Operators of about 1,100 Honeywell TFE731-2, -3 and -4 engines have until December 31 next year to replace fan rotor discs with improved ones under a new Airworthiness Directive (2001-23-09). The AD supersedes two previous directives that required the removal of certain older discs and established life limits on that disc series. Estimated cost for parts is $20,400 per engine.