Is it correct to say the W&B envelope as published in the AFM (and as calculated by electronic means) is valid for takeoff and landing, but will actually be a larger envelope (but not published) in cruise due to the increase in airspeed, and hence an increase in lift (force, up or down) achievable by the control surfaces....? Asked in relation to a passenger moving from a middle seat to the rear of the aircraft if the CoG is close to the aft limit of the envelope.

Excellent question showing a fine degree of thought. Unfortunately, I have to disagree with your post.

Is it correct to say the W&B envelope as published in the AFM (and as calculated by electronic means) is valid for takeoff and landing, but will actually be a larger envelope (but not published) in cruise

Absolutely not the case (unless the POH limit explicitly provides for such a consideration). The Type Certificate envelope is a hard limit and the aircraft is required to be operated within that limit at all times during a flight.

The operator is responsible to ensure that this requirement is met and this, generally, is done by means of the loading system scheduled for the aircraft.

These days, where the usual light aircraft POH follows the GAMA format, the Section 6 loading system is more or less similar in style from one aircraft to another but this is not necessarily the case. In addition, the operator may choose to have an appropriate WCA holder design, approve and issue a quite different system.

Now, as you have identified, we have an obvious problem with folks in larger aircraft where people can move from here to there inside the aircraft with an associated change in CG. So how is this addressed ?

The usual approach is to conduct an envelope curtailment exercise as part of the loading system design development. In effect, what the WCO does is run a bunch of calculations to determine the extent to which such CG excursions may compromise loading and then restricts the envelope, as drawn in the loading system, so that the problem is constrained.

This results in the loading system's presenting the envelope as a reduced, or constrained, set of data so that, by keeping within the revised envelope, any reasonably likely error/excursion is not going to take the actual aircraft CG out of the TC/POH specified envelope.

Asked in relation to a passenger moving from a middle seat to the rear of the aircraft if the CoG is close to the aft limit of the envelope.

Which is the main sort of problem. Generally, in the design, we allow for a reasonable movement of folks around the aircraft, eg pilot to rear WC, rearmost passenger to the front WC, cabin attendant movement, etc.

Thanks for the reply - it's hard to get in depth info re W&B without doing a course.

Am I interpreting the below correctly...

This results in the loading system's presenting the envelope as a reduced, or constrained, set of data so that, by keeping within the revised envelope, any reasonably likely error/excursion is not going to take the actual aircraft CG out of the TC/POH specified envelope.

.... meaning that if the W&B calculation pre flight is close to the aft limit, but within the CoG envelope prior to departure for the TOW and LDW plots, that any movement of (say) one pax from the center to the back of the aircraft (in our case about 4m) is accommodated for and will not cause a 'handling issue', based on the envelope being 'constrained'...?

Thanks for the reply - it's hard to get in depth info re W&B without doing a course.

Given that I am in the top handful of WCOs in Australia, feel free to run your questions here and I'll do my best to answer them. As most of the courses around address CAO 100.28/CAO 100.7 and those Orders don't address your concerns, the typical course isn't going to give you any satisfaction.

.... meaning that if the W&B calculation pre flight is close to the aft limit, but within the CoG envelope prior to departure for the TOW and LDW plots, that any movement of (say) one pax from the center to the back of the aircraft (in our case about 4m) is accommodated for and will not cause a 'handling issue', based on the envelope being 'constrained'...?

Ah, the devil is in the detail, as they say.

Unfortunately, in Australia, the WCA training emphasis is on the maintainer stuff ie weighing and LDS issue, rather that the engineering side of things such as the development of more complex loading systems. As a consequence, we have many WCOs whose detailed knowledge of the engineering side of things may be a bit light on. Over the years I have seen numerous examples of poor loading systems due to the lack of knowledge which comes back to (in my view) an inadequacy in the requirements of CAO 100.28. Indeed, I would venture that, were you to line up a few hundred WCOs at random, very few, if any, would have any idea what is involved in a curtailment exercise.

Reading between the lines, you aren't concerned about a puddle jumper, here, rather something in the order of a corporate jet or, perhaps, a third level airline style of aircraft. Without seeing the detail, I can't do much more than generalise. If you want to take it offline for some more detailed discussion, you might like to contact me directly at This email address is being protected from spambots. You need JavaScript enabled to view it..

Your question is fine IF the loading system design has been subject to a detailed and reasonable curtailment analysis and the final loading system sensibly addresses these sorts of curtailment considerations. Otherwise, all bets are off.