ETA
Hi.
Apologies as i am a non pilot but need advice of pilots to settle an arguement!!
I use OS maps to climb mountains and i can calculate my ETA using distance (in km) from the map and my walking speed in km/hr.
So, how do pilots calculate their ETA? i understand that airspeed is measured in knots, but surely they have to use a distance in km or miles from a map (assuming you dont have GPS). so if this is the case, do you have to use an estimated ground speed in km/hr to calculate your trip time?
cheers for any response.