Hi Bearfoil,
Originally Posted by Bearfoil
Doesn't the Computer (FCS) take as much as TEN SECONDS to validate a LAW? In some situations, one imagines ten seconds may be an eternity, and in danger, delay is the Devil. (Unless it is appropriate, there's the rub).
Right. The EFCS will need 10 seconds to validate that ALTERNATE LAW 2 will be irreversably maintained at PRIMs level.
But then, what you don't understand is that EFCS logic is one thing that is different from Pilots information logic.
When you are flying this machine without system failure, you are protected by the system all the time. Most of the system single failures won't change the flight laws, they are completely transparent for the Pilot Flying as everything (protection) is maintained. They will trigger ECAMs for troubleshooting purpose.
As soon as a system failure is occuring that will change the EFCS flight law (generaly dual or triple faults), by following the EFCS logic, it will be translated into a degraded mode called "ALTERNATE" or "DIRECT", from the consideration of the flight controls on each axis.
But the Pilot Flying doesn't need to follow the same logic as EFCS : what he first needs to know is what protection remains available, or better, which one of the protection is removed. Remember that this is not linked with those LAW, sub-LAW modes, but to the specific nature of each failure => anything "NORMAL" that can be maintained is kept, anything affected is removed.
In fact, this information is displayed on his PFD where he can see what protection is working or not, it is all that will matter for him at this point. Any protection removed (flags or reconfiguration on each PFD) will mean something lost. following computer logic, a single protection lost is called "ALTERNATE" mode... you will know it immediately if any part of your PFD will get amber crosses or red flags instead of usual values.
Now, following computer logic, this translate also into ECAMs triggering and other warnings if an action is to be expected immediately. But most of this is not aimed at the PF (beside auto flight controls). This is for PNF troubleshooting and it doesn't really matter if an ECAM saying "ALTERNATE LAW (PROT LOST)" is delayed by 10 seconds or more.
The reason is that the PF is not taking this information from the ECAM console. It is taken on his PFD where he can see directly what is really affected. Then, it will be obvious for him as soon as ALT2 mode logic is triggered by EFCS in one second when CAS becomes monitored following a sharp variation: his PFD will be reconfigured without displaying any of those protection function nor those characteristic speeds. If he also get the red warning flashing on his PFD : "use manual Trim", he'll know immediately that DIRECT law (computer logic) was also triggered.
"ALTERNATE" by itself means nothing for the PF as to what is possible or not, being related to specific failures. His PFD would tell him everything needed (
at least, it "should" tell him everything).