Descend via Speed

[BrianCoyote]

Whats the difference between descending via speed vs. path. If I program to cross a WPT or VOR at say 11,000MSL, would descending via speed still cross at 11,000?

[Litjan]

The VNAV SPD DES is in effect a FL CHG descent - the plane will simply descend with idle power and stay exactly at the specified speed.

The difference to FL CHG is that it will level off to honour altitude restrictions (I think) , and it will also honour speed restrictions (like slowing to 240kts below 10.000 feet).

So it is a bit more comfortable and less error-prone. I am not very familiar with the SPD descent, since I have never ever used it in the real aircraft.

Cheers, Jan

 

[sdflyer]

Perhaps little bit off topic. I'm new in XP and using version 11. I know 737 is not compatible with 11, but with little tweak it works perfectly! First of all, I want to say  a very impressive representation of 737 classic. Really enjoy flying it. Saying this I have a small issue and I'm not sure if it's XP11b2 related or perhaps come from "in-house feature".

On several occasions when I used FL CHG on descent and autopilot got out very close to Vne. Outside my comfort zone  I'd say. Is that how  real  737-300 is acting or perhaps something that XP11b in control of?

Also my friend is captain for American Airlines  NG series and told me that NG series kind of  hard to decelerate and require careful  planing  action for descent. Does it also apply to 737 classics?

 

Thank you 

[BrianCoyote]

On 12/13/2016 at 2:52 PM, sdflyer said:

Perhaps little bit off topic. I'm new in XP and using version 11. I know 737 is not compatible with 11, but with little tweak it works perfectly! First of all, I want to say  a very impressive representation of 737 classic. Really enjoy flying it. Saying this I have a small issue and I'm not sure if it's XP11b2 related or perhaps come from "in-house feature".

On several occasions when I used FL CHG on descent and autopilot got out very close to Vne. Outside my comfort zone  I'd say. Is that how  real  737-300 is acting or perhaps something that XP11b in control of?

Also my friend is captain for American Airlines  NG series and told me that NG series kind of  hard to decelerate and require careful  planing  action for descent. Does it also apply to 737 classics?

 

Thank you 

737s in general tend to keep their speed up in descent, a bit too easily. That includes the 737CL. Unfortunately, the IXEG 737 doesnt seem to handle VNAV descents too well, combined with a realistic flight model, makes descending on VNAV near impossible. A 280kt descent is the target for most carriers and this can be achieved by simply descending 15-20 miles earlier than when it wants. Also, speed brakes are your best friend.

Jan has much more experience on this, I'd like to see what he has to say

[Litjan]

For me our 737 descends perfectly on VNAV as long as the arrival is not complex (no restrictions) and there is no wind. The plane plans and flies an ECON speed PATH descend very well (even more precise than the real aircraft, due to the "perfect" simulation environment).

Jan

 

[sdflyer]

Thanks for the answers. I let my friend to try  IXEG 737. He is American Airlines captain and flies NG series, but his type rating covers all 737 including 300. He was very impressed with level of details. He told me tend not to use speed breaks on descent as long as he plan in careful. I have to try that! 

[BrianCoyote]

4 hours ago, Litjan said:

For me our 737 descends perfectly on VNAV as long as the arrival is not complex (no restrictions) and there is no wind. The plane plans and flies an ECON speed PATH descend very well (even more precise than the real aircraft, due to the "perfect" simulation environment).

Jan

 

I don't know about Europe, but here in the states the STARS are pretty dang complex which makes descending on Vnav impossible with the IXEG.

 

Heres teh AARCH1 I came in on last night, VNAV was completely incapable of handling it. http://aeronav.faa.gov/d-tpp/1613/00360aarch.pdf#search=KSTL

[Litjan]

Yeah, I fully agree on your asessment of current VNAV status - but you can still fly them using planning and FL CHG or V/S (or - gasp - manual flight!)