Aviation Topic of the Week
By Michael Oxner, August 15, 2004


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This week's topic:
VFR Flight Example, Part 6: Inbound to Halifax

Last week, our pilot successfully avoided hitting some airplanes at Debert, thereby allowing our VFR Flight Example to continue. We'll pick up where we left off: just clearing the ATF area around Debert, climbing out toward Halifax.

Class D Basics
Entering Class D Airspace
Getting the ATIS
Setting Up for the Approach

Class D Basics

The big rules regarding Class D airspace, from our perspective, are that two-way radio contact must be established prior to entry, and that ATC has the authority to restrict activities of VFR aircraft within the areas. The reason is that ATC has the responsibility of providing "conflict resolution" within Class D airspace between IFR and VFR aircraft (equipment and workload permitting), in addition to the normal provision of separation between IFR and IFR. Also, where equipment and workload permit, ATC may provide conflict resolution between VFR aircraft. Conflict resolution is traffic information along with instructions which will keep aircraft apart. More will be discussed below. Most airport control towers have Class D control zones, so those familiar with these areas are also in the know for the Class D airspace around a busier terminal area.

So what's the deal? Do we need a clearance to enter? The answer is "no". No clearance is required for VFR aircraft to enter Class D airspace, such as is the case for Class B. The difference is subtle. In both cases, the pilot must talk to ATC first. In Class B, the pilot must obtain a clearance prior to entering. In Class D, the pilot need only establish communication with ATC to be allowed to enter. This means that a radio call answered with "standby" actually allows the pilot to enter, unlike Class B. Seems strange, doesn't it? If ATC were busy and needed a pilot to stay outside in order to limit the number of aircraft in the area, he actually must state that. The pilot would then, all else being equal, comply with that instruction, since ATC has the authority to control that area. For aircraft without working radios, or with receiver only (RONLY), special provisions must be made. This usually amounts to a telephone call to ATC prior to entry (which typically means prior to take-off) to get permission to enter.

As mentioned earlier, ATC has the authority to restrict traffic within Class D airspace. This doesn't just mean the number of aircraft, but also restrictions on the flights, too. Such as assigning a VFR aircraft a minimum or maximum altitude for operation. "Not above two thousand five hundred," for example. Or, "Remain west of the Chocolate River," and so forth. Typically this is done to ensure aircraft don't come into close proximity with other aircraft, or with high traffic corridors. The pilot may refuse such a restriction, but he had better be prepared to justify such a refusal. For example, if ATC tells a VFR pilot to remain at or above 4,500 feet, but that restriction means the aircraft might enter cloud ahead. This would be justification. Depending on the reason ATC had for the restriction in the first place, the pilot refusing such a restriction had better be prepared to orbit outside for a while until the traffic permits further entry at a lower altitude, or on a different route. Any pilot operating within Class D airspace must also maintain a continuous listening watch on the appropriate ATC frequency while operating within the Class D airspace. Moving right along...

Entering Class D Airspace

As mentioned last week, the pilot was clearing the ATF area south of Debert. He is climbing through 2,500, and the floor of the Class D in this area is 2,900, so the radio call had better come soon. The pilot tunes in the VFR Frequency (118.7), listens to make sure he doesn't talk over anyone, and then:

CGOOF: "Halifax Terminal, Cessna Golf Oscar Oscar Foxtrot."
CYHZ_TCU: "Cessna Golf Oscar Oscar Foxtrot, Halifax Terminal."
As mentioned earlier, the pilot is now technically allowed to enter the Class D airspace.
CGOOF: "Oscar Oscar Foxtrot thirty miles north of Halifax out of two thousand six hundred for four thousand five hundred, following highway one-oh-two inbound for Halifax."
CYHZ_TCU: "Oscar Oscar Foxtrot, altimeter three zero zero four. Squawk four three one seven."
CGOOF: "Oscar Oscar Foxtrot."

Some readers might find it offensive that our pilot didn't read back the code or the altimeter setting. Neither is actually required. The vast majority of pilots will readback at the altimeter setting, and most will readback the code. Personally, I encourage the readback of altimeter settings, since it offers another chance to catch an error. As for the code, ATC will notice if you dial in the wrong code on the transponder and they will correct you anyway.

CYHZ_TCU: "Oscar Oscar Foxtrot is radar identified."
CGOOF: "Oscar Oscar Foxtrot."

In these last two transmissions, a couple of  things were actually said. First off, Halifax ATC has actually verified CGOOF's Mode C. The pilot stated his passing altitude when he called in, and since ATC has radar identified the aircraft (using the code change as confirmation) without mentioning the altitude, it must have agreed with the Mode C readout on the radar. Secondly, ATC has essentially granted permission to the aircraft to fly along the stated route of flight and altitude, since he didn't attach any conditions. As such, it is just good airmanship to acknowledge a radio call.

Those aware of Halifax's facilities, and those simply aware of a piece of equipment that is found at most airports served by their own terminals, may have noticed something that neither our pilot has made mention of so far, nor has ATC. Strange, since that's actually part of the deal, isn't it? I'm talking here about the ATIS. Before contacting ATC, the pilot is actually supposed to listen to the ATIS to ensure he has the current information regarding the airport and current operations. Our pilot intentionally skipped this step, since he was rapidly approaching the floor of the Class D airspace and didn't want to level. Halifax ATC, in this instance, is probably waiting for the pilot to acknowledge receipt of the latest ATIS message, but probably giving a few minutes to accomplish this, given that the aircraft is a Cessna 172 (read: slow moving) and he is still 30 miles or so from the airport.

CYHZ_TCU: "Oscar Oscar Foxtrot, do you have information Echo?"
CGOOF: "Negative, sir. Request permission to leave the frequency to get it."
CYHZ_TCU: "Oscar Oscar Foxtrot, roger, advise when you have it."

While not being explicit, ATC has approved the change of frequency so our pilot can get the ATIS.

Getting the ATIS

Upon tuning up the ATIS (the frequency is found in the Canada Flight Supplement), our pilot hears this:

"Halifax International Airport information ECHO, weather at one seven zero zero zulu. Winds three three zero degrees magnetic at five knots, visibility one five miles. Seven thousand scattered, two five thousand scattered. Temperature one eight, dewpoint seven. Altimeter three zero zero two. Approach, visual runway three three. Landing and departing runway three three. Simultaneous intersecting runway operations in effect. Landing distances available: to land runway three three and hold short of runway zero six - two four, three thousand seven hundred feet. To land runway zero six and hold short of runway one five - three three, eight thousand two hundred. Advise ATC on initial contact you have received information ECHO."

A couple notes here. First off, ATC gave us an altimeter of 30.04, and the ATIS says 30.02. Which do you use? Always use the current one, and this is obtained from ATC directly. The ATIS generally gives what's on the weather sequence (the primary exception is when the altimeter changes rapidly but the rest of the weather doesn't -- ATC is required to update the ATIS if the altimeter setting changes by 0.04 or more). In this case, we use the altimeter of  30.04 as provided by Halifax TCU.

The other biggy here is the intersecting runway operations. At some airports ATC is allowed to clear aircraft to land simultaneously on intersecting runways and tell one aircraft to "hold short" of the other runway. Also, they may clear one aircraft to take-off one one runway and allow another aircraft to land on the intersecting runway with a "hold short" instruction attached to the landing clearance. Before using such an instruction, both pilots are given traffic, landing distances available, wind direction, and then he will be asked if he can accept the operation, or told that he will be expected to land and hold short, or that traffic will be landing and holding short of his runway. This is the time for a pilot to say "yes" or "no" to the operation. If he says nothing negative about it, ATC will assume he is accepting it, and the plans will proceed. If he says he can't accept it, ATC will make alternate plans, which may include sending you further downwind, or widening your base leg or whatever he needs to do to delay you or the other guy. Some airlines do not allow their pilots to participate in such operation as a matter of principle. ATC considers the "stopping distance group" of aircraft types and, according to rules they have, determines if this is a possibility before the operation is even contemplated. There are many rules to the intersecting runway operations that take into consideration the runway surface conditions, time of day, tailwind component, and so on.

CGOOF: "Terminal, Oscar Oscar Foxtrot has ECHO."
CYHZ_TCU: "Oscar Oscar Foxtrot, roger."

Now the terminal controller knows the pilot is aware of what's going on at Halifax, right down to the runway lengths available if he were asked to land and hold short. Many pilots would say something like, "Terminal, Oscar Oscar Foxtrot back with you..." By the mere fact that the radio transmission comes through, ATC knows you are "back with him". No need to say that.

Setting Up for the Approach

CYHZ Now that he knows what approach is being used, he begins to plan his approach. This is good practice, even though ATC hasn't told him what to do yet. In fact, the terminal controller isn't likely to get into telling the pilot how to join the circuit, either. That's the tower's job. The terminal controller is primarily responsible for the airspace around the control zone. The CZ itself belongs to the tower, just as with an airport that isn't served by a TCU. Eventually, the pilot can expect to be changed to the tower for further instructions.

Referring to the map at right, you can see that highway 102 goes right past, just to the west, of the airport. This allows the pilot (and ATC) a convenient approach path to join a right-hand downwind for runway 33. Especially since it keeps the aircraft out of the approach of runway 24 in the process. In all likelihood, this is what the tower will tell our pilot to do. Planning on this, he figures out when he wants to begin descent. I'll let you think about that, too, for a mental exercise. An example is part 5 of this flight example as our pilot approaches Debert.

CGOOF: "Terminal, Oscar Oscar Foxtrot would like to begin descent."
CYHZ_TCU: "Oscar Oscar Foxtrot, descent at your discretion. Contact tower now one one eight four."
CGOOF: "Oscar Oscar Foxtrot."

Is it really required for a pilot to ask for descent? I don't believe so. Where ATC didn't place any restriction on initial contact, our pilot really isn't restricted. A report of commencing descent is important, just as it would be if the pilot were operating in uncontrolled airspace (Class G). It's just a matter of what frequency the report is done on. This allows someone to know what he is up to, and it provides an opportunity for someone to catch a problem before it gets out of hand. Halifax ATC said, "descent is at your discretion" simply to confirm for the pilot that he has no restrictions in place for him.

Again, for the radio etiquette part, the frequency need not be read back. A simple acknowledgment will do. Anyone who has read my previous topics will know just how important the acknowledgment of a frequency change is to me. It's such a simple thing, why not do it?



Well, here we are. Getting ready to approach our destination. Next week, we'll look at the tower's side of things. For now, I'm happily taking any e-mails at moxner@nbnet.nb.ca. Got a beef with anything said here? Looking for clarification on something? Send it along. I'll try to justify it to you. Thanks again, as always, for taking the time to read!