Aviation Topic of the Week
By Michael Oxner,
November 16, 2003
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:
- Stating the heading, in three digits, without grouping the digits
"CVA116 fly heading three four five"
- Specifying the direction of the turn and the heading to be flown
"CFC82 turn left heading two seven zero"
- 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!