Cessna 172S and Sonex Aircraft XENOS mid-air collision near Longmont, Colorado, September 17, 2022
On September 17, 2022 at about 2:53 pm local time, 2 aircraft, Cessna 172S (N2117Y) and Sonex Aircraft XENOS (N255BF), were involved in a mid-air collision near Longmont, Colorado. 3 people were killed. The weather was visual conditions (good weather).
The NTSB's probable cause their words, unchanged
The pilots’ inability to see and avoid each other, resulting in a midair collision.
The pilots’ inability to see and avoid each other, resulting in a midair collision.
Source: NTSB aviation accident database, copy made October 5, 2026. Docket and reports at the NTSB.
What the record shows
- Date
- September 17, 2022 · about 2:53 pm local time
- Place
- Longmont, Colorado · map
- Type
- Accident · mid-air collision
- Injuries
- 3 people were killed.
- Weather
- visual conditions (good weather)
- Aircraft 1
- Cessna 172S, built 2004 · all 172Ss on the register
- Registration
- N2117Y · no longer on the register · serial 172S9622
- Damage
- Destroyed
- Flight
- Instructional flight · general aviation rules (Part 91)
- Aircraft 2
- Sonex Aircraft XENOS, built 2016, amateur-built
- Registration
- N255BF · registry record · serial X0046
- Damage
- Destroyed
- Flight
- Personal flight · general aviation rules (Part 91)
The NTSB's narrative for the Cessna 172S final · quoted from the NTSB record
The flight instructor and student pilot took off in a Cessna airplane from their home airport and proceeded north to a practice area to perform practice maneuvers. The Sonex pilot departed from an airport east of the practice area about 5 minutes earlier and proceeded westbound toward the vicinity of the Cessna. Both airplanes climbed to 7,000 - 7,500 ft mean sea level (msl) and operated under visual flight rules (VFR). When the Cessna reached the practice area, it made a left 360° turn consistent with a clearing turn, which according to the flight school was standard procedure. On completing the turn, the Cessna proceeded eastbound. The Sonex approached the same area from the east and tracked west-northwest toward the vicinity of the Cessna. The flight track data showed the two airplanes come together at an altitude of about 6,939 ft msl and subsequently showed both airplanes rapidly descend. Fragmented sections of the outboard left wings of both airplanes were found in a field below the point where the two flight tracks merged. Both airplanes came down in fields about 2,400 ft apart and were destroyed on impact with terrain. Postaccident examination of both airplanes showed no preaccident failures or malfunctions that would have precluded their normal operations. The Cessna was equipped with automatic dependent surveillance - broadcast (ADS-B) “in/out” equipment and transmitted ADS-B data during the accident flight. The Sonex did not transmit ADS-B data during the accident flight; ATC records indicated the Sonex last transmitted ADS-B data on July 14, 2022. An examination of the GPS and transponder from the Sonex determined that the units were configured to not transmit position data via ADS-B. Investigators were unable to determine the exact configuration of the cockpit traffic displays for the Cessna. The sun was in the east (108o) about 24° above the horizon. A visibility study showed that the respective airplanes would have traversed the respective windscreens from right to left and left to right over the 60 seconds before the collision. However, the instrument panel, canopy frame, compass, and sun glare would have obscured the view of each pilot presenting challenges to detecting the respective airplanes. Toxicology specimens from the student pilot revealed Cetirizine in liver and muscle tissue. Cetirizine is an antihistamine available over the counter and is used to treat allergy symptoms. It may cause drowsiness. However, it is uncertain whether the student pilot was experiencing any sedating effects of this medication at the time of the accident. Given the circumstances of the accident, including the presence of a qualified flight instructor, it was unlikely that the student pilot’s Cetirizine use contributed to the collision.
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 Sonex Aircraft XENOS final · quoted from the NTSB record
The flight instructor and student pilot took off in a Cessna airplane from their home airport and proceeded north to a practice area to perform practice maneuvers. The Sonex pilot departed from an airport east of the practice area about 5 minutes earlier and proceeded westbound toward the vicinity of the Cessna. Both airplanes climbed to 7,000 - 7,500 ft mean sea level (msl) and operated under visual flight rules (VFR). When the Cessna reached the practice area, it made a left 360° turn consistent with a clearing turn, which according to the flight school was standard procedure. On completing the turn, the Cessna proceeded eastbound. The Sonex approached the same area from the east and tracked west-northwest toward the vicinity of the Cessna. The flight track data showed the two airplanes come together at an altitude of about 6,939 ft msl and subsequently showed both airplanes rapidly descend. Fragmented sections of the outboard left wings of both airplanes were found in a field below the point where the two flight tracks merged. Both airplanes came down in fields about 2,400 ft apart and were destroyed on impact with terrain. Postaccident examination of both airplanes showed no preaccident failures or malfunctions that would have precluded their normal operations. The Cessna was equipped with automatic dependent surveillance - broadcast (ADS-B) “in/out” equipment and transmitted ADS-B data during the accident flight. The Sonex did not transmit ADS-B data during the accident flight; ATC records indicated the Sonex last transmitted ADS-B data on July 14, 2022. An examination of the GPS and transponder from the Sonex determined that the units were configured to not transmit position data via ADS-B. Investigators were unable to determine the exact configuration of the cockpit traffic displays for the Cessna. The sun was in the east (108o) about 24° above the horizon. A visibility study showed that the respective airplanes would have traversed the respective windscreens from right to left and left to right over the 60 seconds before the collision. However, the instrument panel, canopy frame, compass, and sun glare would have obscured the view of each pilot presenting challenges to detecting the respective airplanes. Toxicology specimens from the student pilot revealed Cetirizine in liver and muscle tissue. Cetirizine is an antihistamine available over the counter and is used to treat allergy symptoms. It may cause drowsiness. However, it is uncertain whether the student pilot was experiencing any sedating effects of this medication at the time of the accident. Given the circumstances of the accident, including the presence of a qualified flight instructor, it was unlikely that the student pilot’s Cetirizine use contributed to the collision.
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 Cessna 172S from the NTSB's investigation tables, in plain English
What happened, in order
- Midair collision during enroute defining event
The NTSB's findings
- Personnel issues › Psychological › Attention/monitoring › Monitoring other aircraft › Pilot
- Personnel issues › Psychological › Attention/monitoring › Monitoring other aircraft › Pilot of other aircraft
Flight instructor
- Certificate: commercial pilot
- Ratings: single-engine land; instructor: airplane single-engine; instructor: instrument airplane; instrument: airplane; rotorcraft: unmanned (suas)
- Flight time: 295 hours in all; 224 in this make and model
- Last flight review: July 24, 2022
- Medical certificate: Class 1 (without waivers/limitations)
- Seat: rgt
- Injury: fatal
Dual student
- Certificate: student
- Flight time: 45 hours in all; 45 in this make and model; 42 in the last 90 days; 22 in the last 30 days
- Seat: left
- Injury: fatal
The aircraft
- Airframe total time: 3,817 hours
- Last inspection: annual inspection, August 10, 2022
- Maximum gross weight: 2,550 lb
- Seats: 4
- Landing gear: fixed
- Engine: Lycoming IO-360-L2A (piston); 3,817 hours total
The flight
- Departed from: BJC Denver CO at 2:43 pm
- Destination: BJC Denver CO
- Flight plan: none
- A second pilot was aboard
Weather at the time
- Light: daylight
- Visibility: 7 statute miles
- Sky: clear
- Temperature: 68°F (20°C), dew point 46°F (8°C)
- Altimeter: 30.05 inHg
- Observation at 8:55 am from KLMO, 5 miles away
Weather report (METAR): KLMO 171455Z AUTO 00000KT 7SM CLR 20/08 A3005 RMK AO2 T01960079
Injuries
| Fatal | Serious | Minor | None | |
|---|---|---|---|---|
| Flight crew | 2 |
The factual record for the Sonex Aircraft XENOS from the NTSB's investigation tables, in plain English
What happened, in order
- Midair collision during enroute
The NTSB's findings
- Personnel issues › Psychological › Attention/monitoring › Monitoring other aircraft › Pilot
- Personnel issues › Psychological › Attention/monitoring › Monitoring other aircraft › Pilot of other aircraft
Pilot
- Certificate: private
- Ratings: single-engine land
- Flight time: 102 hours in all; 102 in this make and model; 10 in the last 90 days; 1 in the last 30 days
- Medical certificate: BasicMed
- Seat: left
- Injury: fatal
The aircraft
- Airframe total time: 102 hours
- Last inspection: condition inspection, August 13, 2022; 1 hours since
- Maximum gross weight: 1,275 lb
- Seats: 2
- Landing gear: fixed
- Engine: Aero Vee (piston); 102 hours total
The flight
- Departed from: 18V Hudson CO at 2:38 pm
- Flight plan: none
Injuries
| Fatal | Serious | Minor | None | |
|---|---|---|---|---|
| Flight crew | 1 |
Documents from the investigation the NTSB's docket: the evidence folder behind the report
18 documents, released by the NTSB on September 5, 2024. 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.
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.