B737 LNAV MEL
 

I recently had an aircraft with the mode control panel LNAV switch on MEL. The MEL document did not specify any specific operating procedures (O). However, in the remarks section, is the following statement: "Except for ER operations, may be inoperative provided RNAV operations, both enroute and terminal, are not conducted." To be clear, the LNAV switch simply allows the FD or autopilot to directly track the selected course to the active waypoint. Any deviation from the course will be displayed on the course deviation indicator on the ND. Therefore, it is possible to track the LNAV course in heading select rather than using the LNAV switch. Talking with colleagues, there seems to be some disagreement as to what is required to be in compliance with the MEL. Terminal RNAV operations seems to be well defined: any procedure with the word RNAV in the title. However, enroute operations do not seem to have this nice distinction. I would be interested in a discussion about whether tracking an LNAV course to a waypoint in the enroute phase using Heading Select instead of LNAV would be in compliance with this particular MEL.

Enroute operations in Europe are BRNAV. I don't see that happening, without even opening our MEL.

Not sure about HDG Select, but having had a LNAV fail in Europe a few years ago (737 Classic) while en-route, we were offered Vectors, but instead flew VOR to VOR ,with VOR/LOC, worked a treat, as an aside, the VIP's were were taking, one had a radio and was listening to our ATC conversations, they were rather impressed with the FO that day, got a nice tip at the end of the trip.

Whether you can dispatch, well that's a different ball of wax, if you ferry old aircraft, there are times the FMC will not have the database you want in it, if its not GPS, it a Classic, then it can be interesting inputting the VOR/DME and NDB's into the FMC.

Plenty of Classic out there with dual GPS. Some of them even with SBAS capability.

and I can assure you there are plenty 737-300/500 without GPS for navigation. Those of us who have extensive ferry flight experience can testify to that.
Of course the Classic's are becoming less common now, mainly late ones for Cargo ops, but even there early NG's are getting snapped up

AP/FD coupling for RNAV 1 and 5 is recommended, but not required.

According EASA you don't need a FD for RNAV 1 and 5, however, according the Boeing RNP capability document for B737 you do need a FD for all PBN specifications except RNAV 5.

My company interprets this as FD with LNAV function (and VNAV for RNP APCH with VNAV minumums and RNP AR APCH). Thus, with LNAV not available we would be limited to RNAV 5 and conventional approach.

Which seems a very sensible solution to the problem. At the end of the day an aircraft grounded is costing money.