Re: Extending a /64

[Tony Whyman <[e-mail]>]

On 17/11/2020 02:55, David Farmer wrote:
> ou mention that airplanes can fall out of the sky, it would be really 
> bad if an airplane every fell out of the sky, or collided with another 
> airplane, because of an address conflict. 

I should probably make it clear that irrespective of whatever addressing 
plan we come up with - this will never happen. There is strength in 
depth in the system.

1. There are application level checksums that bind the aircraft identity 
and flight identity to the message and these would have to fail before 
any mis-addressed message even made it into the cockpit. Address 
conflicts should always result in lost messages rather than 
mis-delivered messages. The safety case already assumes that some 
messages will be lost and includes procedures to recover the situation 
using voice communication.

2, An instruction that was received by the wrong aircraft would have to 
make sense to the pilot in their current context if they were to action 
it without query.

3. There are automatic surveillance systems on the ground that are 
constantly monitoring aircraft movements and trying to predict any 
possible collisions or near misses - and these are in addition to Air 
Traffic Controllers themselves constantly monitoring each aircraft. 
Aircraft are instructed to take evasive action in the event of any 
possible conflict.

4. Aircraft are equipped with TCAS. This is an autonomous system that 
alerts pilots to the proximity of other aircraft and advises each pilot 
on the correct course of action to avoid any possible collision.