fume events, and airlines refused to allow flight attendants to carry air samplers after Congress mandated chemical measurements. The FAA has revoked the medical certificates of several pilots who developed neurological issues after fume events. A judge who awarded workers' compensation to a pilot who had suffered toxic encephalopathy (brain damage) from a fume event condemned the airline industry's obstructionism around fume events. In July 2015, pilots on a Spirit Airlines flight were partially incapacitated by fumes in bleed air. Bleedless aircraft Bleed air systems have been in use for several decades in passenger jets. Recent improvements in solid-state electronics have enabled pneumatic power systems to be replaced by electric power systems. In a bleedless aircraft such as the Boeing 787, each engine has two variable-frequency electrical generators to compensate for not providing compressed air to external systems. Eliminating bleed air and replacing it with extra electric generation is believed to provide a net improvement in engine efficiency, lower weight, and ease of maintenance. According to Boeing internal documents, eliminating the use of bleed air as a source of cabin air also translates into the “elimination of engine contaminants potentially entering cabin air supply.” Benefits A bleedless aircraft achieves fuel efficiency by eliminating the process of compressing and decompressing air, and by reducing the aircraft's mass due to the removal of ducts, valves, heat exchangers, and other heavy equipment. The APU (auxiliary power unit) does not need to supply bleed air when the main engines are not operating. Aerodynamics are improved due to the lack of bleed air vent holes on the wings. By driving cabin air supply compressors at the minimum required speed, no energy wasting modulating valves are required. High-temperature, high-pressure air cycle machine (ACM) packs can be replaced with low temperature, low-pressure packs to increase efficiency. At cruise altitude, where most aircraft spend the majority of their time and burn the majority of their fuel, the ACM packs can be bypassed entirely, saving even more energy. Since no bleed air is taken from the engines for the cabin, the potential of engine oil contamination of the cabin air supply is eliminated. Lastly, advocates of the design say it improves safety as heated air is confined to the engine pod, as opposed to being pumped through pipes and heat exchangers in the wing and near the cabin, where a leak could damage surrounding systems. See also Aerotoxic syndrome