Definition
An enclosed area on a graph in the aircraft's weight and balance documentation, plotted with total aircraft weight on one axis and total moment (weight multiplied by arm) on the other. If the point where the loaded aircraft's weight and total moment intersect falls inside the envelope, the aircraft is loaded within approved center of gravity limits for safe flight.
Plain English
A shape printed on a chart that shows the safe combinations of how heavy the aircraft is and how its load is distributed. If you plot your aircraft's numbers and the dot lands inside the shape, the load is safe. If it lands outside, it isn't.
Context Anchor
Seen in the weight-and-balance section of an aircraft flight manual, especially before a flight when checking fuel, passengers, baggage, and cargo.
Derivation
Envelope here comes from the mathematical sense of a boundary that encloses all acceptable values, not the paper kind. Moment is the engineering term for a turning effect, calculated as weight times distance from a reference point.
Why Pilots Care
Remaining inside the envelope keeps the aircraft stable and controllable; going outside can cause loss of control.
Analogy
Think of it like plotting a dot on a map with a fenced safe area. If the dot is inside the fence, the loading is acceptable. If it is outside, something about the load must change before flight.
Intuition Check
Envelope does not mean a paper envelope here; it means the boundary of allowed values on a chart. Moment does not mean a short period of time here; it means the turning effect caused by weight located away from a reference point.
Example Sentence 1
After calculating the loaded weight and total moment, the pilot plotted the values on the chart and confirmed they fell inside the center of gravity moment envelope.
Example Sentence 2
The aft limit of the center of gravity moment envelope was exceeded, making pitch control sensitive.