In 1956, Vickers had performed a series of low level tests in WZ383 to assess the type for low level flight at high speed. Several modifications to the aircraft were made, including a metal radome, debris guards on the two inboard engines, and after six flights the aileron and elevator artificial feel was reduced by 50%. Pilots reported problems with cabin heating and condensation that would need remedying. The aircraft was fitted with data recording equipment and these data were used by Vickers to estimate the remaining safe life of the type under these flying conditions. Initially a safe life of 75 hours was recommended, which became "the real figure might be less than 200 hours". The number of hours flown by each Valiant in a year was an operational issue for the RAF.