PPRuNe Forums - Altitude Range Arc

Like 2dmoon, I find it very useful in checking, at a glance, if a particular level can be achieved by a specified waypoint.

Beyond simple checking, it is extremely useful in enabling aircraft performance to achieve the level / position requirement.

Don't forgewt that the 'green banana' (Altitude Range Arc) is computed for your present Flight Path Angle, as you climb further and G/S varies along with Vertical Speed, the arc will gradually move out as FPA decreases. How I use it is -

(1) Check that the 'banana' is comfortably before the waypoint, if so, no further action required for the moment, but keep checking.

(2) If the 'banana' is at or beyond the waypoint, engage FPA, and firmly plant the banana right on, or slightly before the waypoint. FPA relates to the 'real earth' and is not a manometric value (like V/S), and, if maintained will give you a TOC just where it says it will without variation. Where you must exercise extreme caution, is to ensure that any speed bleed which follows, as inevitably it will, is within acceptable limits. I use it frequently, and regularly see the waypoint and the altitude constraint occur at exactly the same moment.

Don't forget that the Altitude Range Arc relates to the MCP set altitude, and not the final Level set in the FMC. The T/C prediction relates to the FMC set altitude.

It is just as useful on descent, e.g. reach F/L 280 by TNN - Set 28000 on the MCP, use FPA to put the arc over (or just before) TNN, and set the MCP speed to that desired. FPA will put you 'on rails' on an exact descending flight path, Auto-Thrust will maintain the desired speed. In the same circumstances, if ATC required a steep descent, use FLCH, and the arc will indicate just how much speed brake that you require to achieve the constraint.

There are numerous other uses, an example being - Can I achieve the ILS commencement altitude by the IAF?

Don't know about Airbus. It would surprise me if they didn't have it.

Regards,

Old Smokey