Small M and B Q

[Cron]

I would be most grateful for your suggestions as to the correct answer for the below. I guess the only candidates are a) or d) but being somewhat dim I can't differentiate.

Thank you in advance for your help.


The zero fuel mass of an aeroplane is always:
a) The maximum take-off mass minus the take-off fuel mass.
b) The take-off mass minus the fuselage fuel mass.
c) The take-off mass minus the wing fuel mass.
d) The take-off mass minus the take-off fuel mass.

[littco]

Zero fuel mass is

Basic empty Mass + variable Load + Traffic Load.

In other words

Weight of the plane
Crew, Crew Baggage and special Equipment
Passengers
Freight

In this case I would have to say the answer was D . If the answer looked for the Maxiumum Zero Fuel Mass then A would be correct but that would mean that maximum weight that could be allow with out any fuel loaded where as this question is just asking for the ZFM Ie the weight of the plane without any fuel, which has to be the total mass of the plane at takeoff minus the take off fuel mass. Hope this helps

[High Wing Drifter]

D can't be the answer as takeoff fuel is but a fraction of the total fuel and is the same as A anyway. MZFM is related to the strength of the wing root for many aircraft. Therefore the closest is C.

[littco]

Sorry High wing drifter But I disagree.

Answer D says TAKE OFF FUEL MASS.. Which is the mass of the fuel at takeoff , not the fuel required to take off.


Just to edit, I Think the question is very poorly worded, as we where taught that in some cases the fuel in the fueselage could be included, so I guess C could be correct as well In which case the HWD I appologise..

Can we appeal it!!!

[jonjon]

Hi,

I would go for C too

JJ

[EGBKFLYER]

I think D too.

HWD - wording is v confusing. I think 'take-off fuel mass' means the fuel in the aircraft at take-off, not the fuel used for take-off.

ZFM is just the aircraft mass without fuel! Only one that fits the bill is D.

[jonjon]

Is this a question from the actual feedback question bank?

I haven't come accross it yet...

[EGBKFLYER]

I would say not - doesn't sound like the normal wording, though you never know...

[High Wing Drifter]

Ans A is the same as ans D. Also, confusingly, MZFM does sometimes include fuel in centre tanks.

[EGBKFLYER]

Agree, though A is more likely to be MZFM, which is obviously still a ZFM. Two right answers - maybe it is a JAA question after all!

[High Wing Drifter]

No just one. Ans C I tell you

[SpiralStability]

Hi Guys

Just thought I'd have a glance through this forum to pass some time, and noticed your thread. I'm flying the 737, so may have a useful opinion!

I believe littco is totally correct

MAXIMUM ZERO FUEL MASS is a structural limitation
ZERO FUEL MASS is a day to day mass ie actual weight excluding useable fuel (I think that's where the confusion re the centre tanks comes in - ZFM definitely excludes ALL fuel, but I seem to remember it does include any unuseable fuel, which is a very small amount!)

TAKE OFF FUEL MASS is the mass of the fuel at take off, so is therefore ramp fuel less taxi fuel (only 2-300kg normally)

So therefore D is definitely the right one. A is totally incorrect as it uses the structural limitation of MZFM and not the operational ZFM about which the question is asking.

Think I may have made it more confusing, but I can see it in my own mind...hope it helps!

[High Wing Drifter]

Just to prove I'm not "confused", althought I may still be incorrectly identifying the most suitable answer!

JAR-OPS1 1.607:

Maximum Zero Fuel Mass. The maximum permissible mass of an aeroplane with no usable fuel. The mass of the fuel contained in particular tanks must be included in the zero fuel mass when it is explicitly mentioned in the Aeroplane Flight Manual limitations.

Also, out of interest, check out the wording on the Boeing 737 airworthiness directive here (search for "zero").

I suppose another problem I have with Ans D is it doesn't take account of taxi fuel.

The word "always" at the end of the question effectively means non of the answers are correct unless you apply the logic that you will never exceed the MZFW if you include centre tank fuel in the calculation.

[Cron]

Thanks for the discussion - as per usual with PPrune the input always brings more useful information than the just the Question answer.

I've located the Question source; it is Question number 6 in the JAA Sample exam questions 'Flight Performance and Planning (1) Mass and Balance' and checked the wording which is a faithful reproduction.

[EGBKFLYER]

Wonder what they thought the answer was then?

[High Wing Drifter]

Where's Keith Williams, Send Clowns or Alex when you need them

[Chesty Morgan]

Originally Posted by Cron

The zero fuel mass of an aeroplane is always:
a) The maximum take-off mass minus the take-off fuel mass.
b) The take-off mass minus the fuselage fuel mass.
c) The take-off mass minus the wing fuel mass.
d) The take-off mass minus the take-off fuel mass.

The most correct answer is D.

You can write off B and C straight away as, collectively, they imply that you have both wing AND fuselage fuel. And therefore, they imply that you have one or the other. Which is incorrect.

As the question doesn't ask "What is the Maximum Zero Fuel mass of an aeroplane" you can ignore A.

HWD

The mass of the fuel contained in particular tanks must be included in the zero fuel mass when it is explicitly mentioned in the Aeroplane Flight Manual limitations.

I think this is refering to the "Unusable fuel" in the tanks which is usually stated in the AFM. As SpiralS says.

There is no need to mention taxi fuel. As ZFM is the actual mass of the aeroplane minus the total usuable fuel onboard at any time.

Simply put, the more fuel you use, the less you have to subtract from the total mass. You will always get the same answer.

[EGBKFLYER]

Maybe we should turn this thread into a poll - like 'ask the audience' on WWTBAM...