COMMONWEALTH OF AUSTRALIA (Civil Aviation Regulations 1998), PART 39 - 106 CIVIL AVIATION SAFETY AUTHORITY SCHEDULE OF AIRWORTHINESS DIRECTIVES AlliedSignal (Lycoming) Turbine Engines - ALF502 and LF507 Series AD/ALF/6 Replacement of Fuel By-Pass Valve In Dual Heat Exchanger 6/87 Applicability: ALF 502R series which have dual heat exchanger P/N 2-303-491-01 installed. Requirement: Remove from service or rework dual heat exchangers P/N 2-303-491-01 in accordance with Lycoming SB ALF 502R-79-0151 Rev 1. Compliance: Unless already accomplished within 100 flights after 4 June 1987 but not later than 31 July 1987. Background: This Directive is issued requiring the installation of a new fuel by-pass valve which will prevent engine fuel system icing when fuel load temperature at take-off is above 10º C.