Why can't pilots avoid mid-air collisions?

Question

Isn't TCAS supposed to prevent mid-air collisions with another aircraft? Off the top of my head I can think of 2 instances when a crash happened because pilots failed to obey TCAS orders. Pilots are supposed to be taught that no matter what ATC tells them, TCAS has the final say. Still these crashes happen. Why?

Answer 1

Pull up, pull up,  pull up, pull up! It comes out of the clear blue and it shocks the h**l out of you. Before grabbing the yoke pulling back and putting all the passengers into a gut-retching 2-3 G manoeuvre, crews like to get a visual reference and make sure it's not a false warning. Sometimes the approaching aircraft also gets a pull-up advisory and you can pull-up into one another.

As someone who spends a lot of time in the cockpit, I can tell you that it's not abnormal to get false warnings of trouble and the worst thing you can do is panic.

Answer 2

To err is 'human'. After all, pilots are humans.

PS: They do not collide intentionally. Their foremost aim is to ensure safety of the aircraft, passengers and the crew.

Answer 3

Human error that is why we mechanics have a (HF Course) human factor course, pilots were given also what is known as CRM or Crew Resource Management course.

Answer 4

i avoided them for forty years. whadayamean why can't we avoid them. TCAS never has the final say my friend. the PIC ALLWAYS HAS THE FINAL SAY.

Answer 5

pilot also has a window to watch for other aircraft

Answer 6

human error mostly, or conflicting information, or mechanical failure. murphy law "if it can break, it will" humans also fall into that category

american pilots are taught to obey TCAS no matter what. however pilots of other nationalities may not be or, because of tradition do not.

this is the case of the American 757 colliding with a Ilyushin. the American pilots, obeying TCAS, descended but the Russian pilots, more accustomed to obeying a human, in this case, the ATC ordered them to descend also. this led to the mid air collision.

human error, on the part of the Russian pilots and the ATC who was having his radar repaired and who was doing the job  of 2 ATCs.

another collision i can readily think of is when a piper single engined aircraft took the tail off a DC-9. that was because the single engined plane's pilot was lost and it had a very basic transponder which meant the ATC did not get any altitude data. Neither did the TCAS of the Dc-9

mechanical error/human fault

another case, not a mid air collision, but nearly. two 747s collided because the pilots on one aircraft mistook a controller direction for permission to take off. again communication error

TCAS does not have the final say. its a good rule, that all pilots should obey TCAS but

"dying right does not make you any less dead"

so i guess, whoever took the action and came out alive has the final say.

**EDIT*

visual avoidance is easy when your in a small aircraft but it is a lot harder when you are flying a commercial jet because of the limited visibility you have and the speed at which two oncoming aircraft are flying at.

commercial airliners fly IFR, or Instrument Flight Rules. Most of the time, the pilots are looking at their instruments, not outside. throw in a malfunctioning transponder, which means that TCAS will not display a warning, and there you go, a mid-air collision. (this was the case of a brand new embraer legacy jet and a boeing 737 flown by GLO airlines)

even if pilots do look outside, depending on aircraft speed, the combined closure rate could be greater than 1000knots. This means the pilots will have less than 15 seconds to decide what to do and do it. many times, close collisions have gone unnoticed by either pilots and are only found later when ATC records are examined.

studies indicated that average pilots take 4 seconds to see something, and decide that the thing is coming directly towards you. Most of the time, since you are not expecting to see something coming towards you at cruising altitude, your brain may take even longer to decide or you may think that you were mistaken. there are many false readings and false sightings so everyone likes to be sure before putting the aircraft and the people on board through a violent aerial maneuver.

Answer 7

TCAS doesn't have any "say" in pilot decisions.  It's an aid to avoiding traffic.  The primary responsibility is with the Pilot in Command, and the primary methods of separation are visual observation, altitude separation, route following, and ATC clearances.

I flew professionally for 37 years and never came close to a mid-air collision.  How did you get the impression that "pilots can't avoid mid-air collisions?"

Answer 8

A> human error

B> not all planes have TCAS on them.... most general aviation airplanes are not that well equipped yet

C> conflicting information. There is still debate between some as to who's order should be followed, TCAS or ATC.

D> Pilots flying around without using a radio, hence limiting others from knowing where they are, and they them selfs not knowing what is around them.

E> Commercial jetliners fly a around 500+ miles per hour. Closing time between two airplanes goes down to a matter of seconds, not enough for evasive action.

Answer 9

Pilots are human. Also, in at least one of the crashes, one pilot was trained to listen to the ATC, and did. The other was trained to follow the TCAS, and did. Result=crash.

   Also, being human, there is a strong instinct to ignore instrumentation and "go with your guts". Good training overcomes most of this, but under extreme stress even a well trained person may fall back to instinct.

   Finally, there is always the chance of a mechanical failure of the system, either on the ground or with TCAS. I'm not actually aware of one of these, but the possibility resists. Our technology is good, very good, but we've not managed to reach that theoretical state of perfection.

Answer 10

1) Yes, TCAS is supposed to help prevent mid-air collisions.

2) Probably at least one of those crashes is the reason pilots are told to give TCAS priority over ATC.

3) The Pilot has the final say.

Think about this, you're flying along minding your own business. You hear a robotic voice, "Traffic, Traffic". You look for traffic where the TCAS says, but don't see any. Maybe it's behind you.

Then you hear an urgent human voice in your headset, "PULL UP IMMEDIATELY! Collision warning!" and weakly under it you barely hear a robotic voice, "Descend. Descend now".

Which are you going to follow in the three seconds you have to make a decision? Let's hope the other pilot made the same choice you did.

Answer 11

Human errors... People are just so d**n stubborn!