A system to accurately detect skewing of high lift devices. In one embodiment, the invention provides a system to sense the position of the inboard and outboard ends of each flap. This system preferably detects development of a skewed condition and shuts down the flap drive system before unacceptable aerodynamic or structural conditions occur. In one embodiment, a commercial aircraft has two trailing edge flaps on each wing. Each of the four flaps on the airplane is driven by two ballscrews, one near the outboard end and one near the inboard end of each flap. All ballscrews on all flaps are driven synchronously by a mechanical drive system. By comparing the revolutions of the ballscrews, the differential ballscrew travel can be determined. This differential is a direct measure of flap skew.