Near mid-air collision article sent by a friend with comments to follow.

[Parvaz]

British Airways flight seconds away from mid-air disaster
By RAY MASSEY - Last updated at 00:20am on 7th November 2007

Hundreds of passengers watched in horror as their British Airways
jumbo narrowly avoided a collision with another airliner over France.
The Johannesburg-bound flight from Heathrow was suddenly forced to
climb to avoid an Argentinean passenger jet.
Aviation insiders said the planes had allegedly been put on to the
same flight path by French air traffic controllers.
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A BA Boeing 747: The jumbo was carrying 292 passengers and 18 crew
The danger was so great that the BA 747's automated collision
avoidance system was triggered, prompting the pilot to take emergency
action high over Marseilles.
The system triggers an audible alarm, with a loud and insistent
instruction to "climb, climb, climb".
The BA captain took immediate evasive action to climb steeply and bank
right to avoid the other plane, an Aerolineas Argentinas 747, near the
Mediterranean.
Once the emergency was over, the captain went into the cabin to calm
passengers. BA later confirmed there had been 292 passengers and 18
crew on board its plane.
One BA eye-witnesses told colleagues: "It was a very close run thing.
The two aircraft were put on the same flight path by French air
traffic control in Marseilles.
"Passengers at the rear of the aircraft saw the other plane
approaching and were very frightened. The captain took evasive action
by going into a steep climb and turning right.
"Afterwards, when things had calmed down, the captain left the flight
deck and went to the rear cabin to reassure the passengers and pacify
them."
The incident happened on Saturday, September 29, but has only now come
to light.
BA was yesterday reluctant to go into detail about the near-miss,
short of confirming that it had happened. Insiders said it had been
"hushed up".
A long-haul aircraft such as a Boeing 747 would typically fly at
around 37,000ft. Aircraft usually have to be five miles apart
horizontally and with a 1,000ft difference in altitude to reduce the
risk of a mid-air smash.
A reduction in either distance will trigger what aviation officials
call a "loss of separation" - known to ordinary fliers as "a near
miss".
Another insider said: "French air traffic control is said to be to
blame for putting them on the same flight level on a collision course.
It happened a few weeks ago, but has been hushed up."
BA declined to say at what altitude or on what bearing the two planes
were when the near-miss occurred.
A spokesman said: "Flight crew on the BA55 from London Heathrow to
Johannesburg received a TCAS (traffic collision avoidance system)
warning while on route.
"Our crew are trained to deal with such an event and they took the
required action.
"Safely is paramount to British Airways and we would never compromise
it. Our aircraft are fitted with TCAS to ensure that should this type
of event occur the flight crew have plenty of warning to take
avoidance action.
"We have filed our air safety report. The actual investigation is
subject to French Air Traffic Control jurisdiction. There was no issue
following the TCAS warning."
Aerolineas Argentinas confirmed it had a record of "an incident"
involving an Airbus A340 traveling from Rome to Buenos Aires.

[Parvaz]

Reading the above article credited to Ray Massey of the Daily Mail
made me want to discuss three topics: traffic separation, TCAS and
"incidents".

Traffic separation. Just as there are two directions on most roads,
and you can divide the globe into eastern and western hemispheres so
there are two directions when flying. You are either flying in a
westerly or easterly direction. Organizing the airspace in this way
allows us to separate aircraft cruising at high altitudes. At cruise
jet airplanes are separated vertically by a thousand feet (in RVSM
airspace: Reduced Vertical Separation Minima). For example easterly
bound airplanes would be assigned 33,000', 35,000', 37,000', 39,000',
41,000' and so on. Westbound traffic would be either a thousand feet
above or below the eastbound traffic at 32,000', 34,000', 36,000',
38,000', 40,000'. It is common to have airplanes over the same spot
at the same time, what keeps this from being a disaster is they are
separated by altitude. There should be a thousand feet between the
two of them.

At altitude jets are also separated laterally from each other.
Frequently your flight has traffic to your left and/or to your right
at the same altitude headed in the same general direction. What keeps
this from being a problem is that there will be distances of miles
separating the two airplanes from each other. You can also have jets
lined up like one freight train after another, going along the same
track, but they will be separated by miles between them. One of the
primary functions of air traffic control is to monitor the separation
between jets and issue directives to one, or both, if a conflict
arises. That is why they are called air traffic CONTROL

Using ground based radar stations, working in concert with technology
aboard the jets; air traffic control has a clear 3 dimensional view of
the airspace they are actively controlling. Often as pilots we are
assigned a new heading, told to alter our speed or instructed to climb
or descend by the air traffic controller who is moving us out of the
way of another jet. Moving one or both jets is necessary, because not
doing so would result in the two airplanes getting too close to each
other. When that happens it is called a loss of separation. A worst
case scenario would be having two planes collide causing a major
aviation disaster such as Tenerife http://en.wikipedia.org/wiki/Tenerife_disaster
The dreadful Tenerife accident occurred on a runway but it was the
result of a loss of separation, two heavily loaded 747s being at the
same place and time resulting in a massive loss of human life.

In summary it is air traffic control's responsibility to sequence
traffic making sure that safe distances are maintained between the
airplanes under their control. The pilot's responsibility is to
follow directions and have the jet when and where they are directed,
in compliance with their clearance (permission to operate) from air
traffic control.

TCAS, Traffic alert/Collision Avoidance System. Most airplanes have
an instrument called a transponder. Air traffic control uses ground
based radar to scan the sky for traffic. The transponder receives
this signal from ATC's radar and transmits additional data back to the
ATC site. On the radar screen a much larger return is generated and
other encoded information is displayed: airline, flight number,
altitude, airspeed and rate of climb are some of the data
transmitted. Each flight is issued a unique 4 digit number to enter
in the transponder; this number is assigned by air traffic control
prior to departure and is unique for that flight at that time.

The onboard TCAS system actively monitors a "bubble" of airspace
around the jet. The "bubble" is approximately six miles in front of
the jet, two miles behind, four miles to both side, and several
thousand feet above and below the jet. If another aircraft, with a
functioning compatible transponder, enters this bubble of airspace
that aircraft's position is displayed to the pilot on an instrument on
the flight deck. The TCAS system plots the flight path of each target
comparing it to the flight path its own jet is on. Inside the bubble
of airspace there is a safety zone. Should another aircraft be
projected to penetrate this safety zone then the TCAS system will
begin to issue (verbal & pictorial) instructions to the flight crew to
successfully evade the threatening aircraft. There are several layers
of these TCAS system generated warnings. They depend on rate of
closure and how close the target is projected to get. The system is
built to provide enough reaction time for the pilots to get the jet
out of the way without the need for violent evasive maneuvers. The
beauty of the most advanced TCAS systems is that they will work in
concert with each other to provide each jet involved in the event
separate and coordinated evasive maneuvers.

If we were to have two jets on a collision course at altitude
somewhere over the ocean, out of direct radar contact, with
functioning TCAS systems the scenario would play out something like
this. The first thing that would happen would be that both aircraft
would display the other as an acquired target. Along with the target
symbol would be an indication that this target was at the same
altitude and not climbing nor descending. And that the lateral space
between the targets was decreasing. Soon afterward, as the threat
increased, the color of the target symbol on the display would change
and precautionary verbal warnings would be issued. Typically you
would hear "TRAFFIC TRAFFIC!", and the pilots would be prompted to
visually locate the threatening aircraft using the pictorial display
in the flight deck to aid them in locating the actual aircraft out the
windows. Soon thereafter the pilots would be issued "resolution
advisories" where the TCAS system would command the flight crews to
descend or climb the airplane to mitigate the danger. This maneuver
would be coordinated, one aircraft being told to climb the other to
descend.

Incidents. How do you create a safer aviation system? One way would
be to come down hard on people for making mistakes; criminalize
errors, throw them in jail, terminate their employment, take away
their retirement and berate them in front of their coworkers and the
general public. I remember being sneered at by one instructor years
ago and being told that this was the school of "fear, intimidation,
and ridicule". Figure out who make the mistake and crush the person
responsible. The result would be that would build a culture of blame
and fear. Another direction would be to create a mechanism where
those who are directly involved are actively encouraged to fully
disclose any perceived compromise to safety, or failure on their own
part to correctly follow the rules. They would be free to do this
with the assurance that disclosing would not put them in jeopardy
(provided it wasn't intentional or done during the course of
committing some crime). There are several such programs in effect.
Most people would agree that the second method would be more effective
in creating a greater level of overall safety. There are programs at
most airlines where employees can freely report their own inadvertent
errors or any other safety related matters without fear of
recrimination by their employer or the FAA.

The reality is that there are numerous occurrences every month that
compromise safety and could have resulted in the loss of life. The
fact that these two large jets did not crash into each other is a
testimony to the effectiveness of gathering relevant data and applying
what we learn from real world reports to mandate changes that result
in a safer system. TCAS itself is a result of the quest for a safer
airspace system. The more effective route would be to figure out what
went wrong and why it went wrong and then fix the problem, rather than
look to fix the blame. It is a very good thing that we have a system
in place where people are encouraged to truthfully disclose their own
involvement in a potentially unsafe event with the intent of fixing
the problem rather than hiding from the consequences or dodging
responsibility.

The information presented here has to do with aircraft operating at
high altitudes. The systems I discussed do not apply to every
airplane in every situation. Looking up at the light general aviation
aircraft you see buzzing overhead, they may or may not have
transponders and they may or may not be talking with air traffic
control. Depending on how high above the ground they are they may or
not be following any specific altitude in relationship to direction of
flight either.

Respectfully,