@SeanAloysiusOBrien@tenforward.social Two things: use of recirculation fans in planes since 1980 to reduce bleed air requirements in order to save fuel. Airlines have the option of flying with the recirc fans off, providing more fresh air but using slightly more fuel, but having less risk of bleed air fumes. True: putting in sensors or having the engine manufacturer redesign the bleed air system might be an option.