used2flyboeing:
A significant reason for Airbus' PIP for the A340 was due to IAE's failure to provide an engine (the IAE 2500) capable of producing the required design thrust. Hence the switch to the CFM-56 series. Incidently, the original A340 didn't have winglets, and they were added as part of the PIP in addition to the engine upgrade to meet performance guarantees.