B747-400 fuel burn

[Skipness One Echo]

Hi guys, am only SLF so apologies if this is an obvious question to some. Have been reading that the B747-400 is something less than cutting edge on fuel burn, not surprising as the design is a late 1980s one, dating back to the late 1960s in a few areas. So here's my question :

Is there going to be any fuel burn differential between two aircraft like BA's first N744 G-BNLA dating from 1989 and the 57th and last, 1999s G-BYGG. One is ten years older but I would guess the fuel burns would be almost identical? Is that about right?

Cheers.

[ratarsedagain]

Yep, fuel burns are basically the same, as the engines are the same throughout the fleet.
However, a lot of the engines have had new 'cores' fitted to them, which have improved the fuel burn, and reduce the EGT's on those engines. You tend to find a lot of the aircraft on the fleet have a mix of the new and old cores.

[parabellum]

When I worked for SIA, (52 744s), they had an average burn for the fleet and at the top of each computer flight plan would be a small percentage number with a plus or minus sign that showed that particular aircraft's divergence from the average, usually shown as, for example, +1.2% or -0.56% etc. etc. and the fuel burn for the trip was adjusted accordingly.
On that fleet, (Pratt & Whitney engines), the older machines did tend to be a bit more thirsty but not always.

[Arrowhead]

No idea about Boeing, but Airbus has a schedule where you can calculate the theoretical deterioration in fuel burn over time. It is then recommended that you apply this extra fuel burn to your flight planning. We have A320 MSN805 which has +7.8%! I believe that you can reduce this figure if you monitor the actual burn performance.

As to why the burn increases, if the engines are the same type (and replaced every few years), it can only be weight or airframe. I can only guess that the airframe gradually bends slightly out of shape.

[mutt]

One is ten years older but I would guess the fuel burns would be almost identicalNot identical as the airframe and engine wear differently. Airlines run Aircraft Performance Monitoriting programs that with the aid of ACARS allow the recording of the actual engine/airframe performance, this is compared to the theoretical values and a deterioration value is set, this in turn is used for flight planning purposes.

Mutt

[N1 Vibes]

skipness

the diff now between the 21 yr old machine and the 9 year old machine will be negligible, from a powerplant perspective, since all the engines will have been through a repair/refurbish at least once. A refurbish is never going to recoup 100% of the fuel burn capability of a new manufactured engine, but will get to within about 1-2% of the original figure. There will also be some slight aerodynamic deterioration on the airframe.

arrowhead

it's 90% down to your engines, we are just studying our fleet of 320/321's V2500 engines and they lose about 1-1.5% fuel burn a year. When you put them in the shop for perf restoration they come out within about 1.5% of a new engine.

Regards,

N1 Vibes

[Skipness One Echo]

Thanks chaps !

[Private jet]

Older airframes do tend to be slightly heavier than newer ones (up to a couple of hundred kilos on the heavy metal) This is apparently due to the gradual accumulation of dirt over the years! Obviously however this has a negligible effect on the fuel burn.

[parabellum]

This is a story as told to me in a bar, so take it for what it is worth!

A particular BOAC VC10 always performed much worse than her colleagues, very sluggish on the T/O roll, used more runway, burnt more fuel, landed more heavily etc. etc. When in the hangar for a check it was discovered that she was carrying several tons of water that had some how accumulated between the floor and the skin but thanks to Vickers engineering had not leaked out or screwed up the electrics or whatever else ran through that part of the aircraft.

Possibly urban myth but I got it from the BOAC Station Engineer in AUH at the time!

[Sir Richard]

I heard it was a couple of tonnes of ice accumulated over two or three winter days going to JFK and back when it had no chance to thaw and drain:}

[point8six]

Wear and tear on the airframes and flight controls of older 747-400s results in higher fuel burn. This can be included as 'fuel factors' on the Ident page of the FMC. For example, a brand new a/c will have 0.0 entered, whereas a 15 year old hull may have 4.0 entered. The overall fuel burn is not significantly higher.

[Pinkman]

It would have had to have been G-ARVI. As a long suffering expatriate kid commuting between BAH and LHR I was stranded in Rome, Dharan, and many other places - and ONLY on that aircraft. It was a standing joke amongst the kids that the hijackers blew up the wrong VC10 at Dawsons Field.