-
Asked by howe7r2 to Drew on 14 Jun 2011.
-
Drew Rae answered on 14 Jun 2011:
Hi Howe7r2. Nothing we make is perfect – there can be hidden problems, and even if there aren’t, there is still a small amount of risk. Parts can break, or wear out, or be installed incorrectly. Once someone did some routine part changes on all four engines of a plane, and left out a small rubber washer on all four engines, which ran out of fuel.
Sometimes people make mistakes in controlling planes and trains, or they get bad information. Two planes crashed in Europe when the air traffic controller told one to go down and the other to go up. Trouble was they both had computers which said the exact opposite. One pilot listened to the controller, and the other listened to the computer, so they both went in the same direction.
-
Comments
lolmartsecurity commented on :
Drew, I would appreciate if you would elaborate on this incident in Europe that you used as an example. Was this the one where the DHL 737 collided with the Aeroflot Tupolev somewhere near Russia? I am always interested in this kind of thing, and to be honest I think my family has had enough!
Drew commented on :
Sure, that’s the one I was talking about. I’ve just got a chat starting at 13:20, then I’ll come back and elaborate.
Drew commented on :
Ok, I’m back. Aircraft use a system called TCAS to avoid midair collisions. When two planes get close, their TCAS talks to each other, and tells one plane to go up, and one plane to go down. In the accident near Uberlingen, the DHL obeyed TCAS and the Tupolev didn’t. Seems straight forward, but …
TCAS had a known problem. If there are three aircraft in the area, TCAS could steer a plane straight into the third aircraft. The Tupolev couldn’t see a third aircraft, but they had heard the air traffic controller speaking to one earlier. If the air traffic controller knew about the third aircraft and TCAS didn’t, then the smart thing to do is to listen to the controller. But …
The controller can’t hear TCAS. The controller didn’t know that they were giving opposite instructions to TCAS, they were just instinctively trying to recover a bad situation. They were overworked, and their phone system wasn’t working properly for them to get help. The controller was later murdered by the spouse of one of passengers on the Tupolev.
This sort of thing is common in accidents. You find lots of things that were wrong, or things that were right in themselves, but wrong in combination with other things. We call safety an “emergent property” meaning you can put together a bunch of things that are safe, but that doesn’t mean that the combination is safe.
howe7r2 commented on :
Ok thanks drew