Of course condolences to all affected by this crash; and of course, as with nearly all such disasters, it will take a while to figure out what actually occurred. For roundup of first reactions, see this Atlantic Wire item. But as a basic reference document, it's worth being aware of the info shown below. It is a scan, from an aviator in Pakistan, of a Jeppesen approach plate* for the airport in Islamabad where the crash occurred. This is the approach -- ILS DME Runway 30 -- the plane was reportedly attempting when it crashed.
What this shows and why it matters:
- Nothing in and of itself. It's just a basic document for understanding the airport and one of its "instrument approaches," which planes would use to land in bad weather;
- It helps put in perspective one analysis in a Pakistani newspaper (also quoted in Atlantic Wire), which made it sound as if the pilots might have been doing something rash or unsafe with a "circling" landing. This analysis was:
If you are using runway 12** as it seems (the Murree road side) there is no ILS [instrument landing system]. The ILS is on runway 30 (the opposite side). So the procedure (which I never thought was safe) is you fly the ILS to 30 and then you break off and turn right and fly parallel to the Margalla hills and then turn back in and land on 12. It's not a circle but more of a race-track pattern.
You may ask why not have the aircraft turn left rather than right towards the Margalla Hills. The reason is that on the left of runway 30 is Dhamial Air Base, GHQ and so on and as far as I remember that is all so-called "Restricted" airspace. You cannot fly over it.
Final point, when you are flying parallel to the Margalla Hills, you are required to keep the airport on your left in sight. So I can visualize the captain in the left seat looking left. Maybe the [flight officer] was flying and craning his neck too. They just seem to have drifted into the Margalla Hills -- perhaps because of high winds. They lost what is called "Situational Awareness". Basically they did not know where they were.
Well, maybe. The bottom pane on the approach chart shows the "decision altitude," or "minimum descent altitude," for the airplane under different circumstances. Basically this is how close to the ground the airplane is allowed to get while relying strictly on instrument guidance. If the pilots cannot see the ground (or runway lights etc -- there are elaborate rules) by that point, they have to abort the approach and execute a "missed approach," also known as "going around," in which they climb away from the runway and then try again or head somewhere else.
In the best circumstances, with the plane headed for a "straight-in" landing in the same direction as the approach, this ILS procedure would allow them to get within 309 feet of the ground purely on instrument guidance. But for a "circle to land," approach, in which the plane would intend to land in the opposite direction from the approach, the minimum descent altitude could be as high as 842 feet above the ground. It would be illegal to go any lower than that if they couldn't see.
In a "circling" approach, the airplane would descend from the southeast -- the lower right of the chart shown above -- and then, once the pilots saw the runway, fly parallel alongside it to the other end (upper left of chart), at which point they would turn around and land in a northwest-to-southeast direction. You do this when the instrument approach guidance works only in one direction, but the winds favor a landing the other way.