What happened
During the landing of flight PA07 and the Boeing 747 on runway 25R at Karachi International Airport, the aircraft touched down with an approach speed of 152 knots. Following touchdown, the crew engaged reverse thrust on engines number 1, 2, and 3. However, engine number 4 was not configured for reverse thrust due to an unserviceable reverser and remained in forward idle.
As the aircraft decelerated to 70 knots, the level of reverse power was reduced. At this moment, the engine pressure ratio on engine number 4 increased rapidly. This asymmetry caused the aircraft to drift left of the runway centerline approximately 7,400 feet from the approach end. The aircraft eventually exited the runway edge at 8,000 feet, with 2,500 feet of runway still remaining.
During the excursion, the pilot flying reported a loss of nose wheel steering and braking capability, prompting the captain to attempt manual assistance via the brakes and tiller. The aircraft traveled 380 feet through soft mud before stopping 2,100 feet from the end of the runway. During the event, the nose gear struck a VASI light installation and its concrete base, causing the gear to collapse. This impact caused significant damage to the forward cargo hold, the first-class floor, and the upper deck stairway. While the aircraft sustained substantial damage and was subsequently retired, all 243 occupants evacuated without injury.
Findings
The primary cause of the excursion was the unintentional increase in forward thrust on engine number 4 while reverse thrust was being reduced on the other three engines. The crew failed to identify the resulting asymmetric power condition and did not properly monitor engine parameters or follow established landing procedures.