B737NG - Fuel Quantity Gauges Accuracy Tolerances

[Centaurus]

The B737 Classics fuel quantity indicators are accurate to within 2.5% of the full scale reading. See Vol 2 under Fuel Chapter 12. This means if you are on very low fuel you need to allow for gauge accuracy when calculating time to empty tanks, or landing with say 30 minutes fixed reserve.

The B737NG Vol 2 does not state a figure for fuel quantity indicator accuracy. Does that mean the accuracy is perfect?

[Brenoch]

Mine says it's the same. +/- 2.5%

Regs

[Prop's ????]

Brenoch

Thanks for that informative post.

Now could you please tell me where in the 737NG manual does it state +/- 2.5%?

:confused: :confused: :confused:

[Flight Detent]

Hi Prop's,

Well, my B737-700 Vol II, mentions that +/- 2.5% of the fuel tank's maximum capacity -

Fuel - Controls and Indicators - 12.10.3 (29MAR04 page)

Good luck, Cheers, FD

[Prop's ????]

Flight Detent

Thank you.

I have update March 28, 2005. No sign of it in my manual.

[Bart O'Lynn]

Ah the old gauge accuracy thingy.
Does it mean its innacurate by 2.5 % at the max quantity thus reducing pro rata , or inaccurate by 2.5% at all quantity.i.e ther is a permenant error of 525 kgs. Methinks the former. I have Landed with final reserve after a very bad day. The claculated upllift using actual s.g. compared to actual was not out by 525kg Our daily gross error check has a tolerance of 5% using an average s.g. but usually around 100 kilos,at fuel quantities that would give a 2.5 error of 100 to 300 kilos based on the pro rata theory

2.5% of 1200kg (final reserve i.e in the ****) is 30kg

2.5% of 21000 (full tanks) is 525kg.

That would suggest that the problem may be range issues , not running out of fuel. if you are in a situation where 30 kilos will make a difference ie 30 secs on two engines at low level , then you are f@cked anyway. If at 1200 kilos you have an error of 525
i would have thought the aircraft would not have got a uk aoc for use with jar flightplanning minima.

Iam curious for the right answer but would suggest that you dont obsess yourselves with the pointless detail gentlemen look at the big picture. your ATPL's are over now so less theorising and more airmanship.

[A37575]

Bart. The tolerance is on the full scale reading and does not reduce with fuel usage. Thus if you were planning on landing with actual 1200 kgs remaining in the tanks, then to cover your backside you need to have an indicated fuel gauge reading of 1200 kgs plus 2.5% of the full tanks reading. Murphy's Law would surely ensure that just when you were on real minimum fuel, the fuel gauges tolerances would be at their max!

[john_tullamarine]

Subject to correction by any Boeing specialists in the sandpit .. it's like any mensuration consideration regardless of the means of display .. electronic, electrical, or mechanical. The system has design accuracies which provide for certification or similar assessments, and actual calibrations for the particular system in the particular bird. It follows that the actual cal will be not worse than the design limit accuracy.

There should be a cal card on the dash somewheres from the last cal and this is what you should be using in anger.

[Dehavillanddriver]

I have never seen a fuel gauge calibration card in any aeroplane, let alone a 737-300/400/700 or 800.

[Piltdown Man]

And if the gauge is accurate, how sure are you that the flow rate is accurate? And that the specific gravity of the fuel matches the calibration conditions of the fuel system?

[Sniff]

May I suggest that its 2.5% of the full tanks figure, but that relevant tanks are taken into account, i.e. for final reserve, the centre is irrelevant (considered dry?).

For the 737 classic the figure should be around...

2.5% of 9.2T = 230kg. Small.

You have to bear in mind that this is worst case....

[Ziggy]

I have my old revisions still on file......the statement of the accuracy has been removed from the books on the revision dated 27th September 2004.

It said: "• accuracy is ± 2.5% of the fuel tank’s maximum capacity."

That's 325kgs on my center tanks (max 13066kgs full), but they are usually empty when it really starts to matter.

On my main tanks that's 98kgs on each tank (3915kgs full).

Greeting Z.