Originally Posted by Morrissey
That's not correct. If you want to book an F saver award, as long as ONE segment is available in F, you can book it as an F award and then waitlist for the other flights on the itinerary (unless it's a Star award, in which case you can't waitlist and have to keep checking back for availability).
My experience has been that unless all segments eventually clear into first class you will not be allowed to book the ticket. YMMV.