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alloneword
5th May 2002, 16:50
Being a thick ATCO I was wondering if someone could help with these two questions:

1. How much extra fuel would a typical "charter" jet, eg, A320/B757 burn if it were held down after departure at, say, FL200, for about 150 miles when it could have normally expected continuous climb to at least FL310?

2. If there is a fuel penalty to operate as above, would it be a similar amount of extra fuel on the return leg if same aircraft had to decend from say, FL370, to FL200 about 100 miles or so before normal?

Thanks.

G.Khan
5th May 2002, 23:57
The guys that fly the types will be able to tell you exactly what the penalty is for being at FL200 instead of optimum for 16mins. out and 12mins. back, the point I make is that whereas outbound this extra burn can probably come from the contingency fuel on the homeward leg the contingency may already have been used!

TE RANGI
6th May 2002, 18:28
1) An MD-83 would burn roughly 13% more fuel at Long Range Crz at FL 250 than at Long Range Crz at FL 310. (sorry, don't have a chart for FL 200 handy). For a distance of 150 NM/20 min this would be about 300 lbs difference, less than for an average taxi. Other types that I have flown would show similar percentages. Since most airlines carry a contingency fuel of 5% the total trip fuel, this would pose little problem.

2) Some computer flight plans take into account intermediate level-offs caused by ATC handovers. If not and I anticipated it I would add -at least- that amount as extra fuel, although this is supposed to be covered by the route reserve (contingency).

fantom
6th May 2002, 19:10
not enuff to get excited about...

(I only deal in the rough numbers).

:p

GMS
6th May 2002, 20:36
At a typical weight of 97T for a 3:30 hrs flight on a 757 the optimum level is 350. Flying at FL 200 for 150 nms after departure would consume about 300 kgs more. For your arrival scenario 100 nms at FL 200 would consume about 250 kgs more.

m&v
7th May 2002, 18:18
As commented above,the extra fuel burn on the 320 would be covered by the 'contingency'fuel boarded just for the reason.One becomes a little thoughtful when 'stuck'down at 280 for 2.5hrs on a friday night ex canaries(thankfully it's summer).
flying a different alt ,than planned,for a couple of hours would only realize an extra 300K......cheers:rolleyes:

alloneword
7th May 2002, 19:15
thanks for all the replies.

as some of you may have realised my question was prompted by recent ATC staff shortages in the London area.

it seems that, in my scenario, the extra fuel burn is sufficiently small to make little difference overall, or could the small amounts suggested affect the profitability of an individual flight?

cheers

GMS
8th May 2002, 08:03
The spot price of jet fuel is about U$250.00 a tonne, so 300 kgs would be U$75.00.

Cheers,

GMS

Young Paul
8th May 2002, 17:14
... and to be quite honest, the statistical variation of fuel burn is probably around that sort of mark. The difference between a slick, in the groove operation with a visual approach, best speeds and avoiding unnecessary power changes, switching on the APU so that it is only available the second it is required, ..... and a careful, vectored approach, sticking to speed restrictions, not pestering ATC for climbs etc, being cautious with anti-ice is - I would guess - around 250 kg for a narrow body flight. The difference for inaccurate winds, vectors for spacing (departure, en-route and approach) is probably about another 200 kg. Once round the hold is maybe 200 kg.

Neither is the correct sort of operation. Remember the objectives of airline operation - "safe, punctual, efficient". The point is that half these effects are indeterminate, and half depend on the crew on the day. The effect of any fuel policy that will save less than 2% of fuel would probably not be perceptible over less than a season of flying.

Incidentally, do you know how much fuel you save by doing "two minute legs" in the hold? About 50 kg per hour in a B737. Again, the effect of this "economy" is so marginal as to be lost in the statistical variation of fuel burn.

wysiwyg
8th May 2002, 21:23
Before we all start dismissing 250-300kg of fuel, let's just remember that could easily be the difference between getting embarassed or not. In these cost cutting days everyone is trying to pursuade us to cut back on extra fuel and leave us close to the wire.

GlueBall
9th May 2002, 18:40
Whenever I go into busy airports with crowded skies in marginal weather, I tanker an extra 5000+ Lbs of fuel, no matter what the dispatcher had planned. I endeavor a certain comfort level upon arrival in the hold over destination. Needles to say, captains at my company have a long leash. Having landed with too much fuel has never triggerd much concern...as opposed to having landed with too little. Likewise on the taxi out at an airport where you'll be No. 17 for takeoff, you'll have to pack extra taxi fuel that may not be included on the computer flight plan. :cool:

Young Paul
9th May 2002, 19:39
The point I was making is that it's pretty meaningless for a company to get shirty about that 250-300kg fuel. I know there are accountant types who will work out precisely how much it will cost in extra fuel burn having this additional fuel on. However, it equates to about 10-20 kg per hour flying. The point is that the normal variation of fuel burn will be of the order of 200-300 kg per sector. So it is virtually impossible to detect this "saving" in the normal variation. On the other hand, it is very easy to work out the direct costs of a diversion because you can't land with less than final reserve fuel. It isn't so easy to work out the secondary costs - those people who won't fly with your airline again, the knock on cost of the delays etc.

One thing that interests me is that, if you take sector fuel, and get away a few minutes early with no delay at the hold, you might not be able to hold until your scheduled arrival time before diverting.

"Ladies and gentlemen, we are diverting to another airport."

"But we're not even supposed to arrive for 20 minutes!"

411A
9th May 2002, 19:59
Advice for Captains
....take what you need, OTHERWISE the FAA/CAA/DGCA might find otherwise.....and wouldn't you look silly at the board of enquiry saying.....the company made me do it.
YOUR license...not the Companies.
It all comes down to being the COMMANDER.
Any COMPETENT management will understand.

G.Khan
10th May 2002, 00:35
Probably still quite accurate - in the days of Air Europe, in the charter world, it was calculated that a diversion would cost the company the revenue/profit from its next SIX flights!.