 Investigations conducted by RSAF reveal that although there was plenty of fuselage life left, the Wright J65 turbojet engines in use by the Skyhawks was too old and the associated spare parts were becoming both difficult and expensive to obtain.Consequently, the RSAF decided to upgrade the A-4S/TA-4S rather than to replace them.With SAI contracted as the main contractor for the upgrading project and a non-afterburning General Electric F404-GE-100D turbofan engine selected as the new engine, the upgrading project would later be extended to cover the entire fleet of newer A-4S-1s as well as taking the opportunity to completely modernize the avionics package (newly installed equipment now included a Pave Penny laser seeker mounted in the nose, an Inertial navigation system (INS), a Tactical air navigation system (TACAN), fore & aft Radar warning receivers (RWR) and chaff/flare countermeasures) of the aircraft.