A United Airlines Boeing 727-200 equipped with the first autonomous landing guidance (ALG) system was expected to be flown from Mojave, California, as Flight International went to press, marking the start of a three-month pilot evaluation programme.

The aircraft has been fitted with elements of the enhanced-vision system as part of efforts to achieve Category III landing capability on Cat I runways. The trial is funded by the US Defense Advanced Research Projects Agency (DARPA), and involves FLIR Systems, Interstate Electronics, Lear Astronics, Northwest Airlines, Norton Plastics, Sextant Avionique and United. NASA Ames and several US Air Force laboratories are also involved.

"The main purpose of the new series of 727 flight trials is evaluation. We want pilots to tell us how we can make it better and we need as much of that sort of information as we can get," says team leader Lear Astronics, which supplies the 94GHz millimetre-wave (MMW) imaging radar. The radar sees through most weather, apart from heavy rain, and provides a real-time image of the approach, which is overlaid on the standard guidance imagery provided by the Sextant head-up-display.

Two FLIR Systems forward looking infra-red sensors are mounted below the radome and provide a fused image in two bands, 1-5 microns and 8-12 microns. Where the radar's usefulness in ground manoeuvres is limited by airport clutter, IR provides the high-resolution image. The radome itself is modified to be transparent to the standard X-band weather radar and the MMW set.

The ultimate goal of the programme is to prove that the fidelity of EVS-equipped aircraft will permit use of the global-positioning system (GPS) for sole navigation means and safe Cat IIIa landing capability.

The flight test phase marks the last stage of the current effort, which began with technology development from August 1994 to December 1995.


Source: Flight International