RTA function in Airbus 320 MCDU
 

Hello Everyone

Quick question

Some may be aware of the "trick" where you can "override" Cost Index managed speed and force the plane to do best forward speed to the destination, while in managed mode. This involves putting an RTA at the destination. With that said, my question is this: We recently had a ATC directed speed restriction, for example "Cross ABC at 280 knots and 15,000". We entered that but the plane had no intention of slowing to this user-inputted constraint. So we were wondering if the RTA had something to do with it.

Thank you

RTA stands for Required Time of Arrival, it is not a "trick" and should be used for what it is meant to, i.e. cross a specific waypoint (or destination) at a specific time. I suggest You don't fall in those bad habits of some smart Captains you get to fly with, because the day you end up in overspeed and will have to file a report explaining that you were cruising at 0.81 without a valid reason there will be lots of tea and biscuits waiting for you at the safety office.
With that being said, I do not have the FCOM handy right now but most likely the speed restriction you inserted was disregarded because of the RTA.

thank you Sonic. appreciate the candor and agree.

Not sure why you'd want to "trick" the plane, but an easier method (if you insist on managed speed) would be to use the CONST MACH function.

Can trigger A.FLOOR during turn..

this seems like a better method, I will try this. Thank you

What’s the benefit of using an RTA rather than just put in a different cost index? Any, we just use selected speed to go fast and enter a new descent speed for a more accurate profile calc.

Because at my homebase, we are not allowed to land before 0600 lt. During a nightflight the RTA is very usefull to slow down the ac after shortcuts.
For faster flying I indeed use another cost index.

Never used it to slow down, but that seems like a fair way to use it. Drives me crazy when i fly with people who have some reason they're rushing home and do everything they can to shave off a minute here or a minute there. Puts everyone on edge the whole day, risk taking increases massively, pressure on the other person to do something they're not comfortable with goes up, etc etc. and what do they achieve? arriving at home base 3 minutes ahead of the original time? great. well done. good for you. glad we almost flew an unstable approach for that.

I understand using it for a time constraint, that’s what it’s there for, I don’t understand using it to “fool” the plane into going fast when you can just go fast either by using a higher cost index or selected speed for cruise and changing the managed speed for descent.

good points, some Captains think (correctly or incorrectly) that dispatch or big brother is watching Cost Index changes and therefore they would rather pull speed.

My argument is pulling speed means one more thing to "monitor" and Airbus wants you to fly as managed as possible at all times. So I am looking at the other methods to fly faster/slower in a managed scenario.

Thank you to everyone for the points and feedback

It's a very simple aircraft at the end, either pull speed or change the CI. RTA is there for what it stands for. Keep it simple.