Aviation Topic of the Week
By Michael Oxner,
September 28, 2003
This week's topic:
Airport Operations Part 1: Apron Movements
Beginning another little series, we'll start with some basics around airports.
This part, Apron Movements, is only a short one, meant to give some idea
of what to look for when pushing back and getting ready to taxi. Also, we'll
have a look at taxiing in after landing.
Definitions
Apron Designations
Private Aprons
Terminal Aprons
Uncontrolled Aprons
Apron Advisory
Taxi To and From Aprons
Definitions
There are a couple of definitions that should be remembered when operating
at an airport, since knowing where you are will determine what rights you
have, and who you may have to call before you can do anything. The AIP
offers these definitions, curiously enough in the Definitions section
in GEN.
Manoeuvring Area: That part of an aerodrome intended to be used
for the taking off and landing of aircraft and for the movement of aircraft
associated with take-off and landing, excluding aprons. This definition
includes runways, taxiways, and helipads, and when a control tower is in
operation, clearances are required to operate on these surfaces unless specifically
told otherwise, such as a note in the Canada Flight Supplement regarding
a taxiway being uncontrolled.
Apron: That part of an aerodrome, other than the
Manoeuvring Area, intended to be accommodate the loading and unloading
of passengers and cargo; the refueling, servicing, maintenance and parking
of aircraft; and any movement of aircraft, vehicles and pedestrians necessary
for such purposes. Hence, this includes basically every other part of
an aerodrome. Aprons are often referred to as "Ramps", especially in the
military. In the civilian world, the term "ramp" was replaced some time
ago by the name "apron". Calling an apron a ramp isn't technically correct,
but it will be understood by most. Another term that is often heard, especially
overseas, is "tarmac". The Merriam-Webster definition of tarmac includes
roads, aprons, taxiways and runways -- essentially any portion of an aerodrome
that is paved.
There are a couple of other terms that should be addressed, even though
I'm sure most are familiar with them.
Push Back: The act of pushing an aircraft back from a gate or
away from other aircraft at parking areas, to allow for an aircraft to begin
taxiing under its own power. A 'mule' is another name for a tractor-like
vehicle used for towing aircraft, and these are used during push back. Remarkably,
these vehicles can be large, and are often much heavier than they seem in
order to move the weights they move. I once asked a B747 pilot if he knew
the weight of the mule they used, and after consulting with his ground crew,
he informed me that his mule weighed in at about 200,000 lbs. The push back
can be straight back, or can have a turn to the left or right to allow the
aircraft to start taxiing without requiring a turn when he starts moving.
Also, most aircraft start engines after the aircraft is pushed back from
the gate, either while still being pushed back, or once the push back is
complete. When ground crews are pushing the aircraft back, they have the
responsibility for ensuring there's nothing behind the aircraft that would
cause a problem.
Power Back: The act of employing thrust reversers, or
reverse pitch on propeller driven aircraft, to back the aircraft away from
the terminal building or other parked aircraft to allow the aircraft to taxi
for take-off. This procedure is not as common these days. It requires
starting the engines prior to leaving the gate and using fairly high power
settings to provide the thrust required, meaning high noise levels. Since
a pilot doesn't have rear view mirrors, he doesn't have much of a way to
see what's behind him.
I want to include a couple of other items that I will discuss below, as
well. These are not officially defined in the AIP, but it is important
to understand the differences. These are Private Aprons and Terminal Aprons.
Read on for more.
Apron Designations
Runways are designated with numbers backed up by letters. Taxiways are
designated by letters, with numbers as required. I didn't mention in last
week's topics how aprons were designated. At many airports, they are not
designated at all, or are simply named by their owners. "Taxi Alpha to the
Air Turbulence apron", for example. At some airports, apron designations are
either desired or required. On the charts, these will be marked with Roman
numerals, and spoken as numbers. So to taxi to Apron VIII, the controller
would say, "Taxi Alpha to Apron Eight". Some airports will designate different
areas of a continuous piece of pavement with different numbers for reference
sake. As a pilot, you would call up with your position on the field, stating
which apron you're on by number, if you're on or near one of those spots.
These are not to be confused with parking spots or gates not connected to
a terminal building by a finger. These are normally marked on a separate chart
in the Canada Air Pilot titled a Parking Area chart, and these will
be drawn on the chart as numbers in circles.
Private Aprons
Private Aprons are those that generally belong, or are leased to, companies
that conduct business at an aerodrome. This would include, but would not
be limited to, flying clubs and schools, Fixed Base Operators (or FBO's for
short), maintenance companies, and even hangars for airlines.
Many of us are familiar with flying clubs and flight training operations,
so I won't go further into these except to say that often these groups will
share apron space with other operators. A Fixed Base Operator, or FBO, is
the aviation equivalent of a service station for cars. In fact, this is big
business. They go to great lengths to provide clean, modern and well-connected
facilities to attract business, especially the corporate bigwigs and their
high-priced bizjets. They often offer flight planning facilities, briefing
areas, and typically a certain amount of maintenance services along with
the fuel and parking, both in a hangar and outside on their apron. These are
the places where those who love to fly the business jets and other private
aircraft are likely to park when they arrive at an airport in VatSim.
Some airports have facilities meant more for maintenance than the average
FBO. Generally they have a hangar where their work is done, and sometimes
they specialize: some will do mechanical maintenance, others will do electronic
installation and repair, for example.
Lastly, from the abbreviated list of airport tenants above, the airlines
and other commercial aviation companies. Anywhere an airline has a base
of operations, they're likely to have some amount of hangarage on an apron
that is typically separate from the main terminal apron(s). This is where
they will sometimes try to park their aircraft, if they have room, for overnight
stays, since they often incur fees for parking overnight on a terminal apron.
Since airlines will employ their own technicians and maintenance engineers,
their own hangars come in handy for airframe maintenance. While some minor
issues can be tackled at a gate, some issues require a little more work.
Cargo companies will normally establish their own aprons with their sorting
facilities at airports they serve, as well.
From a control standpoint, private aprons are rarely controlled. The owner/operator
of the property may have a frequency, and in fact often do, for pilots to
communicate directly with them. They will often direct pilots where to park
and so forth, when to start the engines, when to taxi, and do any other movements
are all normally the responsibility of the pilot on a private apron. Ground
control for the airport normally has no reason to get involved with aircraft
movements on private aprons, and also will have little desire to even know
about them. The only time GND becomes involved is when an aircraft wants
to taxi between two neighbouring aprons that are not joined, and must use
a taxiway that makes up part of the manoeuvring area. Then, as usual, the
aircraft must talk to GND for authorization to enter the taxiway. That'll
be another topic for the near future.
Terminal Aprons
Terminal Aprons are the ones most air travelers, and I suspect
most flight simmers, are aware of. These are the largest paved areas at an
airport where the airlines park their "big iron", and the little "prop jobbies",
for loading and unloading passengers. At larger airports, they have "fingers",
or pedways that run from the terminal building to the aircraft. Most airports,
including the larger ones, have at least some gates where the passengers
actually leave the terminal building through a door and walk across a portion
of the terminal apron to board the aircraft. At many airports, private operators
are not allowed to park on terminal aprons so they must seek out an FBO when
they visit. It's a good idea to call ahead to find out where parking is permitted.
Uncontrolled Aprons
Most of the smaller airports in Canada with control towers have uncontrolled
aprons. As mentioned in the segment about private aprons, someone may determine
where your aircraft will park, but once you're off the taxiways, you're
on your own. Ground control typically does not have any authority, nor any
responsibility, to control aircraft while taxiing on an uncontrolled apron.
Engine starts, push backs and power backs are all someone else's responsibility
as far as GND is concerned. Having said that, GND typically will, workload
permitting, give traffic information on aircraft they can see or are aware
of that are taxiing in close proximity to an aircraft that advises they
are pushing back. Standard practice has pilots at least declaring their
intentions, if not asking permission, when the apron is uncontrolled. If
a pilot asks for push back at an uncontrolled apron, GND has direction from
ATC MANOPS to respond with the phrase, "Push back at your discretion".
The intent is to remind the pilot that he is not "cleared to push back",
and that GND will not be holding other traffic away from the aircraft on
the push back. GND must be contacted for authorization prior to entering
the manoeuvring area of the aerodrome as defined above.
One little glitch with this in VatSim: Often ground controllers online
will not know that the real world airport is not an uncontrolled apron, and
may therefore attempt to control movements on the apron. I would recommend
not getting into a fight over a voice or text channel and just going with
the flow. If the airport you're operating out of is normally an uncontrolled
apron, broadcast your intentions to GND and see if he expects you to have
his approval first. If you're a controller and don't intend to control an
apron, let the pilot know this when he asks. Whatever side of the radio you're
on, try to be polite about it. Nobody wins a fight over a frequency. This
is, afterall, a hobby.
Apron Advisory
At some larger airports, there is another function called "Apron
Advisory", or some title similar to that. This is not an ATC function, and
therefore not a controller position, either. It is simply a way of confining
all the requests for push back, gate assignments, coordination of aircraft
movements and so forth on an apron to a frequency other than GND. This way,
all that radio chatter can be done as required without interfering with
ATC and aircraft movements on taxiways and runways (the Manoeuvring Area
as defined above). Such a function will be advertised in the Canada Flight
Supplement and in the Canada Air Pilot's Airport Diagram for
an airport if it exists. Prior to engaging in any movement on an airport's
terminal apron, a pilot should report his intentions on this frequency so
that other aircraft operating around him are aware of what's about to happen.
This frequency only applies to the terminal apron, and aircraft still have
to call GND for taxi authorization prior to entering any controlled portion
of the aerodrome, including taxiways not specifically designated as uncontrolled
in the Canada Flight Supplement or other similar document detailing
specific airport operations.
Here's the good news for VatSimmers: I haven't yet seen anyone man an
airport advisory frequency on VatSim. Maybe it has happened, but most controllers
online would rather control aircraft in an actual control position, so you're
not likely to encounter such a beast online.
Taxi To and From Aprons
Well, I've already talked about this in a few different places above,
but this seems like a good place for a recap. As long as you're on the manoeuvring
area of an airport, you should be talking to the controlling agency. In
VatSim, this could be the APP controller if no TWR is online, or TWR while
you're taxiing if GND isn't there. If in doubt, ask.
When you're getting ready for departure, you would generally call for IFR
clearance (for an IFR flight only, of course), either shortly before of
after engine start. As long as you're on an apron, you're movements are
up to you, making your movement calls on the apron advisory frequency if
one is designated for your apron (not needed in VatSim in most places, anyway).
Before you enter a taxiway, or before you block one would be better airmanship,
you would contact the controlling agency, normally GND, for authorization
to enter any of these areas. Then it's normal taxiing operations from there,
to be discussed in a future topic.
Now after landing, you clear the runway onto a taxiway, and you get your
taxi instructions from GND. This will often include a statement such as,
"Taxi Foxtrot, Golf to the apron". GND is authorizing you to proceed on Taxiways
G and F, to the apron, but has nothing to do with you once you're there.
It's your responsibility to look left and right once you reach the apron
to make sure you don't run into anyone who's already there.
Similarly, if you're taxiing between aprons on taxiways, GND must be contacted
prior to entering the taxiway. The pilot should also monitor the GND control
frequency as long as he's on the taxiways, too. The authorization from GND
to use the taxiway only includes that portion of the ground run that is
on the taxiway, as mentioned above. The pilot is on his own while on the
apron before he enters the taxiway, and as soon as he leaves the taxiway.
Also, in the real world, visibility is sometimes limited. This could be
because of a hangar obscuring a specific portion, or fog or snow which covers
the entire airport. In these cases, GND has the intricate job of controlling
the taxiways without being able to see them. He will do this by reports.
Having aircraft "report passing taxiway Delta", or "report clear of Alpha",
etc, establishes the position of aircraft on the field for him. When asked
to make reports, please remember to do them. Otherwise, GND will have to
badger you for the report needed. Larger airports have the benefit of ASDE,
or Airport Surface Detection Equipment. ASDE is a high frequency, rapid rotation,
short range primary radar (meaning no equipment is required on aircraft or
vehicles to be seen) which allow them the top-down view of an airport that
VatSim's GND controllers all have the luxury of seeing.
Well, there's the basics of aprons. If I've left anything major out, or
if you take exception to anything I've said, I'd be happy to accept feedback
at my e-mail address, moxner@nbnet.nb.ca.
Thanks again for reading!