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Guest frankathl

Auto/Manual Tuning of Nav Beacons

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Guest frankathl

The navigation radios in the classic 737s have an AUTO/MANUAL function which allows nav beacons to be tuned automatically by the FMC, or manually by the pilot(via the AUTO-MAN switch). While, presumably, this function is also available in the NGs, there is no such switch on the VHF NAV panel. How, then, to distinguish between the two functions in the NG?BR,Frank

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Do you realy beleve that???NGs doesn't have auto tuning, but PMDG is making the auto tune on the B744.Check out A-net. and you will see.

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Guest frankathl

Hi Ramon,I was speaking of the real aircraft.Are you suggesting the NG has no FMC auto tune function? Perhaps you were referring to the PMDG implementation only?BR,Frank

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>Hi Ramon,>I was speaking of the real aircraft.>Are you suggesting the NG has no FMC auto tune function?>Perhaps you were referring to the PMDG implementation only?>BR,>Frank Yes Ramon is correct, there is no Auto tuning on the real NG aircraft and neither in the PMDG sim. You must manually tune the navs. Best Wishes,[h4]Randy J. Smith[/h4]http://www.rawbw.com/~bdoolin/shinault/southparkcartmad.gif[h3]PMDG 747![/h3]Caution! Not a real pilot, but do play one on TV ;-)ASUS KV8 DLX | AMD 3200 64 | 1 GIG PC 3200 DDR | GIGABYTE 5700 ULTRA | ViewSonic VP192b 19" |

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Guest frankathl

Thanks, Randy!In that case, how does the NG use VOR and DME stations to update its position(these are not manually tuned)? The flight manual is slightly ambiguous("in AUTO, if applicable"), but I take the following description to cover the NG as well as the Classic:"The navigation radios are automatically tuned by the FMC(s) for the purpose of radio updating (in AUTO, if applicable). The stations to be tuned are selected based upon the best available signals (in terms of geometry and strength) for updating the FMC position, unless a specific station is required by the flight plan. Radio position usually is determined by the intersection of two DME arcs...."BR,Frank

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Guest Lenny Zaman

This radio updating is in fact the reason. One could ask Boeing to put auto-tuning in the NG, no problem.But for Boeing to keep the NG certified they needed to have some form of position updating and these days most aircraft have built in GPS systems which accurately update the position of the IRS's calculation. SO in fact the GPS replaced the 'auto-tuning' of the nav radios.That's why the old 737 still has this autotuning, to keep that 'RNP' level(required naviation performance) high enough for the aircraft to be certified as at those times GPS was not common(737 EFIS is a pretty old tech plane)Cheers(edited for spelling)

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Guest frankathl

Thanks, Lenny!"SO in fact the GPS replaced the 'auto-tuning' of the nav radios."The flight manual seems to disagree, Lenny? The description below specifies the priority order by which the aircraft updates its position. Although the GPS is the primary source of position updates, if this fails, radio updating is used. 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???"In flight, the FMC position is continually updated from the GPS (as installed), navigation radios, and IRS. Updating priority is based on the availability of valid data from the supporting systems.FMC position updates from navigation sensor positions are used in thefollowing priority order:

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Guest frankathl

Hi Ramon,Yes, but what if GPS updating fails?See my response to Lenny above.BR,Frank

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Guest Lenny Zaman

Hi Frankagreed, the DME's provide updating aswell. I think i might not have explained what i meant correctly, but your explanation is alike mine only explained in a more clear way(english is not my mother tongue)I'll get an update from my instructor as soon as i see him.Cheers

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Guest frankathl

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

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Guest frankathl

Thanks a lot, Lenny!Yes, I see that we are agreed:-).Appreciate your help.Best wishes,Frank

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Guest frankathl

Thanks, Ramon!See my response to Mats.Best Regards,Frank

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"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.

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

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>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]

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Guest frankathl

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

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Guest frankathl

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

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Guest frankathl

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

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Guest frankathl

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

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

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Guest frankathl

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

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>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.

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