Allowances are normally variable pay. There are various ways to pay for this:
- for every flying hour.
- for every sector.
- for every duty hour.
- for every standby.
- for every nightstop.
- for every day flying or on duty ("dietas" in Spain).
- etc.
So for instance your airline may decide to pay 50.000 euros basic and then 20EUR per every flying hour and 80EUR per standby. If you fly 800 hours in a year and do 20 standbies, you will earn:
50.000 basic
16.000 flight time
1600 home standby
-------------
total = 67600 gross salary in a year
As I said, every airline works differently and pays different things.
EDIT: obviously if for any reason you did not fly in a year or in a portion of the year (very rare apart from sickness, which is another story, but has happened to people I know because of lack of training available for instance) then you will only get basic salary.