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27 votes
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Are controllers aware of TCAS RA taking place?

ATC was and is still generally not aware of RAs before being informed by the pilot In general ATC is not aware of any RA occurring in aircraft, and is neither aware of the RA content. The crew informs ...
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19 votes

How is a near miss defined?

First I'd just like to comment that "near miss" is a bad term (as falstro also noticed). It seems to say that the planes "nearly missed", implying they didn't miss. The FAA uses the terms "Near Midair ...
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19 votes
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Would TCAS ever issue a "climb, climb!" RA that would stall a jet with a low airspeed?

The FAA publishes Advisory Circular 20-151A, which says in section 2-17(a): Because TCAS II can only accept a limited number of inputs related to airplane performance, it’s not possible to ...
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17 votes
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Can TCAS cope with situations involving more than two aircraft?

TCAS can deal with conflicts with multiple aircraft, a so called Multiple Threat Encounter. It will attempt to resolve the conflict but it will be limited in its options. Examples of a MTE are rare, ...
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15 votes
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How is a conflict between aircraft with TCAS I and II resolved?

TCAS 1 will only give a Traffic Advisory (TA). The crew will lookout for the other aircraft and take evasive action if necessary. They also may contact ATC for instructions. They will follow ATC ...
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14 votes

What is the correct procedure to deal with a TCAS RA during intercept?

The correct procedure for the interceptee would to follow the TCAS Resolution Advisory as they have generally no idea that they are being intercepted. The interceptor must ensure that no TCAS RA is ...
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14 votes

How does a TCAS system avoid unnecessary (RAs) resolution advisories when aircraft are operating on separate closely spaced parallel runways?

The TCAS logic is adjusted when the aircraft is in the terminal area. It does this through the following inputs: Radio Altitude - Controls TCAS parameters when below 2350 feet AGL Landing Gear, Flaps,...
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14 votes
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Why is 5 seconds the time to respond to a TCAS RA?

If the pilot reacts at impact it is too late to avoid collision If the pilot reacts one second before impact it is too late to make any significant altitude change and to avoid collision. If the pilot ...
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13 votes
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What is the range of TCAS?

Short answer If a single range should be stated for ACAS II, it would be the reliable range of 14 NM, even if targets can displayed by current TCAS II up to 30/40 NM. Reliable means here: a track ...
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13 votes

Why are both ATC and TCAS tasked to prevent collisions although TCAS takes precedence anyway?

While ATC's primary goal is to prevent collisions, it is also responsible for the efficient movement of aircraft through the airspace. That requires a strategic approach to managing air traffic to get ...
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13 votes

Can a drone be seen on TCAS?

No, a drone will normally not be visible on an aircraft TCAS. The TCAS system is based entirely on direct communication between aircraft transponders, so both parties (aircraft and drone) must have a ...
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13 votes
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On an ADS-B In display, do the pilots see the squawk code or call sign for other aircraft?

ADS-B is part of a system that compromises a number of different things. ADS-B (In) means that your aircraft is capable of receiving the ADS-B data, FIS-B and TIS-B as well. FIS-B broadcasts ...
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12 votes

When receiving a TCAS RA, DESCEND DESCEND, and starting the descent, if a pilot received GPWS warning, TERRAIN, what would they do?

TCAS (II) does not give the descend RA below 1200 ft AGL while climbing or below 1000 ft AGL while descending. Image from FAA Advisory Circular 20-151A Table 2 In case such an unlikely event happens ...
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11 votes

What's going on in this "confusing" TCAS Resolution Advisory video clip?

The TCAS responded to the other aircraft not following the flight profile that was observed earlier. If you watch closely, you will see that the other aircraft started to descend as well after the ...
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11 votes
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What action should the pilot take when a TCAS RA (Resolution Advisory) provides opposite guidance to ATC instructions?

In the 2002 Überlingen mid-air collision, one crew followed the ATC instruction to descend instead of the TCAS Resolution Advisary to climb. This caused the deaths of 71 people. Equipment and ...
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10 votes
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Can TCAS be used to confirm "traffic in sight"?

No, "in sight" or "visual contact" means seeing the actual traffic visually, with your eyes. When you report "traffic in sight," then the controllers are allowed to issue a clearance such as "maintain ...
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10 votes

If all aircraft were TCAS-equipped, how would this change ATC routines?

Think of the ATC system as the road network, traffic lights, road signs, and police. TCAS is a standalone device in your car that warns you the guy coming at right angles to the intersection in front ...
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10 votes

How does the TCAS decide which aircraft to climb and which to descend

The threads linked in the comments provide an answer, but only when read in conjunction with each other. In isolation, for a level intruder, TCAS will produce a descent - which would tell the other ...
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9 votes

What's going on in this "confusing" TCAS Resolution Advisory video clip?

See below for a description of how the TCAS (Traffic Collision Avoidance System) display is showing another aircraft approaching in each frame: 900 feet below and climbing 800 feet below and climbing ...
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9 votes

Can you have TCAS RA if your other traffic only have TCAS TA?

If both aircraft in an encounter are equipped with TCAS and are operating in TA/RA mode, then both will receive a coordinated RA. That is the RA will be coordinated between them using the Mode S ...
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9 votes
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Does the RA (resolution Advisory) from TCAS II take into account the stall margin required?

Yes, but not directly. The TCAS is a generic box that doesn't really know anything about the aircraft performance. What it does have is a number of input discretes that allow other aircraft systems to ...
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8 votes
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Why does TCAS not issue turning commands as Resolution Advisory?

TCAS gets fairly accurate altitude information from the same source as the transponder. Thus any extrapolation from this information can yield a fairly accurate prediction of whether two aircraft may ...
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8 votes

Would TCAS ever issue a "climb, climb!" RA that would stall a jet with a low airspeed?

There is no more risk of stalling an aircraft from a TCAS alert than from being instructed verbally by ATC to climb to a higher altitude for traffic avoidance. Or, (in the case of slow flight at ...
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8 votes
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Why are both ATC and TCAS tasked to prevent collisions although TCAS takes precedence anyway?

TCAS is sort of a fallback, last-resort system used in case all else fails. TCAS works within the scope of what happens within the next minute or so, and will require the involved aircraft to perform ...
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8 votes
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In what scenario would a "climb, crossing climb" or "descend, crossing descend" be issued by a TCAS system?

When a TCAS RA is issued, the system first selects the sense (up or down) and then the required strength. During the sense decision, an altitude crossing is avoided if the required vertical separation ...
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7 votes

When receiving a TCAS RA, DESCEND DESCEND, and starting the descent, if a pilot received GPWS warning, TERRAIN, what would they do?

I would pull up and once in a stable climbs I would turn in either direction in this situation. If I get a warning to descend it is to prevent a conflict with another aircraft, whereas a terrain ...
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7 votes

Can a TCAS be alerted when the intruder aircraft has a transponder in stand-by mode?

No. If the intruder's transponder is in standby it will not respond to interrogations and will be invisible to the TCAS. TCAS can't act on targets it can't interrogate.
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7 votes

Is transponder required to turn off in formation flying?

See also: In a part 91 formation flight within a mode C veil, are all the aircraft required to have their transponders on? Yes, the transponder should be off/standby. From AIM 4-1-20-a-4-c (c) When ...
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6 votes

How is a conflict between aircraft with TCAS I and II resolved?

According to AC 120-55C, the TCAS II aircraft will issue a TA (Traffic Advisory) and an RA (Resolution Advisory) if necessary and the pilot should follow any RA immediately and safely. The TCAS I ...
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