Hi all,
Just thought I'd post a few thoughts. These are not responses to any particular questions, instead some "NB's".
1). The GE90 is designed (at least the 115/110K thrust versions) to allow an overboost mode in which more thrust is provided for a certain period of time if one engine were to fail. Since the GE90 is capable of generating 127K lbs of thrust, it is already quite capable of delivering more than necessary.
2). The reason why there are payload restrictions is because of runway lengths. You all speak of the 772ER and how AA and delta are able to fly such long trips out to India without any restrictions and our carrier is "useless and pathetic"--> well here's a little tidbit. I apologise in advance to any pilots or those who are "in the know" about all things aeronautical.
All aircrafts cannot takeoff with maximum fuel AND maximum passengers. Each flight is a compromise between the two. The longer the route, the more likely that more fuel will be taken and less passengers and vice versa. Now, onto the more interesting bit. When an extremely long route is taken, full fuel is pretty much obvious, but passenger/cargo load ability suffers. The resulting weight of the aircraft is pretty much at its absolute maximum or thereabouts.
Now, when an aircraft is at maximum weight, it will take longer runway length to get into the air. The problem? Karachi/Lahore/Islamabad have short runways for the 777. I heard from another source who heard from a PIA 777 Captain that ALL PIA 777's are payload restricted out of Pakistan. Now, if one looks at this document:
http://www.boeing.com/commercial/airpor ... 7rsec3.pdf
We are shown the maximum runway lengths under certain conditions that the 777 will takeoff at.
Here is the data on, for example, Lahore airport's runway lengths:
http://en.wikipedia.org/wiki/Allama_Iqb ... al_Airport
As logic would prevail, it seems that at maximum weight even the 772LR or 773ER need a lot of runway to get airborne, our problem? Our runways are not long enough.
So you see, lets not blame the 777's performance in haste.
The American carriers that operate out to India have the benefit of more runway length in India than we do here.
As for the A340-600, I am sure that aircraft with more overall weight and less combined thrust? will take a considerably large amount of runway length more than any equivalent 777.
Furthermore, just a little final tidbit, unrelated, but necessitated. The GE90 relies extensively on its front fan to generate its thrust. This means less air is combusted and more air is simply blown out. However, this is fine at low altitudes, but at 30Kfeet+, the total output of the engine is somewhere around 25Klbs per engine because of less dense air. Compared to the 115K lbs on the ground, pathetic, no? Well this affects all engine's. However, engines that combust more air, like the RR Trent 500 (as fitted to A345/6) are able to retain more of their thrust at higher altitudes. Each Trent 500 may only kick out 15K lbs at 35K feet, but multiply that by 4, and you have more overall thrust than the GE90 powered 772LR or 773ER--> (25Klbs x 2). This is why the A345/6 are able to cruise higher and get higher quicker than their counterparts assuming both at full weight.
Let's not bicker about which plane is superior and instead be happy that (despite) our airline's continous trouble's in one form or another, that we ought to be grateful to the Almighty for providing Pakistan, nearly each variant of the B777 and all brand new. Who knows? Perhaps better things may lie in PIA's future.
