Aviation Topic of the Week
By Michael Oxner, November 16, 2003


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This week's topic:
Radar Vectoring Revisited

After reviewing the information I had posted a while back on Radar Vectoring, I felt I just couldn't leave that topic alone. I stated there weren't too many things to say about vectoring but to get out and do it, but I did leave an awful lot of things unsaid in that topic. So, I'll try to clean up my act by getting back to it and filling in the blanks I left behind on that one.

Methods of Initiating Radar Vectors
Vectoring from a Tower
Aircraft on RNAV STARs
    Cancellation of the STAR
    Open RNAV STARs
Vectoring Fast Aircraft
Vectoring IFR Departures

Methods of Initiating Radar Vectors

I stated that initiating radar vectors is as simple as stating the heading you want an aircraft to fly. ATC MANOPS 543.1 says there are three ways to initiate a radar vector:
  1. Stating the heading, in three digits, without grouping the digits "CVA116 fly heading three four five"
  2. Specifying the direction of the turn and the heading to be flown "CFC82 turn left heading two seven zero"
  3. Specifying the direction of the turn and the number of degrees to turn "Romeo Alpha Tango turn left one five degrees"
The first two are pretty simple. You state the heading. The last one is used quite commonly since you can correct an aircraft's heading without needing to know what he's on to begin with. It's on days when wind drift is high when this last one comes in handy for saving words. For example, an aircraft that is tracking straight east with a stiff wind from the south would actually have his nose turned into the wind, perhaps heading 105°. So if you as a controller wish to turn the aircraft 10° to the right, you might look at the easterly track of 090° and say, "SAC117 turn right heading one zero zero". And the pilot has a range of answers to this, from asking "We're on a heading of one zero five already. You want us to turn further right?" to actually making the 355° turn to the right and ending up 5 degrees left of where he started. While I haven't yet seen this move done, real or online, yet, it does leave you to wasting words and radio time to get a vector started. It's often best to either ask present heading first, then issue a new heading to accomplish what you want, or say "SAC117 turn right ten degrees and say new heading." This accomplishes what you desired to begin with, the ten degree course correction, and it also lets you know what heading the aircraft will be on. Since you will now know the heading and you can observe the track, it also gives you a good feel for the amount of drift for successive aircraft in the same airspace, such as when you're vectoring more than one aircraft to final. I have seen some pilots online hear "turn left ten degrees" and make a left turn to "heading zero one zero". Close, but not quite doing what he was told to do.

Personally, I will often issue first turns in this last form, since it almost always accomplishes my results with a minimum of both words and subsequent corrections. You see what the aircraft is doing now, you know how much you want to change the heading, so you accomplish that most often in one transmission. If you don't know how much wind drift to expect, issuing a heading by stating the numbers may have you issuing a new heading once the aircraft settles in the new track. That being said, if the turn is a high magnitude, like 60°, 90° or worse, I believe it's better to issue the actual heading. Don't forget that when you initiate the vector, state the purpose of the vector, too. Most pilots wouldn't feel too happy about getting a 90° turn, but when you tell them in a stressed out voice "vectors around traffic", they'll generally listen up and take it quickly without wasting your radio time with an argument.

One more note on this: ATC might say something to the effect of, "continue inbound on V300 and depart the VOR heading one one zero for vectors to the ILS runway 29". This is a vector just the same as any other heading issued. The difference is that the vector doesn't begin right away, but rather after you pass the VOR.

Vectoring From a Tower

Normally, airport controllers don't get into vectoring, at least not directly. As indicated in past topics, they may tell aircraft to "extend downwind" or "turn base leg now", which gets an aircraft going in the direction he wants, but it's done without specifying a heading. When a heading is specified, it brings a pilot's eyes inside the cockpit, which is normally a bad idea when flying in a traffic pattern around an airport. The more time the pilot spends looking out the window, the better.

Radar vectors are used by Tower controllers when necessary, though. In the case of two aircraft within the control zone that are coming together and are having difficulty seeing each other, the tower controller may issue vectors to help them see each other so that they can maintain visual separation, or he may issue vectors to keep them apart as a last ditch effort. Pilots of VFR aircraft must realize that they are responsible for remaining in Visual Meteorological Conditions (VMC) (AIP RAC 1.5.4) and for meeting terrain and obstacle clearance while on a radar vector (AIP RAC 1.5.5). Vectors issued to VFR aircraft normally include the phrase "Maintain VFR" at the end to reinforce this requirement.

VFR pilots on radar vectors are also, like any pilot, the final authority as to whether the vector can be accepted, and are ultimately responsible for separation from other traffic. ATC may not see an aircraft on radar nearby, due to equipment limitations of either the radar system or, say, the lack of a transponder on an aircraft, so if a radar vector issued will take a you too close to another aircraft, make sure ATC knows. This is just like the refusal of any ATC clearance: If you refuse, make sure they know you are refusing and why. Don't just acknowledge and disregard it.

IFR aircraft are the responsibility of the IFR ATC unit, and will be vectored by the IFR unit. VFR aircraft may request radar vectors from either unit. Workload and equipment permitting, a tower controller may, if requested, issue radar vectors, such as for practice IFR approaches. Remember, pilots, someone still has to look out the windows, which is why an instructor must be present when a student is "under the hood".

Aircraft on RNAV STARs

Many modern aircraft operating at busier airports prefer to fly RNAV STARs. This provides the pilot so equipped with the opportunity for a Flight Management System to calculate Top of Descent (TOD) and an optimum airspeed and descent rate to fly the published flight path to transition from the enroute phase of flight to the approach phase without ATC intervention that would typically come in the form of radar vectors. ATC MANOPS 541.1 tells ATC to allow aircraft operating on RNAV STARs to fly on their own navigation to the extent possible. The "extent possible" might be canceling the STAR outright from the beginning and vectoring the aircraft, or allowing the aircraft to get to the downwind leg before a vector has to commence. It may mean not even vectoring the aircraft at all. The idea is to let the aircraft do his own thing unless you have to prevent it for separation. If he's number one, it's generally practicable. If he's number 2, or 4, or 10, it may be easier for you as ATC to remove him from an RNAV STAR by use of radar vectors to ensure a smooth flow of traffic. There are some things to remember when dealing with such a situation, from both sides of the radio.

For a pilot, if ATC initiates a radar vector to an aircraft flying an RNAV STAR by any one of the methods above, the RNAV STAR is automatically canceled. The pilot is now to proceed as it normally would on radar vectors, and has no authority to rejoin the STAR. If the vector is terminated any time before the aircraft is established on final (perhaps the traffic that required the vector has now passed, for example), the pilot must obtain from ATC authority to rejoin the STAR. This can either be stated by ATC when vectoring is no longer required, or a clearance requested and received from ATC to rejoin the STAR. Such a clearance would include a routing to a fix on the STAR (normally directly to a fix), and then the restatement of the RNAV STAR and the runway number to use. "CVA822 is cleared direct LOGPO and the balance of the FUNDY 6 for runway 24."

Now from the control side. As stated above, try to let an aircraft who has flight planned an RNAV STAR fly the STAR. If traffic becomes an issue, don't hesitate to tell the aircraft to change course. Issue a heading, if necessary, to remove the aircraft from the STAR's route. If it becomes reasonable to let the aircraft rejoin the STAR, try to choose a fix that is a reasonable place to do so. For example, if a STAR contains FIXA, FIXB, FIXC , FIXD and FIXE, and the aircraft has already passed the first two fixes but is almost right over FIXC, consider clearing the aircraft directly to FIXD and then the balance of the STAR. Clearing him direct to FIXC might cause the aircraft to overshoot FIXC by the time the pilot programs the route and therefore cause problems with an unexpected, sharp turn. If FIXD isn't practical for your situation, consider continuing the radar vector, or use of FIXE if the turns aren't too sharp.

With an open RNAV STAR, the pilot is automatically on a vector if he hasn't received an approach clearance by the time he reaches the Downwind Termination Waypoint (DTW). Clearing someone for for the "FUNDY6 runway 24" and clearing someone for "the ILS runway 24 approach via the FUNDY6" are two different things. The second allows the pilot to complete the approach without flying outbound for vectors at the DTW. The first example would force the aircraft to depart the DTW on the depicted heading, and the pilot is to consider himself on radar vector as per the usual at that point.

Vectoring Fast Aircraft

While the same concepts hold true for someone flying fast when being vectored to intercept a localizer, this section is primarily meant for aircraft at high speeds at enroute altitudes. Further, it is meant more for when a vector is needed to maintain separation from other traffic or something more immediate than just a course correction. I work Moncton's low level specialty where many of our vectors are comparatively small, like 10 or 15 degrees. Our high level specialty, on the other hand, rarely gives less than 30 degree turns to aircraft requiring vectors. The difference? A Dash 8 at 3,000 feet doing 180 knots initiates the turn quicker and the course alteration shows on radar sooner than for a B747 cruising at FL390 with a groundspeed of 550 knots. The first example above can have a turn radius as little as a mile or so, while the B747 can take many miles before any perceptible track change shows up. Also, two Cessnas closing at 100 knots each (combined 200 knots) leave you plenty of time to effect corrective action. Two aircraft with a combined closing speed of 900 knots race together quite quickly, especially considering how shallow the turn will be once issued. For this reason, if a turn is needed for an aircraft at high speed and altitude, considerable room is required to see the desired change take place. Therefore, the turns our high level issue as noted above need to be issued early and positively in order to ensure adequate spacing is obtained. You may not get a second chance to increase the degree of the vector. For the sake of trivia, I have an excellent, detailed book on the SR-71 that includes the turn radius for the Blackbird at Mach 3 at 85,000 feet: An incredible 150 nautical miles! They can turn quicker, but it means a huge loss of altitude to keep from overstressing the airframe at those high operating temperatures.

Vectoring IFR Departures

One last word for now, is how to handle departures on radar vectors. As mentioned before, the aircraft has to be at or above an MRVA before you can start vectoring him. Since many busier airports commonly use Radar Vector SIDs, the majority of aircraft will depart and take the heading on the SID plate and "expect radar vectors to assigned route" as it is worded on many SID plates. I don't believe there are any airports that are at or above Minimum Radar Vectoring Altitudes in Canada (bad humor?), so how do you start vectoring them on departure? The aircraft cannot be expected to make turns until reaching a safe altitude. The good news is that most airport runways are assessed for diverse departures. For IFR aircraft this means that crossing the departure end of the runway at 50 feet AGL or higher, climbing to 400 feet AGL before commencing any turns and maintaining a climb gradient of at least 200 feet per NM will be safe. Turns can be commenced lower than the MRVA, but you should leave that up to the pilot. When he calls in and you radar identify him, use a term like, "...  at your discretion, turn left heading ..." or "... when able, fly heading..." If the aircraft has already reached, or is above, your MRVA, you know it's safe to make turns, so omission of these statements is OK, just as though you were vectoring him any other time. "Fly heading 305" or "turn left heading 180" is all good, now, without having to say, "at your discretion" or "when able".

So where do you vector an aircraft on departure? To his assigned route in the IFR clearance that was already issued to him on the ground. If he filed an airway, you could vector him to intercept the airway at a convenient spot just like you would vector him to a localizer (ie, 30° intercept). You could also give him a vector to fly "til able direct" to a NAVAID and then "on course". For example, the Preferential Route from CYHZ to CYYZ is "CYHZ MLT VLV J509 YOW J546 YSO V37 CYYZ". Since direct to MLT is the first leg, a departure who calls in could be issued, "CVA822, Halifax Departure, radar identified. Fly heading 305 til able direct MLT and proceed on course, climb to FL280". As soon as the pilot is receiving MLT VOR, or as soon as he sets up the RNAV or GPS for present position direct if he has either of these, he may commence his own navigation. Some pilots tell you when they begin doing their own thing, but since the clearance above lets the pilot do it on his own, you need not be too concerned about when he starts doing his own navigation. A simple "roger" is all that's needed in such a case. You should continue to monitor the flight to make sure the heading you gave is good. Changing winds at different levels, or even from day to day, might require some fine tuning of the heading issued.




Well now I hope that I have saved some face and completed what I should have said with that last topic about vectoring. This topic can be read by clicking on this link. Truly, the info contained in the last one is valid, and so it must be used in conjunction with what is said here. Any praise or criticisms will be warmly received at my e-mail address, moxner@nbnet.nb.ca. Thanks again for taking the time to read!