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INCREASE TAKEOFF GROSS WEIGHT USING CFM56-7B26/B2 THRUST RATING AND ALTERNATE CENTER OF GRAVITY

The technical flight demonstrations were performed using the CFM56-7B26 thrust rating, which currently is the highest thrust rating certified on the 737-700. A new thrust bump rating, CFM56-7B26/B2, has been offered to Druk Air as a new product. The CFM56-7B26/B2 thrust rating will produce at least 2% more thrust than the CFM56-7B26 rating at the Paro International Airport elevation. The additional thrust is worth approximately 2,100 lb (953 kg) of additional takeoff gross weight at Paro.

Takeoff gross weight can be increased further by using the optimal airplane takeoff center of gravity (CG) location instead of the conservative forward-limit location specified by the standard airplane flight manual (AFM). The increase is achieved by using the AFM-alternate CG takeoff performance option on the 737-700, which allows the operator to select one of two specified CG locations. Using CG locations aft of the forward limit decreases airplane drag and lowers stalling speeds, thereby increasing takeoff performance. For example, using a 23%MAC CG location instead of the forward-limit location for runway 15 increases 737-700 takeoff gross weight by 1,200 lb (544 kg).

Airport conditions and terrain constraints limited the demonstration takeoff gross weight to approximately 115,000 lb (52,163 kg). However, by optimizing the turn procedures and using the CFM56-7B26/B2 thrust rating and alternate CG performance, takeoff gross weights in excess of approximately 120,000 lb (54,431 kg) are achievable. This improvement would allow Druk Air to fly a 737-700 with a full passenger payload from Paro to all its current initial destinations.

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