# What are these “F,S,O” characteristic speeds?

I am leaning for an avionics exam and I encountered a question asking for the meaning of F, S and O . They appear to be "Characteristic speeds", which are calculated by the flight management system (FMS):

• What's the context? Could you quote the entire question, for example? – user Oct 4 '17 at 11:57
• I've never heard of the term in 20+ years in avionics. Closest thing I could relate it to would be the DME Free Scan Mode. Could they be referring to this as Free Scan Operation? – Gerry Oct 4 '17 at 11:58
• I found a slide in which $F, S, O$ appear. Maybe that help. It is right of $V1$ $VR$ and $V2$. – MrYouMath Oct 4 '17 at 12:35
• When asking this type of question you need to specify the context, ie the aircraft or manufacturer. In this case, you're talking about an Airbus. On the speed tape (on the PFD) there are various marking which refer to critical speeds that the pilot needs to know about - marked by the letters F, S and O. Airbus experts will chip in with the exact definitions of these speeds. – RAC Oct 4 '17 at 14:27