Be careful out there guys.

As NASA prepares to release the safety survey to the public, we already know that the skies are crowded.

RVSM, LAHSO, PRM, (and all the others) are capacity tools, NOT safety tools.

here is all the technical stuff about tcas ii version 7. In a nut shell the mode s transponders communicate with one another. The then calculate the posibility of an impact and then count how far away the impact is. once it gets to a set threshold the TCAS system in both planes will give a TA. A TA is a traffic advisory. The TCAS system is letting you know someone is intruding in the protected space around the airplane and that the potentional for a collision exist. Then if the planes continue with no change on a collision course the TCAS system will give an RA, or Resolution Advisory. During a resolution advisory the Systems of both planes communicate with eachother to avoid a collision. For example if one plane is descending into another, the TCAS system in the plane descending will tell the pilots "DONT DESCEND" will telling the pilots in the other plane either "monitor vertical speed" or "descend".

http://www.skyaid.org/images/tcas2.gif



[LEFT]Note in the picture below almost the entire VSI is red except for a little green part. the TCAS system is telling you to put the needle in the green to avoid a collision.
http://www.allstar.fiu.edu/aero/images/2-48.gif




TCAS II provides traffic advisories and
resolution advisories (RA), i.e.,
recommended escape maneuvers, in the
vertical dimension to either increase or
maintain the existing vertical separation
between aircraft. Airline aircraft, including
regional airline aircraft with more than 30
seats, and general aviation turbine-powered
aircraft use TCAS II equipment.
The TCAS concept uses the same radar
beacon transponders installed on aircraft to
operate with ATC ground-based radars. The
level of protection provided by TCAS
equipment depends on the type of transponder
the target aircraft is carrying. The level of
protection is outlined in Table 1. It should be
noted that TCAS provides no protection
against aircraft that do not have an operating
transponder.
[LEFT]The TCAS Computer Unit, or TCAS
Processor, performs airspace surveillance,
intruder tracking, its own aircraft altitude
tracking, threat detection, RA maneuver
determination and selection, and generation
of advisories. The TCAS Processor uses
pressure altitude, radar altitude, and discrete
aircraft status inputs from its own aircraft to
control the collision avoidance logic
parameters that determine the protection
volume around the TCAS aircraft. If a
tracked aircraft is a collision threat, the
processor selects an avoidance maneuver that
will provide adequate vertical miss distance
from the intruder while minimizing the
perturbations to the existing flight path. If the
threat aircraft is also equipped with TCAS II,
the avoidance maneuver will be coordinated
with the threat aircraft.
Because of the selective address feature of the
Mode S system, TCAS surveillance of Mode S
equipped aircraft is relatively straightforward.
TCAS listens for the spontaneous
transmissions, or squitters, that are generated
once per second by the Mode S transponder.
Among other information, the squitter
contains the unique Mode S address of the
sending aircraft.
Following the receipt and decoding of a
squitter message, TCAS sends a Mode S
interrogation to the Mode S address contained
in the squitter. The Mode S transponder
replies to this interrogation and the reply
information is used by TCAS to determine
the range, bearing, and altitude of the Mode S
aircraft.
To minimize interference with other aircraft
and ATC on the 1030/1090 MHz channels,
the rate at which a Mode S aircraft is
interrogated by TCAS is dependent on the
range and closure rate between the two
aircraft. As the target aircraft approaches the
area where a TA may be required, the
interrogation rate increases to once per
second. At extended ranges, a target is
interrogated at least once every five seconds.
TCAS tracks the range and altitude of each
Mode S target. These target reports are
provided to the collision avoidance logic for
use in the detection and advisory logic and
for presentation to the pilot on the traffic
display. The relative bearing of the target is
also provided to the collision avoidance logic
so that the target.s position can be properly
shown on the traffic display. The bearing
information is not used by the collision
avoidance logic for threat detection and
advisory selection.

In a TCAS/TCAS encounter, each aircraft
transmits interrogations to the other via the
Mode S link to ensure the selection of
complementary RAs by the two aircraft. The
coordination interrogations use the same
1030/1090 MHz channels used for
surveillance interrogations and replies and
are transmitted once per second by each
aircraft for the duration of the RA.
Coordination interrogations contain
information about an aircraft’s intended RA
sense to resolve the encounter with the other
TCAS-equipped intruder. The information
in the coordination interrogation is
expressed in the form of a complement. For
example, when an aircraft selects an upward
sense RA, it will transmit a coordination
interrogation to the other aircraft that restricts
that aircraft’s RA selection to those in the
downward sense. The strength of the
downward sense RA would be determined by
the threat aircraft based on the encounter
geometry and the RA Selection logic.

It would be nice to know the ARTCC involved...

Please keep in mind guys that everything these systems function off of are the transponder, which is dependant on the altimeter sending the correct figures to the Xponder. That is why it is absolutely imperitive that you cross check your xponder to altimeter readings frequently for the xponder selected and in use.

*** And gals!!! :D

Just as a correction above...mode S transponders aren't required...TCAS works with Mode-C as well. The TCAS system figures out collision hazards and not the transponders. If one aircraft has TCAS and the other doesn't the aircraft with TCAS will still get an RA.

FMS navigation is so acurate now, that if you are on an airway and converging with someone on the same airway in opposite directions.... it is directly head on.

We had a C141 one day pass 1000 feet above us about a year ago, and ATC cautioned us he would pass overhead (they arent required to and they dont all the time) and with the angle of the sun we didnt see that guy until it would have been too late. Probably around 800-900 knots closure.

Another reason to ditch the GPS ;-)

this is correct. the only time tcas 2 doesn't work is if the other guy either has no transponder, or he doesn't have an altitude encoding transponder. you will still get a TA if the other guy has a transponder but no altitude encoding. you will not get an RA in this situation. all the system will show you is a yellow circle indicating the possibility for collision exists, but the TCAS system doesn't know the altitude of the intruding aircraft,, they could be several thousand feet below you.

all mode s transponders talk to each other, and send each other airplane data, such as altitude, so the system can analyze the threat level.

here is another example of what can happen when you dont follow an ra

http://www.faa.gov/about/office_org/...Y_BULLETIN.pdf

Most systems allow you to program in an offset so it intentionally flies off airway centerline....I've used one mile on heavy traffic airways where I kept getting wake.