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Guest mdamstel

backup when FMC fails

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Hi fellow sim pilots,does anyone know what real life pilots use as a backup when their FMC fails?Regards,Mdamstel

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If its only the FMC Computer the fails (basically the FMC), then you still have the CDU! (The CDU is what is located in the cockpit)You can still fly all the waypoints that are in the legs page, and you can add waypoints by using the lat/long coordinates.Other FMC functions are not available, however.If you meant a complete FMS (FMC+CDU) failure, well, then you can still request radar vectors if you have radar coverage (most parts of the earth) or you'll simply navigate using VOR's and ADF's.basically the way you navigate in a non GPS equipped GA aircraft.Regards,Mark

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Some operators only choose one FMC for the 737!(You still have two CDU's!)Regards,Mark

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Easy, fly the way REAL MEN did ;-)sorry couldn't resist.Lance

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>If you meant a complete FMS (FMC+CDU) failure, well, then you>can still request radar vectors if you have radar coverage>(most parts of the earth)The CDU is just the display interface for the FMC though - it's my understanding that if you have a dual FMC failure, you're not doing anything with the CDU as well because it's just displaying that data that's being computed by the FMC.Also - most parts of the world are NON-radar environments unless you're talking developed countries like the US, Europe, certain places in South America etc. The 75% of the earth that's covered by water is defintely not covered either... [;)]

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Also - most parts of the world are NON-radar environments unless you're talking developed countries like the US, Europe, certain places in South America etc. The 75% of the earth that's covered by water is defintely not covered either... ;)Then do it like REAL MEN used to! Celestial Navigation ;-)I'm on a roll, LOL ;-)Lance

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Now that's what a lot of people think!Actually, the CDU is given too little credit! It is much more than just a display interface!As I said, you can use a CDU with no FMC at all for navigation (with some limitations though!)!Regards,Mark

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Celestial navigation tricky without the sunroof! Mayve through the eyebrow windows...Real answer to question is... Refer to QRH:- No LNAV and VNAV. Resume conventional navigation.- use the SPD REF selector to set the reference airspeed bugs- use the N1 SET to set N1 bugs

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Hi MarkI would like to know how you can use the CDU without the FMC? As I've understood it the CDU is the interface to the FMC while the MCP is the interface to the A/T and AFDS. Somehow it doesn't make sense... Please enlighten me? ;-)Cheers

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"I would like to know how you can use the CDU without the FMC? As I've understood it the CDU is the interface to the FMC while the MCP is the interface to the A/T and AFDS."Many FMC CDU's have a back up navigation called "ALTN NAV". The CDU is often a standalone mini-navigation computer, but the inputs and outputs (especially on the NG) are very limited. Not being overly familiar with the 737NG, I had to look into the Bulfer manual (p197 in the latest 737NG book). The 737NG ALTN NAV system uses GPS as a reference (other Boeing types may use IRS). It can only compute LNAV data (no VNAV data), there are no outputs to the ND, to the A/T or the A/P.I'd imagine that you would have to fly the aircraft using the MCP HDG selector (but you would have to convert TRU course data (displayed on the CDU) into magnetic course data. A "GPS PROGRESS" page on the CDU will help you figure out if your calculations have been correct.Hope this helps.Cheers.Ian.

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Thanks a ton Ian!Seems the CDU can work as a navigational calculator then, but no interaction between CDU and AFDS. Is this correct?PS. Does anyone have a schematic on how all the different components are interlinked in the FMS?Cheers,

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"Seems the CDU can work as a navigational calculator then, but no interaction between CDU and AFDS. Is this correct?"Correct(in this particular mode)."Does anyone have a schematic on how all the different components are interlinked in the FMS?"Have you seen the one in the Bulfer Manual? It seems to be quite good (BTW, I thought you were going to buy it, Mats?) None of the ones in the Boeing Maintenance Manuals are particularly enlightening.... or comprehensive.Cheers.Ian.

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Hi Ian!>Have you seen the one in the Bulfer Manual? It seems to be quite >good (BTW, I thought you were going to buy it, Mats?) None of the o>ones in the Boeing Maintenance Manuals are particularly >enlightening.... or comprehensiveI did buy the Bulfer Guide and the Cockpit Companion when I started to learn how the DF734 worked a couple of years ago! But I don't remember seeing a schematic in the Guide. Maybe it's in the updated version? Have to give Bill a shout about that I guess. Will look again! Thanks for the heads up! ;-)

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