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lowew79

fuel planning J41

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Hey guys I've read the tutorial (1200 lbs 1st hour, 1000 lbs. per hour after that, then 800 lbs reserve).

 

This has worked fine for me until today.  I ran into some weather at altitude today.  It increased my flight time from 1.5 (normally for this route) hours to 2.0 hours.  I had to eat into my reserves, and I got in trouble (FSPax lol) for not landing with enough fuel (29 mins of reserve instead of 45mins).

 

At any rate my question is, when deciding how much fuel to put into the aircraft how does one account for weather like that?  Is there a formula like x times headwind/ flight time or something?  Or do pilots and airlines just add extra from the hip?  Or is 800 lbs not enough reserves?

 

Thanks for the help.

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FSPax is not allowed on my machine for reasons like this.  You didn't mention allowance for an alternate.  You added 45 min reserve and due to weather had to use 16 min of it... that's what the reserve is for; well, that any other unknown that happens.  In a small plane like the JS41 you'll find the approximate rules work very well. Add fuel for taxi, flight time (including winds), a trip to an alternate and then the extra 45 min.  That will give you plenty of safe reserves and if you do run into contingencies you will not get in trouble with the chief pilot.

 

Instead of FSPax giving you a grade, set your own expected results and see how you do. I do that every flight.

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Hi Inigo,

 

First of all good question that covers some of the basics of IFR flight planning. 

 

*IF* you're operating under FAA rules you will need the following fuel requirements. These are a somewhat different if you operate under EASA, or other state rules. 

 

So lets take a look at the 14 CFR 91.167 which states that at take-off, you must have enough fuel to complete the flight to the first airport of intended landing; fly from that to an alternate and after that continue for an additional 45min at normal cruise speed. 

 

So reaching our destination we must have fuel in our tanks to proceed to our destination, and after that fly for 45 minutes. So what Dan wrote here is not entirely true: "You added 45 min reserve and due to weather had to use 16 min of it... that's what the reserve is for; well, that any other unknown that happens." - The unknown could be that you had to hold over your alternate, or over your destination if you hadn't selected a alternate, but in this case there are weather requirements, BUT you must never use you reserves doing the leg from departure to destination. 

 

If there is adverse weather enroute I suggest you add even more fuel. Try add 15-30 min of extra flight time.

 

So to keep it simple: take your total flight distance divide by average ground speed. This gives you flight time in hours. From this you can work out your fuel requirements. Many third party weather programs can give you an average ground speed if you put in cruise altitude and true airspeed. 

 

If you want to go advanced you can always resort to looking into the performance tables in the FCOM.

 

Hope this helps.

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Much like the other posters, I can't say I care for FS Passengers either, some of the rules it enforces seem very arbitrary. One such example is landing lights on below FL100, in the J41 you should turn them off whenever the gear is up (they're attached to the landing gear legs) and use the conspicuity lights in their place.

 

As regards fuel planning, this is the advice from Intercity Airways, that has served me well:

 

We recommend you use the loadsheet included with the PMDG Jetstream 41: set the 'Flight Duration' in decimal hours on the left and adjust the 'Fuel (-taxi)' so that the 'Landing Fuel' reads 1200 lbs. You can then load the 'Fuel (-taxi)' amount using the Fuel and Payload function from the FSX menu.

The above (trip fuel plus 1400 lbs) should cover most circumstances, but remember that you must land with at least 450 lbs remaining or declare an emergency; so if you have nominated a distant alternate or believe you will need to hold for a long time, you should add more fuel. A fuel planner is also available at FuelPlanner.com.

The 450 lbs is what's known as "final reserve", which if memory serves is 30 minutes holding above the destination airfield.

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I've taken the easy route in fuel planning, and use the website; fuelplanner.com. Good or bad weather, it hasn't failed me yet, even if I had to go to an alternate airport. I use it as a guide, and tweak it if necessary, but rarely do I find myself doing so.

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So what Dan wrote here is not entirely true:

 

True but I did quality myself stating that alternates were not mentioned in the sentence before you quoted.  It's legal not to include alternates if the weather at destination is forecast to be above certain requirements (if Part 135, which normally applies to commuter/taxi service, ceilings >1500 above highest minima  ....etc).  I tried to keep it simple and on topic but it is good you introduced the topic that alternates may be required and the requirement depends on the regulations that apply to your operation.  I'm just lazy and try to answer short.

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Id flown that route before and it is a 1.5 hour flight, in good weather (okay, in GREAT weather, as in FSX clear all weather theme).  With the weather my speed was slower and my fuel burn was higher, so it took 2 hours.  I just didn't know that it would be that much longer.

 

The tutorial suggests having 800 lbs reserve, but is that only for that, relatively short, tutorial flight?  Do airlines put more reserves, the longer the flight?  (SO like 800 lbs for a 1 hour flight, but 1500 pounds extra for a 3 hour flight?).

 

The rules in the tutorial obviously don't account for weather lol, but they also don't seem to account for payload. Isn't that a factor too?  (Or is the difference only appreciable on large aircraft)

 

From the responses it seems like there is not a set formula for weather or anything, just a company policy of you will need XXX lbs reserve, not counting alternate as first officer said above.

 

In real life do pilots have to work these numbers out themselves or does whoever does flight planning for them tell them how much fuel to load?

 

I will definitely check out fuelplanner.com.  And thank you all for the advice!  

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Inigo, I think the step you're actually missing is checking the predicted winds aloft for your routing. If you check that, then you'll know your predicted flight time to the destination airport and can use the lbs per hour estimates for calculating the flight time fuel. Then you need to add fuel to your alternate, and then the required reserve to allow you to hold for 45 mins. 

 

The easy way (I find it the easy way anyway) is to use SimBrief.com. This will plan your flight, check the weather, suggest an alternate if you don't input one, and work out how much fuel you'll need. It gives you the same kind of pre-flight briefing you'd get from a dispatcher, and so far it has never failed me ... even in adverse weather.

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I can only speak for our own operations on the JS31/32. We get our fuel figures from planning software called PPS. We refresh this shortly before the flight to include the most recent winds. It will give us a minimum required fuel load that includes all the legal requirements. On top of that it's common sense.

 

If there are strong winds, you take more trip fuel. Reserve can stay the same. Payload only plays a role in such a manner that if you can't take enough fuel to be legal, you need to take less payload ;). And yeah, you are missing the step where you check winds. Next time if you are experiencing heavy headwinds, try flying lower. Windspeeds generally increase with altitude (again, generally). So there's a good chance that flying lower will give you a higher ground speed with the same fuel burn.

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Inigo, I think the step you're actually missing is checking the predicted winds aloft for your routing. If you check that, then you'll know your predicted flight time to the destination airport and can use the lbs per hour estimates for calculating the flight time fuel. Then you need to add fuel to your alternate, and then the required reserve to allow you to hold for 45 mins.

 

The easy way (I find it the easy way anyway) is to use SimBrief.com. This will plan your flight, check the weather, suggest an alternate if you don't input one, and work out how much fuel you'll need. It gives you the same kind of pre-flight briefing you'd get from a dispatcher, and so far it has never failed me ... even in adverse weather.

Excellent data source.

I've just tried a dry run and it looks promising. As well as fuel predictions it also does flight plans.

Thanks for the tip.

Note to self, change simbrief's units to pounds or prepare to get wet.

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