Protective ‘bubble’ plan to shield terror targets

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 risky.

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 autopilot.

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.

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