You DO NOT want a TAS indication for landing, you want an IAS indication.
The relationship, if you don't understand it is...
IAS = Indicated Air Speed (as seen in the cockpit)
<correct for system errors to give....>
CAS = Calibrated Air Speed (also known as RAS, Rectified Air Speed)
<Correct for compressibility to give... >
EAS = Equivalent Air Speed (which determines structural loads)
<Correct for density to give...>
TAS = True Air Speed
<Correct for wind to give...>
GS = Ground Speed.
For virtually any light aeroplane, you'll be glad to know that CAS=EAS so you can ignore that correction. However, if you want to be clever with your electrickery, the two things you can try and give your chum is...
- IAS=CAS (essentially calculate out the system errors in real time). But bear in mind that all of the current safety limits are based upon the current errors, not upon CAS, so you'll need to agree changes in IAS limitations with the authority (PFA?).
- TAS, for navigation purposes only. For this, you'll need pressure and temperature feeds into your system.
But, you'll get nowhere if you don't go and learn the maths and basic equation proofs for airspeed and altitude. Any half-decent undergraduate textbook on aerodynamics should cover this adequately.
Finally all current knowledge and research shows that a dial gauge indicator (or it's linear equivalent - a speed strip) is the best, safest, and most user-friendly indication of airspeed (for handling purposes at-least). So th IAS/CAS display should NOT be digital in nature.
G