FMC VNAV and RC4

[Tigh 6]

I hope I haven't missed the info for this in the tutorials :/I normaly use SIDs to depart and have RC4 set on Departure with Altitude Restrictions. When I engage VNAV the FMC will limit my altitude at certain waypoints however, I get clearance from ATC to higher altitudes so I am obliged to turn off VNAV and set the autopilot climb rate.For example, climbing out of EHAM the first waypoint is meant to be at FL060 and my FMC duly levels me out at this altitude. However, ATC has already cleared me to FL150.What would be the real world procedure here and what should I do?Many Thanks,Dan Parkin

[jd 57]

you always do what the controller says.or you check the box that says instrument departure no alt restrictions, then do what the fmc saysjd

[ronzie 21]

You could also program altitude as AT OR ABOVE if you are concerned about minimums declared in the DP. Remember that in a VNAV climb (at least on the 737NG) if you have the correct declared expected cruise level it will only still climb to the altitude set in the MCP ALT window which in this case would be your current cleared altitude of FL150. It would then level off until you increased the MCP setting up to the next step.Once you are past the intial climb this could be the preferred method to maintain efficient climb flight profile, whereas FLCH uses the most expedient profile at your selected N1 max climb rate.If you are in a congested airport area there may be indeed altitude maximum and minimum restrictions to maintain vertical seperation from adjacent airport traffic patterns. In this case. which RC does not simulate unless AI on a conflicting path is present, choose the alternate departure method so you can fly the altitudes you've declared in your FMC. As an example look at the area around London City which is in the traffic pattern of other London airports.

[Tigh 6]

Thanks guys. I'll have a play around.Dan

[Guest Douglas Thompson]

The manual under Departure Procedures, starting p109.

[Guest mmcevilley]

>You could also program altitude as AT OR ABOVE if you are>concerned about minimums declared in the DP. Be careful! If the DP defines an altitude of 6000 for a waypoint it would be inappropriate to program that into the FMC as 'at or above 6000'. If a programmed DP has altitude constraints and you are cleared above those constraints, then you can remain in VNAV and simplly DELETE the altitude constraints that ATC has superseded.Check the procedures for your FMC about how to do that.BTW: You can ALWAYS hand-fly the departure! Folks seem to forget that! ;-)-michael

[ronzie 21]

I was referring to DP stated minimums as indicated by an underline under the altitude. This may be for terrain or vertical seperation.While RC will recognize terrain clearance based on its terrain sampling area, in certain cases it might be better to fly the DP altitudes where where a lower altitude is demanded for various reasons and the path is between points of high terrain causing too high an altitude restriction from RC's wider sampling. The preference needs to take "bumpy" terrain into consideration.My preference is to use FLCH (or MCP altitude), not VNAV, during the early stages of departure once I've reached 1000 ft AGL so A/P can be engaged. Likewise I use HDG once at 1000 AGL to engage a predictive path indication on the ND to the first or second waypoint depending on the DP.