I know I'm a bit late to the discussion, but I've no doubt that an example, or probably several, of each will be preserved when the time comes, a 150 or 156'd be simpler and less expensive to maintain than a 158, mind. Anyway, 153s are going the same way as the Pacer, Doomed? Slightly melodramatic, isn't it? Anyway, don't these new rules, whatever they are exactly, don't come in until about 2020 or whatever? heavens, surely they'd be about ready for retirement then anyway. So talking about what would need to be done to make them compliant is all a bit academic, is what I'd think.