The official word:

"The addition of Aviation Partners Blended Winglets to the 737 Next Generation has demonstrated drag reduction in the 5 to 7% range that measurably increases range and fuel efficiency . In addition, the Blended Winglets allow the 737-NG to take off from higher, hotter airports with increased payload. "

"By increasing Payload Range and Overall Performance, Blended Winglets add flexibility to fleet operations and route selection. Air Berlin notes, "Previously, we'd step-climb from 35,000 to 41,000 feet. With Blended Winglets, we can now climb direct to 41,000 feet where traffic congestion is much less and we can take advantage of direct routings and shortcuts which we could not otherwise consider."

"Winglets lower drag and improve aerodynamic efficiency, thus reducing fuel burn. Depending on the missions you fly, blended winglets can improve cruise fuel mileage up to 6 percent, especially important during a time of rising fuel prices. "Were saving a minimum of 4% on fuel and up to 6% on our longer flights," says Air Berlin Technical Director Sigfried Olivo."

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