Not really. Radio power decreases with the square of the distance. So at if "blackout" is at 10 feet then at 100 feet your at 1% of your original power. So realisticly your blocking your GPS signal and partially obstructing signals for 2-3 cars adjacent to you and likely less than that. You wouldn't be reaching any planes without a lot of power and a big transmitter.

Planes avionics are more then sufficient to navigate and fly the plane without GPS. And planes will most definitely land without GPS as a.) GPS isn't the predominant tool for altimetry and b.) a plane has to land or it will crash. GPS is primarily used for navigation of routes and most critically for planning approaches and landings. It enables the tower to send an approach plan directly to a plane. So, really important for packing the skies with planes, but a malfunctioning gps unit isn't going to stop a plane from landing at its designated airport. May stop one from taking off though. This really only applies to big planes. Small planes don't always have gps and don't always land at airports using gps. Still really nice to have so you don't get lost, though.

Accurate GPS is a fairly recent luxury as until the 90s it was made inaccurate by design as only the military could access the full radio spectrum, and only recently has the full constellation of current gen sats been fully deployed. Also interestingly commercial gps receivers won't function beyond 600 mph and/or 60 000 ft to prevent people from using them for missiles. Military ones (in missiles) or if you home brewed it won't have this restriction though.

You are right though. Running a jammer is illegal as hell and you can really fuck other people's day. Especially do not try bring a jammer on a plane. They monitor radio very closely at and around airports. You will be caught and you will be sent to federal "pound me in the ass" prison.