Simultaneous approach

A Normal Operating Zone (NOZ) is defined airspace extending to both sides of a final approach course in an instrument approach. A No Transgression Zone (NTZ) is airspace established between extended runway center lines, where flights are normally not allowed. In the United States, according to Federal Aviation Administration (FAA), when runway spacing is no more than , the NOZ is established with a constant width of . When runway spacing is at least , the NTZ is established with a constant width of , located equidistant between parallel runways or SOIA final approach courses. International Civil Aviation Organization (ICAO) recommends establishing the NTZ based on surveillance capability and runway spacing, and NOZ's width determined by the NTZ. Breakout In case of an encroachment of the NTZ, an air traffic controller (ATC) will issue the threatened aircraft a "breakout" — a vector off the final approach course, which pilots must fly manually to be able to quickly respond. ICAO mandates that the break off vectoring must not result in a heading change of more than 45°. == Types ==

Simultaneous dependent approach , ATC will provide aircraft wake category pairing for the approaching traffic. ATC will provide a vertical separation of or a radar separation of at least of between aircraft during "turn on", the stage of the approach immediately before the parallel approach begins. After that, ATC provides the following minimum diagonal radar separation based on runway spacing: • 1 nautical mile, for (FAA) or (ICAO) ≤ runway spacing ≤ ; • 1.5 nautical miles, for < runway spacing ≤ ; • 2 nautical miles, for < runway spacing ≤ . For airports with less than runway spacing, also known as "Closely-Spaced Parallel Runways" (CSPR), ATC will provide no less than the minimum authorized diagonal separation with the leader always arriving on the same runway. , eight airports across the United States have approved simultaneous dependent approach to CSPR. Simultaneous independent parallel instrument approaches Simultaneous independent parallel instrument approaches (SIPIA) permit simultaneous approaches to parallel runways with centerlines separated by at least 4,300 feet. Unlike dependent parallel approaches, independent parallel approaches do not use staggered radar separation procedures. For runways between 4,300 and 9,000 feet (9,200 feet for airport elevation 5,000 feet) apart, a no transgression zone final monitor controller is assigned. ICAO requires adjacent missed approach courses to diverge by 30°. Simultaneous close parallel (SCP) PRM approaches permit runway spacing between 2,500ft and 4,300ft, but under certain adverse weather conditions, such operations may be suspended due to safety concerns and large number of deviation alerts. The NTZ and NOZ between the final approach courses are considered independent; one ATC is assigned for each approach course. A separate final NTZ monitoring ATC can interject on the tower frequency. A secondary PRM frequency is also used and required to be monitored by pilots, so that in case the tower frequency is congested, pilots can still receive the breakout instruction. Simultaneous offset instrument approach Simultaneous Offset Instrument Approach (SOIA) allows simultaneous approaches to runways spaced less than 3,000 feet, but at least 750 feet apart, and with one final approach course offset by 2.5° to 3.0°. The SOIA procedure utilizes a straight-in PRM approach to one runway and a PRM offset approach with glideslope to the adjacent runway. In SOIA, aircraft are paired, with the aircraft conducting the straight-in PRM approach always positioned slightly ahead of the aircraft conducting the offset PRM approach. After clearing from the cloud, the offset aircraft is given at least 30 seconds before reaching missed approach point or decision altitude to obtain visual acquisition of the leading straight-in aircraft. but has phased out from it in favor of closely-spaced parallel runway operation procedures instead. Although no airport across the world implements active SOIA , FAA still requires SOIA trainings for transport pilots, seeing SOIA potentially implemented in the future. and Philadelphia International Airport. Dependent converging instrument approach Dependent converging instrument approach (DCIA) is another option for converging or intersecting runways, where the converging aircraft maintain a stagger so that in the event of double missed approach, the traffic separation is guaranteed even at the intersection of flight paths. Converging runway display aid, a software that aid controllers by displaying a "ghost" target of an aircraft on other courses, is required to be operational. The runways are angling between 45° and 110°, with missed approach courses straight out until crossing the common point, beyond which the courses diverge 45° or greater. The minimum authorized stagger distance is 2 nautical miles and can go up to 8 nautical miles when the aircraft being followed is an Airbus A388 or if the runway is sufficiently long. Philadelphia International Airport currently implements DCIA for its RNAV approach to runways 27R and 35. Amsterdam Airport Schiphol considered implementing DCIA, but Luchtverkeersleiding Nederland declined the proposal in 1998, as it requires regular ATC training given how infrequent the operation is. == History ==

Prior to 1962, simultaneous approaches were already being used for two parallel runways at Chicago O'Hare International Airport after analysis on lateral deviation of aircraft on ILS approach. In 1974, based on experience with William B. Hartsfield Atlanta International Airport, which had runways 4,000 feet apart, FAA reduced the runway spacing requirement down to 4,300 feet. In the late 1980s, with the development and testing of PRM radars, the FAA permitted simultaneous approach to runways 3,400 feet apart. Another FAA project, called Multiple Parallel Approach Program, advanced the investigation and development of simultaneous approaches to three parallel runways. In 1986, the FAA Order 7110.98 established simultaneous converging instrument approaches. == Operation considerations ==

Pilot responsibility Pilots will be informed by ATC and/or automatic terminal information service that simultaneous approach is in use. Pilots need to closely monitor and strictly execute instructions from ATC to reduce ATC intervention or penetrating the no transgression zone. 10° interception for aircraft on track-to-fix is recommended to minimize alerts from TCAS and flight management systems and decrease overshoots. • Mode 1: independent parallel approaches; • Mode 2: dependent parallel approaches; • Mode 3: Independent parallel departures; • Mode 4: segregated parallel operations, where at least one runway is used exclusively for approaches or departures, while the other one may have exclusive or mixed operations. The minimum runway spacing for mode 4 is required to be at least 2,500 ft, but may be decreased down to depending on the staggering between arrival runway and departure runway. Capacity A theoretical maximum arrival capacity may be achievable with independent parallel approaches, followed by dependent parallel approaches. However, difficulties with implementation and pilots' lack of familiarity hinder the effectiveness of simultaneous approaches. == See also ==