Something which gets overlooked alot that I would like to bring to attention.
S400 detection range is roughly 400km (370km to be precise). It is a real threat but nothing is 100% effective and against a fighter that is severely less, which is why they can still be taken out by salvos of ranged or anti radiation weapons. And detection can be avoided by using terrain advantage.
Actual threat to aircraft from the S400 will be from it's 9M96/9M96E2 (max range 120km) and 9M96E (max range 40km) missiles which can engage maneuvering targets. The higher ranged missile are for fixed trajectory targets. Both these missiles by the time the aircraft is in it's range, the aircraft will also be able to fire it's standoff weapons or anti radiation missiles.
And then there is curvature of the Earth, one of many factors to limit long range missile range.
https://www.foi.se/report-search/pdf?fileName=D:\ReportSearch\Files\e1539f62-de49-421b-93ad-f4e960e0eacc.pdf
"One long-range weapon that has attracted considerable attention in Sweden is Russia’s S-400 SAM system. Its nominal range of 400 km means that the S-400 could theoretically reach Swedish territory. However, the actual range of a SAM is limited by a number of factors. An obvious factor is the curvature of the earth. Figure 11.1 shows that at a distance of 400 km, an aircraft needs to be at an altitude of 12 000 metres to be visible from the ground. Conversely, anobserver needs to be at an altitude of 12 000 meters to be able to detect an object on the ground from this distance. Another limiting factor is the flight time of the SAM. It takes about ten minutes for a SAM to travel 400 km, which is enough time for a fighter aircraft to fly more than 100 km in any direction. Consequently, a longrange SAM would need to receive real-time updates of the target’s position and velocity in order to adjust its trajectory. This would require airborne or surface-based sensors to track the target and transmit data to the missile via a data link. All of this requires line of sight between the target and the sensors, as well as between the data-link transmitters and the missile. Terrain masking poses an obvious challenge for detecting and tracking targets at low altitude. Furthermore, the missile has a limited supply of velocity, which would be quickly drained as the target manoeuvres. All of this means that while a long-range SAM system such as the S-400 would certainly be a threat at a very long range to an airliner cruising at 36 000 feet, the actual effective range against a fighter at low altitude could well be under 20 km, depending on the terrain. Figure 1. Required altitude for visibility of objects at a distance. Hence, long-range SAMs constitute only a limited and to some extent manageable threat to fighter aircraft. For a SAM system to reach its full potential, it needs to be an integrated part of a network of sensors, command and control functions, and weapons. To be effective at long range, airborne sensors are required. Thus, the threat posed by a long-range SAM system in Kaliningrad or on Gotland, for example, cannot be described as a circle on the map with the nominal range as the radius. An aircraft taking off from an airbase in Sweden could not be shot down by SAMs based on the other side of the Baltic shortly after it left the runway"
View attachment 478084
PAF routinely practices 500(152m)-1000ft (304m) low altitude flight and from interviews of pilots I gather the routine is 500ft.
So remaining undetected and taking out the S400 threat is not a impossibility, it will be difficult and risky but then again it's what our fly boys train day and night for.
And then there are terrain hugging cruise missiles in Pakistan's inventory for a saturated attack.
So things are not grim for PAF.
