Table of Contents

Tower — Spacing and Sequencing Last updated: 2017-12-02

1. Traffic pattern operations


The essential part of a local controller’s job is to establish a sequence between arriving and departing aircraft. The separation requirements and tools available for you to achieve them will differ depending on numerous factors. They include (but aren’t limited to) airport runway layout and the distance between the runways, present weather conditions, surface area dimensions, participating aircraft’s weights and same runway separation (SRS) categories. Normally, you will establish the landing sequence by adjusting the arriving aircraft’s traffic pattern; and the departure sequence by timing your takeoff clearances.

Traffic pattern is a standard rectangular traffic flow that is prescribed for aircraft landing at or taking off from an airport runway. The standard traffic pattern is located to the left of the runway (when looking from the direction of landing.) At some airports, due to terrain or other factors, the traffic pattern may be located to the right of the runway. The components of traffic pattern include the following:
Upwind leg. A flight path parallel to the landing runway in the direction of landing.
Crosswind leg. A flight path at right angles to the landing runway off its takeoff end.
Downwind leg. A flight path parallel to the landing runway in the opposite direction of landing.
Base leg. A flight path at right angles to the landing runway off its approach end and extending from the downwind leg to the intersection of the extended runway centerline.
Final approach. A flight path in the direction of landing along the extended runway centerline from the base leg to the runway.
Departure leg. The flight path which begins after takeoff and continues straight ahead along the extended runway centerline. The departure climb continues until reaching a point at least 1/2 mile beyond the departure end of the runway and within 300 feet of the traffic pattern altitude.





There are a number of tools that a controller can use to sequence aircraft in the traffic pattern.

a. Circling the airport. “Circling” means adjusting an arriving aircraft’s flight path so as to enter the traffic pattern. Under most circumstances, simply instructing a pilot the pattern direction and/or leg to enter will be sufficient, e.g. “enter left downwind to runway 19L.” If the aircraft is in a position where it isn’t obvious how it should enter the pattern, you may issue specific circling instructions to the pilot.

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CIRCLE THE AIRPORT (direction of circling, pattern direction and/or leg to enter, additional restrictions as required)

For example, if an aircraft arrives from a side of the airport opposite to that of the traffic pattern, you may want to take him directly over the airport and 500 ft above the traffic pattern altitude until he enters the downwind, so as to keep him out of the way. Let’s take KBUR as an example, where we use right traffic to runway 15 at 1,800 ft. An instruction for a VFR arrival from the east could go like this: “circle the airport to the west for a right downwind to runway 15, maintain at or above 2,300 until downwind.”


b. Extended downwind. This is a maneuver when an aircraft extends its downwind leg outside the
standard rectangular pattern dimensions to delay its arrival at the runway threshold. When is this useful? Let’s look at an example with two aircraft: the aircraft “A” in on downwind leg midfield, and the aircraft “B” is on 4-mile final to the same runway. Not taking any action from the controller will likely result in a conflict between the two aircraft. To establish sequence, you should first determine who will be #1 for the runway and who will be #2. In this example, aircraft “B” is the best candidate to be #1 — there’s little room for leeway on final, since the aircraft is already headed directly to the runway, so there’s not much we can do to alter its flight path. The aircraft “A,” in turn, is on downwind, which takes him away from the runway — the longer we keep him that way, the longer his flight path will be, delaying his arrival. Now that you know what sequence you want to establish, get to the tools of achieving it. Instruct the aircraft “A” to extend its downwind until you observe that the aircraft “A’s” flight path takes him behind the aircraft “B.” At this point, you may instruct the aircraft “A” to turn base leg, completing the maneuver. (A good reference point you can look for is when the aircraft “A” is abeam the aircraft “B” on final. Clearly, unless speed difference is a concern, their flight paths will never cross, and the aircraft “A” will end up behind the aircraft “B.”)

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EXTEND DOWNWIND
(and once the spacing is achieved)
TURN BASE LEG NOW

c. Two-seventies and three-sixties. These are the common terms used to reference maneuvers when aircraft turns around its axis by the specified number of degrees. Such maneuvers are aimed to delay the aircraft’s arrival.
Two-seventies can be used when aircraft is transitioning from one pattern leg to another. Instead of making a natural 90 degree turn to the next leg, you may request the pilot to make a right/left two-seventy turn. The direction of turn should be opposite to that of the traffic pattern direction. In left traffic, you would assign right two-seventies, and vice versa.


Three-sixties are obvious; an aircraft makes a complete loop and returns to its previous course. Three-sixties can go in any direction a controller deems appropriate, although it’s a good idea to keep the three-sixties outside the pattern box, because an aircraft attempting to fly a three-sixty inside the traffic pattern may conflict with another aircraft climbing on a departure leg.


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MAKE LEFT/RIGHT THREE-SIXTY/TWO-SEVENTY

You may consider using two-seventies when you want to delay an aircraft on downwind due to another aircraft on final (a concept similar to extended downwind, except that two-seventies leave no room for controller’s intervention for when the pilot should enters base – he’ll do so as soon as he completes the turn at a standard rate.) Three-sixties delay the aircraft for even longer, and can be used when considerable increase in spacing is required.


d. Short approach. This is a maneuver when instead of flying the standard rectangular traffic pattern, the pilot makes tighter turns from downwind so as to make a short final approach and arrive at the runway threshold earlier. Let’s reference the same example with aircraft “A” and “B;” except now, the aircraft “B” is still 8 miles out, while aircraft “A” is already abeam the runway threshold on downwind. Once again, not taking any action may result in a conflict between the two aircraft. If you try extending the aircraft “A’s” downwind to put him behind the aircraft “B,” it’ll probably take the aircraft “A” outside your airspace, which isn’t good. Instructing the aircraft “A” to make short approach resolves it. Short approach cut the normal distance an aircraft flies from abeam the numbers to final by roughly a half, leaving room to spare before the aircraft “B” crosses the runway threshold.

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MAKE SHORT APPROACH

Keep in mind, that a short approach authorizes the aircraft to turn base as soon as the pilot deems safe. Hence, only assign a short approach to an aircraft it is #1 for the runway, so that it does not overtake another aircraft you may have landing before him. If the aircraft assigned a short approach is not #1 for the runway, he has to report the preceding traffic in sight prior to being issued a short approach (the pilot executing the short approach is then responsible for not overtaking the preceding traffic.)

The actual flight path of aircraft executing a short approach will vary. A short approach may start with a base leg one half the distance of normal from the runway; or in more extreme cases, with base legs abeam the numbers, to base leg 1500 feet down the runway.


e. Immediate Takeoff. There will be times when you have an arrival on short final and a departure waiting for takeoff from the same or crossing runway. You may estimate that there is a sufficient time window for the departure to takeoff prior to the arrival if departure takes off immediately. In this kind of situation, when the conditions warrant expeditious pilot compliance, add the word “immediate."



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CLEARED FOR IMMEDIATE TAKEOFF


EXAMPLE-
“United twenty five, runway 25R, cleared for immediate takeoff, traffic is a 737 on a 3 mile final”


f. “Go-around” is an instruction for an arriving aircraft to abound its approach to landing. Go-around may be initiated by a pilot if he deems safe landing cannot be made, or assigned by ATC for separation. A more thorough explanation of go-around procedures will follow up in the Topic 6 “Arrival Procedures and Separation.”

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GO AROUND (additional instructions as necessary).

EXAMPLE-


"United twenty five, go around, fly runway heading, climb and maintain two thousand."


g. Touch-and-go, stop-and-go, and low approach. These are maneuvers commonly used by aircraft performing pattern practice, they’re aimed to provide pilots with an expeditions transition from arrival to departure phrase of flight.
Touch-and-go is an operation conducted by an arriving aircraft, when the pilot commences a normal approach and landing; but before coming to a full-stop, the pilot advances the power and departs again.
Stop-and-go is different from touch-and-go over the fact that the aircraft commencing stop-and-go will come to a complete stop on the runway before the pilot will apply power and depart again.
Low approach is an operation when the arriving aircraft commences normal approach to the runway, but prior to completing the approach and landing, the pilot applies power and departs directly from the approach phase of flight, never touching the runway.

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CLEARED:
TOUCH-AND-GO,
or
STOP-AND-GO,
or
LOW APPROACH.

Consider an aircraft cleared for touch-and-go, stop-and-go, or low approach as an arriving aircraft until it touches down (for touch-and-go), or makes a complete stop (for stop-and-go), or crosses the landing threshold (for low approach); and thereafter as a departing aircraft.


h. “Cleared for the Option” is a universal form of granting an arriving aircraft a touch-and-go, low approach, missed approach, stop-and-go, or full stop landing clearance – at the choice of the pilot.

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CLEARED FOR THE OPTION
or
OPTION APPROVED

The other side of this procedure is that once ATC approves the option, the controller won’t know exactly which maneuver the pilot will perform on the runway. This may not be a concern when the aircraft granted the option is the only traffic for the runway, but may add complications if there’s additional traffic for the same runway directly behind the option aircraft. Particularly, stop-and-go and full-stop landing maneuvers may significantly increase the runway occupation time of the option aircraft. During this time, the separation between the aircraft stopping on the runway and the trailing airborne aircraft for the same runway may decrease significantly. Hence, controllers should exercise caution when approving the full “option” procedure. Sometimes, it may be more beneficial to only grant a single or limited number of landing options to an aircraft, so as to avoid the possibility of this aircraft blocking the runway for excessive period of time.

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UNABLE OPTION, (alternate instructions)
UNABLE (type of option), OTHER OPTIONS APPROVED.

EXAMPLE-
“Unable option, cleared touch-and-go.”
“Unable stop-and-go, other options approved.”


{Reference: FAAO 7110.65 3-8-1 “Sequence/Spacing Application;” 3-8-2 “Touch-and-go or Stop-and-go or Low approach;” AIM 4-3-2 “Airports with an Operating Control Tower.”}


2. Simultaneous Same and Opposite Direction Operations.


Simultaneous same and opposite direction operations may be conducted at airports with parallel runways. There’re advantageous by the fact that the possible number of airport operations increases, allowing more airplanes to depart and land over a specific time. Since the distance between the participating aircraft is significantly smaller than that of a standard terminal separation, however, there is a number of specific requirements for simultaneous operations to be authorized.

a. Simultaneous same direction operations on parallel runways may be authorized only when the following conditions are met:
(a) Operations are conducted in VFR conditions unless visual separation is applied.
(b) Two-way radio communication is maintained with the aircraft involved and pertinent traffic information is issued.
(c) The distance between the runways centerlines is in accordance with the following minima:


Category I or Category II: 300’
If either aircraft is a Category III: 500’
If either aircraft is a heavy: 700’

A common example of simultaneous same direction operations at vZLA is LAX, where an aircraft may be departing runway 24L while another aircraft is landing on runway 24R at the same time, or an aircraft may be departing runway 25R while another aircraft is landing on runway 25L at the same time.

b. Simultaneous opposite direction operations on parallel runways may be authorized only when the following conditions are met:
(a) Operations are conducted in VFR conditions.
(b) Two-way radio communication is maintained with the aircraft involved and pertinent traffic information is issued.



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TRAFFIC (description) ARRIVING/DEPARTING/LOW APPROACH, OPPOSITE DIRECTION ON PARALLEL RUNWAY.

(c) The distance between the runway centerlines is in accordance with the following minima:
Between sunrise and sunset: 1,400’
Between sunset and sunrise: 2,800’

Simultaneous opposite direction operations are less common, and you’ll only encounter them at vZLA during the over-ocean configuration at LAX, where aircraft depart 25R and arrive 6R.

{Reference: FAAO 7110.65 3-8-3 “Simultaneous Same Direction Operations;” 3-8-4 “Simultaneous opposite direction operations.”}

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