The Boeing 737 MAX is starting its last wind tunnel test phase, with high-speed testing getting under way in the company’s transonic facility March 19 in Seattle.

According to Boeing Commercial Marketing VP Randy Tinseth, the low-speed portion of the wind tunnel work started in February at QinetiQ’s facility in Farnborough, U.K. Together with the high-speed work in the transonic tunnel, the ongoing evaluation in the U.K. “will update the model to incorporate the minor changes we’re making for the MAX and the larger engine nacelles. These initial test runs will give our engineers a baseline of the current airplane’s performance that they can compare with the MAX’s optimized design.”

Major aerodynamic changes for the MAX, compared with the current 737, are focused on the aft fuselage, wing, wing-to-engine integration area and the larger-diameter nacelle housing the 68.4-in. fan of the CFM Leap-1B engine. The revision of the aft fuselage includes a lower-drag Section 47/48 and tailcone, the elimination of an aft-body join and changes to the aft pressure relief port cavity to reduce drag.

The MAX also is thought to feature an improved trailing edge for high- and low-speed flight, possibly using mini-split flap technology from the joint Boeing-FAA Continuous Lower Energy Emissions and Noise (Cleen) program. Other changes also may include a rerigged outboard flap section, dropped aileron tabs and structural improvements. The leading edge Krueger flap also is changed to suit the revised nacelle lines and to provide adequate thrust reverser clearance.

The horizontal and vertical tail also is expected to incorporate drag-reduction streamlining as part of the MAX redesign and will incorporate a revised fin leading edge, as well as a new low-drag fairing at the root of the horizontal stabilizer, which would also be strengthened. The baseline 737NG model used in the current tests will slowly begin transformation into the MAX configuration as tests progress. Firm configuration is expected to be reached in 2013.