Aircraft could soon be prevented from flying
directly into buildings thanks to technology
being developed by US aerospace firm Honeywell.
Since the terrorist attacks of 11 September,
avionics experts have been looking at ways of making similar
acts impossible, including a 'hijack mode', which would see
aircraft locked on to autopilot, either by the pilot or by
air traffic control on the ground.
But some critics question the safety of controlling
an aircraft from the ground, and argue that the possibility
of terrorists hacking into air traffic control systems and
gaining remote control of the plane would make the idea too
Instead Honeywell is developing
a system that would effectively create a protective bubble
around skyscrapers and tall buildings, forcing the aircraft
to fly around them, said Ben McLeod, director of aviation,
safety and security at the firm.
The system is an extension of existing technology
built into the autopilot programme of some aircraft, which
prevents pilots from stalling planes. The anti-stall system,
already in use on Airbus aircraft, will not allow the plane
to reach an attitude that would cause it to stall, no matter
how hard the pilot pulls back on the throttle.
'This is simply an extension of that, using
databases of cities showing the buildings, radio towers, etc.
We can build protective envelopes so it would be impossible
for the aircraft to fly into these: the autopilot would just
turn away,' he said.
The system would also involve a modification
of the existing Enhanced Ground Proximity
Warning System, which is designed to keep pilots aware
of the aircraft's position in relation to the local terrain.
It provides a colour-coded cockpit display of the terrain
and sounds an alert at least one minute before a likely collision.
Instead of an alarm, the structure avoidance system would
simply direct the aircraft away from the building.
'We are not just focused on what happened
on 11 September, we are trying to look beyond that to cover
other things terrorists might try,' said McLeod.
At present no commercial aircraft carries
an autopilot system that cannot be turned off. This would
have to be changed. A pilot would put the aircraft into an
emergency state as soon as a threat was discovered, at which
point the autopilot would be locked on, and the hijackers
would be unable to take control.
McLeod says: 'These systems are much like
a car alarm. If a thief wants your car enough, he'll probably
get it. But if there are layers of protection, the thief will
be deterred, and may decide there are better things to prey
on. Such things are meant to slow the thief down and make
theft more difficult - to make it so that many things have
to go just right for them to succeed.'
The proposed new avoidance system would also
be useful in normal flight mode, according to McLeod, as it
would prevent pilots from inadvertently flying into a building
or mountain in heavy fog.
Flying by autopilot without any opportunity
for pilot intervention will demand an increase in the integrity
and safety requirements of aircraft avionics systems. As yet
Honeywell has not even begun to discuss with its customers
the likely cost of the changes needed to lock aircraft on
But Chris Partridge, aviation analyst at Deutsche
Bank, said the technology should involve a relatively low-cost
'tweaking' of existing terrain avoidance and on-board mapping
systems. 'In the overall scheme of things, I do not think
it is beyond the existing technology at all. It would probably
be a case of changing the way the on-board mapping system
operates. It would be working off a digital database [of cities]
that already exists.'
The only remaining question would be making
sure there was no possibility of any hijacker on board the
aircraft overriding the system, he said.