Fuel calculation rules of thumb

[Olendirk]

Guys,

how do you quickly check fuel consumption versus fuel on board and remaining time to fly? Like the 737, what fuel flow calculate on the approach, for example how many go arounds i can fly, how long can i stay, looking for a good help to calculate in my mind.

thanks, i appreciate you opinion and help!


OD

[KristianNorway]

In terms of number of go arounds I would be very interested in seeing a figure myself.

A figure taught to me is one of 44 - 40 kgs fuel consumption per minute in a holding situation above the airfield. That's what we use to asses approximate holding time following a go around on the 737-800.

[A37575]

Now this is going back many years for the 737-200 but I recall the basis of the 30 minutes fixed reserve (Australian CAA terminology for 30 minutes holding where it is expected the touch down will be with 30 minutes of fuel remaing) - was to cover a go-around at the flare plus a 1500 ft circuit on two engines to a five mile final (from outer marker) and with reverse thrust on landing - and the expectation the aircraft would have insufficient fuel remaining to taxi off the runway.

So although 30 minutes holding fuel (nominally 1200 kgs I think) sounds fine, in reality, with the enormous fuel flow rate under the conditions described above, you could be in real strife and quickly using up your 1200 kgs. And don't forget to allow for fuel gauge tolerances worst case in both tanks of three percent of the full tanks figure - around 135 kgs per wing tank - so you could be as low as 1200 kgs minus 270 kgs (if your luck is down) equals 930 kgs total fuel on board on the go-around...scary stuff

[mcdhu]

I'm not sure if this is what you are after, but I find it helpful in holding situations.

Knock the last digit off your current FF and the result is 6 mins worth.
Eg A319 - 2000kgs (total)/hr: 200kgs is 6 mins worth and then work in packets of 6 mins and 200kgs.

Cheers
mcdhu

[mathy]

Rules of thumb 700-800 models.

If you have 600kg of fuel remaining then you have no option but to land immediately! That amount of fuel is sufficient for good conditions and visually rejoining at 4DME.

A better situation is 1200kg for go around plus one hour’s fuel. At 1200kg/hr/eng that would be landing with 3600kg remaining.

Take a B737 with operating weight 37800kg and weight limitations of ZFW 54600kg; LDG 57400kg.

Landing at 57400kg with 3600kg fuel gives ZFW of 53800kg which is within limits.

Maximum payload is derived from ZFW-37800 = 16000kg.

Estimate 300kg in descent.

From 1200kg/hr/eng a cruise of 20mins burns 800kg.

Top-of-climb weight = ZFW+800+300+3600 = 58500kg.

Estimate 2.5% of Gross Weight is consumed in climb.

Climb fuel is therefore 1500kg.

Take-off weight is 58500+1500 = 60000kg.

Max distance thus configured say 100nm climb to FL330-340, 140nm cruise, 100nm descent from FL330-340. EGLL-EGPH is about 325nm by way of example.

If 148 pax at 76kg apiece that is 11400kg leaving a maximum of 4600kg for bags and cargo. Suppose the company limits you to 22kg per person hand and hold baggage then that is typically 14700kg for people and 1300kg cargo.

Sorry if that is all a bit rushed and very broad brush but that is what rules of thumb are for and I have tried to flesh out the fuel figures.

[Tmbstory]

Reminds me of the time (a long time ago) when I was lucky enough to be given a ride in a Mirage Jet Fighter simulator.

Two things stick in my mind, the rate 1, 3degree a second rule, I was asked to make a turn so I thought I would use 45 degrees of bank but it still went straight ahead ( our speed was high) and the second thing was the low fuel "clanger" every few seconds. It got your attention.

Enjoyed it immensely, even the whiff of smoke as you touch down.

Tmb