The difference between the net and gross flight paths/performance is as follows: The gross performance is the average performance that a fleet of aircraft should achieve if maintained satisfactorily and flown in accordance with the techniques established during flight certification and subsequently described in the aircraft performance manual. Gross performance therefore defines a level of performance that any aircraft of the same type has a 50 percent chance of exceeding at any time.

The net performance is the gross performance diminished to allow for various contingencies that cannot be accounted for operationally, e.g., variations in piloting technique, temporarily below-average performance, etc. It is improbable that the net performancel flight path will not be achieved in operation, provided the aircraft is flown in accordance with the recommended techniques, i.e., power, attitude, and speed.

Normally, performance graphs show net performance; however, some performance charts, especially for three-engined aircraft, assume gross is equal to net performance. This means that no margin exists between what the graph suggests the aircraft will achieve and what the aircraft will achieve.

• The net gradient refers to the minimum attainable vertical profile following failure of the critical power unit on take-off (assuming the AFM is adhered to).