Reading a few of these posts, has been a frightening experience.
Try flying around parts of Africa with those sort of reserves and you may come unstuck very quickly indeed.
It amuses me when an alternate is chosen depending on weather. What if an a/c lands, burst the tires and the runway is closed. Then where will you go?
Hard to say if you're suggesting that weather is an inappropriate criteria, or if you're suggesting one should always designate an alternate. We choose the latter; we always designate an alternate. However, obviously the alternate is designated based on weather...it does very little good to designate an airport for an alternate which will be unuseable due to weather. Therefore, weather always plays a factor. We designate more than one alternate, where the situation requires. Questionable destination weather, or long overwater legs with multiple ETP's are examples.
I don't think it's reasonable to make assumptions on the miriad of possibilities which could occur at the destination or alternate; surely someone could blow a tire, but then you could come under attack from flying saucers or both have thousands of streaking nudists take the runway, too. The safe solution then, is to always have an alternate, and that's out policy.
Our normal fuel is fuel to the destination plus ten percent of that amount, then to the alternate, then 30 minutes holding at 1,500'. We do have island fuel allowances which are to the destination and then 2 hours, in cases where one just doesn't have alternates. By and large, we always have an alternate. We have an allowance which reduces the margin of reserve slightly, which allows us to take the ten percent value and reduce it to ten percent of the class II time. This occurs on the premise that when not Class II nav, we have a greater selection of alternate fields from which to choose.
We also do re-release, with ten percent of the fuel to the re-release point. Within two hours of that point we recalculate along with the dispatcher for the remaining leg. If we can do the remaining leg with ten percent of that leg plus the required alternate and reserve, then we go on...if not, we divert to the re-release point field.
In either case, we still carry ten percent overage on the enroute portion, plus the full alternate diversion, plus holding fuel at the alternate.
The area that really can bite us is the Equal Time Point fuel, which is figured at a minimum of fifteen minutes fuel remaining at the ETP alternate, in a worse-case scenario. I think it would be a rare situation for that to occur, but that's the legal minimum. Based on our regular fuel loads, I think invariably we'd arrive at the ETP alternate with substantially more...but then more can occur that places the aircraft outside the planned ETP envelope (one ETP for two-engine drift down, a different one for depressurization, etc...but what about two engines out and depressurized...that's not a profile that's planned, and that changes things).
The company has no desire to carry more fuel than necessary; we figure an approximate 5% overburn for tankered fuel, so it can certainly be costly and wasteful, yet at the same time we have no desire to park an airplane in the sea.