The fuselage is basically a Faraday cage, blocking out most radio signals. In the back, the windows are portals for EMF. Up front, the windshield blocks RF due to deposited gold or other metals in the heating elements leaving only the side windows. The small RF passageway combined with all of the EMF noise from instruments, inverters, fans etc makes for a pretty tough operating environment for a handheld. When the aircraft is powered, good luck with VHF band signals.
Actually, I've seen handheld R/T's demoed by AOPA types on the flight deck on modern Boeings and Airbuses. They do work, perhaps could get you by in an emergency.
Older GPS's don't work from the flight deck of the newer planes but recent models with the SiRF III chipset seem to work fine. I carry a PDA GPS and a Microsoft USB GPS for my notebook, they are usable near the side windows. ADS-B planes have a separate GPS in the CDTI electronics, seems like you can get a latlong readout from one of the maintenance pages.
There have been previous A-310's that have lost all the screens and IRS's, usually due to equipment cooling faults. One of these was a TXL based PAA plane as I recall.
There was a massive overwater Boeing EFIS malfunction in 1996 that was finally blamed on a faulty main battery shunt:
ASN Aircraft accident Boeing 767-31AER PH-MCH Boston-Logan International Airport, MA (BOS)