strange fmc behaviour

[Popolama]

hi all
sometimes when you try to get the route into the FMC,you have that annoying "invalid entry" message coming up.ex

you put UMXXX then the waypoint (ZZZ) it accept the route but not the waypoint, it is very strange.
for some reasons when you put another waypoints it will accept it

any thoughts ?:bored:

[Captain Stable]

Popolama, it might be a help to people in answering your question if you were to say what type of FMC - what type of aircraft is it fitted to, what software release etc.

My first answer would be to question it with your technical people.

[dusk2dawn]

WPT is probably not part of the AWY definition...?

[Old Smokey]

Popolama,

Having spent (literally) thousands of hours at my PC building Company route data bases for transfer to the on-board FMC, I would have to agree with dusk2dawn that your selected WPT is probably not part of the Airway definition.

It is not at all uncommon for the NDB at a particular location to be the 'defined' waypoint for a particular location on an airway, in lieu of the 'expected' VOR nearby, and vice versa. This will not always be evident if cross checking against small scale en-route charts, it may only be visible on a larger scale chart, or, in some cases, the terminal area chart. This will be even more so when a particular terminal area has a multitude of VORs, NDBs etc.

Another valid reason may be that you've inserted an upper airway that is identical in routing to the lower airway, but does not include many of the the lower airway's 'non-compulsory' reporting points (the open triangles). If in doubt, use the lower airway, and discard the other extraneous waypoints.

[Notso Fantastic]

Popolama, instead of entering UNXXX to waypoint ZZZ then the next airway, try entering UNXXX, then below the next bit of airway on your flight plan. The computer looks to see where the airways intersect and enters itself the waypoint ZZZ. Saves a bit of time if it works on your system.

[Turbine Cowboy]

If th e wpt in disscusssion is an NDB, try to add the suffix NB to it

Example: BOZ = BOZNB:ok: :ok: :ok: