All handholds suffer from some Faraday effect when transmitting from inside a vehicle be it a plane a car or whatever. Your best bet is splicing into your external antenna.
Another good idea is to looking into how and why different antennas are made and take a crack at it. If you're lucky enough to survive an aerial catastrophe and all you have is your back-up handheld you can greatly increase the TX distance of your handheld just by using parts of your craft to "MacGyver" a possibly lifesaving antenna.