CSTR button? (Airbus)

[abeesley]

Can someone please explain what this button does?. .. .I did my avionics course using the VACBI system and it didn't go into great detail about what it did. From what I can remember it stands for "Constraint", I'm none the wiser from it's meaning!

[Hand Solo]

It shows flight plan constraints on the Nav Display, i.e. altitude/level, speed or UTC contstraints.

[abeesley]

Thanks for that. But what exactly is a constraint? Please could you elaborate. . .. .We engineers are given little information on how the flight plan is actually used. If a fault is reported either by the crew or the CFDS, I would try reloading the database, failing that I would replace the FMGC and so on. I wouldn't know how to enter a flight plan with waypoints etc.

[moleslayer]

ECAM MSG....... .. .When the aircraft reaches the point it has calculated as 'Top of Descent', it has worked this out assuming a 'Thrust Idle' segment.It then starts down using the previous cruise Mach No.in order to reach a point roughly 12miles from touchdown at min.clean speed.All very well in an ideal world!! However in the real one we operate in, ATC require us to be at particular locations,at a specific Altitude and at a specific Speed.These CONSTRAINTS upon the Airbus predicted ideal profile can be pre-programmed into the FMGC.The engine thrust setting & consequent change in the 'Rate of Descent' will now alter the vertical profile in order to achieve what is required.The CSTR p/b on the EFIS control panel just allows these contraints to be indicated on the pilots ND, he can then make manual alterations to the flight path, using the FCU (vs,speed etc.)to ensure that they are satisfied if ATC require further changes (as if!!) <img border="0" title="" alt="[Big Grin]" src="biggrin.gif" /> <img border="0" title="" alt="[Big Grin]" src="biggrin.gif" />. . . . <small>[ 05 March 2002, 14:23: Message edited by: moleslayer ]</small>