 On 23 December 1937, the first production "Wellington Mk I", "L4212", conducted its first flight; "L4212" subsequently participated in an intensive flight programme.Flight trials with "L4212" confirmed the aerodynamic stability initially encountered by "K4049", but also revealed the aircraft to be nose-heavy during dives, which was attributed to the redesigned elevator.Accordingly, modifications, including the interlinking of the flaps and the elevator trim tabs, were successfully trialled on "L4212" to resolve the issue.