VNAV Path Descent (Quiz)

[BertW 0]

Hi folks,I think you all love to discuss the FMC VNAV Descent modes. I picked up the following question from a 737NG computer based training lesson for pilots.You are on a VNAV Path Descent and you shall cross XXX at 8000 and YYY at 6000. Which statement below is correct?1) The FMC will command an idle thrust descent to cross XXX at 8000. After XXX, the FMC will command increased thrust and level flight until the idle thrust descent path to YYY.2) The FMC will command an idle thrust command to cross XXX at 8000. After XXX, the FMC will continue the idle thrust descent to 6000. Then FMC will command increased thrust and level flight until YYY.3) The FMC will command an idle thrust descent past XXX and YYY. The FMC will not make sure the altitude constraints are met.4) The FMC will command an idle thrust descent to cross XXX at 8000. After XXX, the FMC will command increased thrust and a descent to cross YYY at 6000.Cheers,Bert

[Guest Bjorn Ghezzi]

Hi,nice little quiz.Wouldn't it depend on the distance between the two waypoints? Sometimes if their close together and that requires a too steep descend path VNAV will disconnect. But I would believe answer 1 is the correct one.Regards,Bjorn

[clayton4115 56]

Well i will take a punt!i will go for (4):-jumpy :-jumpy

[crvm 0]

This depends Bill on whether we are talking about PTH or SPD descents. If we are talking SPD DESCENTS then the FMC will command level off till passing YYY then resume (Not the path but descent only), so it will command ALT RESTRICTION but not path. [h4]Best Wishes,Randy J. Smithhttp://img.villagephotos.com/p/2003-8/196432/winglets_lg.jpg [h3] AMD XP 2200 |MUNCHKIN 512 DDR RAM |ECS[/b ][i] K7S5A MB[/i] |GF2 MX 32 MEG and still runs GOOD!|WIN XP PRO |MITSUBISHI DIAMOND PLUS 91 19"[/h3]

[Mats_J 2]

Nice one!That depends on the software in the FMC. Prior to U10.3 it would be number 1. But as we have U10.3 or later in our FMC it will be answer 4. :-)What's the prize?

[BertW 0]

>Nice one!>>That depends on the software in the FMC. Prior to U10.3 it>would be number 1. But as we have U10.3 or later in our FMC it>will be answer 4. :-)>The software lesson I referred to was from 1996, so I suppose it was prior to U-10.3 and the answer for that version was indeed number 1, i.e. FMC stays on the VNAV path, FMC command increased thrust and level flight after crossing a waypoint with an altitude constraint. The idle thrust descent starts again at the next idle thrust descent path.Can you tell me where I can find information about the changes in the different versions? Is that included in the FMC Users Guide by Bulfer?I read from another document (dated Nov. 2002) that Intermediate T/D points exist when path segments between altitude restricted waypoints produce a level path segment, and that an intermediate T/D point is shown on the map as green open circles with the label T/D-XXXXX(altitude). Is that also a change included in U-10.3?Cheers,Bert

[crvm 0]

That's where up to date manuals come in handy ;). [h4]Best Wishes,Randy J. Smithhttp://img.villagephotos.com/p/2003-8/196432/winglets_lg.jpg [h3] AMD XP 2200 |MUNCHKIN 512 DDR RAM |ECS[/b ][i] K7S5A MB[/i] |GF2 MX 32 MEG and still runs GOOD!|WIN XP PRO |MITSUBISHI DIAMOND PLUS 91 19"[/h3]