I'm driving in an unfamiliar city, on my way to the airport in a rental car. I have directions that are supposed to get me right onto the main airport road, but the road unexpectedly bifurcates and I'm pretty sure I was supposed to be on the other half of it. It's not a strict grid system and there are bridges and underpasses, so I can't just turn right and reconnect with the proper road. I pull over and pull out my flight bag GPS.
Of course it's an aviation GPS, so it knows where the airport is. It doesn't know where the roads are, but it's a big enough airport that I figure if I can get going in more or less the right direction for the airport, I'll find a sign with a picture of an airplane on it, and I can just follow those to the airport. The GPS will tell me if I'm getting closer or further from the airport, the bearing direct to it, and if there are any large bodies of water barring my way.
With this dubious logic, I pull back into traffic, casting a glance at the screen once I have forward motion and the GPS can orient itself. Yep, this is kind of the right way. I continue. At the next light it's still showing that I'm going pretty much the right way. Then as the road curves I glance at it again and laugh. The whole screen has gone red! If I travel at a speed greater than would be commensurate with taxiing, terrain within a certain distance turns red to warn me of obstacles. The GPS is terribly concerned that I'm flying too low for safety.
As I go under a highway underpass I spot a sign on the highway above giving directions to the airport. I take the next right and get on that highway. The car is returned and I find my airplane.