"The primary purpose of the ATC system is to prevent a collision between aircraft operating in the system and to organize and expedite the flow of traffic."
Sounds simple doesn't it? That one sentence is the meat and potatoes of Air Traffic Control. It's amazing how complex the system has to be to accomplish that one sentence.
For airplanes within "the system," we make sure they don't hit. That's the meat. Still, if all controllers had to do was make sure airplanes didn't hit, we'd have a relatively simple job. It's the "and" portion of that statement that makes it complex. As in, "... and to organize and expedite ..." That's the potatoes. Everything else is just gravy. Keeping the airplanes moving in the general direction they want to go is the part that makes this job tough. You could train a monkey to keep two airplanes apart.
Speaking of monkeys, you should see controller trainees the first time they run a basic vectoring exercise in class. I can still remember my first time. There are four targets lined up north to south on the left (west) side of screen. The objective is to vector them though a "gate" on the other side (the east side) of the screen. When the problem starts, all four targets start moving due east at the same speed.
In terms of vectoring, nothing could be simpler. Constant speed. No altitudes to worry about. It just doesn't get any easier. And it makes a monkey out of every person who tries it for the first time. After a few minutes of complete chaos the instructors invariably yell, "Stop the clock!" freezing the screen so they can explain the error of your ways.
The secret is that you have to point the airplanes at each other. It isn't intuitive. Everything in your brain says to turn them away from each other. If you do (and we all do), you wind up with a mess. But if you'll take the guy on the bottom (south side) of the screen, turn him 90 degrees left (due north), pointing him right at the next target, by the time he gets to where that target was, he'll be behind him.
In case you think I'm telling you about this just for nostalgia's sake, it's time to pay attention:
N12345, VFR traffic, two o'clock, two miles, northbound, altitude indicates 5,500.
Well, wait a minute ... you're going east at 5,500. If you're like some folks, you'll start a turn to the left -- you think it is away from traffic -- as you ask the controller for a vector around the traffic. If danger lies to your right, your brain says go left. And you'd be turning the wrong way. Like I said, it isn't intuitive. The controller knows that if he turns you toward where the traffic is now, it won't be there when you get there.
N12345 turn 90 degrees right, heading 180, vector behind traffic.
If you were already turning left, the controller probably hasn't noticed it. Don't ever forget that radar shows what has already happened, not what is occurring. Depending on the type of equipment the controller is using, his information could be several seconds old. When you get in tight -- when it's crunch time -- seconds count.
If you started making the left turn and the controller didn't notice it, you've just lessened your chances for a successful outcome. Even worse, you don't have time to inform the controller; and even if you did, he doesn't have time to do anything about it. It takes time for you to turn. It takes time for you to talk. It takes time for a controller to listen. It takes time for a controller to understand and to react. It takes the one thing that you don't have: time.
If there's a bigger lesson I can leave you with (besides the fact that it can make sense to turn toward traffic) it's this: Confusion can get you killed in this business. Besides all the problems you normally associate with confusion, the biggest problem is that it eats up so much time. Being a Monday-morning quarterback is easy because you have the luxury of time. You're not sitting there watching the seconds tick off.
If you find yourself in a situation where you're confused, you need to call a time out. If you can. In this case (and many others) you don't have that luxury. The next time you read an accident report, keep that in mind. The pilot either didn't or couldn't call a "time out." You might be able to buy some time, but you can't ever stop the clock.
Now that I've got your attention as to how serious this subject is, let's take a look at some of the fundamentals. There are actually two separate instances where controllers call traffic. The first is "traffic advisories" and the second is "merging target procedures":
2-1-21. Traffic Advisories
Unless an aircraft is operating within Class A airspace or omission is requested by the pilot, issue traffic advisories to all aircraft (IFR or VFR) on your frequency when, in your judgment, their proximity may diminish to less than the applicable separation minima. Where no separation minima applies, such as for VFR aircraft outside of Class B/Class C airspace, or a TRSA, issue traffic advisories to those aircraft on your frequency when in your judgment their proximity warrants it. Provide this service as follows ...
We'll deal with the "as follows" part in a little bit. Merging target procedures are contained in Chapter 5 of the FAA 7110.65. For those who don't have their 7110.65 memorized, Chapter 5 is entitled "Radar."
5-1-8. Merging Target Procedures
a. Except while they are established in a holding pattern, apply merging target procedures to all radar identified:1. Aircraft at 10,000 feet and above.
2. Turbojet aircraft regardless of altitude.
3. Presidential aircraft regardless of altitude.
b. Issue traffic information to those aircraft listed in subparagraph (a) whose targets appear likely to merge unless the aircraft are separated by more than the appropriate vertical separation minima.
There's a ton of minutiae in those two paragraphs if you'd like to get bogged down in the details. I'll point out "separated by more than the appropriate vertical separation minima" versus "less than the applicable separation minima" and the fact that one is found in the "General Control" chapter while the other is in the "Radar" chapter. Just in case you'd like to do some deep thinking on the subject. The rest of us are going to move on.
If I could get you to read both paragraphs in their entirety you might notice something. Neither paragraph mentions the weather. Neither paragraph mentions anything about "courtesy." And I'm not Olive Oyl.
Just in case the preceding paragraph leaves you confused, I guess you would be one of the rare pilots who answers a traffic call with quaint phraseology like "Negative Contact." Some pilots seem to be under the impression that controllers only call traffic when the pilot stands a chance of seeing the traffic. (Don't feel bad -- some controllers are too.) So they'll answer a traffic call with a weather report: "We're IMC, Center."
Having talked to a few pilots in my career, I know that some are under the mistaken impression that we call traffic as a courtesy. I guess there are times that we do but the main reason is because the books says we're supposed to. So when we do (call traffic) we're expecting one of two replies: "Negative Contact" or "Traffic in sight." Actually there is a third reply we should expect, but it's so rare that when anyone asks for a vector around traffic it tends to surprise us.
What we don't expect is confusing phraseology. "Traffic not in sight." "I've got him on the fish-finder." I don't consider the term "no joy" confusing but I don't see it in the book either. Ditto for "tally ho," "looking," "searching," and "radar contact." And yes, I know what "popeye" means, sailor man, but most other landlubbers don't.
Let's get back to the section on traffic advisories:
2-1-21. Traffic Advisories
Provide this service as follows:
a. To radar identified aircraft:
1. Azimuth from aircraft in terms of the 12-hour clock, or
2. When rapidly maneuvering aircraft prevent accurate issuance of traffic as in 1 above, specify the direction from an aircraft's position in terms of the eight cardinal compass points (N, NE, E, SE, S, SW, W, and NW). This method shall be terminated at the pilot's request.
3. Distance from aircraft in miles.
4. Direction in which traffic is proceeding and/or relative movement of traffic.
NOTE -- Relative movement includes closing, converging, parallel same direction, opposite direction, diverging, overtaking, crossing left to right, crossing right to left.
5. If known, type of aircraft and altitude.
It's as simple as 1, (2), 3.
Cessna 12345, Traffic (1) two o'clock (3) two miles (4) north bound (5) Cessna 172 level 5,000.
In case you can't imagine why we'd use number 2: Imagine you're in a holding pattern making an almost constant turn. It's real difficult to accurately tell where your 2 o'clock is at any given moment when viewed on the radar scope.
Cessna 12345, Traffic (2) southeast (3) two miles (4) north bound (5) Cessna 172 level 5,000.
If someone's brain is screaming "A-ha! Gotcha!" you don't have to apply merging target procedures in a holding pattern. The paragraph on traffic advisories doesn't mention holding patterns. I told you there were a lot of details.
6. When requested by the pilot, issue radar vectors to assist in avoiding the traffic, provided the aircraft to be vectored is within your area of jurisdiction or coordination has been effected with the sector/facility in whose area the aircraft is operating.
7. If unable to provide vector service, inform the pilot.
In my opinion, pilots don't ask for a vector around traffic nearly enough. I've mentioned this before but it bears repeating. If you wait too long, vectoring becomes a less and less desirable option. This is especially true in the Centers. I know a mile sounds like a lot of space to a pilot, but at the Center, the target on our display can be a mile long depending on the range we've selected on the radar. If you wait, you may find yourself in a situation where it is too close to call. When it comes to avoiding VFR traffic, I'm a believer in the TUE principle: Think Ugly Early.
8. Inform the pilot of the following when traffic you have issued is not reported in sight:(a) The traffic is no factor.
(b) The traffic is no longer depicted on radar.
If the pilot doesn't ever say, "Traffic in sight," then sooner or later I'm supposed to advise the pilot, "Traffic no factor." I will readily admit that this part slips a controller's mind on a regular basis. Not as an excuse but as a frame of reference: Telling a pilot he's clear of traffic isn't nearly as high on a controller's priority list as calling the traffic in the first place.
I suppose this could be why some pilots respond to a traffic call with, "We're in the soup." They're just trying to let us know they never will see the traffic. It's understandable. Sometimes it can even be helpful. As long as you know what is going on, what the controller is doing and apply some good judgment, I won't harp on it. But if a controller is talking 90 miles an hour to a dozen airplanes and your reply to a traffic call is a 30-second dissertation on the weather, I'm going to question the good judgment part.
Traffic Collision Avoidance System. What's a controller to say? On one hand, we're glad pilots have a greater appreciation for just how many airplanes are out there. On the other hand, anything that can be used can be abused. Some pilots, being the clever individuals that they are, will abuse it. No, I'm not going to detail how. Let's just say I don't think TCAS was designed so pilots would feel comfortable getting closer to other airplanes.
Lets look at what the books say. Your book first (AIM):
4-4-15. Traffic Alert and Collision Avoidance System (TCAS I & II)
a. TCAS I provides proximity warning only, to assist the pilot in the visual acquisition of intruder aircraft. No recommended avoidance maneuvers are provided nor authorized as a direct result of a TCAS I warning. It is intended for use by smaller commuter aircraft holding 10 to 30 passenger seats, and general aviation aircraft.
Let's pause right here. "No recommended avoidance maneuvers are provided nor authorized ..." While researching this article I also stumbled on this -- a Flight Standards Handbook Bulletin:
3. TCAS I Operational Approval Requirements
The use of TCAS I requires operational approval. This requirement includes FAA approval of pertinent training modules, checklists, operations manuals, training manuals, maintenance programs, minimum equipment lists (MEL), and other pertinent documents.
How long have we had TCAS? Believe it or not, this is the first time I've ever heard of any training requirement for TCAS I. Here's your chance to educate me. In your training for TCAS, did your instructor tell you never ever to use this phraseology?
"We've got him on TCAS."
No? Then why not? Stand by for a rant.
You might care that you've got him on TCAS. I don't. What am I going to do with the info? I can't quit calling traffic. I've already quoted the rules for ATC. TCAS can't substitute for having the "traffic in sight." TCAS can't be used for visual separation.
Want to know why that phraseology really chaps my hide?
Airliner123, traffic 2 o'clock, five miles, west bound, a Boeing 737, flight level 310.
"Roger, we've got him Center." (Big pause.) "Well, we've got him on TCAS, anyway."
I'm not making that up by the way. That actually happened to me the other day. You do that below FL180 when I'm trying to set up a visual separation scenario and we're likely to have a problem. A big problem. Use TCAS for what it was designed for: to visually acquire the traffic.
Let's go back to that bulletin for a second:
A. Airplane Flight Manual (AFM). The AFM supplement for aircraft with TCAS I installed should contain the following statement in the Limitations Section: "The pilot should not maneuver the aircraft based solely on the traffic displayed by TCAS I." The Normal Procedures Section of the AFM supplement should clearly state the following recommended flightcrew actions when a TCAS I traffic advisory (TA) is issued:(1) The flightcrew should attempt to visually acquire the intruder aircraft and to attain/maintain safe separation in accordance with regulatory requirements and good operating practices.
(2) When the flightcrew cannot visually acquire the intruder aircraft but perceives the intruder as a threat, the crew may contact air traffic control (ATC) to obtain information that might help in locating the intruder aircraft.
B. Operational Procedures. TCAS I operational procedures should include the procedures outlined in 3.A.(1) and (2) above and the following:
(1) Pilots should not maneuver horizontally based solely on TA information. TCAS I TA display information is inadequate for collision avoidance maneuvers. A pilot maneuver based ONLY on this information might result in a loss of separation with the intruder (e.g., a turn toward the intruder). Pilots should maneuver horizontally only on receiving guidance from ATC or on acquiring visual contact with the intruder. Guidance from ATC will not be given unless the pilot asks for assistance per Air Traffic Control Handbook, 7110.65J, Chapter 1, paragraph 2-1-27. TCAS I information should not be used to "second guess" ATC.
(2) If an intruder cannot be acquired visually but is perceived as a threat and additional information is not available from ATC, vertical maneuvers which permit the aircraft to remain within 200 feet of the assigned altitude are permissible. Changes in climb or descent rates when approaching an intruder aircraft are not viewed as evasive maneuvers.
I'm really curious whether pilots using TCAS have read all this. I can assure you, most controllers haven't. I'm also curious if pilots perceive any problems that I (as a controller) do. On one hand, the AIM says, "No recommended avoidance maneuvers are provided nor authorized as a direct result of a TCAS I warning." On the other hand, this bulletin contains the language, "... vertical maneuvers which permit the aircraft to remain within 200 feet of the assigned altitude are permissible. Changes in climb or descent rates when approaching an intruder aircraft are not viewed as evasive maneuvers."
It would seem "evasive" doesn't always mean evasive. Just something to ponder. More to the point, if a pilot using TCAS I really believes that an intruder on his TCAS is going to hit him, you can bet your bottom dollar he's going to perform some kind of "evasive" maneuver regardless of what the rules say. So you might want to know this from my book:
2-1-27. TCAS Resolution Advisories
c. Once the responding aircraft has begun a maneuver in response to an RA, the controller is not responsible for providing standard separation between the aircraft that is responding to an RA and any other aircraft, airspace, terrain or obstructions. Responsibility for standard separation resumes when one of the following conditions is met:
1. The responding aircraft has returned to its assigned altitude, or
2. A crew member informs you that the TCAS maneuver is completed and you observe that standard separation has been reestablished, or
3. The responding aircraft has executed an alternate clearance and you observe that standard separation has been reestablished.
I want to make sure you understand this part. If you're using TCAS I and make an evasive maneuver, you're going out on a limb. If you advise the controller that you're doing something that you're not supposed to be doing, first he's going to be surprised and second he's going to fall back on his training (which is for TCAS II) -- even if his training doesn't fit the situation. You're going to be on your own until you get clear of the traffic you're trying to avoid and any other traffic that you may or may not be aware of.
If you'll take the time to read the books and what they have to say on this subject, there are a million things you could learn. Hopefully, I've laid this article out in a logical way that has allowed you to pick up some major points.
Resolving conflictions is usually easier in the vertical plane. TCAS I allows you some wiggle room on altitude and TCAS II only provides vertical Resolution Advisories. There's a reason behind that. Vectoring for traffic (using lateral separation) isn't an intuitive process.
Controllers train for years, learning how to vector. It's many more years before they become an expert in the skill. For instance, running in-trail to a major hub requires extensive vectoring. Ask any controllers and they will tell you that kind of vectoring is still more art than it is science. It isn't a skill that a pilot can pick up in a weekend seminar, much less retain any proficiency in over the years. Vectoring is tough. It's the reason we advise rookie controllers to "think altitude." You, as a pilot, might want to consider that advice too.
The last point I want to hit (again) before ending this article is how critical time becomes in a confusing situation. Take the time to think this stuff through while you have the luxury of time. You won't have that luxury -- time to think -- when you get into a tight traffic situation. You will have to make a decision and you will have to act. TCAS can be an asset if used properly. But it takes time to use it.
Back before TCAS, when controllers called traffic, we knew pilots were looking out the window. Now I wonder how much time they are burning up with their heads down, looking at the TCAS display instead of looking out the window. If you haven't wondered the same thing, then you're probably spending too much time with your head where it shouldn't be.
This system was the safest in the world long before TCAS came around or I started writing these articles. If you've been operating in the system safely then don't let any new information you receive from either a person or a machine radically alter your habits. Take the time to think things through and make sure you're improving your habits, using new information and technology to enhance the safe operation of your aircraft. Time in which to think clearly is a luxury. Use it wisely.
Have a safe flight.