Following the third prototype, several design improvements were developed and incorporated into further aircraft. Because of excessive smoke emissions by the RD-93 engine, the air intakes were widened. Reported control problems found in testing resulted in alterations to the wing leading edge root extensions (LERX). The vertical tail fin was enlarged to house an expanded electronic warfare equipment bay in the tip. The redesigned aircraft had a slightly increased maximum take-off weight and incorporated an increased quantity of Chinese-sourced avionics; however PAF had selected Western avionics for their aircraft, postponing PAF deliveries from late 2005 until 2007. Pakistan evaluated British, French, and Italian avionics suites, the winner of which was expected to be finalised in 2006. PT-04, the fourth prototype and the first to incorporate the design changes, was rolled out in April 2006 and made its first flight on 28 April 2006.