Ask the Captain: Why cargo loading is so important for safety

— -- Question: In the 1970s I worked for an airline which had a staff specially trained for making the trim sheet (loading measurements and instructions). They would then direct how passengers and cargo were to be loaded for balance. Is that practice followed today?

— submitted by reader psseshadri

Answer: With larger operators, much of the trim-sheet calculations are computerized. This information is then uplinked to the airplane prior to departure. The location of cargo forward or aft is predetermined based on the anticipated passenger load. With modern airline jets, the allowable center of gravity range permits zone loading. Normally this simplifies the boarding and loading process. Occasionally, seats have to be blocked to keep the center of gravity within the limits.

While the execution of the process you detail has changed, the theory remains the same. Pilots and load planners ensure that the airplane is properly loaded prior to departing the gate.

Q: Captain, I have a question regarding plane cargo loading. How does the pilot know how the ground crew are actually distributing weight in the hold below? It would seem to make a great deal of difference in CG (center of gravity) where heavy containers are loaded and how much they weigh. That combined with passenger distribution would affect the final CG for takeoff. Is this not a factor in your configuration for takeoff?

— APhelps

A: Loading the airplane properly is extremely important. Specially trained load planners take the known weight of cargo, luggage (using an approved average weight), passengers (using an approved average weight), and fuel to determine the exact weight and center of gravity. Usually using a customized computer program, the optimum location of items is determined. Cargo holds have "zones" which simplifies the process. An example would be a load planner telling the ground staff to place 35 bags in the forward bin zone 1. This ensures that the weight is where it should be.

If an airline is small and does not have load planners, the pilots oversee the loading.

Q: Captain, in a previous question you addressed the taxi, takeoff and landing weight restrictions on aircraft. Since airlines only weigh checked bags and not passengers or carry-on bags, how are they able to predict their taxi, takeoff and landing weights accurately enough to meet FAA requirements?

— jasmith1

A: The weight of the payload (cargo, bags and passengers), is added to the fuel (trip, reserve and contingency), and the basic operating weight of the airplane to determine the gross weight. The FAA allows a standard weight to be used for passengers and bags. These calculations ensure that the weight does not exceed the maximum allowed by performance or structural considerations. A predetermined amount if taxi fuel is subtracted from the ramp gross weight to calculate the takeoff weight. The fuel consumed is subtracted from the takeoff weight to determine the landing weight. If the fuel actually consumed is less than predicted, it is possible to approach the destination airport exceeding the maximum landing weight. This was the case in the previous question.

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John Cox is a retired airline captain with U.S. Airways and runs his own aviation safety consulting company, Safety Operating Systems.