Hey friends and followers, today's question is another really important one: Joe, can you explain what is
TCAS? This is a vital topic, especially if you want to become an airline pilot and you'll be dealing with this system a lot,
so let's get started. [intro audio]
In 2002, a tragic event happened in commercial aviation
history. Two airplanes crashed in mid-air over Überlingen, a city close to Lake Constance in southern Germany.
A Boeing 757 and a Russian Tupolev were on a collision course
when the TCAS of both planes kicked in, and the Tupolev pilot gave a false input.
The air traffic controller requested the Tupolev crew to
immediately start descending to a lower level although the TCAS of the Tupolev ordered the crew
to climb whilst the Boeing crew was ordered to descend. The Tupolev pilot followed the orders by the air traffic
controller and also initiated descent, and disregarded the resolution advisory of his TCAS,
and a few seconds later, both airplanes crashed in mid-air.
So what does TCAS stand for? Get out your notebook and write down this abbreviation.
TCAS stands for Traffic Alert and
Collision Avoidance System.
So let's talk about the traffic alert part of the system first. Commercial jets have to be fitted with a Mode
Sierra transponder. The transponder sends out signals showing the aircraft's position,
altitude (or flight level), and current vertical speed. The TCAS
scans the airspace around the aircraft for other aircraft fitted with such a transponder at a 40 mile radius
horizontally and
9900 upwards and downwards
vertically.
Therefore, the TCAS has two antennas fitted -- one at the top of the fuselage, and one at the bottom.
So the antennas are on a constant lookout for transponders of intruders,
because from the transponder signals, the TCAS determines for each intruder its relative bearing,
its range and closure rate, its relative altitude (if available).
Why do I say "altitude available?" Because many glider planes and other smaller aircrafts only have a Mode Alpha
transponder, which only indicates their position and not their altitude. But more about transponders in another video.
So once another aircraft gets into your TCAS airspace, this little diamond will pop up on the navigation display,
showing you where the aircraft is, and its vertical separation to your aircraft. So in this example,
the airplane is at 2,000 feet above you. (above, indicated by the little plus symbol --
minus would obviously be below), but in this example, there is no imminent threat. The little arrow pointing
down or upward indicates that the aircraft is either in a climb or descent relative to your aircraft.
Now in this picture, the little diamond has turned fully white,
indicating a proximate intruder, meaning the other airplane is within six nautical miles radius,
but no threat if it maintains its altitude
separation. Now the intruder is suddenly descending, and the diamond turns to an amber dot. That's where the
avoidance and collision system comes active. An aural warning is automatically called out
[traffic, traffic] because the TCAS now indicates the other plane as a potential threat.
The TCAS predicts a so-called
closest point of approach within 40 seconds of the intruder. When the amber dot turns red,
the TCAS predicts a closest point of the approach in twenty-five seconds and calls out for a resolution advisory for both
airplanes. One of the airplanes will get the advisory to [climb, climb]
and the other [descend, descend].
to increase the vertical separation to each other. TCAS optimizes vertical orders to ensure a sufficient
trajectory,
separation, and minimal vertical speed variation, considering all intruders.
Giving orders like [adjust vertical speed, adjust] or
[maintain vertical speed, maintain]
and TCAS is a so-called memory item, meaning the entire procedure is done by memory,
starting with a call-out
"TCAS, I have control" and in case of the resolution advisory, you would call out "autopilot off,"
"flight directors off," and follow the aural message and give the necessary rudder input and
monitor your vertical speed. Most
importantly is to give smooth rudder inputs to not create another TCAS
alert with another plane in the vicinity
due to an excessive vertical speed. After completion of the procedure, you resume back to you given flight level, activate
the autopilot and your flight directors, and notify ATC by saying,
"Speedbird 125, clear of
conflict." Now you might ask how often does a resolution advisory happen. I've been in the airline industry
for seven years now, and I have received probably a TCAS alert every four to five months,
but I've never had to actively avoid another plane by a resolution
advisory. There are few tricks on how to reduce the risk of a TCAS alert.
Very often, departure routes cross arrival routes, like in Munich, for example.
So you want to use vertical speed mode when approaching your first cleared level, because you already know that
other airplanes are descending from above and will level off at a thousand feet above you
which is a minimum separation.
But if you climb to your cleared flight level
at an excessive climb rate (as you would do because the engines are much more powerful at low levels), you
decrease your climb rate by either flying it manually, or use the autopilot's
vertical speed mode. I've heard by many colleagues that this issue is a common problem with the Boeing 737
because it's so overpowered and it climbs like a rocket in the initial climb phase. Now you might ask,
why do you turn off the flight director during that procedure?
The flight director receives his orders by the FMGS (the Flight Managing and Guidance System), and
the FCU (the Flight Control Unit), and
because the resolution advisory is a non-normal situation for the FMGS
and no inputs are made in the FCU during that procedure,
the flight director bars would stay in place, and would be more of a distraction in that situation than of any help.
But more importantly, at the same time turning off the flight directors will
activate the auto thrust into speed mode,
meaning that, for example, when the TCAS wants you to climb,
the thrust will apply power to keep your speed during that climb, or decrease the power in case of descent.
It's as easy as that, to be honest. I hope you enjoyed this basic introduction video about the TCAS system.
There's more to learn about the TCAS in future videos, but I hope you got the basic principles of it.
Thank you very much for your time.
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with your friends. All the best, farewell, your Captain Joe.