AERO-ALPHABET - On

On Mark (On Mark Engineering)
On Mark Executive
On Mark Marketeer
On Mark Marksman

Onciul (Radu Onciul) {ErZ}
Onciul R.O.-1
Onciul R.O.-2

OneAircraft (Celje, Slovenia)
OneAircraft One

One Aviation (Albuquerque . NM . USA)
Eclipse 550
Eclipse 700
Kestrel K-350

ONERA (Office National d'Études et de Recherches Aérospatiales)
ONERA Deltaviex

Ong (William Ong Aircraft Corp. - [8.3.8. Richards Rd.] Kansas City . MO . USA) {ErZ}
Ong M-32-W Continental

Onishi
Onishi OSG3