Discretionary fuel decision making

[I-WEBA]

Hello everyone,

I’d like to ask your opinion if you have a structured method (or just which process) you normally use to decide discretionary fuel. As FO I try to pick up captains method and most of them even asked this question just don’t have one. Tbh I see quite commonly “let’s take 500 extra” which is valid from every kind of situation.
i know some airlines used acronyms or I’d just would love to see your flow in order to take this decision.

[hunterboy]

Does your Flt plan have statistical contingency fuel? You can see from the stats what % of time extra fuel has been used on that route and think, is today one of those days? Experience will play a large part of that decision, and on long haul, there is usually someone on the crew that has been to the destination recently. If no-one has, and the weather is looking marginal, there is your decision made.

[Doug E Style]

I consider the following, in association with the statistical fuel figures we get.
1. Am I likely to be taxiing for longer than the plan suggests?
2. Am I likely to be able to fly from A to B at the planned flight level without having to deviate for weather?
3. Am I likely to be able to make an approach without holding?
4. Am I likely to need fuel for more than one approach (if the wind is close to limits, for example)?
Then, based on the above, and on what has happened to me on that route in the past, I take a sensible amount of extra fuel if I think it’s necessary. An old sage once said to me, “I can choose to worry about the weather, or the fuel on board, but I’m not going to worry about both on the same flight.”

[FlyingStone]

Some good stuff already above. I'll just add to check OFP for what runway has been planned for departure and approach - with automated flight planning widely in use these days, OFP might not match the reality, and you might have to adjust the figures a bit.

Also a good idea to think of extra fuel in minutes, rather than weight - 30 minutes of extra taxi or 30 minutes of weather avoidance will result in a widely different figure.

[PENKO]

Originally Posted by I-WEBA

Hello everyone,

I’d like to ask your opinion if you have a structured method (or just which process) you normally use to decide discretionary fuel. As FO I try to pick up captains method and most of them even asked this question just don’t have one. Tbh I see quite commonly “let’s take 500 extra” which is valid from every kind of situation.
i know some airlines used acronyms or I’d just would love to see your flow in order to take this decision.

I basically have three modes:
A.zero discretionary fuel for days where I do not expect any problems
B.half an hour extra for days I expect manageable difficulties like isolated thunderstorms, LVP’s, windshear go-arounds
C.load her up with an hour extra fuel or whatever it takes when we have no idea what we will encounter on the way, like severe thunderstorm activity etc

This is in no way systematic or structured. It’s just what I’ve grown comfortable with over the years. My airline accepts the risk of a diversion when plan A does not work out so I am happy to take flight plan fuel most of the time. In the end the fuel figure does not really matter, it’s what you do with it!

[JH870]

Originally Posted by PENKO

I basically have three modes:
A.zero discretionary fuel for days where I do not expect any problems
B.half an hour extra for days I expect manageable difficulties like isolated thunderstorms, LVP’s, windshear go-arounds
C.load her up with an hour extra fuel or whatever it takes when we have no idea what we will encounter on the way, like severe thunderstorm activity etc

This is in no way systematic or structured. It’s just what I’ve grown comfortable with over the years. My airline accepts the risk of a diversion when plan A does not work out so I am happy to take flight plan fuel most of the time. In the end the fuel figure does not really matter, it’s what you do with it!

Same airline and same line of thinking here, funnily enough!

[Bullethead]

G'day I,

As an FO I tried to make a logical fuel decision but I was continually over ruled by whoever the captain was so I decided to just order the flight planned fuel, which couldn't be argued as it was company policy, and let the captain make his decision and avoid the drama and some of them were very dramatic.

A tip I was given was to never make any extra fuel decision an even 1000 but to make it a semi random figure in order to make the boss think that you had actually thought about it and calculated a sensible number.

Once I had my command things were much easier and I was never over ruled.

Cheers,
BH.

[framer]

I am very similar to Doug E Style with how I choose my fuel. It’s a really good question that the OP has asked. One thing I have noticed is that the flight plan is normally within 20 mins or so of what I think is sensible but once every few months it’s either a lot lighter or a lot heavier than what I think is sensible. Sometimes more than an hour difference on a 3 hr flight. It is worth building a strong and repeatable method ( the same every time) of independently calculating what you think is a sensible fuel figure for those days when the computers don’t quite get it right.
For the OP: I would suggest you choose a method from this thread that you like and try it out for a month, jot down your independently calculated number on a piece of paper before the Captain has discussed their thoughts and then when you and the Captain are different by a significant amount, respectfully tell them in the cruise that you’re trying to develop a good technique and ask if they could explain their thought process. Most Captains would be more than happy to explain their view , be impressed that you’re trying to better your skills, and if they aren’t then you’re probably not missing much! Also keep in mind that everyone has different risk tolerance and that’s ok.
What aircraft type do you fly?

[I-WEBA]

Thank you everyone for your great and detailed replies. There are very good tips that I will try on my next flights

Originally Posted by framer

I am very similar to Doug E Style with how I choose my fuel. It’s a really good question that the OP has asked. One thing I have noticed is that the flight plan is normally within 20 mins or so of what I think is sensible but once every few months it’s either a lot lighter or a lot heavier than what I think is sensible. Sometimes more than an hour difference on a 3 hr flight. It is worth building a strong and repeatable method ( the same every time) of independently calculating what you think is a sensible fuel figure for those days when the computers don’t quite get it right.
For the OP: I would suggest you choose a method from this thread that you like and try it out for a month, jot down your independently calculated number on a piece of paper before the Captain has discussed their thoughts and then when you and the Captain are different by a significant amount, respectfully tell them in the cruise that you’re trying to develop a good technique and ask if they could explain their thought process. Most Captains would be more than happy to explain their view , be impressed that you’re trying to better your skills, and if they aren’t then you’re probably not missing much! Also keep in mind that everyone has different risk tolerance and that’s ok.
What aircraft type do you fly?

Thank you for your kind words Framer, I mostly fly A320 and A319 (CEO/NEO engines). Rarely but sometimes happens A321N

[Doug E Style]

Originally Posted by FlyingStone

I'll just add to check OFP for what runway has been planned for departure and approach - with automated flight planning widely in use these days, OFP might not match the reality, and you might have to adjust the figures a bit.

Quite right, I missed that one from my list but I always check. It doesn’t happen often but I’ve had some glaring errors in that respect. OFP had a straight in approach onto 13R at LHBP/BUD with a wind for the entire period of 300/8.

[sonicbum]

Originally Posted by I-WEBA

Hello everyone,

I’d like to ask your opinion if you have a structured method (or just which process) you normally use to decide discretionary fuel. As FO I try to pick up captains method and most of them even asked this question just don’t have one. Tbh I see quite commonly “let’s take 500 extra” which is valid from every kind of situation.
i know some airlines used acronyms or I’d just would love to see your flow in order to take this decision.

Many valuable inputs already exposed in this thread. If I may emphasize, always consider the discretionary fuel you decide to take as extra time in the air for a specific purpose. This list can be pretty much endless depending on the threats of the specific day out. Generally speaking the "big families" which will lead you to take discretionary fuel are: Wx (some Extra could already be included in min block.), Notams (expected delays for many different reasons, from runway closures to VIP movements, etc..), MEL (must be included in the OFP as Additional Fuel), Local aerodrome knowledge (i.e. non radar-environment where you get to hold over the IAF till the preceeding traffic is somewhere on short final and so on). Tons of variables.
Try to come up with something that makes sense. For example, Enroute CAT forecasted? Might consider 1-2 FL downs fuel to increase the coffin margin. Destination Wx with gusty winds and/or showery/stormy phenomena at a big messy intercontinental airport? Consider anywhere between 30 to 60 min additional for instance, depending on how dodgy the SigWx/TAF look. Also if the destination looks frisky, make sure your alternate looks peasy. In case change the alternate or have the dispatcher change it for you. These are just a few points, but every single day on the line you will find threats which could well be mitigated also (not exclusively) by carrying additional fuel.
The worst thing you can do as a professional is just throwing a number out, like "let's take 500 extra" or "1000 extra" just for the sake of it without knowing what those KGs are potentially going to be used for. For example if you want time to hold at destination because of TS forecasts, then local climatic knowledge will also be useful, i.e. average length of TS, where do they form mostly, etc.. generally speaking plenty of this information is covered in OM-C.
Bottom line try to learn day by day and fine tune your skills over time.

[PENKO]

Originally Posted by Bullethead

G'day I,

As an FO I tried to make a logical fuel decision but I was continually over ruled by whoever the captain was so I decided to just order the flight planned fuel, which couldn't be argued as it was company policy, and let the captain make his decision and avoid the drama and some of them were very dramatic.

A tip I was given was to never make any extra fuel decision an even 1000 but to make it a semi random figure in order to make the boss think that you had actually thought about it and calculated a sensible number.

Once I had my command things were much easier and I was never over ruled.

Cheers,
BH.

I can't prove it of course but I have the a suspicion that those who are most 'generous' with their discretionary fuel uplift are also those equally likely to piss it all away by flying faster than prescribed. One moment they add another three hundred kilo's on top of whatever fuel figure you come up with, next it's Mach .80 all the way from Hurghada. Left seat and right seat.

You'll never see them slow down to preserve that precious fuel...
Sometimes I have a feeling that this job is 3% Newton, 97% psychology

[Propellerhead]

Also, how likely are you to actually divert? If the weather at destination is fine and there’s multiple runways I’d be less likely to take extra fuel for avoiding CBs en-route etc as I know I can likely dispense with the alternate (and probably get a direct routing after weather avoidance). If it’s a single runway, with no ILS in the Caribbean, I would be more cautious.

[framer]

If I may emphasize, always consider the discretionary fuel you decide to take as extra time in the air for a specific purpose.

This is good advice. Know what your machine burns in ten minute blocks so that when you’re deciding on your final figure you can add ( for example ) ten minutes for the hold that you’re 80% sure you’ll get inbound due to the runway configuration for example. Also, when you shut down on the gate, point at the fuel gauges and think “am I happy with that amount?” as that will form part of your future decision making.
Question for the OP; do you have a figure in mind that you want to land with on a perfect day? For example, if the TAF is perfect, the traffic is light, there are no MEL’s etc….. what do you think is a sensible amount of fuel to plan to land with? For me this is the foundation of my planning decisions. Think about arriving on that perfect day and then getting a moderately complex non normal when on final approach, doing the missed approach, running the checklist, doing the second approach and landing…..what do you want to see on the gauges when you land? How much did you burn in the missed approach and running the checklist? Do you want to have 30 mins fuel left when doing the second approach? Everyone will be slightly different on this one but figure out what yours is and tell us if you’re brave enough to Again, good question.

[Airmann]

Originally Posted by Propellerhead

Also, how likely are you to actually divert? If the weather at destination is fine and there’s multiple runways I’d be less likely to take extra fuel for avoiding CBs en-route etc as I know I can likely dispense with the alternate (and probably get a direct routing after weather avoidance). If it’s a single runway, with no ILS in the Caribbean, I would be more cautious.

Yes that's why I work backwards. Start with destination weather. Decide if you see something which makes you believe that you could face a delay for landing. If so take extra fuel for the destination and then be more aware of anything enroute which could use up your contingency.

If weather at destination is fine and more than two runways available then I wouldn't take extra unless I foresee contingency fuel being completely up used up and then some.

[Chesty Morgan]

😈

The chances of ever needing to use discretionary fuel are actually quite slim. Just take minimum, fly at ECON and use the well prescribed procedures we have for low fuel situations should you need to. Which you probably won't.

[FullWings]

Originally Posted by Propellerhead

Also, how likely are you to actually divert? If the weather at destination is fine and there’s multiple runways I’d be less likely to take extra fuel for avoiding CBs en-route etc as I know I can likely dispense with the alternate (and probably get a direct routing after weather avoidance). If it’s a single runway, with no ILS in the Caribbean, I would be more cautious.

That’s the way I look at it. Also, the planned remainder is worth taking note of as that shows how much holding time you will have if you do commit to destination; sometimes that can be considerable if the alternate is a fair distance away for commercial/political reasons, so you can absorb significant delays without needing any extra fuel.

Looking back through my logbook, the most common cause of diversion has been medical followed by airspace closures. I can’t remember the last time I had to go somewhere else through lack of fuel at destination and I rarely take any extra.

[framer]

Looking back through my logbook, the most common cause of diversion has been medical followed by airspace closures. I can’t remember the last time I had to go somewhere else through lack of fuel at destination and I rarely take any extra.

Thats very interesting. Do you fly long haul? I ask because in the last 20 years of passenger flying I have never diverted due to medical or airspace but have diverted many times due to weather. I imagine the length of the flight impacts the likelihood of medical diversions and the part of the world influences the weather related diversions.

[framer]

The chances of ever needing to use discretionary fuel are actually quite slim.

Again really interesting to me because every couple of months I will burn my entire contingency allocation because of getting held down at FL 300 or FL 310 due traffic for two or three hours with unfavourable winds. The OP will know if that’s likely where they operate I guess.

[FullWings]

Originally Posted by framer

Thats very interesting. Do you fly long haul? I ask because in the last 20 years of passenger flying I have never diverted due to medical or airspace but have diverted many times due to weather. I imagine the length of the flight impacts the likelihood of medical diversions and the part of the world influences the weather related diversions.

Yes, LH. thinking more about it, the last time I actually diverted due holding capability was pre-COVID when DXB went into LVPs but the actual weather was good CAT I. The flow rate was so low that it was effectively shut and EATs were 2hrs+, so we went to MCT and waited for the delays to subside. To take enough fuel to cover that scenario would have put us over MTOW, so the option wasn’t there anyway.

When I feel the need for more fuel, I have no problems loading it but it’s a fairly rare event. When I did SH in Europe, divs were more common as many more sectors and more exposure to summer storms and winter snow/fog/gales. As an estimate, I would say I get a medical issue on LH that requires discussing it with doctors over the satphone on average every 10 sectors or so but it doesn’t often lead to a div. I had to declare a medical emergency last week but that was into destination.

I fly the 777 which is pretty robust when it comes to getting in, as long as you see something at minima. CAT III NDH excepted!