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Calculating the amount of packets echo question

• Posts: 14

aalim21 created the topic: Calculating the amount of packets echo question

Good evening everyone how are we?

Just having some confusion in regards to this question which is found in Bob Tait's practice exam (CFPA Exam #4). As I was running through the calculations or flow chart are we meant to divide our subtracted weight (23.44KG) by our quantity of packets (8pck) or the weight of packets (10kg)? Thanks
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• John.Heddles
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• ATPL/consulting aero engineer
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John.Heddles replied the topic: Calculating the amount of packets echo question

are we meant to divide our subtracted weight (23.44KG) by our quantity of packets (8pck) or the weight of packets (10kg)?

Would dividing a weight to get rid of by an unrelated number produce a result of any value ? No. You are after the number of packets to exceed the required weight. So you have to divide the weight by the packet weight and round up to the whole packet weight.

Mind you, subject to volumetric etc. considerations, it might have made a little more sense to rearrange the cargo ?

Engineering specialist in aircraft performance and weight control.

• Posts: 14

aalim21 replied the topic: Calculating the amount of packets echo question

Hi John thank you for your reply. The reason why I have asked this question is when running the calculations longhand by using the formula or flow chart the answer results to 2.34 packets. As we got to remove 23.44 KG from the rear compartment to stay in balance throughout flight I divided the weight removed by the weight of the packets (23.44KG/10KG) which should result in 2.34 packets. When rounded becomes 2 packets. What I'm trying to get around is the fact the answer is 3 packets as shown in the attachment.

• John.Heddles
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• ATPL/consulting aero engineer
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John.Heddles replied the topic: Calculating the amount of packets echo question

..but you need to be conservative to get into the envelope. If you only have fixed weight packets, then you are going to have to round up so that you don't end up a tiny bit still outside the envelope if you round down. We are not looking at the mathematical conventions, rather we need to be inside the envelope at all stages during flight.

Engineering specialist in aircraft performance and weight control.
The following user(s) said Thank You: aalim21

• Posts: 14

aalim21 replied the topic: Calculating the amount of packets echo question

Thanks!! That makes much more sense, and is a more logical approach to keep the aircraft balanced at all stages of flight. It's much more safer to round up simultaneously looking at the envelope and doing a CoG check . We'll keep that in mind

• Posts: 1191

Stuart Tait replied the topic: Calculating the amount of packets echo question

Also that question was missing a graphic in the answer, might of helped to make sense.

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The following user(s) said Thank You: aalim21