The internal GPS in Apple devices uses so-called Assisted GPS data from cellular towers, but the receiver wasn’t designed for aviation. That’s why it’s not uncommon for an iPad or iPod to struggle with maintaining a GPS signal lock in flight. That makes a remote GPS receiver necessary.

Most Bluetooth GPS receivers are compact enough to toss on top of the glareshield, where it receives the best reception. But it can also become a dangerous projectile in a crash and in turbulence.