Changing crz FL between China and non-China airspace

[conchulio 0]

Hello everyone,

i recently conducted a flight between Hong Kong and New Delhi. I use PFPX for flight planning and at the boundary between China and Myanmar i had to change my flight level from FL361 to FL360. So what i did was to simply put   /FL360 at the waypoint LINSO (which is the first waypoint for Myanmar airspace). The FMC accepted it and i thought everything is fine.

However, it seems now that my aircraft believes i am already in the decend phase. The VNAV page of the FMC states "ACT LIM SPD DES" instead of the usual CRZ page. 

What did i do wrong? What was i supposed to do instead of what i have just described above?

Thanks for any help!

 

Dominik Teda

[harvester21 34]

If you were to enter FL360 in the Cruize Level field on the VNAV page or PERF page, I think it will revert to CLB or CRZ (depending on settings). I am not at my computer now so I can't try, but I think that should work.

[xkoote 57]

Not sure what happened there. The /FL360 is for planning purposes mainly until activated. I am not sure, however if you are maintaining FL361 in your MCP and in your CRZ page, entering FL360 at a waypoint should keep it in ACT CRZ with a T/D slightly before the boundary waypoint. Maybe you can verify if it is a repeatable error by doing the same once more.

- MCP 36100

- FMC FL361

- Set waypoint restriction

- That is it. And see what happens.

 

cheers,

[downscc 1,327]

Don't enter the FL360 on the legs page.  First of all, steps are entered as FL360S and secondly you are only making a 100 ft adjustment.  Keep it simple. When ATC gives you the altitude change, simple dial 360 into the MCP ALT and press the button.  Automating the step change is not realistic because in RW you are sticking to a ATC clearance.

[conchulio 0]

5 hours ago, harvester21 said:

If you were to enter FL360 in the Cruize Level field on the VNAV page or PERF page, I think it will revert to CLB or CRZ (depending on settings). I am not at my computer now so I can't try, but I think that should work.

I tried that, however, after inserting FL360 into the CRZ page again and pressing EXEC. the FMC did its calculations but came back to the situation before my input, i.e. again being in the "Decend phase".

 

5 hours ago, xkoote said:

Not sure what happened there. The /FL360 is for planning purposes mainly until activated. I am not sure, however if you are maintaining FL361 in your MCP and in your CRZ page, entering FL360 at a waypoint should keep it in ACT CRZ with a T/D slightly before the boundary waypoint. Maybe you can verify if it is a repeatable error by doing the same once more.

- MCP 36100

- FMC FL361

- Set waypoint restriction

- That is it. And see what happens.

 

cheers,

What i did was the following:

I inserted FL360 into the legs page where appropriate (LINSO waypoint). The FMC has added a T/D point shortly before that WP and informed me via the EICAS that i had to put FL360 into the MCP. I did that and pressed the ALT button and the aircraft decended such that it reached FL360 at LINSO. However, it remained in the decend phase for the rest of the flight.

 

Dominik Tedja 

[conchulio 0]

3 minutes ago, downscc said:

Don't enter the FL360 on the legs page.  First of all, steps are entered as FL360S and secondly you are only making a 100 ft adjustment.  Keep it simple. When ATC gives you the altitude change, simple dial 360 into the MCP ALT and press the button.  Automating the step change is not realistic because in RW you are sticking to a ATC clearance.

Thx for the hint Dan. 

I inserted FL360 into the legs page for convenience so i don't forget to be on the appropriate FL when leaving Chinese airspace. So i guess simply dialing in a different FL into the MCP will automatically take care in this particular case? Even if i have to decend to a lower altitude?

Dominik Tedja

[downscc 1,327]

1 hour ago, conchulio said:

Thx for the hint Dan. 

I inserted FL360 into the legs page for convenience so i don't forget to be on the appropriate FL when leaving Chinese airspace. So i guess simply dialing in a different FL into the MCP will automatically take care in this particular case? Even if i have to decend to a lower altitude?

Dominik Tedja

I've done it many times but still don't remember the exact steps... I know I changed MCP ALT from 361 to 360 (for example) but I may have also pressed the FLCH button..., I think that is required but not sure and it doesn't matter.  You'll know as soon as you press the ALT button if you also need the level change action.

[xkoote 57]

Ok I get it. As Dan correctly pointed out, if you don't insert the S, the FMC will think you have commenced the descent. That is why it remained so in the FMC. The S lts the FMC know you are selecting a new cruise altitude. 

 

[conchulio 0]

Ah, alright! I will try it the next time i fly in or out of Chinese airspace.

Thanks for your help guys, much appreciated!

Dominik Teda