Aviation Partners Boeing (APB) has had to delay the planned supplemental type certification (STC) of a winglet-equipped Boeing 737-300 retrofit due to low-speed handling issues discovered during the final phases of flight tests in Arizona.

The company, which originally hoped to obtain the 737 STC as early as mid-January, plans to conduct a short flight-test programme to evaluate the effect of outboard vortex generators on the handling deficiencies which occurred at high gross-weight take-offs around V2 (engine out safe climb-out speed). The aerodynamic modification will be made to the wingtips where flow separation was seen to occur around the transition to the winglet.

"We don't anticipate any impact on the cruise performance," says Aviation Partners vice-president of programmes Jay Inman, who says overall results of the tests are "around predictions". When tests began in late 2002, the company predicted a 6.5% drag reduction from the 2.1m (7ft)-tall composite blended winglets. Although less than 10h of flight tests were required to complete certification, Inman says further work is required.

Source: Flight International