Opponents reckon they have colluded in making up optimistic projections about the speed with which airlines will change to yet-to-be-built clean, quiet aircraft.

• 对于改用清洁、安静的飞机后可以对航空公司产生的变化，反对者们声称已经做出了最乐观的预测，尽管这飞机还没有研发出来。