ssreekanth2000 wrote:The 77W obviously is far more capable and economical for long-haul but I was curious about which would make more sense for medium haul distances like ME-India. I can't see an obvious answer as the 773 is lighter while the 77W has the more efficient GE-90-115B.
CX Flyboy wrote:CX 'misuses' 77Ws on its short haul network but more as something to do for the aircraft instead of sitting on the ground between longhauls. We also have a fleet of very hard working 773s. In our configs, the 77W carried either 275 or 340 whereas our 773s carry 398 pax and burn less fuel doing it. I dont have figures at hand but it is obviously a complicated mix of direct operating costs, lease costs, pax yield, aircraft usage etc..
jagraham wrote:CX Flyboy wrote:CX 'misuses' 77Ws on its short haul network but more as something to do for the aircraft instead of sitting on the ground between longhauls. We also have a fleet of very hard working 773s. In our configs, the 77W carried either 275 or 340 whereas our 773s carry 398 pax and burn less fuel doing it. I dont have figures at hand but it is obviously a complicated mix of direct operating costs, lease costs, pax yield, aircraft usage etc..
How much less fuel? For your airline? City pairs too if you can.
jagraham wrote:How much less fuel? For your airline? City pairs too if you can.
zeke wrote:jagraham wrote:How much less fuel? For your airline? City pairs too if you can.
What you are asking is a bit unfair in terms of expecting an employee to divulge how much an airline is burning over a city pair. I have put together some generic numbers below, these are from interpolation of data not found in our company manuals but elsewhere. This has been done for close enough to the same payload for both aircraft (around 50 tonnes), the OEW was taken from the ACAPS.
For a 777-300 with PW4090 engines to FAA rules, this is based upon an OEW of 351700 lb from the ACAPS and a payload of 110210 lbs, giving a landing weight of 461910 lb with a 310/0.84 climb, LRC, 0.84/310/250 descent with 4000 ft step climbs above optimum altitude
Trip (nm) Fuel (x1000 lb)
1000 35.3
1500 51.5
2000 68.1
2500 85.1
3000 102.6
3500 120.7
4000 139.2
4500 158.3
5000 178.0
For a 77W with GE90-115BL engines to FAA rules, this is based upon an OEW of 370000 lb from the ACAPS and a payload of 11000 lbs, giving a landing weight of 480000 lb with a 310/0.84 climb, LRC, 0.84/310/250 descent with 4000 ft step climbs above optimum altitude
Trip (nm) Fuel (x1000 lb)
1000 34.6
1500 50.2
2000 66.1
2500 82.7
3000 99.9
3500 117.5
4000 135.4
4500 153.8
5000 172.5
This is only one part of the total operating cost, it shows that the 77W will burn 2-3% less fuel than the 777-300 with the PW4070. However I think the ownership and maintenance costs would be much lower on the 777-300, making it the overall winner.
Disclaimer, I didn't actually check if any limits were exceeded above, some of these scenarios may not be possible.
jagraham wrote:Any insight as to why the 77W is better than the 773 on short lengths? And why the difference - for about the same TOW - is so small??
Stitch wrote:jagraham wrote:Any insight as to why the 77W is better than the 773 on short lengths? And why the difference - for about the same TOW - is so small??
The GE90-115B is more fuel-and propulsive-efficient than the PW4090. The 77W also entered service with better aerodynamics than the 773 (some of which are retrofittable to the 773 via a PiP) and the 77W received another engine and aerodynamic PiP in 2016.
jagraham wrote:I agree with all you said. However, zeke's numbers show a 2% to 3% advantage for the 77W. I would have expected better, especially as the stage length increased.
jagraham wrote:It would appear that the main advantage of the 77W over the 773 is that the 77W flies farther with no penalty at any stage length. 2% to 3% on fuel burn is good, but not enough to ditch a paid for 773 for a 77W.
jagraham wrote:.
It would appear that the main advantage of the 77W over the 773 is that the 77W flies farther with no penalty at any stage length. 2% to 3% on fuel burn is good, but not enough to ditch a paid for 773 for a 77W. What am I missing?
zeke wrote:jagraham wrote:.
It would appear that the main advantage of the 77W over the 773 is that the 77W flies farther with no penalty at any stage length. 2% to 3% on fuel burn is good, but not enough to ditch a paid for 773 for a 77W. What am I missing?
The 77W is used as a long haul aircraft, like all aircraft it is subject to payload limitations. So generally the aircraft will be configured with 1-200 seats less than a regional 773. The comparison I made was based upon carrying the same payload, around 50 tonnes. With the reduced seat count on the 77W you would have to carry a lot more cargo than a 773, in reality this is not the case. Regionally a 77W does not carry much more revenue payload than a 330, similar seat capacity as a long haul 77W and carries the same amount of cargo.
The disclaimer I put above I said I did not check to see if limits were exceeded, the MTOW of the 773 with those engines is between 560,000 and 660,000 lb. I will let you work out which ones I could not do.
On a total cost and total revenue basis, I would think regionally the 773 would be the clear winner over the 77W. The minor fuel burn difference is minor in the total cost when maintenance and ownership costs are taken into account. Being lighter the 773 also is charged less for enroute and airport charges. The 773 with more seats installed would generally be able to generate more revenue.