However, the legacy airlines are following the trend, and an economy seat that used to have a seat pitch of 32 to 34 inches now typically has 31 inches. an economy seat that used to have a seat pitch of 32 to 34 inches now typically has 31 inches. United isn't the only airline making more room on existing planes with smaller seats.
According to data from SeatGuru, the roomiest economy seats on the four biggest airlines are all smaller than the smallest seats were in the 1990s."
— Jessica Plautz, Mashable
“The case of the shrinking airline seat is getting so ludicrous that aircraft giant Airbus has stepped in and called for action.
It wants the aviation industry to set a minimum standard of 18 inches (45.72 centimetres) in order to improve the comfort of long-haul flying.
That's because an 18 inch limit improves passenger sleep quality by 53 per cent when compared to the 17 inch standard set in the 1950s, according to new research by The London Sleep Centre that was commissioned by Airbus.
Conditions, including lighting and background noise, were carefully controlled to mimic the experience of a long-haul flight.
‘All passengers experienced a deeper, less disturbed and longer nights' sleep in the 18 inch seat,’ Dr Irshaad Ebrahim from The London Sleep Centre said.
‘They went from one sleep stage to the next as you would expect them to do under normal circumstances. Whilst in the narrower 17 inch seat the passengers were affected by numerous disturbances during sleep - which meant they rarely experienced deep restorative sleep.’
Despite the population's growing waist lines, most planes still have 17 inch seats, and in some cases passengers have to squeeze into 16 inch seats.'”