B737-700
Flight Crew Air Transport Pilot (ATP)
Confusion; Human-Machine Interface; Situational Awareness; Training / Qualification; Troubleshooting
ATC Issue All Types; Aircraft Equipment Problem Critical; Deviation / Discrepancy - Procedural Clearance
Air Traffic Control Provided Assistance; Air Traffic Control Issued New Clearance; General Maintenance Action
Aircraft
As we crossed the Florida panhandle shoreline I noticed many flashing warning lights advising the airplane had disconnected LNAV. On both MCDUs the FMC prompt was missing; and we were unable to interact with either FMC. Along with this the MCDU message 'FMC1 Failure' or something like that was displayed. Interestingly; 'FMC2 Failure' was never displayed; and the original course was visible on the First Officer's navigation display; but we had no way to interact with the course. Of course we ran the QRH checklist; but there is not much help for this situation.I notified ATC that we had lost our area navigation capability and needed a vector to pick up an airway. Much radio time and brain cycles were spent trying to collaboratively figure out with ATC if we were still legal to stay in RVSM airspace; and if we were; what was our slant suffix for the flight plan. These issues took valuable mind space while we were trying to fix more immediate concerns; such as what was wrong with the airplane and would something else fail shortly. We were cleared direct MCN but it seemed to be offline as neither of our VOR receivers could receive it. We continued on vectors and I tuned other VORs nearby; and they came in fine. Later on in the flight we were cleared direct to HNN but were once again unable to receive its signal. The next fix; JPU; a low class VOR on the arrival was coming in fine; and we were cleared direct. Yet another problem occurred; as the next VOR was; again; indicating no course although the DME function seemed to be operational. Our destination was VFR; and we performed an uneventful visual approach to Runway 28L although the ILS the glideslope was NOTAMed out of service. Fortunately we didn't have to do the 'dive-and-drive'.My concerns are multiple. First; the possibility of a dual FMC failure is supposed to be almost nil. What happened to cause BOTH FMCs to go out on us? If number 1 fails; number2 should be completely separate so as to have backup. There is; in actuality; zero redundancy if the failure of number 1 can propagate to number 2. My second concern is that if we happen to have this situation happen on a WATRS route; we are basically a blind airplane. The INS coordinates were still displayed on the overhead unit; but trying to navigate with that to any kind of accuracy standard would be impossible. Basically; we would have to declare an emergency if this happens in WATRS airspace; and I'd like some kind of language added to the WATRS training program to address the fact that if you lose both FMCs in WATRS airspace you are required to immediately declare an emergency. I don't honestly remember if that was covered already in our training syllabus; but if it wasn't; it should be. My third concern is that the reliability of the nation's VORs seems to have significantly degraded. To have three VORs unusable but not NOTAMed out of service (ATC acted like they were surprised that they all were non-functional) is pretty poor reliability; and if we're heading down the road to getting rid of the VOR system; we're going to need a more reliable backup. Dual FMC failures obviously do occur; no matter what the odds are against it happening. If this situation would have been coupled with a communications failure; now that airplane is truly on its own; without navigation or radar vectors.My final concern is that after we landed; I called maintenance and they deferred both FMCs; authorizing continued service! Now I understand that is perfectly legal according to our MEL. But it is nevertheless very stupid. Pilots who may not have flown airways in a decade are simply not safe to fly them without expecting some kind of accidental deviation. There you have it - this should not be allowed in my opinion. I did my best to find the next Captain who was taking the airplane on; and I finally did see him as we were arriving at the hotel and he was heading to the airport. I told him the situation; and that he hadno FMCs - he'd be doing old-school navigation. He laughed at this with bravado. I'd love to see the radar track of that flight; is all I'm saying.
A B737-700 Captain discussed the problems he encountered upon losing both FMCs in RVSM airspace and subsequently finding several of the VORs by which they attempted to navigate an airways clearance were out of service although not NOTAMed to be so.