This is by Michael Oxner, used by permission. A great read for controllers and pilots alike

Choosing an Active Runway

The airport controller's first duty is to choose an active runway. Normally, the active runway is the runway most nearly aligned into the wind. If the runways at an airport are 06, 15, 24 and 33, and the wind direction is 220 degrees (magnetic), then the runway closest to this is ruwnay 24, and therefore runway 24 would normally be the active runway. Typically, a wind speed greater than 5 knots is the point where winds should be considered in choosing an active runway. 5 knots or less can be considered calm, and the "calm wind runway" may be chosen. The calm wind runway is the runway that is chosen by default when the winds are low. This runway may be the longest runway on the airport, it may be the one that carries airplanes away from a nearby city for noise abatement issues, or it may be the most convenient for taxiway layout. Any number of issues may come into play.

There are many other conditions that may come into play to determine an active runway. For example, if the wind is calm but the ceiling is really low, a runway with an instrument approach procedure might be chosen as the active. Heavier aircraft prefer longer runways that provide an extra margin of safety. Even if the winds favor another runway, they may want an out-of-wind runway for the extra length, especially if the runway is slippery. If heavier aircraft are a large portion of the traffic flow, perhaps chosing the longer runway would be a good idea.

In any case, ATC may approve a pilot's request for an out of wind runway, traffic permitting. Basically, the active runway is the one to use by default. If a pilot doesn't request another runway, this is the one that will normally be assigned. In the same way that a pilot may request a runway other than the active, ATC may suggest using another runway to a pilot. Typically, some sort of advantage may be gained thourhg using another runway, such as a shorter taxi distance after landing, a shorter traffic line which might facilitate less of a delay for departure or arrival, etc. When initiating a suggestion for use of another runway, the tower controller should provide the winds to help the pilot in making the decision. It's also helpful to state the winds if a pilot makes a runway request, just to make sure the pilot has all the information he needs.

Taxiing aircraft:

When a pilot advises he is ready to taxi, give him the runway, wind, time, and altimeter followed by taxi instructions.

Hotel Oscar Victor, runway 29, winds calm, time 0136, altimeter 3006. Taxi Bravo, hold short runway 29
Air Canada 123, runway 24, winds 240@10, time 1415, altimeter 2995. Taxi Delta, across runway 24. Hold short of runway 33
LOB taxi Delta, across R24, hold short of R33
HOV taxi A, G, F, R15, hold short of R24

Note in the second example above the statement "across runway 24". This is to be included, as a confirmation that the pilot has authority to cross runway 24. Taxi instructions should always be specific. If a pilot is expected to taxi across a runway, say so. If he must hold short, say so. Detail which taxiways are to be used, and which runways are to be used for taxiing or crossed along the route assigned. This also should be done for aircraft that have landed and are taxiing in to the gate.

IFR Clearances:

VFR aircraft are easier to handle in that less communication is required in most areas. In class D, E and G airspaces, which cover the majority of Canadian airspace where VFR flight normally takes place, no clearances are required. A VFR aircraft can call up for taxi for a couple of circuits, and you just give him taxi instructions and let him go.

For IFR aircraft, an IFR clearance must be delivered prior to take-off. At larger airports (CYYZ, CYVR, CYUL, CYHZ, CYWG, etc), this is normally delivered by the Clearance Delivery position, or by Ground if DEL is not operating. Sometimes at smaller airports (CYYG, CYQY, etc), some IFR aircraft will ask for taxi clearance and then ask for IFR clearance while taxiing. Copying the IFR clearance on the taxi can save time, sometimes. In any case, there is always a "clearance limit" (typically the destination airport), the SID if one is being assigned (at many larger airports, the only time a SID won't be issued is when _APP or _DEP, or _CTR in their absence, specifically tells you what to issue), the words "flight plan route", followed by a transponder code.

ATC clears Golf Lima Oscar Bravo to the Halifax Airport via the St.John's Two departure, flight plan route, squawk 5201
ATC clears GLOB to the Gander Airport, via the CYYT2 departure, flight plan route, squawk 5206

Departing aircraft:

Try to keep aircraft moving as much as possible. For example, with an aircraft on a touch and go, or after an aircraft has landed, if another aircraft is holding short of the runway, you may taxi a waiting departure to position as soon as the landing aircraft passes the departure's position.

CVA822 taxi to position runway 29 and wait
SAC117, taxi to position runway 24 at Echo and wait

This allows him to enter the runway and line up, but not to take-off. If other traffic were on final, this couldn't necessarily be done, depending on timing, of course. Then, when the moment is right, you issue a take-off clearance.

Romeo Oscar Golf, winds 240@10, right turn out approved, cleared for take-off runway 24

For IFR aircraft, they need a validation from the IFR ATC unit before you can clear them for take-off. The IFR can be APP, DEP, or CTR if neither of those are online. While the aircraft is taxiing, or perhaps while being put out to position on the runway, ask the IFR unit for permission to release him. For example, in a private message, type, "Req release KFA185 R29." Eventually, you'll be given your release and you can then clear the aircraft for take-off. You may have conditions to meet, too. "After LOB lands, release KFA185 on 29." Or perhaps, "release KFA185 on 29, you have 2 minutes to get him airborne." Maybe, "KFA185 is valid on runway 29, canceled if not airborne before ACA123 reports the QM NDB final." Note in conditions like the second and third examples, that's to get him airborne, not just cleared for take-off, by the time the condition is met, so judge accordingly. If you are unable to grant take-off clearance right away, advise the pilot of the reason for the delay. Typically it's other traffic.

Take-off clearances often have other information, instructions on which way to turn if needed, or perhaps a frequency change. Maybe more than one of these examples. It is normal, unless we coordinate otherwise with the IFR unit, to turn an IFR departure over to them right away. So we normally add the frequency change to the take-off clearance. Departing VFR aircraft are normally held on TWR's frequency until they clear the control zone.

KFA185 contact departure 133.15 airborne, winds calm, cleared take-off R29
LOB contact Terminal 133.15 when airborne, winds calm, cleared take-off R16

Sometimes it makes sense for an aircraft to use less than the full length of a runway. For example, a PA28 doesn't need full length of a 10,000 foot runway. Perhaps an intersecting runway has traffic operating on it, and the pilot of a small aircraft can make use of a taxiway intersection to take-off beyond the runway intersection, thereby lessening the delay he would encounter due to the other traffic. These are called "intersection departures" whether they take place from the intersection of a taxiway and the runway to be used, or the intersection of another runway with the desired one. While it is the usual practice to make the full length of the runway available to the pilot, he may request an intersection departure. Also, if ATC may see an operational advantage, such as reduction of conflicts or delays, he may suggest an intersection departure. Include with such suggestions the runway length remaining from the intersection if initiated by ATC.

Dynamic 22, are you able departure runway 24 from Delta with 6,300 feet remaining?
Jazz 8842, an intersection departure from Hotel is available, that leaves 6,000.

If a pilot accepts such a suggestion, or requests it, clearance that allow the aircraft to taxi to position or take-off should include the fact as well.

Dynamic 22, winds 240@10, from Delta, cleared take-off runway 24.
Jazz 8842, taxi to position runway 15 at Hotel.

An aircraft may not be cleared for take-off if another aircraft is still on the runway ahead of him, or if a slower airplane has recently departed that may cause a traffic confliction for the subsequent departure. For example, it's poor form to clear a B747 for take-off with a C172 just off the departure end unless the Cessna has begun a turn to get him out of the way. Similarly, if a DC10 has landed and hasn't yet left the runway on a taxiway, a take-off clearance should not be issued to the next departure. If a taxiing aircraft is crossing a runway, do not clear an aircraft for take-off until the taxiing aircraft has crossed and is clear. In a similar frame of reference, operations on crossing runways should be conducted the same way. A take-off clearance cannot be issued to an aircraft until an aircraft landing or departing a crossing runway has crossed the runway intersection.

Traffic Pattern:

Aircraft in the circuit are required to make a downwind call. This is the TWR's opportunity to make sequencing decisions. A sequence number is normally given, and any other instructions necessary to make it happen are given here, too.

IMP #2, follow Piper in right downwind
APE extend your crosswind, traffic landing on 34, 3 miles final
DOG #3, follow B737 on long final
LOB, #4, do a three-sixty to the right for spacing

Never give a clearance for a landing or touch and go with the downwind call. Always give this sort of clearance on final. A typical sequence would be:
Pilot: LOB downwind R29 touch and go
TWR: LOB #1
followed by...
TWR: LOB cleared touch and go R29, winds calm. -- when LOB is on final. You need not wait for an aircraft to report final to issue a landing clearance. It may be considered poor form to force aircraft to report on final to get such a clearance.

Inbound Aircraft:

When inbounds make initial contact, IFR or VFR, be sure to give them runway, wind and altimeter, along with any instructions you require.

Pilot: Moncton Tower, Citation Golf Lima Oscar Bravo, fifteen miles south, inbound VFR
TWR: Citation Golf Lima Oscar Bravo, R29, winds calm, altimeter 3006. Cleared left base R29
Pilot: Lima Oscar Bravo

HOV, R16, wind 140@10, altimeter 3005. Cleared right hand downwind
ACA123, runway 29, winds calm, altimeter 2918. Report the Moncton NDB on final.

If you specify nothing, or say, "cleared to the circuit", a pilot is supposed to enter the standard pattern for that runway, which is left hand unless otherwise published. A left-hand pattern or circuit is one that ha a pilot making left hand turns at each corner. Therefore, a pilot will often make a right hand turn to enter left downwind, from which point all successive turns will be made to the left. For IFR aircraft, you can't do as much with them since they are operating on an IFR clearance. Typically, it's easier to move other aircraft around them, since they are often established on a straight-in IFR approach when the TWR gets them.

Managing a Circuit:

When sequencing multiple inbound aircraft, it is often easier to leave the one on the straight-in approach alone and move the guy on base leg next, then the one on downwind. The further away from the runway threshold, and the more turns they have to make anyway, the more sense it generally makes to do something. Common techniques in spacing include:

• Instructing aircraft to make a 360 (spoken as "three-sixty") in the downwind.
• Instructing them to do a 270 (spoken as "two-seventy") in the opposite direction to the circuit pattern at one of the "corners" -- ie in a left hand circuit, asking a pilot to do a right hand 270 to join base instead of the normal 90° turn to the left.
• Asking a pilot to widen out his circuit
• Asking a pilot to "keep the circuit in tight" if trying to squeeze him in front of another aircraft -- Note that this one leaves few "escape routes" if the pilot's interpretation of tight and yours differ.
• Asking a pilot to extend his downwind to a certain point (like crossing a river or road near the airport) or "until further advised" -- just remember to advise further at a reasonable point.
• Asking one or more pilots to do a right hand circuit rather than a left hand pattern.

Using any of the above techniques, it's important to keep a few things in mind. If you've had the opportunity to watch a pilot in an unrestricted circuit, it may give an idea of what a wide circuit may be for him. The faster an aircraft flies, the wider his circuit will likely be, with the exception of military manoeuvers such as overhead breaks and "closed" patterns. The heavier an aircraft is, the wider his circuit will be. Not all pilots fly the same width of a circuit, however circuit altitude is normally 1,000 feet above aerodrome elevation (AAE). This may be specified otherwise in publications. With aircraft of similar performance (speed) in the circuit, assigning different sides of the circuit may not be to your advantage. It's easier for a pilot to follow another if they're on the same side. Having said that, even having two aircraft of different performance may cause troubles, such as a business jet or military fighter behind a Cessna or Piper. Or a light aircraft following a heavier category aircraft. In such cases, it's often best to put them on different sides of the runway so they only conflict on final and departure, rather than being trouble for each other all the way around. Another situation would be where a left hand circuit overlies an approach path for another runway -- a right hand circuit may be required to keep the circuit traffic out of the way of inbound traffic for the other runway. Individual circumstances vary. It is not unreasonable to make statements such as, "right hand circuits til further advised," or, "Make this one a right hand circuit," later to return to left hand circuits, and so forth.

Sometimes pilots will ask for touch-and-goes, other times a stop-and-go. In the first example, the airplane is not supposed to stop on the runway. It lands, slows a bit, sets up for take-off, and then takes off again. In the stop-and-go, the pilot will actually bring the airplane to a complete stop before setting up for take-off. The pilot is not to backtrack the runway for the take-off unless specifically requested and approved by the tower since this could occupy the runway for long periods of time. This practice takes longer on the runway and may interfere with following traffic. ATC has no obligation to provide a pilot with a stop-and-go clearance, but should endeavor to provide it if requested, or at least provide the pilot with as much notice as possible that a stop-and-go will not be granted. Another possibility is a request for "the option". This is a request to have the runway for whatever the pilot wants, from a "low and over" where the plane doesn't touch the runway, a touch-and-go or a stop-and-go. ATC shouldn't provide a clearance for the option unless requested by the pilot.

Something that some new people feel is a good idea is to vector aircraft -- issuing headings to them in the circuit. A circuit is best managed by the above techniques. Pilots of VFR aircraft are primarily flying their airplanes by looking out the window to see and avoid other aircraft. By issuing vectors, you're asking the pilot to look inside the cockpit, and that's not the right place for his eyes in a traffic pattern or while flying an approach. It's best to use descriptive methods like those examples above to tell a pilot what to do. If you can't accept a pilot in the circuit due to other traffic, for example, don't issue a holding clearance as would be done for an IFR aircraft. Find a prominent landmark that the pilot can see clearly (like a lake, a tower, etc) and ask him to orbit there and wait for further instructions. That keeps him out of the way. Also, assigning an altitude to a VFR aircraft is a method of last resort. Try restricting the pilot's flight first, rather than nailing it down. Saying "Not below 2,500 til advised" is better than saying, "maintain 2,500," for example. The best thing to do is to point out traffic to a pilot and let him keep himself away from the others. That's what visual separation and VFR flight is all about -- see and be seen, as they say.

Landing Aircraft

What goes up must come down. And when they want to, they need landing clearances. Typically a landing clearance is only issued when an aircraft is on final. A report on final, or turning final, is not required for ATC to issue a landing clearance. Before a clearance to land may be issued, the runway has to be clear of vehicles, taxiing aircraft, and aircraft that have just landed or are departing. It is permissible to issue a landing clearance to an aircraft that is on final when other aircraft are present, provided the runway will be clear by the time the aircraft is on short final. A landing clearance may be issued to an aircraft when a preceding landing aircraft has not yet cleared the runway provided the pilot is advised of the position and intentions of the preceding aircraft, and the preceding aircraft is far enough down the runway that he will not cause a problem for the successive aircraft. For example, if a C172 is on final and a B737 is at the far end but not yet clear, the Cessna will not need that much runway for a safe landing without overtaking the B737, so a landing clearance may be issued. However, if the C172 has landed and hasn't used much of the runway, a B737 on final stands a good chance of overtaking the Cessna, so a landing clearance shouldn't be issued unless the C172 is clear.

For crossing runways, an aircraft should not be given a landing clearance until a preceding aircraft landing the crossing runway has crossed the runway intersection, or until the preceding aircraft has landed, slowed and read back an instruction to hold short of the intersecting runway.

Some examples of phraseology:
Echo Oscar Papa cleared to land runway 34, winds 330@10.
ACA123, winds 220@10, check the Dash 8 clearing runway 24 in Charlie, cleared to land runway 24.

Helicopters

Often new controllers are confused by helicopters. At some airports, helicopter operations are somwhat rare, as they typically are in VatSim. When IFR, they are handled just like any other aircraft, since IFR operations are tailored for Instrument Flight Rules. They still need an IFR clearance, and the clearance often uses a runway as a starting point with departure instructions just like any IFR clearance. Some airports have specific departure agreements or arrangements and IFR clearances to helicopters may be different from the description above. In any case, with an IFR unit online, an IFR helicopter may not be cleared for take-off until a validation has been received from the IFR unit, just as with any aircraft. For IFR arrivals, a helicopter will normally fly an instrument approach procedure. These are often the same ILS, VOR, or other approaches that are flown by fixed-wing aircraft. They will not always land on the runway aligned with the approach. Typically they'll break cloud and ask to land elsewhere on the field, or "land" on the runway and "air taxi" from there. Read on for more on this.

For VFR flight, helicopters without wheels will normally look to take-off from where they are, for obvious reasons. Normally, the parking areas are part of the control area. As such, ATC shouldn't clear the helo for take-off, but rather advise the pilot that lift off is at pilot's discretion, provide the winds, and then any instructions or information deemed necessary. For example, if a helo wants to depart and cross a runway that's in use, it may be necessary to get the chopper to depart and parallel the runway centerline until you can allow him to cross, or just to hover nearby and wait for the opportunity. For landing, a tower controller can allow a helicopter, traffic permitting, to fly directly to the point at which he wants to land. An IFR helicopter may, once he breaks cloud and sees the airport environment, opt to air taxi to a parking area, but this must be approved by the airport controller. When the pilot breaks out and advises seeing the airport, the tower controller should provide the helo with a clearance to proceed to the parking area via runways and taxiways, or directly to it if traffic permits. As with departures from uncontrolled areas of the airport, the pilot should be given winds, and advised that landing is at his discretion. Should a pilot wish to take-off or land from a controlled portion of the airport (a runway, taxiway, or controlled apron), landing and take-off clearance should be issued as normal.

Sierra Uniform Bravo, winds 120@10, depart the flight school at your discretion.
Cougar 42, stay east of runway 18 until advised, cleared take-off from taxiway Alpha.
Spanner 22 proceed directly to IMP and land at your discretion, winds 240@5.

Helicopters without wheels may occasionally want to reposition on the field, or move to a runway for an instrument departure. Having no wheels makes taxiing on the ground difficult, so they "air taxi". This action is slow flight, less than 100 feet AGL, and is treated just the same as an aircraft wheels who wants to taxi. Pilots are given clearances to air taxi via taxiways and runways, and told to hold short of intersections or runways just as other aircraft are. Any air taxi clearance with a "hold short" must be read back by the pilot, just as with a ground taxiing aircraft. Helicopters with wheels have the choice of ground or air taxiing, and they should specifically request the operation. An authorization to "taxi" doesn't represent authority for "air taxi" operations. Air taxi operations are legitimate in IFR weather conditions.

Air taxi example: Wolf25A air taxi to runway 24 via C, across ruwnay 29, D, and hold short of runway 24.
Ground taxi example: Sierra Alpha Bravo taxi Alpha, Golf, Echo, hold short of ruwnay 24.

In the real world, helicopters air taxiing, taking off or landing stir the air up quite significantly. These operations in close proximity to light aircraft can easily cause upsets and overturn taxiing or parked light aircraft. As such, ATC shouldn't allow these operations in the vicinity of light aircraft on the manoeuvering area of an airport. The term manoeuvering area includes taxiways and runways, as well as any controlled aprons.

Special VFR

In order to have weather conditions acceptable for VFR flight, the ceiling must be at least 1,000 feet AGL, and the visibility must be at least 3SM. Sometimes, VFR weather conditions exist outside a control zone, and a VFR aircraft may want to depart the airport to get out, or may want to enter the zone to land, or just may want to transit the zone. Helicopters quite often desire to operate in below-VFR weather, since they tend to be operated at low altitudes, and their operations are often associated with medevac or other emergency services. In such cases, Special VFR may be granted. If the visibility is at least 1 SM (1/2 statute mile for a helicopter), a pilot may request special VFR to transit, depart or enter the zone for landing. Care must be taken to ensure that SVFR operations don't cause possible problems for IFR aircraft on departure or arrival, since the margin of error is reduced due to the reduced ceiling and visibility. It is often adviseable to leave VFR aircraft requesting special VFR outside the zone if there is any likelihood that they could get in the way of IFR aircraft. if a pilot accepts them, minor restrictions may be issued to a pilot to help keep them out of the way of other aircraft, such as asking them to remain clear of the final approach course of a runway. A pilot must request Special VFR, as it may not be initiated by ATC. The IFR unit must be informed of when SVFR is approved and when it is discontinued.