Proper Cancelling of Speed and Altitude Restrictions

[CaptainLars 21]

Dear Pilots:

Today I was flying from KEWR to OMSJ and used a NAT track, so I entered speed and altitude restrictions like the ones explained in the tutorial 1.5.

 

NEEKO    .83/320S

....

SOVED    E/

 

However, once you have crossed SOVED, the VNAV page functionality is not the same as before: normally, you can choose LRC, or enter a Speed or Mach value in the magenta altitude cipher. This cipher then gets replaced by the dialled Mach number on grey, the values on LEGS page adapt and you can choose to execute the new speed value or not.

I did this before crossing the North Atlantic, and it worked as normal. After crossing the pond, everytime I entered a number in the magenta ECON speed cipher, the chosen number didn't show up, instead the actual ECON speed showed up on grey. The only way to change the speed (besides dialing on the glareshield, of course) was entering new restrictions on LEGS page, cancelling restrictions again with E/. Trying RTA speed always resulted in an "unable RTA" prompt, and the page additionally displayed

START SPD SEGMENT END

.-1000000000/SERADA/.795

The "S" in the second line is from "SOVED", the last waypoint of my NAT restricted chunk of route, whereas "ERADA" is the first wapoint of my second restricted route portion that I entered to arrive on fuel at my Redispatch fix.

Additionally, the step climb window remained empty. This was no problem at first as the recommended altitude remained FL330 (the initial climb to FL330 after SOVED was indicated), but later on the recommended altitude changed to FL350 without being announced on the CDU.

 

So, my question is, if this is normal, if it's a bug, or if I did something wrong. Cheers!

[downscc 1,327]

I don't understand your use of the word "cipher" so I am trying to help without understanding the problem.  You entered E/ at SOVED, the FMC then reverts to ECON speed based on current CI.  So far so good, you now can only change your cruise speeds by cancelling the E/ that you placed on the LEGs page.  This is correct.  Also, you notice that when you enter a manual step such as 320S, all later automatic steps are gone, which is also correct.

The easiest way to do this is to go ahead with the speed constraint entering NAT but manually step to the NAT cleared flight level and keep the step value 0 while in the track.  After leaving the NAT you can delete the speed constraint and enable the step by setting step value to 2000 or whatever.  In reality, you don't want to change altitudes anyway until cleared by ATC so this isn't too much of a stretch.

[CaptainLars 21]

Hi Dan and thank you for the reply.

With "cipher" I wanted to refer to the magenta speed indication on VNAV CRZ page on the CDU, sorry for the misunderstanding. I wanted to say german Ziffer, which is "digit" in English, not "cipher"... Now that I checked a dictionary I understand that it could have come off a bit rare! Sorry. A false friend...

On topic, I wasn't aware that the "E/" positively commands ECON for the rest of the flight, I thought that it would be merely cancelling previous restrictions. OK, how do I cancel the E/ on the LEGS page in the sense of "leaving it open" as before? I. e., can I fly "unrestricted" again after a restriction, and which command would I have to enter? And how do I "reopen" step calculation again after 320S? I thought that this would be cancelled by E/, too.

[downscc 1,327]

I've always left it in ECON and never tried a cruise speed constraint, ECON is a unrestricted mode.  Did you try to change the cruise speed from ECON on the VNAV pg 2, the CRUISE page?  I think you should be able to change from ACT ECON CRUISE to ACT MOD CRUISE simply by change the speed at L LSK2.

 

EDIT:  Finally found my reference: FCOM 11.42.28 explains the constant speed cruise segment, which is what you do when you enter a speed value.  You reenter ECON in your case at the end of the segment.  Are you saying that after reentering the ECON cruise you can no longer enter another constant speed segment?  Different topic:  RTA cannot be used with constant speed segments.

[CaptainLars 21]

Quote

Did you try to change the cruise speed from ECON on the VNAV pg 2, the CRUISE page?  I think you should be able to change from ACT ECON CRUISE to ACT MOD CRUISE simply by change the speed at L LSK2.

Yes, exactly, but after a constant speed cruise segment, it is no longer possible. Only when descent initiated, it is possible to do so on VNAV DES page, but that's not cruise anymore.

 

Quote

Are you saying that after reentering the ECON cruise you can no longer enter another constant speed segment? 

No, I can enter another constant speed segment, but I can't enter a constant speed in the VNAV CRZ page, nor can I select LRC there any more.

 

Quote

Different topic:  RTA cannot be used with constant speed segments.

Yes, but after a constant speed segment, you should be able to do so, and after the FCOM section you cited, you should be able to do so, too. No wonder I wasn't able to use RTA, when on the RTA page the speed restricted segment remains to be shown even when already passed.

 

I always thought, "S" stood for "steady", but now after reading the FCOM chapted you cited I think it's for "step". Perhaps you would have to "close the bracket", like this? I don't know.

 

....

.83/FL320S

....

.83/FL320S

E/

....

[downscc 1,327]

You may have found a minor bug with the constant speed segment.  Good place to go with this is PMDG Product Support (  http://support.precisionmanuals.com ) to submit a trouble ticket.  This is the only way to ensure bugs get checked and entered into the bug tracking system. This is a really good time to do it because they are probably now or are close to working on the 777 again.

Meanwhile, I'd work around this by using the CRUISE page to modify speed instead of the LEGs page.  I also prefer not entering manual steps, even for NATs, presuming I'm don't want to step until cleared by ATC.  Once I get the clearance (from the ATC in my head) then I dial up the MCP ALT and push the button. Keeping it real.

[CaptainLars 21]

Thanks Dan for your suggestions and your input. I will most likely do as you suggest and forward this thread to the PMDG support.

 

Quote

Meanwhile, I'd work around this by using the CRUISE page to modify speed instead of the LEGs page.

I think you mean just the other way round.