AN ADVANCED autopilot that might one day take an aircraft out of the hands of
hijackers and land it safely at an airport has passed its first flight
tests.
Since the horror of 11 September, many ideas for foiling future hijacks have
been suggested. One is a “panic button”, operated by either aircrew or
air-traffic controllers, which would order a plane to seek out the closest
airport and land—while locking the cockpit controls
(91av, 22 September, p 10).
It now appears that a big step towards making this a reality was taken in the
month before the attacks on the World Trade Center and the Pentagon. American
aerospace company Raytheon says that in August a Boeing 727 airliner made six
high-precision automatic landings at Holloman Air Force base in New
Mexico—without the plane’s pilots having to find the airbase, as they do
for standard landings.
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The aircraft was fitted with an experimental autolanding system that uses GPS
satellite data to locate an airport. Called the Joint Precision Approach and
Landing System (JPALS), the system is being designed to aid pilots when
visibility is poor—but it could, with further development, form the core
of an emergency automatic landing system.
Today’s instrument landing system (ILS) relies on pilots navigating towards
the airport and flying towards radar beacons at the end of a runway. The plane’s
ILS system then controls the descent using radar data on elevation and descent
angle. But military and civilian aircraft use incompatible ILS systems, so each
can make instrument landings only at airports with the right beacon equipment.
Aerospace engineers hope that GPS-based systems can solve this incompatibility,
as they will rely mainly on satellite signals that will be available to all.
JPALS measures altitude to within a metre by comparing readings from a single
airport ground station with data from terrain surveys and with GPS readings from
the aircraft. It requires only one ground-based unit per airport rather than one
radar at the end of each runway, making it much cheaper to buy and maintain,
says Bruce Solomon, an expert in air-traffic management at Raytheon in
Marlborough, Massachusetts.
Raytheon leads one of three groups developing the civilian version of JPALS,
which will be called the Local Area Augmentation System. Its backer, the Federal
Aviation Administration, hopes to have a test system up and running at an
airport in two years’ time.
Safety is of paramount concern where remote-control systems are involved,
Solomon told 91av. He would not comment on JPALS’ feasibility
for future emergency autolanding systems, saying that the varied engineering
issues involved have not yet been examined. While the FAA would only confirm it
is “looking at many different measures for improving security”, other observers
warn that centres equipped to remotely control airliners could themselves become
targets for terrorists.