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The number of technical equipments needed to keep the whole aviation system running is impressive. The typical break-down is known as CNS, standing for Communication - Navigation - Surveillance. Communication includes radio and telephone, but also IT networks. The Navigation part is made of approach equipments (ILS), and en-route navigation beacons (VORs). Surveillance includes radar and other ways to detect aircraft positions.

On top of that comes the data processing system for flight plan and surveillance data, which builds the synthetic view displayed to air-traffic controllers. Airport specific systems include power, conditioned air and fuel delivery to aircraft and runway and apron lighting. Handling companies also depend on these systems to know where and when the airplanes they have to care for will arrive.

Behind all these systems is also a common infrastructure, providing essential services: power, air-conditioning, heating, backbone communication systems, building security, access control, and so on. All the safety relevant systems are doubled, if not tripled, and procedures exist to safely handle traffic in case of equipment failure. The whole system is usually quite resistant, and failures usually leads to delays, diversions, and flight cancellations. These are certainly annoying, but not dangerous.

When discussing with airport staff what would be the worst failure, the answer is always the same. Passenger Information Systems. You know, the nice displays indicating at which counter check-in takes place for each flight, and from which gate each flight will depart.

A complete loss of electrical power is normally not possible, as different power sources are available, including own generators. Moreover, power distribution is segmented so that even if a part of the airport loose power, it will not affect all of it.

A complete loss of flight information display could quickly lead to a cahotic situation. Un-informed passengers would ask the ground personel. If no information is availalbe, it could be possible to send passengers to the right terminal - most airlines always operate from the same terminal, but that’s it.

Once there, the passengers would be left with no information. Assuming that sufficient ground staff is available (not exaclty obious…), and that pilots know where to park their planes, the number of not reaching the gate on due time would create massive delays.

I saw once in Frankfurt a day where the system used to print the boarding passes was inoperative. All the rest was working find. Staff at the check-in counters printed boarding passes without gate numbers, and were sending passengers to counters in the correct terminal. Displays were giving correct information, but boarding passes had to be re-printed locally before boarding.

This “simple” problem created an average delay of more than 30 minutes ! Frankfurt being the hub of Lufthansa, the impact of these delays could be felt throughout all Europe. The problem got solved within less than one hour, but the delays persisted all day long, as they were too long to be compensated for in flight.

A complete failure of the whole passenger information system would have the same results, but at a more larger scale ! Even the problems with the new Terminal 5 in Heathrow would look as minor glitches in comparison.

Do you feel like doing a small experiment ? Next time you go through an airport, try counting the number of flight information displays you see. You’ll quickly understand why they are so imporant.