"My understanding is that all such updating is automatic, and is not related to the nav beacons manually tuned by the pilots. Maybe I've got it wrong, though???"Frank...Although the VOR receivers must be manually tuned by the flight crew on the NG, the FMC will still use the data from the manually tuned VOR's for position updating if it needs to. Note that the manually tuned VOR station must be within range (less than 25nm) and there must be co-located DME's available (i.e. the DME and VOR stations must be in the same geographical position). The NG FMC cannot position update using two VOR stations (alone)... I don't believe any FMC can. Of course, GPS will be used under most circumstances for position updating on the NG as it has a higher priority.Yes, there is automatic tuning of the DME's (these are also considered to be nav radios in the real world). There are two DME Interrogators (transmitter/receivers) on the NG as there was on the Classic 737. However, on the NG, there are five "channels" per DME Interrogator (total = 10 channels). The DME Interrogators scan every known DME frequency looking for available stations. The data from 5 of the best (automatically and manually tuned) of these stations (per Interrogator) can be used by the FMC for position updating. "Best" = within range and having the best geometry for a position fix.Yes, the Classic 737 does have VOR autotuning. The NG doesn't. However, autotuning is an expression used to cover VOR and DME systems, so the NG is still considered to have "Autotuning".Hope this clears up most of the misconceptions generated by this message thread.Cheers.Ian.

10-4 sir! ;-)Just got home from my night shift!Cheers,

>Hi Mats,>Yes, thank you. In fact, I contributed to the thread you>mention myself, but will need to re-read everything again to>refresh my memory about all that Kris and others wrote.>>Nevertheless, just to make my main point again(and not to get>too obsessive about it :-))- The NG has multiple methods of>updating its position, none of which makes the other ones>obsolete. What you have is a priority order in which the>updates are taken(with some cross-checking, I assume). Should>the data from any of the nav systems be deemed unsatisfactory>by the FMC, then the next in line method of taking the updates>is used. GPS is the preferred method of providing aircraft>postion, but radio updating is always available if needed.>>BR,>Frank Yes but your whole point was whether the NG has auto tuning for the navs to which it clearly does not. I have not seen you conceed to this fact yet but nevertheless is the case.[h4]Randy J. Smith[/h4]

Hi Mats,Have re-read the thread you mentioned. Yes, it's becoming clearer now! :-)Best Regards,Frank

Hi Randy,Don't mean to appear stubborn and will happily concede if I am wrong!Obviously, I know there is no AUTO/MAN switch on the radio panels(which was what prompted my query in the first instance), so the pilot cannot switch the radios to an auto tuning mode. That's agreed.However....:-), the debate is now on whether auto-tuning of nav stations is a feature of the NG or not, and I think it is clear that it is! See the thread, "Flight director accuracy", on this forum(how do I post a link?), which states clearly that auto-tuning of radio stations is going on behind the scenes:"There are...two DME Interrogators on the NG...{E}ach Interrogator has 5 (internal) channels. Normally, each FMC sends four DME autotuning signals to the VOR/ILS ("NAV") control panels. The manual (pilot set) and automatic tuning data is then sent from the NAV control panels to the DME Interrogators (One Manual plus four FMC tune signals = 5 signals per Interrogator)." [edited quote from Ian's(Qavion) post]I'm not pretending I understand this fully, but the general point about "automatic tuning data" is clear, isn't it?BR,Frank

Yes, it does, Ian! That certainly helps clear up my misunderstanding.Prompts another question, though(:-)):With the AFDS in LNAV, how does the aircraft automatically follow a route(VOR to VOR) if it is unable to auto-tune VOR stations? I had always assumed that when a VOR on the route became the active waypoint it was automatically tuned by the AFDS. Now I don't know how it accomplishes this?More help, please!BR,Frank

Hi Randy,I hadn't seen the post from Ian when I last replied.I now concede that the NG does not have VOR auto-tuning(see quote from Ian's post below)! :-)"Yes, the Classic 737 does have VOR autotuning. The NG doesn't. However, autotuning is an expression used to cover VOR and DME systems, so the NG is still considered to have "Autotuning"."BR,Frank

Well these type of threads are fun though Frank ;-)[h4]Randy J. Smith[/h4]

Hi Randy,Indeed, and always a learning experience. :-)By the way, any ideas on my question to Ian above:"With the AFDS in LNAV, how does the aircraft automatically follow a route(VOR to VOR) if it is unable to auto-tune VOR stations? I had always assumed that when a VOR on the route became the active waypoint it was automatically tuned by the AFDS. Now I don't know how it accomplishes this?"BR,Frank

>With the AFDS in LNAV, how does the aircraft automatically>follow a route(VOR to VOR) if it is unable to auto-tune VOR>stations? I had always assumed that when a VOR on the route>became the active waypoint it was automatically tuned by the>AFDS. Now I don't know how it accomplishes this?Hi, Frank.For the most part, the FMC really doesn't care if the VOR's are tuned... The VOR's may even be inoperative and the FMC would carry on regardless. When navigating, it treats the en-route VOR's as it would ordinary waypoints (i.e. as a lat/long). Really, the only thing the FMC needs is the aircraft's current position. This can still be computed, usually quite accurately, from a combination of IRS, GPS, DME, etc. If the active waypoint is a VOR (but is not tuned or available), it still shows up as magenta on the MAP.One thing I'm not sure of is when a VOR station is critical part of an arrival or departure routine. I don't know if it is legal to fly a routine if the VOR specified on an arrival/departure chart is not operating. In theory, the aircraft should be able to accurately navigate any kind of procedure using GPS and other suitable/available radio aids, but the absence of a signal from this navaid, may reduce the navigational capability of the FMC to the point where the pilots are not permited to fly this routine (You may have seen previous messages on RNP(Required Nav Performance) and ANP (Actual Nav Performance)???).Anyway, I'm sure the real pilots and (real) FMC experts will be better able to answer this kind of question... My manuals often leave out critical details like this ;-)Cheers.Ian.

Ah, I think I understand, Ian! Once the aircraft knows its present lat/long position and direction of flight, and also knows the VOR lat/long position, it can navigate to there by computing a bearing to the station?Thanks a lot,Frank

Well remembering that one must manually tune the NAVS we then look at the FMS here http://forums.avsim.net/user_files/102897.jpg[h4]Randy J. Smith[/h4]