It took Charles Lindbergh 33 hours to fly from Long Island to Paris—roughly the same time it takes an email to travel the route via in-flight Wi-Fi. OK, I’m exaggerating, but airline Wi-Fi has long been pretty awful. The good news is, that’s starting to change. The bad news is, it’s changing slowly.

While there have been noteworthy improvements, such as gate-to-gate connectivity, they’re not ubiquitous. Not all in-flight Wi-Fi is equal, and plenty of it is still pretty bad. How can you tell what you’ll be in for on your next flight? The airlines don’t make it easy. Wi-Fi quality can vary greatly even within a single airline’s fleet, since different aircraft may use different technologies. Generally, “Wi-Fi finder” tools on airlines’ sites or apps don’t tell you the flavor of your plane’s Wi-Fi. And as airlines phase in new satellite-based technologies to replace or supplement their older Air-to-Ground (ATG) systems, the evaluation chore is only getting tougher.