# Introduction

The reason for weighing aircraft is not immediately obvious. It would be natural to assume that an aircraft's weight remains fairly constant throughout its life. However this is not the case and a number of factors affect the weight and weight distribution.

The weight of an aircraft continues to change daily. Accumulations of trapped moisture, dust, dirt, modifications, repair schemes all contribute to weight change. The amount of paint, for instance, required to coat a 747 is around 8-9 tonnes! Although a strict control may be applied to modification embodiment, the other factors involved rapidly accumulate. Therefore, to keep track of this weight growth, periodic weighing of the aircraft is necessary to advise the flight operations department or operator of the current weight and, more importantly, the position of the centre of gravity.

For light aircraft and helicopters, weight distribution is more critical. The balance of helicopters for instance, can be radically affected simply by the addition of equipment such as cameras. Military aircraft are usually weighed on a more frequent basis and their balance is affected by factors such as missile payload and distribution.

The frequency of weighing is determined by the regulatory authority of the country in which the aircraft is registered. As well as regular weight checks, typically every 2 or 3 years, weighing must usually be carried out to determine the centre of gravity after any critical modifications .This will be determined by the appropriate regulatory body and the operator in the interests of safety.

There are a number of recognised ways of weighing aircraft and strict procedures must be adopted to ensure accurate results are obtained. As a result, weighing is usually carried out by certified aircraft weighing companies. All weighing must be done on level surfaces in sheltered conditions-usually indoors. (Any slight upcurrents of air will render weight data invalid.)