|Quoting Gnomon (Thread starter):|
Given that the PW4090 produces roughly the same thrust (90k lbs) as the Trents and GEs that power higher-MGTOW 772ERs, why was the PW4090 subject to the reduced MGTOW in its certification?
Actually, not quite the same thrust. The Trent and GE
-90 are available at slightly higher thrusts. While nominally the engine might produce the same thrust as the pw4090, during an engine out situation, the extra thrust (94k with the GE
-90A IIRC, 92k for the Trent) makes a big difference in allowed MTOW.
The pw4098 was supposed to burn 2% less fuel than the pw4090. Instead, it burns 2% MORE fuel... (4% fuel burn miss). Thus, a 773 or a 772ER actually has more range with the pw4090 than the pw4098 despite the lower MTOW. Recall, the pw4098 core is also heavier than the pw4090 core. If the pw4098 had worked as planned, Pratt would have sold many more engines on the 773's. (To UA
, JAL, ANA, KE
, and possibly NW
. Recall, northwest didn't like the economics of the 772 and the 773 doesn't do MSP
Also, recall there is more in the MTOW than meets the eye. The GE
-90A burns about 2% less fuel than the PW4090. So even though its a slightly heavier engine, for the same MTOW, the GE
-90 will generally have a longer range even though its carrying less fuel.
And note that the Trent 895 is *much* lighter (2,000lbm per engine) than the pw4090! While the trent has the highest fuel burn on the 777, its really hard to overcome a 4,000 lbm (almost 2 metric tons) weight advantage. Weight savings=fuel savings.
The pw4098 fuel burn debacle was the first of three *major* strikes by pratt. (2nd was the pw4172 compressor vent overtemp, 3rd was the pw6022/6024 fuel burn miss). KE
is the only operator of the pw4098 and is pissed with the higher fuel burn. While the MTOW allowed is impressive, KE
bought those airframes to fly to Europe and the pw4098 fuel burn issue has really hurt the airframe economics.
Just to add a bit more: The pw4098 miss resulted in so many Pratt 777 customers already deciding to "jump ship" that there was no support for a follow on 777 Pratt engine. RR
had a loyal following who was willing to launch a larger diameter Trent properly sized for 115k thrust. (Recall, the Trent on the 777 has the smallest diameter of all of the offered engines.) But GE
demanded/paid for an exclusive on the high MTOW frames. If Pratt had made it onto the high MTOW 777 you would have seen a contra-Rotating engine. (A la F119)