Air Traffic Control Rules and Procedures 52

Air traffic control’s role is to maintain safe and efficient operations in the airspace and at airports. Most separation rules are based on aircraft wake categories within the terminal area. The interactions between arrivals and departures can be regulated once these categories are established.

in this runway capacity simulation tool are based on FAA air traffic control guidance as specified in order 7110.65 [48].

In order to minimize the risk of wake turbulence encounters, the FAA establishes minimum separation requirements for all phases of flight. According to the legacy rule, aircraft are put into wake categories (Small, Large, B757, Heavy, and Super) based on their MTOW. The Boeing 757 has its own wake category due to its unique size and wake generating characteristics. The legacy wake category criteria are shown in Table 2-1.

Table 2-1. Legacy aircraft wake categories in the U.S.

Small Large B757 Heavy Super

MTOW MTOW £41,000 lb 41,000 lb < MTOW < 300,000 lb B757 MTOW ³300,000 lb A380, AN225

Minimum separations between pairs of aircraft are specified based on the wake category of the leading aircraft and the wake category of the following aircraft. Each of lead-follow pairs is assigned a required minimum separation distance for arrivals or a required minimum time separation for departures.

Table 2-2. Final approach separation minimums based on FAA 7110.65W (IFR). Arrival Separations

(nautical miles) 7110.65W

Follower

Super Heavy B757 Large Small

Leader Super MRS 6 7 7 8 Heavy MRS 4 5 5 6 B757 MRS MRS MRS MRS 4 Large MRS MRS MRS MRS 4 Small MRS MRS MRS MRS MRS

The legacy final approach separation values shown in Table 2-2 serve as the baseline separation rule for the purpose of this research study. The table shows the leader aircraft wake category on the left column, and the follower aircraft category on the top row. The values specified by Minimum Radar Separation (MRS) indicate the authorized separation on the final approach course within the last ten miles for the approach. MRS is three miles when radar capabilities permit. This can be reduced to two and half miles when the average runway occupancy time on the runway is no more than 50 seconds, the braking action is reported good, and the runway turnoff points are visible from the control tower [48]. Similarly to arrivals separations, same runway departure separations are also specified based on wake categories, as shown in Table 2-3.

Table 2-3. Departure separation minimums based on FAA 7110.65W for wake constrained pairs. Departure Separations

(seconds) 7110.65W

Follower

Super Heavy B757 Large Small

Leader Super 180 180 180 180 Heavy 120 120 120 120 B757 120 Large Small

No additional wake separation is necessary for aircraft pairs with no separation value assigned in the table and standard departure separation can be applied for these pairs. This means that a departing aircraft can be cleared for departure when the preceding aircraft has departed and crossed runway end or turned to avert any conflict, as specified in FAA Order 7110.65W [48]. When both departures are IFR departures, the standard minimum radar separation is ensured between aircraft.

become active when a Boeing 757 or Heavy weight class aircraft is airborne at the intersection [48].

Closely spaced parallel runways are modeled in two operational configurations: when both runways are used for arrivals, and when one runway is used for arrivals, while the other is used for departures. For the arrivals only configuration, the separation rules are specified in the FAA order 7110.308A, often referred to as the “.308 rule” [52]. This rule permits simultaneous dependent approaches, with a 1.5-nautical mile diagonal separation between pairs when the lead aircraft is in the Small or Large wake category. The lead aircraft of the dependent pair is restricted to fly the lower approach, whereas the trailing aircraft is cleared for the higher approach. This approach procedure, illustrated in Figure 2-12, is permitted at BOS, EWR, and at San Francisco (SFO) among other airports.

Figure 2-12. Closely spaced parallel runways dependent approach.

When the CSPR are used in mixed mode (Figure 2-13), a departing aircraft can be released as long as the arriving aircraft is no closer than two miles from the runway at the time the departure commences takeoff [48].

Under the intersecting runway configuration (Figure 2-14), one runway is assigned to arrivals and the other one is assigned to departures. The runway capacity model ensures that arriving aircraft do not cross the landing threshold until the preceding aircraft departs and passes the intersection or is airborne [48]. Additionally, a two-minute separation rule applies when landing aircraft fly through the airborne path of a Heavy or B757 departure on crossing runways.

Figure 2-14. Intersecting runways in mixed mode configuration.

The above-mentioned wake separation rules for single runway and two-runway operations are implemented and enforced by the runway capacity simulation model. These rules serve to establish a baseline scenario for the following chapters, reflecting today’s operational environment and airport capacity estimates.

The last air traffic control component in the simulation model is the separation buffer. The separation buffer is additional separation in excess of the required minimum separation that can mitigate loss of separation and hence, operational error. For departures, buffers come in the form of extra time added before departure clearance. For arrivals, buffers are added as extra time or in

tools, controllers can reduce excessive separations, and hence increase runway throughput. For the purpose of this research study, separation buffers are specified by the user as additional distances (in nautical miles) or additional time (in seconds). The model assumes a normally distributed delivery error (normally distributed error in the inter-arrival times at the final approach fix and at the runway threshold) with a five percent probability of separation violation, based on the work of Harris, as shown in Figure 2-15 [6]. The buffer time is a function of the probability that the required minimum separation will be violated (aircraft are separated by less than the minimum separation).

Figure 2-15. Arrival separation buffer based on normally distributed position error of the trailing aircraft.