## Appendix - A: Technical Talk

Why do we need to weigh an aircraft
An aircraft has a maximum authorised weight that it must not exceed. In order to calculate its safe payload the weight in its basic empty configuration must be determined periodically; on a commercial aircraft that’s normally a requirement every 4 years under EASA/JAR OPS.
The aircraft must be loaded so that its Centre of Gravity (CG) falls within the stated forward and aft limits in order to retain full control surface authority e.g. aileron movement in either direction.

Why do aircraft get heavier?
This may be caused by several factors:
1. | Moisture retention; typically when the aircraft descends and the cabin depressurises the moisture present in the atmosphere forms water droplets that are absorbed by the aircraft’s soft furnishings and soundproofing.
2. | Retention of dirt in the cabin, under the floor and in some of the aircraft compartments that may be exposed to the elements.
3. | Operators’ and manufacturers’ modifications and/or repairs to the airframe.
4. | Paint schemes. Remember that light coloured paint generally needs to be thicker than dark to cover other dark colours.Some aircraft are painted 4 or 5 times with different paint schemes.

Why re-weigh after a new paint scheme?
It is difficult and time consuming to determine accurately how much paint is used on the aircraft and in what proportions it was applied over the various affected surfaces; this may on occasion include the interior. The colour scheme and finish chosen could result in a localised or overall build up of several layers e.g. stripes or lacquer. The difference between a complete paint strip and a rub down can also have a significant effect.

Do aircraft get lighter?
An airframe may get lighter occasionally. For example, if it has had several layers of paint removed prior to re-painting or it is on a long maintenance programme in a warm dry hangar and the items that retain moisture have had a chance to dry out.