FMC Programming

[Ditchlights]

This is not a complaint :-) Rather a question about route discontinuity, what it actually means and how does it happen. But first let me explain my on going perplexity with the FMC.
The FMC is programmed. I then check the Route Legs to study my way points, check speeds and alts and invariably the 1st wpt will indicate a logical speed and alt the next wpt will show a logical speed and alt higher than the first wpt e.g. 9000A. Okay.
That's fine. Then the next wpt shows an alt significantly lower than the the one before e.g. 6000B. Depending on the SID, I may have three of these discontinuities. Are these are the sort of discontinuities the manual refers to? I can't see radical changes in altitude (especially in mountainous terrain) high to lower then higher to lower as representing reality.

What I've been doing to resolve this discont is double clicking the LSK on the CDU adjacent to the problem wpt and an adjustment is made automatically--changing speed and altitude--bringing it more in line with what I perceive is reasonable with the SID. Yet, I do not know if this is the correct way of making the adjustment. With the advent of the new patch, however, I can now do this manually.

What I have just characterized above is not just an idiosyncracy of my favorite airports and flight plan choices. This occurs even with Elmar's fine tutorial, as well. As a matter of fact, I am well into the VALKO SID before I can safely let VNAV take over.

Perhaps someone has insight into this problem. Thank you,


John R Franklin

[whoosh]

Hi John,

You are not experiencing a discontinuity, but rather a discrepancy (and a harmless one ;-))

A discontinuity occurs when the FMC is unable to link two waypoints together for some reason and will result in 'route discontinuity' being displayed on the FMC's legs page, and is easy to fix by deleting the disco.

Best regards, Elmar

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[b]***The FMC Preflight's 8 steps***
1. set Ref Airport on POS INIT page
2. set Origin and Dest on RTE page
3. set Dep and Arr at DEP/ARR page
4. set GW, RESERVES and CRZ ALT at PERF INIT page and EXEC that
5. set OAT temp at TAKEOFF REF page
6. select V1, VR and V2 at TAKEOFF REF page to transfer them to EADI
7. check, confirm, edit your waypoints at the LEGS page
8. go back to RTE and ACTIVATE and EXEC the route

[Ditchlights]

Thank you, Elmar, for your timely response. That having been answered, what remains is an explanation for the descrepancy and how to fix it. As I said before, these altitude descrepancies occur regularly when programming the FMC.


Kind Regards,


John R Franklin

[cptthompson]

first of all, I have about 2700 hr on B737 EFIS. The Discont. mean that after reaching that point the there is either a break in the flight plan between two waypoint or you have reached the last waypoint in the flight plan and you are not at your destination.

[Ditchlights]

Thanks, captthompson, for your reply. It helped.

John