Many people accumulate a lot of frequent flyer miles they will never use. Some of the airlines allow you to donate miles to a very limited set of charities. I can see why they limit it -- they would much rather have you not use the miles than have the charity use them. Though it's possible that while the donor does not get any tax credit for donated miles, the airline does.

However, it should be possible for a clever web philanthropist to set up a system to allow people to donate miles to any charity they wish. This is not a violation of the terms of service on flyer miles, which only forbid trading them for some valuable consideration, in particular money.

The site would allow charities to register and donors to promise miles to the charities. A charity could then look at its balance, and go to the airline's web site before they book travel to see if the flight they want can be purchased with miles. If so, they would enter the exact itinerary into the web site, and a suitable donor would be mailed the itinerary and passenger's name. They would make the booking, and send the details back to the charity. (Several donors could be mailed, the first to claim would do the booking.) In a few situations, the available seats would vanish before the donor could do the booking, in which case the charity would need to try another airline or paid seat.

Donors could specify what they would donate, whether they are willing to buy upgrades or business class tickets (probably not) and so on.

Now it turns out that while the donor can't accept money for the miles, the charity might be able to. Oftentimes non-profit representatives travel for things like speaking engagements where the host has a travel budget. Some hosts would probably be happy to cover something other than airfare, such as other travel expenses, or a speaking honorarium with the money. In this case, the charity would actually gain real money for the donation, a win for all -- except the airline. But in the case of the airline, we are talking about revenue it would have lost if the donor had used the miles for a flight for themselves or an associate. So the real question is whether the airline can be indignant about having miles that would have gone unused suddenly find a useful home.

Now it's true the booking interfaces on the airline sites are not great, but they are improving. And some employee of the non-profit would need to have an account, possibly even one with enough miles, just to test what flights are available. But this will be true in many cases.

Would the airlines try to stop it? I doubt it, because this would never be that big, and they would be seen as pretty nasty going after something that benefits charities.

Miles could also be used for hotel stays and other travel items.