B737-700
Flight Crew Air Transport Pilot (ATP)
Flight Crew Last 90 Days 93
Aircraft Equipment Problem Less Severe; Deviation / Discrepancy - Procedural MEL / CDL; Deviation / Discrepancy - Procedural Published Material / Policy
General None Reported / Taken
Procedure
Aircraft had been modified with the new (latching) audio selector panels. The note in the logbook cover indicated that the latching function of the yoke PTT switches had been deactivated. In fact; all interphone PTT function on both yoke switches were inoperative. Neither pilot could use the yoke switch to transmit on interphone because neither switch could be depressed down to the INT position. Both switches transmitted normally on the radio.We wrote up what we observed and briefed the oncoming crew. The Mechanic showed up; but we had to go to our next flight before there was any resolution from Maintenance. My read of MEL 23-16 is that with BOTH PTT switches in this state the aircraft can not be dispatched. This makes sense when considering that in a situation where both pilots must be on oxygen; their only option to communicate would be to latch the ASP switch to interphone; filling the interphone with the sound of both pilots breathing in their masks continuously. If it was; in fact; an error that Maintenance disabled not only the latching function but also the entire interphone PTT function of both yoke switches on that aircraft; then it may well be an error that has been repeated on multiple aircraft. Recommend that steps be taken to determine if this is; in fact; occurring when ASPs are upgraded and; if so; to re-enable the interphone PTT function of the yoke switches.
B737-700 Captain reported possible maintenance non-compliance with MEL application to inoperative yoke PTT switches.