Section 335 of Part 23 defines several important speeds. The first is the design cruising speed, which, for airplanes with wing loadings of less than 20 pounds per square foot — that is, most small single-engine airplanes — must be 33 times the square root of the wing loading. For a wing loading of 16 psf, VC would be four times 33, or 132 kias. This speed is a purely formal requirement, used to provide a framework for structural and other decisions; many airplanes can't actually cruise at their "design cruising speed." But the design cruising speed provides a basis for another speed, VD, the design dive speed, which is generally 1.4 times VC; and VD is in turn the basis for VNE, the never-exceed speed, which is nine-tenths of VD. If an airplane can't achieve its design VD in flight, then the dive speed attained in flight test, VDF, replaces VD, and VNE is, again, nine-tenths of it.