This looks like a bug to me.

 

Go to "Free Flight" and choose Boeing 747-400. Select airport "Jinnah Intl" which is in Karachi, Pakistan. Now try to take off and you will see it crashes while plane is running on runway. Even if you go slowly like taxing on runway, it still crashes after it reaches a specific point. Is this a bug?

I loaded up my 747 at Jinnah Int'l at a Heavy gate, got my instructions from ATC and proceeded to runway

 

25Left for a smooth and uneventful takeoff.  There was a small radio beacon/ILS structure near the runway

 

but was easy enough to avoid.

Sorry I am a noob so this is what I am doing. As soon as the free flight loads, I press F4 to full throttle. Plane starts to go and then after few hundred feet it says "Crash". Even if I go slowly, it says Crash at that specific point.

Turn off crash detection in FSX. SImple.

Oh I got what charlie is saying. It was crashing due to that beacon close to runway. Since 747 is a big plane so its wings were striking with that beacon.

 

Other planes were small (for e.g. I tried with Airbus A321) and it didn't have this problem.

 

Who the hell places a beacon so close to runway?

Just move more toward the other side edge of the runway for your takeoff.  This is why most people

 

create a new cold and dark startup for their aircraft.  That way you can place yourself at an

 

appropriate gate for your plane, get your flight info from ATC, start your engines and  taxi to your

 

assigned runway, and then take off.

 

This is runway 7Right at Jinnah, Pakistan.

 

Use the free ADE (Airport Design Editor) to move that equipment shack off to the side...