wifi or 3g model?
As mentioned above about assisted GPS - the wifi only model only has assisted GPS which relys on triagulating you position via wifi points etc.
If you are using 3G version then see from Apple Website itself - Google is your friend.
"Additional Information
Location Services, including GPS, do not work while in airplane mode. You can use applications like Maps by re-enabling Wi-Fi while in airplane mode, but you will be unable to determine your position using Location Services."
Regardless you should have the device in airplane mode so it won't work regardless.
Alex.