what was the limit of what could land or take off on half a mile of grass such as the prewar Great West Aerodrome west of London?
Fairey's Great West Aerodrome wasn't used by commercial airliners, so the question is probably better asked in the context of somewhere like Heston, which also had grass runways and was certainly able to take aircraft up to the size of the HP42 and Ju52 with a runway that was initially around 2400' (though later extended).