Aviation Topic of the Week
By Michael Oxner, August 24, 2003


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This week's topic:
VFR Flight Part 2: Controlled Airspace

VFR in uncontrolled airspace is pretty easy. Fly at a suitable altitude, watch out for other aircraft. This segment, we'll look at the rules for VFR in specific types of controlled airspace. You may wish to refer to the Classes of Airspace Topic recently discussed in the Archives.

Transponder Requirements
    Code Selection
General
    Altitude Assignments
    Vectors from ATC
Airspace Rules
    Class E Airspace
    Class D Airspace
    Class C Airspace
    Class B Airspace
    Other

Transponder Requirements

One of the things about VFR flight is the comparative lack of instrumentation requirements over IFR. Many regimes of IFR flight require special certifications for both pilot and aircraft, and special pieces of equipment for navigation and so forth. A VFR aircraft needs only basic instrumentation in most circumstances. CAR 601.03 states some  requirements for aircraft operation in the various classes of airspace with respect to transponder equipment. It says that aircraft operating in Transponder Airspace must be equipped with a functioning transponder incorporating an automatic pressure reporting device. This simply means Mode C.

The AIP RAC 1.9.2 gives us a summary of Transponder Requirements. Transponder Airspace is:
  1. All Class A Airspace
  2. All Class B Airspace
  3. All Class C Airspace
  4. All Class D or E Airspace that is specified as "Transponder Airspace" in the Designated Airspace Handbook, or DAH for short. This includes all Class E airspace upward from 10,000 feet up to and including 12,500 feet ASL within radar coverage.
Code Selection

The AIP RAC 1.9.4 gives us direction for codes in VFR flight. It says to use code 1200 when operating at or below 12,500 feet ASL, and code 1400 when operating above 12,500 feet, unless otherwise assigned by an ATS unit. (ATS stands for Air Traffic Services in Canada, and this includes Flight Service Stations. Many FSS are equipped with a drop from the radar data from their parent ACC, and some may assign discrete codes to VFR aircraft operating nearby.) Note that the codes are independent of the class of airspace, and only refer to the altitude of the aircraft. Since many aircraft may select these codes, they are considered non-discrete. A discrete code is one that is normally assigned to one aircraft in any one area at a time.

It also says that the pilot is responsible for changing the code on the transponder back to an appropriate non-discrete code mentioned above after leaving the airspace for which the discrete code was assigned unless otherwise directed by ATS.

The AIP also gives us a little summary on changing codes when climbing above 12,500 feet when not assigned a discrete code by ATC. It says to keep the transponder selected to 1200 until climbing through 12,500., then select 1400. Likewise, when descending, keep 1400 until through 12,500 in descent, then change back to 1200. Mode C should be selected at all times when the transponder is on while flying in Canadian airspace unless directed otherwise by ATS.

General

When it comes to ATC units and different types of airspace, just remember there are some possibilities as to who is the controlling agency for a given area. I'll refer you to the Classes of Airspace topic I wrote before for more details, but in the ATC world there are IFR units, which include Area Control Centers (ACC) and Terminal Control Units (TCU), and there are towers as well. The IFR units are primarily responsible for control of IFR aircraft under IFR flight, while VFR flights are largely on their own, except where the airspace rules dictate otherwise. TWRs are established to enhance safety at busier airports, and they have been given authority to issue instructions and direction to aircraft operating in a control zone. While the class of airspace in the zones plays a large part of what ATC can tell you to do, there are a couple of things to remember. First, the pilot always has final authority in what the flight will do, since it's his butt that's in the cockpit. Second, because ATC has the "bigger picture", you had better have a darned good reason for not doing what ATC tells you to do, whether talking to a TWR in a control zone, or an IFR unit elsewhere.

Altitude Assignments

ATC should not given specific direction to do certain things in certain classes of airspace (like telling a VFR pilot to maintain an altitude in Class E airspace). If you hear anything like that being said, I'd say you should at least consider it, since he may have a good reason for it, but you should remember in that example above he actually does not have the authority to assign it. As a VFR pilot on a VFR flight, you are responsible to remain in VFR conditions. Now if the instruction were given in Class B airspace, as you'll see below, the altitude must be adhered to if the safety of the aircraft will not be compromised, whether you like it or not.

Vectors from ATC

Also remember the class of airspace you're in when it comes to radar vectors. ATC may be attempting to resolve a conflict between you and another aircraft, and in doing so may assign a heading. In Class E airspace, ATC has no authority to issue vectors and expect you, as a VFR pilot, to fly the heading. In Class C airspace, you have to take the heading unless if will turn you into bad weather or terrain. Which brings us to the one major difference between VFR and IFR when it comes to vectors: When ATC vectors an IFR flight, the controller is responsible for terrain and obstruction clearance. For VFR, the pilot is. If a vector issued will put the aircraft in danger of colliding with terrain, he must not accept the vector and advise ATC as soon as possible of the action taken. The pilot is actually still responsible, according to the AIP RAC 1.5.4, for remaining clear of other traffic as well. One would hope that an ATC issuing vectors has the same intent, but it is always possible that ATC can't see an aircraft, such as the case when the other traffic has no transponder outside of primary radar coverage.

When ATC no longer requires vectors, or can no longer provide them, the pilot should be informed. In the case of a VFR aircraft being vectored for traffic avoidance, the pilot should call when he has the traffic in sight. ATC will use a phrase something along the lines of "resume normal navigation" to let the pilot know he can stop flying the issued heading. If further instructions are needed after termination of a vector, ATC will state these at the time. When leaving controlled airspace, as with IFR flights, ATC will normally terminate radar service as well. The phrase used here is (surprise!) "Radar service terminated". Upon hearing those words directed to you, you may stop flying the heading issued and resume normal navigation. When vectoring is terminated, ATC is supposed to give an aircraft (VFR or IFR) a position relative to a fix or course to tell the pilot were he is to aid in the transition to normal navigation. For example:

"Alpha Bravo Charlie, you're 10 east of the Moncton airport, resume normal navigation"

Use of Airways and Instrument Approaches

There is no prohibition on a VFR aircraft's use of instrument approaches and airways. In fact, is perfectly legal for VFR aircraft to use either. That's one of the reasons for the establishment of different altitudes for VFR and IFR in cruise flight. One caution regarding the use of instrument aids is that the pilot is still responsible for remaining in VFR conditions and looking out the window for other traffic. Remember to stay clear of clouds, even if this means deviating from the airway centerline to get around one, or abandoning the airway altogether.

At a controlled airport, ATC authorization must be obtained to fly an instrument approach aid when simulating, or practicing, IFR approaches. This can be cockpit intensive and the VFR pilot may greatly reduce the time spent looking out the window. For this reason, instructors will be doing the window watching during "hood training" (where a hood or other device is in place to restrict the pilot's view outside the aircraft). It is not legal, nor is it safe, for a lone pilot to do instrument simulation without looking out the window. When ATC authorizes a simulated instrument approach, the phrase "Maintain VFR" is added to the transmission to reinforce this concept. Similarly, if the weather is marginally VFR, perhaps one should consider concentrating on looking out the window, rather try "sliding over" to pick up a localizer for an ILS.

Airspace Rules

There are some rules and expectations that go with each class of airspace. They all have one major thing in common for VFR flight: The flight must be operated in Visual Meteorological Conditions (VMC) at all times. Period. Getting into IMC can be deadly in a short period of time. Even if ATC (or someone else) suggests that you do something that could take you in, under or over weather, you should strongly consider what you're about to do before you do it. ATC might not be aware of IFR weather conditions moving in, and might attempt to direct you into weather unknowingly. There was an excellent write up about an aircraft talking to ATC in Atlanta for flight following and he was approaching a wall of cloud. He advised that he had to change heading. ATC said he could keep clear of oncoming traffic if he kept his current heading for another minute or so (which ATC didn't know would take him into clouds, since the pilot gave no indication of how close he was to the cloud). The next thing you know, the pilot was apologizing to ATC for ending up in a spin as he spiraled to his death. ATC simply suggested something and the pilot apparently took it as an instruction. This is yet another reason why you should be aware of the class of airspace you're in, so you know what rights you have and what to expect from ATC. If you're ever unsure of anything, ask ATC for clarification. Remaining in VFR conditions is of the utmost importance.

Class E Airspace

Class E airspace is the lowest level of controlled airspace. VFR aircraft need no clearance or permission to operate in Class E airspace, and they don't even have to talk to ATC. What's the reason for the distinction, then? The designation of controlled airspace raises the weather minima for VFR flight, thereby increasing the safety margin for the "see and be seen" concept, primarily between VFR and IFR. Any Class E airspace specifically designated as Transponder Airspace will be marked on Visual Navigation Charts, or VNCs. In this case, a Mode C transponder will only be required if it is specifically designated that Mode C is required, and this will be published on the appropriate area of the VNC.

Class D Airspace

Now we start to get into a little different place with rules as we enter a new type of airspace. Most aerodromes with operational control towers are surrounded by Class D airspace, and some terminal areas are also comprised largely of Class D airspace. This was done around certain airports where the mix of VFR traffic and IFR traffic was such that it was believed a safety benefit could be derived from such a designation and the requirements associated with it.

Back to the old AIP, this time section RAC 2.8.4 to begin our look at VFR in Class D airspace.
  1. The aircraft must have equipment capable of two-way communication, and a transponder if the airspace is designated as transponder airspace.
  2. A continuous listening watch is to be maintained on the radio frequency assigned by ATC.
The pilot should not leave the frequency assigned unless authorized by ATC. Any need to modify a flight plan, pick up an ATIS, etc, should be mentioned to ATC and their approval obtained prior to the change.

ATC provides conflict resolution between IFR and VFR aircraft in Class D airspace (workload and equipment permitting) and between VFR aircraft if requested. Otherwise, traffic information will be provided and the pilot is on his own hook to look for and avoid the other traffic. These are the reasons why the pilot must listen to ATC's frequency. It's pretty darned hard for ATC to provide any information to a pilot who isn't listening. Since traffic congestion is part of the reason for establishment of Class D airspace, whether it's a control zone or terminal area, this is vitally important. VFR aircraft may not enter Class D airspace without making contact with the controlling agency. It has been argued that the pilot need only make contact, therefore being told to "standby" counts and the pilot may proceed in. Should a pilot take such an action, vigilance and caution should be exercised, since ATC is probably busy, which may mean traffic.

Class D airspace reverts to Class E airspace when the appropriate unit is closed, so then the Class E rules apply in that area.

Class C Airspace

On to another class of airspace, again with its own issues. VFR may operate in Class C airspace, but they must talk to ATC and receive an ATC clearance to operate in Class C. ATC will provide separation between IFR and VFR aircraft as necessary to resolve conflicts. This means the pilot must obey an ATC instruction or clearance unless safety might be jeopardized. This could include the existence of IMC that ATC is not aware of, for example, or assignment of an unsafe altitude for the aircraft. Traffic information will be provided here, as well. Once traffic information has been provided, ATC will provide conflict resolution upon request.

Conflict resolution, incidentally, is defined as the resolution of potential conflicts between IFR/VFR and VFR/VFR aircraft that are radar identified and in communication with ATC. ATC may issue instructions or restrictions to aircraft operation to provide such resolution, including such things as, "remain east of the four-lane highway to your right", or "not above 3,500 til you have the traffic in sight". Any such tactics are available, since the idea is merely to keep aircraft from hitting. Once the pilots sight each other, the pilots are normally left to provide their own separation from each other, and such restrictions may be lifted.

As with Class D airspace, Class C reverts to Class E airspace when the associated ATC unit is not operating, and Class E rules apply.

For Class C airspace, the AIP RAC 2.8.3 defines the following requirements for VFR in Class C:
  1. The aircraft must have equipment capable of two-way communication, and a transponder with Mode C capability.
  2. A continuous listening watch is to be maintained on the radio frequency assigned by ATC.
Class B Airspace

This is a little different from the others, but it's a logical progression. We went from no requirements for clearance and communications (Class E) to contact and communications (Class D) to clearance and communications (Class C). One thing that is different here is the level of separation provided by ATC. That progression went from nothing (Class E) to information and conflict resolution (Class D) to separation/conflict resolution (Class C). Now we continue the sequence. In Class B, you need to talk to ATC and continuously monitor them, just as would an IFR aircraft. You must also obtain and comply with an ATC clearance, just as you would when flying IFR. You must also have a Mode C transponder in Class B. The big difference here is that you will be expected to fly at IFR altitudes (odd and even thousands, depending on direction of flight) and you will be separated from IFR aircraft and other VFR aircraft just as though you and they are IFR. In fact, flight in Class B airspace is called Controlled VFR, or CVFR. All low level controlled airspace above 12,500 ASL (or the MEA on an airway, whichever is higher) up to but not including 18,000 (FL180)  is Class B airspace in Canada.

You must follow an ATC clearance in Class B airspace, and it will be treated by ATC in the same manor as an IFR clearance. If ATC gives you a clearance to might take you into IFR conditions, you must request either a clearance that can keep you clear of the weather (an altitude change, a route change, etc), or request a clearance to leave Class B airspace to ensure the aircraft can remain in VMC.

The rules of VFR above 12,500 differ between the US and Canada. I'm not sure of the specifics, so I won't go into them.

Other

As mentioned in a previous topic, VFR flight is prohibited in Class A airspace. As for Class F, well, it depends on the nature of the airspace. For restricted airspace, it's simple. These areas are no-fly zones, period. Advisory areas may be penetrated, but due caution is advised, being aware of the nature of the activity taking place in the area. Many advisory areas have frequencies published, and should you enter one of these areas, and doing so isn't advisable, you should monitor the published frequency while you're in the area to give you every possible chance of avoiding being caught up in the activity.




I know this one is capable of raising some more questions, so please fire away. What I wrote here came from the AIP Canada, and it is vague in places. Anything you want to see clarified, please send along to me via e-mail at moxner@nbnet.nb.ca. Thanks for reading!