What factors would necessitate reweighing an aircraft?

Reweighing an aircraft is essential when there are modifications or repairs that impact its weight or center of gravity. Such changes can include the installation or removal of equipment, alterations to the fuselage, or adjustments to the aircraft's structure that could shift weight distribution. These modifications may result in a significant impact on overall aircraft performance, including stability and control, which is why an accurate measurement of weight and balance is crucial.

Understanding the center of gravity is particularly important as it affects an aircraft's handling characteristics. If the center of gravity is not accurately assessed post-modification, it can lead to unsafe flight conditions. Therefore, following any modifications or repairs, the aircraft should be reweighed to ensure compliance with safety regulations and operational standards.

In contrast, mere changes in operation regulations, the change of a pilot, or seasonal weight changes do not typically require a full reweighing of the aircraft, as those factors do not inherently alter the physical characteristics of the aircraft itself.