TCAS or ATC?

sgFish SG

hmm, taking two case studies, namely the mid air between Bashkirian flight 2937 and a DHL 757, and a near miss between two 747s over China, which would you rather trust? TCAS (traffic collision avoidance system) or air traffic control?

In the first case, the TCAS told one aircraft to climb and the other to descend, however an overloaded ATC told the aircraft that should have climbed to descend, resulting in a mid air collision.

In the second case, 2 747s were flying toward one another on the same airway but with a safe 2000 feet seperation given by ATC. however the TCAS on the lower 747 called a climb, and because of this, almost caused a mid air between the 2 of them, and they barely missed each other.

the two incidents

http://en.wikipedia.org/wiki/Bashkirian_Airlines_Flight_2937

http://www.sciam.com/article.cfm?articleID=000B0F26-4F86-1C76-9B81809EC588EF21&pageNumber=1&catID=2

Pitot SG

hello,

I'm not a pilot but i would definitely trust my flight instruments first.

However, pilots do trust atc alot. therefore resulting in the unfortunate accident with the DHL 757.

The command which happened in the second was a error which is very rare.

megatron SG

Bro.

u trust TCAS, most a/c today must hav TCAS II V7 to operate .
U hav 25secs before a TA ( Traffic Alert ) alert collision n immediately u hav to fly into the green band n maintain until "CLEARED of Traffic". the PNF ( Pilot NOT Flying ) MUST contact ATC of the occurrence n once cleared , ask for permission to maintain into flight profile. A SOR ( safety Occurence Report) then have to be filed by PIC.( pilot in command)

ICAO / JAR( Joint Aviation Reg) has recommended that all pilots followed TCAS.

hope it helps.

are u doing ur case study for ur ATPL or some degree? good luck!

sgFish SG

I see. How about when faced with the 2nd case, where you probably know (through atc) that there's a good altitude separation between your aircraft and another that is on a converging track with yours, and the TCAS sounds telling you to climb/descend though you know that would put you and the aircraft into greater danger? Would be a rare occurence of course, but under such circumstances, would you still trust your TCAS, or would you trust that both aircraft adhered to the separation given by ATC? Assuming that closure rate is high and you cannot visually judge it yourself?

haha no la just reading up myself. Currently only doing my PPL(R), taking PPL Airlaw and HPL papers this friday though Mr. Green

sgFish SG

hmm just curious, how does the TCAS actually look like in the cockpit? And how does it tell you stuff?

polarsnake SG

I think the pilot himself also should be able to make a judgement for himself... not too over reliant on either. If he senses something wrong, he should always think twice, be more flexible. Like instead of climbing, why not bank instead? Unless for some reason he can't..? Rolling Eyes

megatron SG

YPDN? haha..u are safe,most traffic are more than 900ft except for that left reciprocal traffic climbing 500 ft abv u at ..what 240Deg?..correct me if I am wrong

Ok this is for fish n all, my 0.02cts worth.

Let's think for a while..using own visual judgement in IFR leads to spatial disorientation, using bodily sensation to judge speed, pitch is very dangerous.
So lets imagine we are in a TA situation, 25secs to react, , if u rely on ATC n ur own visual&bodily cues ( assumin u can see SO FAR ) n follow ATC instructions , the other conflicting a/c follows his TCAS, what will happen?.
2 a/c on Mode S are corresponding in real time to each other, ATCO need time to think n also monitor other a/c , even when the ATC scope sounds the alarm for less than min separation ( usually 10NM lateral and 1000ft RVSM ) he needs time to react n talk to both planes, to think, alert both aircraft, call his Superintendent for near miss ,then issue instructions again for all other planes to siam and then call both affected planes back and maintain flight profile...all that in 25seconds?..I share this with all because I had been in both situations, ground and up there. I am not sayin do not trust ATC, but it is proven n certified now that in this sort of situation, pilots will rely on TCAS.
I wont comment on 2nd case of 2 B744 in S.China sea as there are sensitivites

Human Factors & EMT has proven that it is human error tat contributes mostly today to accidents.

Now, can u guys teach this old bird here how to upload pictures.? so I can upload the TCAS II pics , voice call and procs.

Cheers n thanks for reading.

uote]Originally posted by polarsnake:

[/quote]

megatron SG

Bro,
a word of caution, my colleagues n my safety pilots saw ur link n we agree that one needs to be careful about references n sources.
That is a techno site, if u wan factuals reports , pls go to the AAIB or NTSB one where thees guys are approved regulatories n responsible for what they published.
We hav learnt not to speculate or make non-intelligent guesses..but based reports from approved organisations like ur AOC regulators, NTSB, AAIB,ICAO,FAA ,AIB,BOEING AD or Service /safety bulletins.
I will not speak of things I don't know about but I will find out from credible sources.
Ok?..
remember, this is aviation n we must maintain correct attitude TOWARDS SAFETY & FACTS.
====== BAD ATTITUDE LEADS TO DANGEROUS ALTITUDE!=====

Good luck on ur exams.

Pitot SG

Every computer software will have its bugs..

unfortunately it is something that happens rarely.

Lets take the helios crash for example.

Rapid depressurization was caused by the wire connecting the rear air intake opening burning out.

However, we all know that in an aircraft there will be back up circuits.

But the interesting fact is, both wires run the same tube.
So infact, when one burns out, the other too.

Various organizations have made reccomendations to boeing to make changes..

But boeing have said that the chance of it happening is to small to warrant a change on the 737, one of the most popular aircraft of all time.

megatron SG

exactly! How many " peeps" must die before sumthing is done or sum procedure rectified? Are safety warranted by how many tombstones?
Look at MI185, how much is sacrifice, Lives , lawsuits before a rudder company modify their servotronic actuator and sum poor guy ( Bless his soul)n his family got blamed & broken up for all this.
Journalists!! BAH! javascript:emoticon(' Mad ')
Mad

Pitot SG

humans are always like this.

action after consequence Laughing

sgFish SG

roger, thanks for the heads up Mr. Green

megatron SG

HI ALL
there is a good writeup n pic of the latest TCAS II Ver 7 in the COOL PIC thread posted by Polarsnake.
Hope it answers some of the queries here. HAPPY READING!

Xfr8dog SG

Here is an excerpt from my company's FOM:

ATC may not know when TCAS issues RAs. It is possible for ATC to
unknowingly issue instructions that are contrary to the TCAS RA indications.
Safe vertical separation may be lost during TCAS coordination when one
aircraft maneuvers opposite the vertical direction indicated by TCAS and the
other aircraft maneuvers as indicated by TCAS. Accordingly, during an RA, do
not maneuver contrary to the RA based solely upon ATC instructions.

Maneuvering in a direction opposite to a TCAS RA will negate safe separation
as a TCAS-equipped intruder follows its RA, which has been coordinated to be
in the opposite direction.

If a pilot makes the decision to not follow an RA, the crew should be certain that they have identified the correct aircraft and should consider that the intruder may be TCAS-equipped and may be maneuvering toward the aircraft in response to a coordinated RA.

TCAS Use on PRM Approaches

The TCAS mode should remain set to TA/RA while conducting ILS PRM
approaches. Flight crews should be aware, however, that ATC instructions are the primary means of providing separation. Should a TCAS Resolution Advisory conflict with an ATC instruction - comply with the instruction. If a reaction to a TCAS alert causes the crew to deviate from an assigned clearance, inform ATC immediately.