contingency fuel

[kolenb09]

Hello,

My name is Anthony and I am a student studying in the netherlands to become a aviation engeneer. Right now I am in the middle of a project where I and the rest of my team have to execute a flight from Manila to Amsterdam with a 777-206ER that experiences quite a few problems on the way.
I have to do research on the contingency fuel. My problem is that I cannot find information about the contingency fuel of 1%. Does anybody know about the 1% contingency fuel? I know about the 5% and the 3%.
Also, what is ment by holding fuel?
And last, what is ment by contingency fuel coverage? I read about a 99% contingency fuel coverage and don't know what they mean by that.
Thanks for youre anwsers and help.

Regards
Anthony

[wiggy]

With all due repect to our Engineering colleagues Inflight Contingency fuel is a pilot/planning/despatch issue so you probably need to ask this question somewhere else, probably the "Tech Log" section.

However I'll give this as a starter, and emphasise that this is the methodology my operator uses, other States/Companies may work differently:

As I guess you may already know "Trip fuel" is the fuel needed to fly the flight on an ideal day (ideal cruising altitudes, perfect weather forecast, no holding, etc) and then an amount of "Contingency fuel" is added to cater for extra fuel burnt due to unforseen circumstances, e.g. stronger than forecast headwinds, holding, etc, etc.

Once upon a time the Contingency fuel figure was simply an extra X% of Trip fuel, usually 5%, sometimes 3% depending on circumstances.

Nowadays it's more usual for the airline to monitor the actual fuel used on a particular flight on a particular route over several months, look at fuel burnt in excess of trip fuel and then use that data to calculate a "statistical contingency fuel". The 99% contingency fuel figure means 99% of flights have used no more than than that amount of extra fuel ( so it gives 99% coverage)....the 95% contingency figure is arrived at in the same manner.


As for "holding fuel"...for planning purposes, in very simple terms, it's the bottom line, absolute minimum fuel you should land with (anywhere) and it's usually calculated as being the amount of fuel required to hold at the alternate for 30 min.......

[kolenb09]

While searching for the 1% contingecy fuel I came across this link:
http://www.captainpilot.com/B737/FuelConservationForum.pdf

It's a presentation and in the presentation it is stated that some airlines fly with as little as 1% or 2% contingency fuel.
When and why?

Thanks,
Anthony

[wiggy]

Contingencies of "as little as 1% or 2%" of Trip fuel are not unheard of.

Here's an example:

Take, say, a 747 flying from Singapore to London where the trip fuel could be perhaps 140 tonnes.

Under the old percentage system the 5% contingency fuel figure would be 7 tonnes. Even using 3% the contingency fuel would be just over 4 tonnes. Now in reality the flight may use some extra fuel enroute due to unforecast headwinds and altitude constraints but arriving at, say, 0500 UTC into London in good weather there's normally nil or minimal delay so having an extra 7 tonnes contingency fuel is probably in most cases just a little excessive.

On the other hand the modern statistical system will have analysied the actual fuel burn on dozens if not hundreds of these flights. It will quite conceivably come up with an answer that 1.8 tonnes of contingency fuel will give 99% coverage or 1.4 tonnes will give 95% coverage....which equates to a contingency fuel of around 1% or 2 % of a trip fuel of 140 tonnes.


So no, it's not impossible or odd to see contingency fuels of 1 or 2 % of trip fuel - often it simply depends on the time of day of arrival!