As airlines stave off bankruptcy by cutting amenities and services to their economy classes, there seems to be a shield around the almighty first class. According to the International Air Transport Association, this is because upper-class passengers, although a small minority among international air travelers, account for almost a third of airline revenues. It's not surprising, then, that recent reports show that cabin modifications, especially those that favor upper-class travelers, are the fastest-growing segment of the airline MRO (maintenance, repair and overhaul) industry.