Managing passengers with stable respiratory disease planning air travel: British Thoracic Society recommendations - Ahmedzai, S; Balfour-Lynn, IM; Bewick, T; Buchdahl, R; Coker, RK; Cummin, AR; Gradwell, DP; Howard, L; Innes, JA; Johnson, AOC; Lim, E; Lim, WS; et al. (THORAX, 2011)