Jump to content

Sign in to follow this  
tfm

Can I change waypoint speed without also changing the predicted altitude?

Recommended Posts

Here's a little quirk that's niggled at me for a while:Suppose a waypoint on the LEGS page shows that it will be crossed at "240/3400", meaning 240 knots at 3400 feet. If I want to cross the waypoint at 220 knots instead, I should be able to enter "220/" into the scratchpad and then line select the "240/3400" entry in the LEGS page of the FMC. This ought to substitute 220 knots for the existing 240 knots. It is a helpful little shortcut.But with the PMDG 747 (FS9 and FSX versions), this only works if the existing entry of "240/3400" is a "hard" entry (in large type on the FMC), as distinct from a predicted entry. If the waypoint speed I want to change is predicted rather than hard, I must enter BOTH the speed and a hard alititude: ie, in my example, I must make the full entry of "220/3400" instead of just "220/".The same applies (mutatis mutandis) to entering hard altitudes where the existing speed is merely predicted.This is different from other implementations of the Honeywell FMC, including the Level-D 767X. Is it a known limitation of the PMDG 747? Or does the FMC on a real 747 actually work in this way?Thanks,Tim

Share this post


Link to post

The same issue has occasionally arisen for me so I would also be interested to read any feedback on your question.Renzo


Bill Miller

Share this post


Link to post

Hi, RTFM: Page 350: "Speed constraints must always be entered in association with in altitude constraint." Jan-Paul

Share this post


Link to post

RTFQ. Is this a known limitation of the PMDG implementation? Or is it true to life?Tim

Share this post


Link to post

You should be able to just change or add a Speed Restriction just like you can in a real NG's FMC. The 744 I'm not sure but probley is the same as the NG's.BTW, All speed retrictions are considered by the FMC as at or below restriction.Good luck,John Floyd


John Floyd

Share this post


Link to post

Many thanks: that's all I wanted to know. It seems strangely backward compared with the FMCs on other aeroplanes, but perhaps there is a safety advantage. Tim

Share this post


Link to post

The first hard-entry must contain both the speed and altitude (220/3400) according the manuals. After that, you can change just the speed or the altitude of that hard-entry 220/ or /3400 seperately. At least that's the way I do it.


Regards,
Al Jordan | KCAE

Share this post


Link to post

Create an account or sign in to comment

You need to be a member in order to leave a comment

Create an account

Sign up for a new account in our community. It's easy!

Register a new account

Sign in

Already have an account? Sign in here.

Sign In Now
Sign in to follow this  
  • Tom Allensworth,
    Founder of AVSIM Online


  • Flight Simulation's Premier Resource!

    AVSIM is a free service to the flight simulation community. AVSIM is staffed completely by volunteers and all funds donated to AVSIM go directly back to supporting the community. Your donation here helps to pay our bandwidth costs, emergency funding, and other general costs that crop up from time to time. Thank you for your support!

    Click here for more information and to see all donations year to date.
  • Donation Goals

    AVSIM's 2020 Fundraising Goal

    Donate to our annual general fundraising goal. This donation keeps our doors open and providing you service 24 x 7 x 365. Your donation here helps to pay our bandwidth costs, emergency funding, and other general costs that crop up from time to time. We reset this goal every new year for the following year's goal.


    39%
    $9,970.00 of $25,000.00 Donate Now
×
×
  • Create New...