We DO have such a thing. It is spelled out in Section 23.W.5.a. However it is so mind-boggling complex, with terms like "the sum of the negative integers" that the typical line pilot could never understand it.

But here is what you need to know.

1. If reserves available exceed reserves required for all the days of the trips you are trying to swap, the swap will be granted. That is the easy one to understand. Of course in the summer time especially, and in some categories all year long, that is not necessarily the case.

2. If you are attempting to swap two trips that fly over the same days, you will ALWAYS have the swap approved, unless there is some FAR or contractual reason to prevent it, regardless of reserves available. Do NOT believe the multitude of complaints when guys claim they tried to do that and the system would not let them. In every case I have ever seen, there is always some extenuating factor that the pilot did not consider or realize (tried to swap into a "Q" trip, forgot that trip one blocked in at 2345, meaning his release was 0015 which means his trip was actually a four-day instead of three day, etc).

3. The tricky one is your example. You are trying to swap two trips, both of which fly over days that are short, reserve availability wise. The swap MAY be approved, if by doing so the category is "less undermanned." However as I mentioned at the top of this post, the formula is bizarrely complex, not helpful, and may end up resulting in a lot of denied swap requests, that not only do no favors for the pilot, but actually may not help the company out as well.

What is the true bottom line? That reserves required formula, in 23.W.5 really needs to be updated, to be simpler, more comprehensible, and address the needs of the pilots more.