1470. Philosophy of Automated Balance Calculations

Paper

Abstract

It is the intent of this paper to outline the philosophy, or methodology, developed and used by United Airlines to evaluate and control the balance aspects of a trip departure using a real time computer program.
As large computers become available and have been used for all kinds of data storage and processing in real time in the airline industry, the idea of using them for weight and balance control has been considered. Any numbers of airlines have already implemented programs to perform this function to their satisfaction. United is somewhat of a late comer largely because it proved difficult for us to justify the cost of automating, at last, its time has come.
We have had limited discussions with other operators as to their automated systems. Much of the feedback has been second or third hand and so leaves open questions. In total, we have been unsuccessful in getting concrete information on how other operations perform their task either because our contact did not know or would not say. There is a general impression that the equivalent of the old tabular loading chart, max-min in a controlling cargo pit, is calculated and then stored in the computer as a look-up table. Computer people seem to view method as the easiest and least expensive approach.
At the inception of the specification writing for our automated balance control program, we knew how we wanted to do the job so the effort to learn about the programs was perhaps somewhat academic and largely a reflection of the natural desire to have one’s concepts confirmed or vindicated.
In summary our philosophy is to have the computer do a complete calculation or analysis for each change in loading in order to exploit the loading flexibility as much as possible. This means that we consider the exact passenger count, the exact cargo load, and the exact fuel load – takeoff through burnout. These combinations are measured against the CG limits and related balance variations for the three operating modes of takeoff, enroute and landing to evaluate the critical or controlling case for the flight.
The methodology for performing this task is our so called ‘Protective Level Concept’ of balance control, a statistically based method that measures the variability of all load items in order to arrive at a level of CG limit protection directly related to the passenger/cargo/fuel combination that exists on this trip today.
As an example, the curve representing the familiar passenger seating, window-aisle concept envelop, at a defined one sigma level, is reduced to a polynomial and the coefficients stored in the data base. In this form, the computer program can process it for any passenger count in that class or cabin zone.
All of the statistical data is combined statistically, square root of the sum of the squares, set at the number of standard deviation defined as adequate, and added to any non-statistical variables, such as landing gear retraction, to arrive at the CG limit protective value. We can then calculate the cargo distribution to satisfy this restricted limit condition. At the same time, the takeoff CG position, %MAC, based on mean weight/moment condition can be calculated.
This obviously is the point, that as a number cruncher the computer can repetitively process a large amount of detailed data very rapidly and thus exploit the airplane.