30 pm local time, a 1959 Cessna 172, registered N7137T, was substantially damaged in an accident during takeoff near Skwentna, Alaska. It was a personal flight under general aviation rules (Part 91). 2 people had minor injuries. The weather was visual conditions (good weather).
The NTSB's probable cause their words, unchanged
A partial loss of engine power due to detonation/preignition damage to the No. 2 cylinder. The reason for the detonation/preignition damage could not be determined based on the available evidence.
Source: NTSB aviation accident database, copy made October 5, 2026. Docket and reports at the NTSB.
What the record shows
- Date
- July 16, 2021 · about 8:30 pm local time
- Place
- Skwentna, Alaska · map
- Type
- Accident
- Injuries
- 2 people had minor injuries.
- Weather
- visual conditions (good weather)
- Aircraft
- Cessna 172, built 1959 · all 172s on the register
- Registration
- N7137T · registry record · serial 46737
- 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 during takeoff from an off-airport gravel bar on a river, the airplane experienced a partial loss of engine power. The pilot rejected the takeoff, and the airplane subsequently encountered a “bump,” which pitched the nose down. The pilot then made a hard right turn to avoid going into the water, and the airplane nosed down and impacted the ground with the left wing, which resulted in substantial damage to the left wing. Postaccident examination revealed that the No. 2 cylinder would not produce compression. Removal of the No. 2 cylinder revealed damage, including a hole in the piston that was consistent with detonation and/or preignition. The reason for the detonation and/or preignition could not be determined based on the available evidence.
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
- Loss of engine power (partial) during takeoff defining event
The NTSB's findings
- Aircraft › Aircraft power plant › Engine (reciprocating) › Recip eng cyl section › Failure
Pilot
- Certificate: flight instructor, commercial pilot
- Ratings: single-engine land; single-engine sea; instructor: airplane single-engine; instrument: airplane
- Flight time: 2,300 hours in all; 1,000 in this make and model; 110 in the last 90 days; 45 in the last 30 days; 2,100 as pilot in command; 1,000 on instruments
- Last flight review: July 1, 2021
- Medical certificate: Class 2 (without waivers/limitations)
- Seat: rgt
- Injury: minor injuries
The aircraft
- Airframe total time: 4,652 hours
- Last inspection: annual inspection, April 1, 2021
- Maximum gross weight: 2,200 lb
- Seats: 4
- Landing gear: fixed
- Engine: Cont Motor O-300 D (piston); 0 hours total
The flight
- Destination: SKW Skwentna AK
- Flight plan: none
Weather at the time
- Light: daylight
- Wind: from 310° at 3 knots
- Visibility: 10 statute miles
- Sky: clear
- Temperature: 70°F (21°C), dew point 52°F (11°C)
- Altimeter: 30.03 inHg
- Observation at 11:53 am from PATK, 35 miles away
Weather report (METAR): PATK 161953Z 31003KT 10SM CLR 21/11 A3003 RMK AO2 SLP169 T02110111
Injuries
| Fatal | Serious | Minor | None | |
|---|---|---|---|---|
| Flight crew | 1 | |||
| Passengers | 1 |
Documents from the investigation the NTSB's docket: the evidence folder behind the report
5 documents, released by the NTSB on November 4, 2022. 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, 9 pages | View Download |
| 2 | Accident Location | PDF, 1 page | View Download |
| 3 | FAA Examination | PDF, 3 pages | View Download |
| 4 | Engine Examination | PDF, 7 pages | View Download |
| 5 | Accident Pictures | PDF, 2 pages | View Download |
The same docket at the NTSB · documents without a copy here are fetched from the NTSB when you open them.
Other NTSB records under N7137T 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.