If there was an oxygen-fed fire in the cockpit that was caused by a short with the metal spring in the oxygen hose chafing with a wire bundle I can see how the transponder head and radio control heads could become disabled. It was not a case of the pilots turning off the transponder and not making radio calls, it was an instance of the wiring to those components being melted and burned. The pilots may well have put in an emergency transponder code and tried to make an emergency radio call to no avail.