There are GPS mapping apps that don't need access to data (pretty sure TomTom is one). That's their selling feature. They don't work in Airplane Mode because that mode shuts off all antennas including GPS (although you can turn wifi back on in Airplane Mode, AFAIK you cannot turn GPS back on...would love to be proved wrong on that).
TomTom has certain features that require data such as traffic and Google searches, etc but the GPS receiver itself doesn't require data and TomTom uses locally stored maps. Airplane mode isn't a proper test of GPS without carrier data (see post 4). You might want to reconsider what "pretty sure" means.