# N551X: 2021 Thomas N Helm SONEX ONEX

- Status: Valid registration
- Airframe: [Thomas N Helm SONEX ONEX](https://openairdocs.org/model/thomas-n-helm-sonex-onex) (registry code 05639AQ, 1 seats)
- Engine: [Aeroconver AEROVEE](https://openairdocs.org/engine/aeroconver-aerovee) (registry code 01401)
- Serial number: ONX0137
- Year built: 2021
- Type: Fixed wing single engine
- Engine type: Reciprocating
- Kit: Sonex Aircraft LLC ONEX
- Airworthiness: Experimental, amateur built
- Airworthiness date: June 17, 2021
- Certificate issued: May 12, 2020
- Expires: May 31, 2027
- Mode S code: A7052F
- Registered owner: [Helm Thomas N](https://openairdocs.org/faa-owner/HELM%20THOMAS%20N)
- Location: [Neenah, WI](https://openairdocs.org/faa-place/WI/Neenah)
- Owner type: Individual
- Owner's area on the map: 44.1823° N, 88.5276° W: Placed by OpenAirDocs at the center of ZIP code 54956, within about 4 miles (OpenAirDocs). The owner's mailing address, not where the aircraft is based
- FAA registry: https://registry.faa.gov/AircraftInquiry/Search/NNumberResult?nNumberTxt=551X
- Page: https://openairdocs.org/aircraft/N551X

From the FAA registry file of October 24, 2026. ADs below are matched by the registry's airframe and engine model codes. They may apply; each AD's applicability can narrow it by serial number, part number or installed equipment. This is not a compliance determination.

## ADs that may apply (OpenAirDocs): 0 in force

### Matched by airframe (Thomas N Helm SONEX ONEX)

None in force.

### Matched by engine (Aeroconver AEROVEE)

None in force.

## Information bulletins (advisory)

None matched.

## NTSB investigations

None matched to N551X.

## NTSB investigations on N551X not matched to an aircraft (1)

From the NTSB's public API. Aircraft are matched to registry aircraft by N-number and event date, checked against the reported serial number, make and model; the registry's history has gaps, so older matches can be wrong. Compare the reported make and model.

- [NTSB IAD75AI063](https://openairdocs.org/ntsb/IAD75AI063), Jun 6, 1975: Cessna 320B (N551X), Bowling Green, KY, substantial damage

## FAA accident and incident reports

None matched to N551X.

## Reports on N551X not matched to an aircraft (1)

They name N551X, but no registry record covers the date, the aircraft registered then was built later, or the report describes another aircraft.

- [Accident 19750606021409A](https://openairdocs.org/incident/19750606021409A), Jun 6, 1975: Cessna 320B (N551X), Bowling Green, KY, Substantial damage. Elev push-pull rod attach rivets failed. Plt able stabilize acft in pitch mode thru elev trim.

## Service difficulty reports

None filed for this aircraft. Matched to this aircraft by N-number and event date, checked against the reported serial number, make and model.

## STCs that may be installed (OpenAirDocs)

None matched to this aircraft's models.

## Earlier aircraft with N551X

The FAA can reassign an N-number once a registration is cancelled. These aircraft carried N551X before.

- [Cancelled 2012-04-12](https://openairdocs.org/deregistered/N551X-2012-04-12): Eldredge Kevin S51, S/N 076, built 2002. First renewal notice. Owner: [Hambleton John A](https://openairdocs.org/faa-owner/HAMBLETON%20JOHN%20A), [Ocala, FL](https://openairdocs.org/faa-place/FL/Ocala)
- [Cancelled 1995-07-10](https://openairdocs.org/deregistered/N551X-1995-07-10): Boeing A75N1, S/N 75267. Exported to Paraguay. Owner: [Parker Aviation Enterprises Inc](https://openairdocs.org/faa-owner/PARKER%20AVIATION%20ENTERPRISES%20INC), [Warren, VT](https://openairdocs.org/faa-place/VT/Warren)

## Related

- Other Thomas N Helm SONEX ONEX aircraft: https://openairdocs.org/model/thomas-n-helm-sonex-onex/aircraft.md
- The Aeroconver AEROVEE engine: https://openairdocs.org/engine/aeroconver-aerovee.md

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