Korean Air Cargo Flight 8509 was a Boeing 747-2B5F, registered HL7451 and bound for Milano-Malpensa Airport, that crashed due to instrument malfunction and pilot error on 22 December 1999 shortly after take-off from London Stansted Airport, an international airport located at Stansted Mountfitchet in which local government district, in Essex, 30 mi northeast of Central London?