Hi, I am just having some trouble getting my head around the concept of the ZFW and when to check it and when not?

In particular Exercises 5.5 and 5.10 versus Exercise 5.1. My understanding is that it is the limit weight of an aircraft before any fuel is loaded.

So my first question is what exactly are we checking for when we take the ZFW limit for the Echo of 2630 kg and add it to the total fuel at takeoff? Obviously if the ZFW is 2630 kg we haven't breached this limit?
Also, if we are taking minimum fuel, couldnt we just add additional fuel such that the ZFW plus that additional fuel makes it the greatest out of all the 3 scenarios we check for?

Secondly, I guess I am even more confused as to the reason we don't check the ZFW in exercise 5.5 and 5.10.

Sorry if the questions are confusing and vague. The first two scenarios make logical sense checking for performance limited takeoff weight and and of course the performance limit landing weight plus the fuel burnt, however I can't quite understand this ZFW condition.

Thanks very much for your time in reading.

Ange

The reason we are checking the ZFW in Exercise 5.1 is because it may be a possible limit on the take-off weight. We need to know the smallest of the three possible take-off weight limits to ensure that we will not be over weight for landing. Obviously, if a ZFW of 2630kg plus all the fuel we are carrying makes us too heavy to legally land, we will have to reduce either the ZFW or the fuel itself to remedy the situation.

In exercise 5.5 and 5.10, there is no point in checking the ZFW because we already know the ZFW since all of the weight items except for the fuel are given in the question. It is up to the examiner in these situations to ensure that the load he has given you does not exceed the ZFW limit.

Thanks for the help Bob managed to get my head around the subject and scored 94% last Tuesday, onto the final hurdle in CLWA!

In the Performance manual, Ex 5.1, I get a bit confused about the ZFW limit. If the Echo is loaded to max ZFW of 2630 kg and then the fuel required was, say, only 150 kg ---- this would be less than a Take Off limit of 2800. So why would I chose the lower value? Why wouldn't I load extra fuel up to the limit of 2800 kg? I understand why I would choose the lower of the values from the Take Off limit or the Landing Limit + burn-off but not sure when I would use the ZFW + all fuel value.
Really appreciate your thoughts!

Thanks

Congratulations Toddy you are in fact a bit ahead of the argument. It is true that if ZFW was the limit, you could always load the aircraft to the next limit up providing the extra weight is fuel only. However, if the question specifies a particular amount of fuel, then the ZFW must be considered as a possible limit on the take-off weight. If a question asks for the maximum fuel possible and gives a particular amount of cargo and passengers, then the ZFW limit can be ignored because the ZFW would then be a known quantity.

Bob

Many thanks for such a prompt reply Bob!