Guy Norris/WICHITA
A LOW-COST TERRAIN-warning system for single-engine general-aviation (GA) aircraft is being developed by AlliedSignal and will be available from around April 1996.
The development of the terrain-warning system (TWS) was prompted by the re-emergence of Cessna's light-single product line. "Cessna's going back into business, so we're interested and so are they," says AlliedSignal research fellow, Howard Glover.
AlliedSignal believes that modern integrated circuit-technology will allow it to make the TWS at an affordable price for the GA market.
Until now, the smallest ground-proximity warning system (GPWS) is the former Sundstrand Mk VI for regional airliners. "The key element is the radio altimeter, and an inexpensive one is being developed," says Glover.
The TWS radio altimeter is based on microwave monolithic integrated circuit (MMIC) technology and uses spin-off components from cellular and broadcast television developments.
The TWS receiver and transmitter will be co-located with the antennae for simplicity and active microwave-receiver devices will improve signal-to-noise ratios while cutting component count.
"It will have a reduced capability, because we don't want to encumber the aircraft with all the signals that a full-up system needs," says Glover. Apart from providing a digital read-out of altitude from 30ft to 3,000ft, the radio altimeter-driven TWS will also generate verbal warnings for rising terrain and ground proximity.
Also useful for training, the TWS will provide altitude callouts of "800ft, 500ft, 200ft, 100ft and 50ft on approach," says Glover. Decision height-selection and announcements will be signaled by the word "minimums," which will aid instrument-flight-rule operations, he adds. Additionally, the TWS will warn of "too low, flaps," and "too low, gear," when improper flap and gear position is selected for landing.
The TWS, housed in a single instrument-panel-mounted line-replaceable unit called the TWS-20, will also have a 20min flight-history storage device. "It provides a bit of a record for the owner and can be used for playback by the instructor and student. It is the seeds of a GA flight-data recorder," says Glover. A prototype TWS has been tested successfully on the company's Beech King Air and a Cessna 182.
Source: Flight International
