Apologies PT6A - I have just removed my previous post for editing as you put-in a reply. Hence my new version is below yours! Previously we leaned towards the QRH for landing distance calculations but with the latest software we now use the LPC for multiple failure cases.
I work for easyJet where we have recently introduced a modified landing distance calculation method in both the QRH and the LPC (Less Paper Cockpit - fancy laptop with a software module on it). In all honesty the introduction of it has been less than ideal, and many people have been left confused. However, given the limitations of the process, it is still an improvement on previous mechanisms once you get the hang of it. I am not sure if the LPC the Qatar guys use is the same as ours, but I imagine it is. The key thing to remember is that the QRH is only of any value if you are dealing with simple single failures. If you face multiple failures then you must use the LPC, and that is where the problems begin. Having now given a great deal of thought to the matter and discussed it at great length with other members of the Training Department and people who I consider 'informed' on the issue, I think I have now finally got my head around the issue.
There are however, IMHO, significant limitations with the current LPC software that must be understood before you can safely use it. The first problem is where to consider ice accretion (not something our Qatar colleagues worry about too much I imagine, but a big issue in a European winter!). That is hidden in a drop down menu on the landing distance "anti-ice" menu - from memory it offers 'none', 'engine only', 'wing and engine' and finally 'ice accretion'.
The next problem is how to deal with failures and this is where a conceptual leap is required. The LPC always assumes a 15% landing distance margin plus the use of full reverse thrust on both engines - whether or not you have both engines available! That is a clear software glitch, but that is the way it is mechanised nonetheless. Therefore if you have a failure, you cannot just enter the failure using the F5 (Status) button and then going to an ECAM problem (ie L Eng Shut Down) as it still assumes full reverse thrust! It is theoretically possible to enter 'One Thrust Reverser' inop in the MEL, but if you try and use that with' L Eng Shut Down' on the in-flight failures for example, it will tell you it is an invalid combination. You have to select 'Both Thrust Reversers Inop' in order to obtain a valid calculation. In other words it is a thick system that requires you to make performance assumptions that are different from your actual situation. It is not very satisfactory, but workable once you know the limitations.