Performance of Military Cargo Aircraft Using Required Navigation Performance Departures

Maximum takeoff weight for cargo aircraft is affected by many factors including the aircraft's ability to safely climb out to altitude. When there are obstacles in the departure path, the total weight of the aircraft may have to be reduced to ensure the aircraft will achieve the appropriate climb rate to clear the obstacles. During times of limited visibility, aircrews traditionally rely on predetermined departure paths limited by the aircraft navigation capability and the ground based navigation aids. A Required Navigation Performance (RNP) departure with accuracy down to 0.3 mile could allow the aircraft to safely navigate around obstacles with better precision, allowing a greater takeoff weight. This study compared current instrument departure procedures with predicted RNP 0.3 departures by computing the maximum allowable weight limit for the C-5 aircraft under a range of operating temperatures at three separate locations. The results showed that an increased precision of the RNP 0.3 departures had an operational advantage by allowing an increased cargo, passenger, or fuel load. The amount of weight increase was dependent upon a variety of factors, to include airframe type and location. To receive certification from the FAA to fly RNP 0.3 procedures, specific requirements such as training and equipment are necessary. Current configurations of the C-5 aircraft do not support RNP 0.3 procedures.