20-year Forecast to 2040 shows about 4,000 single-aisle, mainline jets will remain in service by 2040. The majority of these flying today are older generation aircraft.
There will be about 1,000 twin-aisle jets flying today that will be flying in 2040. These can be expected to be Boeing 787s, Airbus A350s and a small number of A330neos. Each is more environmentally friendly than previous generations.
There will be a handful of four-engine jets flying by 2040, most likely cargo aircraft.
Of the sub-100 seat category, there will be fewer than 300 jets flying in 2040 that are flying today. Some of these will likely be end-of-line CRJs plus late-model, older generation E175-E1s. Deliveries of the latter continue well into this decade because the future of the Embraer E175-E2 is uncertain.