Time Based Separation – Transitional Step (TBS-TS) & Crosswind Operations (CROPS) David, BOOTH Senior Expert - Airports david.booth@eurocontrol.int The European Organisation for the Safety of Air Navigation
High-level concept of operations • Procedure change only, with limited system support • Authorise a 0.5NM reduction of wake turbulence distance based separation, between WT pairs (as per ICAO Doc 4444), on final approach • Conditional application – only in specific headwind / crosswind conditions • Both CONOPS mature, only requiring final update after safety assessment 2
Required wind conditions • TBS - Surface headwind component wind is equal to or stronger than 10kt (still to be confirmed) plus a buffer • CROPS - A 6kt crosswind (still to be confirmed) plus a buffer • Wind forecast confirms favourable wind speed and directions for winds aloft for the entire planning period • No significant MET situations are forecasted • Unfavourable MET conditions need to be defined, e.g. thunderstorms, wind shear. 3
Safety deliverables • Safety plan developed • Safety Assessment report supported by more than 5 years of scientific work, including terabytes of LIDAR data, – almost complete 4
Safety assessment of CROPS � Operational objective: – Take advantage of cross-wind effect on wake turbulence transport and decay 09 � Expected benefits: – Increase runway throughput or absorb delays � Scope of preliminary safety assessment: – Specimen final approach segment and IFR arrivals – Safety assurance of acceptability of conditional reduction of WT separation minima – Heavy-Heavy & Heavy-Medium pairs � Guidance to support safety assessment in local implementation 5
Specimen final approach segment (as per ICAO Doc 8168) 6
Safety criteria and strategy � Relative safety criterion: The risk (likelihood) per approach of a WT-induced loss of control accident when reduced WT distance-based separation minima are applied to a Medium or Heavy aircraft on final approach behind Heavy in minimum cross wind conditions as defined by CROPS shall not be greater than the risk per approach of WT- induced loss of control accident when ICAO provisions for WT separation minima as applied today in all wind conditions by European ANSPs � Comparative (quantified) Wake Vortex Encounter (WVE) risk assessment principle: Frequency - f Frequency - f Circulation Strength - � (m^2/s) Circulation Strength - � (m^2/s) � Evidence from (Leader) WV measurements, data processing and computation 7
WT hazardous scenarios and conditions on final approach � Operational threat: WT-induced loss of control � Potential WVE for follower aircraft all along the glide (normal landing) � WVE more likely to occur in low wind conditions 8
WVE risk quantification and comparison (in fault-free conditions) Baseline selection: � Current WT-induced loss of control accident risk in ECAC (considering ICAO provisions applied fault-free) is acceptable in all weather (wind) conditions, incl. low wind WT-induced LoC risk characterisation: � WT-induced LoC risk is characterized by the risk (likelihood) distribution of potential WVE strength (representing the induced roll moment effect) for a given arrival pair at a given time separation, derived from equivalent distance, and in given weather conditions, (further called WVE risk) � Severity metric for WVE risk: WV circulation WVE risk distribution in worst reasonable conditions: � Heavy leader aircraft configuration: all most frequent aircraft types of the category � Use of reference final approach speed per category being representative and conservative � 4D geometry: at minimum separation on final (ICAO minimum DBS-equivalent TBS) � Weather: Low total wind (below 5 kts) for baseline case Approach legitimacy: � Previous cases with similar approach: A380 WT and WIDAO at Paris CDG 9
Acceptable WVE risk for Heavy landing behind Heavy at 4NM in low wind (baseline) CCDF (Complementary Cumulative Density Function) is defined for a certain � , as the probability to observe a wake vortex with a circulation higher than � * CCDF( � *) = P( � > � *) Safety corridor: +/-100m 10
Acceptable WVE risk for Medium landing behind Heavy at 5NM in low wind (baseline) 11
CROPS must be specified to meet safety criteria � Safety performance objectives (fault-free) for ANS/ATM system functions to meet safety criteria / targets: 1. Determination of WT separation minima Conditional reduction in crosswind of WT DBS minima applicable to Heavy sequenced and descending behind Heavy on final approach shall be determined such that the frequency (per approach) of WVE (of a SPO-01a given severity) by this following Heavy on final approach will not be higher than when a Heavy is landing behind another Heavy at ICAO WT separation minimum in low wind conditions. Conditional reduction in crosswind of WT DBS minima applicable to Medium sequenced and descending behind Heavy on final approach shall be determined such that the frequency (per approach) of WVE SPO-01b (of a given severity) by this following Medium on final approach will not be higher than when a Medium is landing behind another Heavy at ICAO WT separation minimum in low wind conditions. 2. Correct application of WT separation minima to arrival pairs (local) WT separation conditionally reduced in crosswind shall be provided (created and maintained) such that SPO-02a Heavy arrival on final approach is correctly separated from preceding Heavy arrival WT separation conditionally reduced in crosswind shall be provided (created and maintained) such that SPO-02b Medium arrival on final approach is correctly separated from preceding Heavy arrival 12
WVE risk comparison for H behind H at 3.5NM WT DB minima with at least 5 and 6 kts surface crosswind or above 5 kt 6 kt 13
WVE risk comparison for M behind H at 4.5NM WT DB minima with at least 5 and 6 kts surface crosswind or above 5 kt 6 kt 14
Safety conditions for CROPS application � For Heavy arrival to be separated at 3.5NM behind preceeding Heavy: A surface crosswind component speed of 6 kts or greater (CW1) shall prevail in order to allow SCO-11a application of WT separation at 3.5 NM for Heavy behind Heavy on final approach A surface total wind speed of 10 kts or greater shall prevail in order to allow application of WT SCO-11b separation at 3.5 NM for Heavy behind Heavy on final approach Wind forecast confirms favourable wind speed and direction during the planned period of application SCO-12 and on the whole final approach segment � For Medium arrival to be separated at 4.5NM behind preceeding Heavy: A surface crosswind component speed of 6 kts or greater (CW1) shall prevail in order to allow SCO-21a application of WT separation at 4.5 NM for Heavy behind Medium on final approach A surface total wind speed of 10 kts or greater shall prevail in order to allow application of WT SCO-21b separation at 4.5 NM for Heavy behind Medium on final approach Wind forecast confirms favourable wind speed and direction during the planned period of application SCO-22 and on the whole final approach segment 15
WV data collection and analysis � WV data collection campaign at EGLL over 2 years � More than 100.000 wake vortex tracks � Correlation with weather and aircraft data � WV data processing and analysis � Data cleaning by filtering � Region of interest � Sanity check 16
Key assumptions, open issues, limitations Assumptions for generalisations: � Wind band of 1 knot � Wind distribution is uniform with each wind band Open issues: � Buffer to be added to cross-wind safety conditions = function of local wind forecast � Manual cleaning check of WV data – on-going Limitations: � Missed approach influence not verified at generic level 17
Local ANS/ATM system characteristics to be considered � Local safety assessment required on changes to ANS/ATM system � Final approach profile and runway occupancy time � Specific WT categories and separation minima � Wind behaviour and forecast accuracy at aerodrome to meet conditional wind criteria � Proposed ANS/ATM system architecture (data quality, tools, procedures, roles) supporting application of CROPS reduced WT separation minima on final approach � Safety objectives to be set consistent with SMS � Safety requirements for ANS/ATM system elements, to be designed and implemented to allow CROPS application 18
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