Originally Posted by
777boeings
VNAV should still provide a reasonably accurate descent profile up to 20 nms to the left or right of the magenta line. This is based on the fact that at distances greater than 20 nms, the next waypoint will not be recognised as one passes abeam the position. In this case, the data will most definitely be invalid, including fuel, dist and time remaining.
Sounds familiar.....isn't that the max distance for a proper offset. Farther will not have WP recognition?
Originally Posted by
flite idol
Maui I agree with your technique for this example. You are on a STAR passing FL160 with a constraint of FL100 at the next waypoint. ATC instructs "turn right heading 270 expedite descent to FL80 for traffic." Heading is selected and 8000 dialed into the MCP. If VNAV is used for the descent then the FMA will indicate VNAV SPD and then capture VNAV ALT at FL100 until passing abeam the constraint in the legs page and the resume the descent to FL8000. ATC will not be very happy with you and a TA/RA may be the result. I think VNAV looks at the distance along track from the abeam point to the waypoint/constraint to calculate the path but will honour constraints abeam to your postion thus the unintended level segment. I too see this lack of awareness from very experienced pilots and I always select FLCH or V/S when taken off the lateral track by ATC for descents.
If this is the case, would an appropriate push of the altitude button help?