Using a wide variety of "traditional" techniques that range from dead reckoning (or "pilotage" which is dead reckoning corrected by landmarks) to politely askin

Using a wide variety of "traditional" techniques that range from dead reckoning (or "pilotage" which is dead reckoning corrected by landmarks) to politely asking a controller if they have you on radar. Airplanes operated under challenging conditions without falling out of the sky for a long time before GPS became a ubiquitous flight instrument (pretty recently, really).