masses

[tinmug]

Is there an easy way of figuring out the relationships between masses eg BEM ZFM TOM Traffic load etc. From the descriptions given in the training manuals and 697 it seems almost impossible.

Question: Given that: - Maximum structural take-off mass: 146 000 kg, - Maximum structural landing mass: 93 900 kg, - Maximum zero fuel mass: 86 300 kg, - Trip fuel: 27 000 kg, - Taxi fuel: 1 000 kg, - Contingency fuel: 1350 kg, - Alternate fuel: 2650 kg, - Final reserve fuel: 3000 kg, Determine the actual take-off mass

[RichardH]

You must understand these terms as in M & B you get direct questions on them, however you shall have your CAP69. in the exam with you.

In simple terms BEM is mass of aircraft on ground with no crew, fuel (except unuseable) or passengers (traffic load). Once you add the crew and flight catering/equipment you get the Dry Operating Mass (DOM).

Then you add the passengers (traffic load) which includes their baggage. The DOM + Traffic Load = ZFM which must not exceed MZFM. Finally add the fuel which will give you Actual Take Off Mass, which must not exceed MTOM. On a normal landing the trip fuel has gone and the aircraft must not exceed the MLM.

ZFM is the actual mass of aircraft without fuel. Do not confuse with MZFM a limit set by Mr Boeing/Airbus.

As said above this is a simple overview and there is a little more to it than this.

[Ptimat31]

Hi,

My guess is something like the Max Landing Mass + trip fuel, contingency and alternate since you'll have to land with Final reserve intact.
Don't get fooled by Taxi fuel since you'll burn it before TO.
You would have a TOM at 124.900 Kg.

[keith williams]

If you carry out enough practice questions you will get to know the definitions of the various masses and the relationships between them. But if that fails you can always use the key facts that are provided in the CAP697. Remember that you will a CAP 697 in the exams.

Question: Given that: -
Maximum structural take-off mass (MTOM): 146 000 kg,
Maximum structural landing mass (MLM): 93 900 kg,
Maximum zero fuel mass(MZFM): 86 300 kg,
Trip fuel: 27 000 kg,
Taxi fuel: 1 000 kg,
Contingency fuel: 1350 kg,
Alternate fuel: 2650 kg,
Final reserve fuel: 3000 kg,

Determine the actual take-off mass

The key to answering this type of question is to note that you must not exceed any of the limiting masses.

So for example your take-off mass must not be so great that having burned the trip fuel you will exceed the Maximum structural Landing Mass.

This means that you must carry out a calculation to find the maximum take-off mass that will not exceed each of the limits.

Max Take-off Mass based on MTOM

Firstly you must not exceed the MTOM so the maximum possible take-off mass is 146000 kg. But other limits may prevent you from using this mass.

Max Take-off Mass based on MLM.

Your landing mass will be equal to your take-off mass minus your trip fuel so to find the maximum take-off mass that will not exceed the MLM just add the trip fuel to the MLM.

This gives Take-off Mass = 93 900 kg,(MLM) + (27 000 kg) = 120900 kg.

So the maximum take-off that can be used without exceeding the MLM is 120900 kg.

Max Take-off Mass based on MZFM

If we load up the aircraft with traffic load until we reach the MZM, than add the take-off fuel we have the maximum take-off mass (with the planned take-off fuel) that will not exceed the MZFM.

Take-off fuel is all of the fuel that will be on board at the start of the take-off run. This does not include the taxi fuel.

So in this case take-off fuel = (Trip fuel: 27 000 kg) + (Contingency fuel: 1350 kg) + (Alternate fuel: 2650 kg) + (Final reserve fuel: 3000 kg) = 34000 kg)

Adding this to the MZFM gives a take-off mass of
(MZFM 86 300 kg) + ( take-off fuel 34000 kg) = 120300 kg.

We now have three maximum values for take-off mass.

146000 kg based on not exceeding the MTOM.
120900 kg based on not exceeding the MLM.
120300 kg based on not exceeding the MZFM.

We cannot exceed any of these limits so the maximum possible take-off mass for this flight is the lowest of the three, which is 120300 kg.