Aviation Topic of the Week
By Michael Oxner, August 29, 2004

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This week's topic:
VFR Flight Example, Part 8: Taxiing In

Our pilot has finally landed at Halifax International. Last week, he cleared the runway, and now has to make it to the Fixed Base Operator (FBO) to finish his flight.

Contacting Ground
Apron Advisory
Taxiing on the Apron
Clearing the Taxiways

Contacting Ground

Once clear of the runway in the taxiway assigned by the tower after landing, our pilot must contact Ground Control for further instructions. First things first, though. How does a pilot know when he is clear of the runway? At an airport like Halifax, there are hold lines painted, meant to show pilots where to stop when taxiing toward the runway. These lines are also used to help a pilot judge when he is clear. They are typically painted 200 feet from the edge of the runway, although there are several exceptions to this rule. According to the AIP RAC 4.4.4, when the pilot has all of his aircraft past this line, or 200 feet clear of the runway in the absence of the lines, he is clear of the runway.

CGOOF: "Halifax Ground, Cessna Golf Oscar Oscar Foxtrot in Foxtrot for IMP."
CYHZ_GND: "Oscar Oscar Foxtrot, Ground, taxi Foxtrot, Golf, contact Apron Advisory on one two two one seven. Call before entering Alpha."
CGOOF: "Oscar Oscar Foxtrot."

Let's take this apart line by line. The first one is simple, the pilot checking in with his type, callsign, position and request. For those who don't know, IMP is an FBO at CYHZ. They provide the standard services of fuel and facilities, as do others at this and other airports, for aircraft while they stay at the field. Ground tells CGOOF to taxi on F and G taxiways, which is a clearance, and then tells him to contact Apron Advisory. A short point before we talk about Apron Advisory is the frequency. Aviation bands in North America us 25 kHz spacing. Historically, many frequencies were whole numbers, or to one decimal place, such as 118.0, and 119.2, meaning 100 kHz spacing, or 0.1 MHz. As traffic grew, ATC's need to sectorize smaller and smaller grew. This meant the need for more frequencies. This lead to halving the spacing to 50 kHz (0.05 MHz), and gave rise to frequencies such as 128.55, between 128.5 and 128.6, naturally. The need increases. So does the available frequency spacing, now including 25 kHz spacing as mentioned earlier. This means frequencies like 127.125 MHz. The issue? Many aircraft radios are capable of tuning in the 25 kHz steps, but still only show 5 digits. Meaning 127.125 will actually show as 127.12. The five is still there, but not shown. Many computer programs, and I believe some commercial radio frequency scanners, incorrectly implemented models of this which rounded 127.125 up to 127.13. ATC has direction to indicate such frequencies to pilots by saying only the first five digits. Pilots know if their radios show the 6th digit that it is a 5 and it is understood that when ATC directs him to 122.17, he will tune 122.175 or 122.17, whichever his radio shows. Back to the analysis of the transmisstion...

The apron is uncontrolled here at Halifax, and Ground will not be keeping other aircraft out of our pilot's way, and that he will not be kept out of the way of other aircraft, either. Some airports do have controlled aprons, or at least portions of them, but most in Canada don't. Some have something in between, such as this airport, where apron advisory is provided, but control service is not. More on this shortly. One last thing about Ground's transmission above: "Call before entering Alpha." Is this really necessary to be said? Not really, but it's not a bad idea, either. The pilot's attention will be directed to the goings on at the apron and may forget that he wasn't allowed yet to travel on Alpha. Telling the pilot to call before entering Alpha may be unnecessary, since he didn't yet receive clearance to taxi on Alpha, but it may be a good reminder to help prevent a problem down the line.

Apron Advisory

Apron Advisory is often provided by ATS staff. That is to say, Ground Control will provide this service. They don't normally issue instructions or authorizations to push back or manoeuver in any other way while on the apron, but they will, workload permitting, advise aircraft of known movements on the apron to the extent possible. If an aircraft reports that he is pushing back, they'll advise other aircraft that report planning to operate nearby of the first aircraft's action. At more complex airports, or airports with special circumstances on the apron (such as parts that are not visible to ATC in the tower), the airport authority may provide the service separately from ATC functions. They will set up a separate "office" and frequency and provide the same service, still without clearances and authorizations. Normally, Ground will switch the aircraft to the Apron Advisory frequency before they enter the apron on the way in. Aircraft departing the apron will be switched to Ground's frequency before leaving the apron so they can obtain taxi authorization in time. For anyone wondering, this information is located in the AIP RAC 1.2.4. In our pilot's case, he has to enter the apron, cross it, and then get back on a taxiway which is controlled by Halifax Ground. So he switches from Ground to Apron Advisory, and then back again to Ground to finish his taxi in.

Taxiing on the Apron

CGOOF: "Apron Advisory, Cessna Golf Oscar Oscar Foxtrot on Golf for Alpha."
CYHZ_APR: "Oscar Oscar Foxtrot, roger, traffic is a southbound Dash eight from the north end of the apron. He'll pass you shortly."
CGOOF: "Oscar Oscar Foxtrot has him in sight. I'll follow to the south end."
CYHZ_APR: "Oscar Oscar Foxtrot, roger. Contact Ground again one two one niner before leaving the apron."
CGOOF: "Oscar Oscar Foxtrot."

Simple enough. One small point to mention: Taxiing a light aircraft behind another, larger aircraft can be dangerous. The Dash 8's propellers are 13 feet in diameter, and they possess quite the ability to stir a large wind. Jets can also generate a hefty blast. As a general rule, the larger the aircraft, the more thrust it needs to get airborne, the more power this requires, and the more dangerous it is to light aircraft. Keep your distance.

Clearing the Taxiways

CGOOF: "Ground, Oscar Oscar Foxtrot, south apron for IMP."
CYHZ_GND: "Oscar Oscar Foxtrot, taxi Alpha to IMP."
CGOOF: "Oscar Oscar Foxtrot. Confirm my flight plan is closed?"
CYHZ_GND: "Oscar Oscar Foxtrot, affirmative."
CGOOF: "Oscar Oscar Foxtrot."

Never I have heard of some pilots insisting on a call when clear of taxiways. As a ground controller, I didn't want that, as a general rule. In a snowstorm, dense fog, heavy rain, or other such weather phenomenon, I asked for it. In good visibility, a ground controller can scan a taxiway to see if anything is on it, or if a previously taxiing aircraft is clear of it. But if visibility is limited or restricted, the controller may want to know when you are off a particular part of the airport. Visibility might be inhibited by hangars or trees, or whatever else that might obstruct the controller's view, as well. If not asked for it, I don't believe it is a necessary communication. If the controller wants the report, he will ask for it. At the time of writing, I could find no written rules that require a pilot to call clear of all taxiways without being asked to do so. Never have I reprimanded a pilot for providing me with such a report when it wasn't necessary, nor do I feel that a ground controller at any airport should.

Upon arrival on the IMP apron, the pilot will then generally call the FBO on the published frequency (if available, it will be listed in the Canada Flight Supplement) for instructions on where to park, etc. That is beyond the scope of this article.

The VFR Flight Example series is finally over. Our pilot has successfully navigated two controlled airports with different levels of service, and two uncontrolled airports, one in an enroute phase and the other for the arrival and departure phases of flight. I hope I have shed some light on some common operations for those who don't get to experience them and for those who intend to. Any comments or questions on this week's topic, or any other topic, can be directed to me through e-mail at moxner@nbnet.nb.ca.