The CSPO Working Group (WG) is focused on eight areas, including those identified by the Joint Planning and Development Office, (JPDO), as having direct impact on closely spaced parallel operations. Those areas are:

Blunder Analysis

A blunder occurs when one aircraft on a parallel approach turns toward another aircraft on the adjacent approach. Blunder angle severity and frequency are key parameters in the determination of parallel runway spacing. Blunder data has been collected in its current format since 2008. As of July 31, 2011, there have been over 1.4 million Simultaneous Independent Parallel Instrument Approach (SIPIA) Instrument Landing System (ILS) operations recorded in less than visual conditions. Of those approaches, there have been 60 confirmed blunders which varied in frequency and severity. The verified blunders predominantly occurred at angles between 5° and 35°, with a majority occurring in the 5° to 15° range. Until 2010, the blunder assumption used for fast time simulations was fixed at 30°, a worst case assumption made in the late 1990’s necessary to meet the agreed upon level of safety. The assumption was needed since there was no blunder data available at that time. The updated blunder distributions determined from the data collected, along with other updates to model parameters, has contributed to more realistic fast-time simulations and analysis.


Fast-Time Simulation Tools

Similar to the original blunder assumption of 30°, the original Test Criteria Violation (TCV) was a 500’ radius sphere. This sphere, used in conjunction with the other assumptions made, met the previous acceptable level of risk. A 500’ radius sphere meets the near mid-air collision hazard criteria within the FAA’s Safety Management System (SMS). To more closely approximate the hazard risk of a collision, a recent study of various geometrical models for aircraft in terminal risk analysis was completed. One of those geometrical models, a cylinder, was chosen to approximate a collision during fast-time simulations of SIPIA operations. The size of the cylinder, a radius of 265’ radius and a height of 160’ is based on two Airbus A380 aircraft. It allows one A380 CG to be located at the center of the cylinder while the second A380 CG is on the edge of the cylinder. (Note: a penetration of the cylinder by the aircraft CG constitutes a TCV).

Below is a picture displaying the original 500’ radius sphere with the new cylinder (265’ by 160’) inside containing a Boeing 747.

Original 500’ radius sphere with the new cylinder (265’ by 160’) inside containing a Boeing 747

The TCV criteria/shape change is just one example of many updated parameters that have been used in the fast-time simulations. The resultant analysis has shown that SIPIA operations to parallel runways separated by 3600’ or more meet the TLS without the use of HUR.



As detailed in the Simultaneous Independent Close Parallel Approaches – High Update Radar Not Required (DOT-FAA-AFS-450-69) technical report, the proposed dual SIPIA runway separation standard of 3600’ was based upon fast-time simulations and resultant risk analysis which focused primarily on Instrument Landing System (ILS). Since Wide Area Augmentation System (WAAS) Localizer Performance with Vertical guidance (LPV) and Ground Based Augmentation System (GBAS) Landing System (GLS) provide lateral performance comparable to ILS, they are included as acceptable navigation systems. Only ILS, GLS and LPV with vertical guidance may be used. This operation does not allow the use of LNAV/VNAV, LOC ONLY, RNAV or RNP.

Analysis was initiated during the 1st Quarter of FY12 using fast-time simulations which integrated ILS and GPS required RNAV/RNP aircraft. (RNAV (GPS) was used as a worst case model for RNP (GPS) performance). The same scenario and blunder assumptions used in the Simultaneous Independent Close Parallel Approaches – High Update Radar Not Required technical report were applied. The simulation results from 200,000 runs showed no increased risk from inclusion of RNAV (GPS) into the operational mix.

A Safety Risk Management Panel (SRMP) met in March 2012, to evaluate potential hazards, assess risk, and develop mitigation strategies, as necessary, pertaining to the use of 3600’ spaced runways found within the National Airspace System (NAS). The results of the GPS required RNAV/RNP analysis are being provided to the SRMP with the intent of having this capability included in final Safety Risk Management Document (SRMD).

A recently approved document change proposal (DCP) amended FAA Order JO 7110.65, Air Traffic. This will allow air traffic control (ATC) to use any combination of ILS and GPS required RNAV and RNP approaches for parallel dependent and simultaneous independent operations. Operations could be conducted to independent duals down to 4,300 feet; independent triples down to 5,000 feet; and dependent duals down to 2,500 feet. This DCP also deletes references to MLS approaches within the paragraph and changes “localizer/azimuth course” text to simply “final approach course”.


Advanced Dependent / Paired Approach (PA) Concepts

Two related CSPO proposals have been made to the FAA separately by MITRE and NASA, in collaboration with AIR-130, regarding the use of advanced technology concepts. This initiative for performance-based dependent approaches in less than visual conditions to closely spaced parallel runways is identified in the FAA's ADS-B Application Integrated Work Plan. These concepts are collectively termed the Paired Approach (PA) concept. These concepts will be implemented in phases in conjunction with the ADS-B rule (ADS-B Out and ADS-B In).

The concepts allow paired aircraft to maintain their respective approach paths, with minimal total system error (TSE), and maintain a specified longitudinal alignment. The aircraft will share their guidance status, relative positioning and velocity via ADS-B data link.

The Paired Approach CAT I (PA CAT I) concept being developed by MITRE, requires rule compliant ADS-B Out and one angled approach to a pair of very closely spaced runways. This concept has shown the ability to provide access to runway spacings as low as 700 ft. This concept does not require an automated breakout maneuver or allow for straight-in parallel approaches but does require an echelon position to provide protection from both risk of collision and wake vortex encounters. PA CAT I requires the following:

  • One angled approach (≤3 degrees), ILS, RNAV (GPS), or RNP
  • ATC to establish the pair of aircraft based on capabilities/performance
  • ADS-B Out (current rule)
  • ADS-B In and Cockpit-based tools to allow trail aircraft to achieve and maintain a defined longitudinal spacing interval
  • Ground based wind forecasting system

This concept can only be used for CAT I minima due to the requirement to use angled approach procedures (e.g., 300 ft DH and one-half statute mile (SM) visibility). These requirements are established considering both separation and wake turbulence mitigations.

The Paired Approach CAT I concept will lay the foundation for future evolutionary growth and benefit available with the CAT II Paired Approach concept. Both concepts are highly complementary. The CAT I concept aims at early deployment with specific early benefits whereas the CAT II concept aims at providing the additional capability with the advanced technology that is expected to become available in the NAS.

Paired Approach CAT II (PA CAT II) is the NASA developed concept previously known as "Simplified Aircraft-based Paired Approach" (SAPA). This concept requires a predetermined escape maneuver and integrates the following:

  • autopilot (potentially auto-throttle (CAT II/III path-keeping capability) equipage,
  • differential GPS or equivalent navigation guidance,
  • ADS-B data link and message processing.

PA CAT II allows abeam and echelon positioning while maintaining both collision and wake avoidance based on design/operational criteria. The trailer is also allowed to pass the leader.

Research into both concepts is ongoing. A concept of operation (CONOPS) will be developed in 2013.


Dependent Operations

An effort is underway to reduce the dependent stagger standard from 1.5nm to 1.0nm on parallel approaches. This effort will enter the safety study phase after completion of the fast-time simulations. Work will be completed and an AFS-sponsored safety analysis will be conducted in the near term.


Radar / Surveillance

Currently, both ASR-9 (4.8 second update rate) and high update rate (HUR) PRM/PRM-A (up to 1 second update rate) surveillance are the primary systems utilized in the CSPO terminal environment. As a follow-on to the recent reduction from 4300' to 3600' without HUR, the runway separation standards of 3000’ and 3400’ with HUR are being analyzed for spacing reductions. Further testing is projected to begin in FY13 that will study the capabilities of ADS-B with FUSION. FUSION is the combination of all available surveillance sources (airport surveillance radar [ASR], air route surveillance radar [ARSR], automatic dependent surveillance – broadcast [ADS-B], etc.) into the display of a single tracked target for air traffic control separation services.


Automatic Dependent Surveillance – Broadcast (ADS-B)

ADS-B integration into CSPO is still in the developmental stage as the technology and bounds for performance are fully vetted. The primary CPSO focus for this combination is its potential to replace older and more expensive surveillance systems (e.g. PRM, PRM-A....etc). To date, ADS-B with FUSION has shown early potential to achieve an update rate of 1 second, but current conservative measures state that an update rate closer to 3 seconds may be the norm for FUSION. Thus, continued research into the benefits of FUSION at 3 second update rate will be required.


Traffic Alert and Collision Avoidance System (TCAS) and Airborne Collision Avoidance System (ACAS)

Working with the TCAS Program Office and MIT Lincoln Labs, the CSPO Program will work to determine TCAS enhancements targeted to the provide effective collision avoidance for procedures with reduced separation. These enhancements are included in the ACAS Xo concept within the ACAS program.