The problem that I have is being on a very tight schedule. This often means I have to fly ORD-FRA for example and not ORD-LHR-FRA ... and ORD-FRA does not have F as it is a 763 on AA. Getting A inventory for AA domestic flights is trivial, yield management will always release it. More frustratingly a few specific routes are really tight for A inventory, for example SYD-JFK or HKG-JFK (but I've never had trouble getting one for the HGK-LAX or HKG-SFO flights on CX, so having that much flexibility helps). Once I had to go HKG-NRT-SJC as everything else was sold out on the specific date (but available the next day, however I couldn't wait a day). But I have observed that many BA flights trans-Atlantic are full in F and it is in part due to a "buy J and fly F one way" offer which expires in December (but probably will be renewed). The problem is that those are booked as taking priority over A inventory despite being J sale (presumably quite a bit more profit in that J sale than A). Finally LHR-CPT is hopeless in A -- there are entire months when nothing is available (but you can go LHR-JNB so it isn't that bad). The inventory has definitely tightened a lot in the past year; enough so that my last AONE4 had precisely *2* flights in A, the rest were in D!