Speed of elderly plane, not the maximum! (4)
I believe the answer is:
rate
'speed of' is the definition.
'elderly plane not the maximum' is the wordplay.
I cannot quite understand how this works, but
'the' could be 't' (the is pronounced as a 't' sound in some dialects) and 't' is found in the answer.
The remaining letters 'rae' is a valid word which might be clued in a way I don't understand.
This explanation may well be incorrect...
Can you help me to learn more?
(Other definitions for rate that I've seen before include "See 16" , "See 12" , "Tear up in tempo" , "Amount measured against another" , "Think highly of; criticise severely" .)