Hi all. im referring to the CIREBON ONE CHARLIE SID out of WIII that states 9000 @ HALIM and 11000 @ NUREN and FL 190 @ PURWAKARTA. When I fly this SID in the NGX, I seem to be hitting the required ALT 10nm before the actual waypoints (In all cases). From my (limited) understanding of ALT constraints, the FMC states 9000.11000 and FL190 without an AT or Below. Just wondering my my NGX is getting to the stated alts "early". Is it something to do with my CI?

 

Should the aircraft get to 9000 on the NAV display (VNAV PATH) AT 9000, not before? My FMC displays     HALIM           250/9000

 

Cheers  Chris

It would probably be quite inefficient to do a slow climb, not to mention this causing ATC some extra work so getting to these alts early is fine. Thinner air = less fuel used.

There is no PATH for climb, hence you're simply climbing at VNAV SPEED and getting to that altitude as soon as possible.

 

As Karl said, it's much more fuel efficient to get higher as quickly as possible.

It would probably be quite inefficient to do a slow climb, not to mention this causing ATC some extra work so getting to these alts early is fine. Thinner air = less fuel used.

 

Bingo.  And also, somewhat bingo.

 

For ATC, the primary reason we have at or below altitudes on departures is to keep you below streams above (either departures from other facilities, or heavily used airways at lower altitudes).  So, a slow climb wouldn't necessarily cause more of a headache, but it's a smart thought.  In the end it depends on the complexity of the airspace at the facility.

Hi and thanks all for all your replies. OK I understand now. I was just thinking that I was setting up something wrong on the NGX.  Cheers  Chris