Originally Posted by
SpiraMirabilis
At one point MAG was using an ERJ-145 (or two) as a spare for the 900 operation at their own expense. I do remember that. Not trying to defend MAG or anything, I don't work there anymore, but if Delta wanted a spare they should have designated one as a spare.
Regionals don't usually contract for spare aircraft. Normally the contract is for X amount of flying, and it is up to the regional to cover it. If they have good Mx, they can use fewer spares, or vice versa, but it is normally up to them.