Worst-case analysis of wake vortex induced risk of 700ft vertical separation Gerben van Baren
Contents Incentive Objective Approach Results Conclusions NLR Air Transport Safety Institute 15-1-2009 2
Incentive Dutch ANSP (LVNL): Integration of Schiphol and Rotterdam traffic IFR traffic to/from Rotterdam need to fly in Rotterdam TMA/CTR at 2000ft Normally speaking: Medium/Light IFR only NLR Air Transport Safety Institute 15-1-2009 3
Incentive VFR routes at 1500 ft NLR Air Transport Safety Institute 15-1-2009 4
Incentive but... VFR traffic at 1500ft, i.e. 500ft vertical separation ICAO recommendation (doc 9426): 1000ft 1000 ft NLR Air Transport Safety Institute 15-1-2009 5
Objective to define a procedure with sufficiently safe separation between Light and Medium aircraft TMA 2000ft 1500ft 500ft ICAO: 1000ft 700ft??? CTR NLR Air Transport Safety Institute 15-1-2009 6
Question Will wake vortex turbulence caused by Medium (or Heavy) aircraft at 2000ft have an unacceptable influence on Light aircraft at 1300ft, i.e. with 700ft vertical separation? NLR Air Transport Safety Institute 15-1-2009 7
Subquestions 1. What is unacceptable / acceptable? 2. What is the strength of wake vortices generated by Medium (/Heavy) aircraft at 2000ft? 3. What is the residual wake vortex strength when arriving at 1300ft? 4. What is the effect of induced forces and roll moments on a Light aircraft? NLR Air Transport Safety Institute 15-1-2009 8
Safety argument Comparison of the proposed operation with current practice 1000ft between Heavy and Light aircraft is considered acceptable today Comparison of encounter severity metrics with reference criteria NLR Air Transport Safety Institute 15-1-2009 9
Strength of wake vortices generated by Medium/Heavy aircraft at 2000ft Generating aircraft parameters: Scenario Sc0 Sc1 Sc2 Sc3 Generating aircraft Heavy Heavy Medium Medium (Large jumbo, (Large jumbo, (Jet, B737) (turbo prop, F50) B747) B747) wing span [m] 64.4 64.4 35.7 29.0 weight [kg] 372.000 300.000 78.200 20.820 speed [kts] 200 200 180 160 initial vortex strength [m 2 /s 2 ] 607 489 255 94 reference scenario NLR Air Transport Safety Institute 15-1-2009 10
Residual wake vortex strength when arriving at 1300ft Simulations with WAVIR wake vortex evolution model (VORTEX) Greene, Corjon & Poinsot two point vortices with initial strength, position, core radius decay due to atmospheric turbulence and stratification Applied in S-Wake, ATC-Wake, I-Wake, AWIATOR Out-of-Ground situation Turbulence (EDR):[0, 0.0001, 0.002, 0.004] Stratification (N): [0, 0.001, 0.01, 0.02] No winds NLR Air Transport Safety Institute 15-1-2009 11
Residual wake vortex strength when arriving at 1300ft Heavy (372,000kg) Sc0 Heavy (300,000kg) Sc1 vertical position [ft] time [s] time [s] 342 m 2 /s at 1000ft 340 m 2 /s at 1300ft NLR Air Transport Safety Institute 15-1-2009 12
Residual wake vortex strength when arriving at 1300ft Heavy (372,000kg) Sc0 Medium (78,200kg) Sc2 vertical position [ft] time [s] time [s] 342 m 2 /s at 1000ft 115 m 2 /s at 1300ft NLR Air Transport Safety Institute 15-1-2009 13
Residual wake vortex strength when arriving at 1300ft Heavy (372,000kg) Sc0 Medium (20,820kg) Sc3 vertical position [ft] time [s] time [s] 342 m 2 /s at 1000ft N/A at 1300ft (not lower than 1600ft) NLR Air Transport Safety Institute 15-1-2009 14
Induced forces and roll moments on a Light aircraft Aircraft parameters Light (C172) wing span [m] 10,9 weight [kg] 736 speed [kts] 108 wing surface [m 2 ] 16.2 aspect ratio [-] 7.32 taper ratio [-] 0.67 C L,α [-] 4.6 C l,p [-] -0.45 I xx [-] 1200 Aircraft at 1300 ft Worst case: aircraft in vortex core NLR Air Transport Safety Institute 15-1-2009 15
Encounter severity metrics Roll control ratio Ratio of induced roll moment and available roll control Equivalent roll rate Roll rate equivalent to the wake induced roll moment, without pilot intervention Maximum bank angle Tatnall s 1 DoF encounter model Encounter duration, pilot reaction time, max roll control Induced load factor, parallel encounter Ratio of induced load and aircraft weight Induced load factor, perpendicular encounter Ratio of induced load and aircraft weight NLR Air Transport Safety Institute 15-1-2009 16
Criteria for Roll control ratio Simplified Hazard Area Prediction (SHAPe) RCR > 0.3 NLR Air Transport Safety Institute 15-1-2009 17
Criteria for maximum bank angle and equivalent roll rate ICAO doc 9426 Severe: Moderate: roll angle > 30 deg with full opposite aileron applied 10 deg < roll angle < 30 deg Slight: roll angle < 10 deg roll angle ~ equivalent roll rate x reaction time (1 sec) NLR Air Transport Safety Institute 15-1-2009 18
Criteria for load factor EASA CS-23.333 Aircraft should be able to cope with load due to vertical gusts up to ~15 m/s load factor due to gust Based on static computation: max load factor ~ 5.5 g 7 load factor [g] 5 0 lateral position [m] NLR Air Transport Safety Institute 15-1-2009 19
Induced forces and roll moments on a Light aircraft Roll control ratio relative vertical position [m] Heavy (372,000kg) Sc0 Heavy (300,000kg) Sc1 Medium (78,200kg) Sc2 max rcr = 5.6 y rcr > 0.3 = 87m lateral position [m] max rcr = 6.4 y rcr > 0.3 = 86m max rcr = 2.3 y rcr > 0.3 = 48m NLR Air Transport Safety Institute 15-1-2009 20
Induced forces and roll moments on a Light aircraft Maximum bank angle maximum bank angle [deg] Heavy (372,000kg) Sc0 Heavy (300,000kg) Sc1 Medium (78,200kg) Sc2 lateral position [m] max bank = 115 deg y bank > 30 = 56m max bank = 135 deg y bank > 30 = 58m max bank = 36 deg y bank > 30 = 30m NLR Air Transport Safety Institute 15-1-2009 21
Induced forces and roll moments on a Light aircraft Equivalent roll rate equivalent roll rate [deg/s] Heavy (372,000kg) Sc0 Heavy (300,000kg) Sc1 Medium (78,200kg) Sc2 lateral position [m] max eq.rr = 149 deg/s max eq.rr = 172 deg/s max eq.rr = 59 deg/s NLR Air Transport Safety Institute 15-1-2009 22
Induced forces and roll moments on a Light aircraft Load factor in parallel encounter Heavy (372,000kg) Sc0 Heavy (300,000kg) Sc1 Medium (78,200kg) Sc2 Load factor [g] lateral position [m] max load = 3.2 g max load = 3.5 g max load = 1.4 g NLR Air Transport Safety Institute 15-1-2009 23
Induced forces and roll moments on a Light aircraft Load factor in perpendicular encounter Heavy (372,000kg) Sc0 Heavy (300,000kg) Sc1 Medium (78,200kg) Sc2 Load factor [g] lateral position [m] max load = 3.9 g max load = 4.7 g max load = 1.6 g NLR Air Transport Safety Institute 15-1-2009 24
Comparison to criteria Parameter Max roll control ratio y rcr > 0.3 Max bank angle y bank > 30 load factor criterion rcr > 0.3 severe > 30 deg 5.1 Sc0 (Heavy) 5.6 87 115 149 56 3.2 3.9 Sc1 (Heavy) 6.4 86 135 172 58 3.5 4.7 Sc2 (Medium jet) 2.3 48 36 59 30 1.4 1.6 Sc3 (Medium turbo prop) - - - - - - - Medium turbo prop (Sc3): negligible impact Heavy and Medium jet: Considerable disturbances compared to criteria Medium jet (sc2) considerably less than current practice worst case (sc0) Heavy jet (sc1) comparable / somewhat worse than sc0 NLR Air Transport Safety Institute 15-1-2009 25
Taking into account ± 100ft uncertainty in vertical position of both a/c Heavy (372,000kg) Sc0 Heavy (300,000kg) Sc1 vertical position [ft] +200ft +200ft time [s] time [s] When considering uncertainties in altitude (and if the N/EDR==0 was excluded), still potential for considerable disturbances in Sc1 NLR Air Transport Safety Institute 15-1-2009 26
Taking into account ± 100ft uncertainty in vertical position of both a/c vertical position [ft] Medium (78,200kg) Sc2 +200ft Medium (20,820kg) Sc3 +200ft time [s] time [s] When considering uncertainties in altitude and/or if the N/EDR==0 was excluded, still potential for considerable disturbances in Sc1 NLR Air Transport Safety Institute 15-1-2009 27
Comparison to criteria taking into account ± 100ft uncertainty in vertical position parameter roll control ratio y rcr > 0.3 bank angle y bank > 30 load factor criterion rcr > 0.3 severe > 30 deg 5.1 Sc0 (Heavy) 1000ft 5.6 87 115 149 56 3.2 3.9 Sc1 (Heavy) 500ft 8.1 (6.4) 88 (86) 178 (135) 221 (172) 66 (58) 4.3 (3.5) 6.5 (4.7) Sc2 (Medium jet) 500ft 3.5 (2.3) 52 (48) 65 (36) 93 (59) 32 (30) 2.0 (1.4) 3.0 (1.6) Sc3 (Medium turbo prop) 500ft - - - - - Medium turbo prop (Sc3): still negligible impact Heavy and Medium jet: Considerable disturbances compared to criteria Medium jet (sc2) still less than current practice worst case (sc0) Heavy jet (sc1) exceeding current practice worst case (sc0) NLR Air Transport Safety Institute 15-1-2009 28
Conclusions 700ft vertical separation between Medium and Light aircraft is acceptable: Impact of Medium turbo prop is negligible Medium jet leads to considerably less impact than 1000ft between Heavy and Light aircraft which is considered safe today also when uncertainty (± 100ft) in vertical position of both aircraft is taken into account 700ft vertical separation between Heavy and Light aircraft cannot be considered acceptable yet: leads to worst-case impacts comparable with today s worst-case, but exceeds today s worst-case impacts when taking into account uncertainty (± 100ft) in vertical position may be possible depending on probability of occurrence, meteo conditions, route geometries Results to be used as an input for decision-making by ANSP in consultation with CAA NLR Air Transport Safety Institute 15-1-2009 29