Appendices Appendix A: LOS collision risk assessment elements For both airborne and runway LOS events, there are four elements that were considered to assess the collision risk. Each element is scored based on the severity of the factor—that is, how much it suggested that there was no control over the separation loss. An element can be scored as elevated risk (15), some risk (10), minimal risk (5), or nil risk (1). When all elements are assessed, the collision risk is calculated by summing the element scores: Elevated risk of collision score of 41 to 60 – Some risk of collision score of 26 to 40 – Minimal risk of collision score of 9 to 25 – Nil risk of collision score of 8 or less – The tables show how each element is scored. Airborne LOS Elements Awareness & Closure rate & proximity Evasive action Relative tracks communication Considering relative aircraft performance, <20 No awareness by seconds to imminent ATS or flight crews Necessary, or Aircraft tracks are collision of imminent collision should have been crossing, reciprocal 15 Altitude +/- 250ft vertically to avoid an or converging Traffic alert (STCA or between aircraft imminent collision (critical) TCAS RA) as last line of defence Laterally separated by <400m Loss of situational awareness by ATS >20 seconds but <60 or Flight Crews seconds to potential Aircraft tracks are Ground based or collision Close conflict crossing, reciprocal aircraft traffic alert 10 Altitude >250ft but <500ft necessitating pilot or or converging activation preventing vertically between aircraft ATS action (critical but not potential collision imminent) Laterally separated by High traffic, >400m but <1,000m frequency congestion Action required to >60 seconds to potential re-establish Aircraft tracks are collision One aircraft of separation standard crossing, reciprocal 5 Vertical separation >500ft the other or ATS (non-critical) or or converging aware of both aircraft Lateral separation should have been critical) >1,000m taken Evasive action not ATS and all required Diverging, parallel or Closure rate and proximity associated aircraft same track 1 not a factor (aircraft were had situation ATS action not never going to collide) awareness (technical required to Tracks did not cross LOS) standard
Appendices Appendix A: LOS collision risk assessment elements For both airborne and runway LOS events, there are four elements that were considered to assess the collision risk. Each element is scored based on the severity of the factor—that is, how much it suggested that there was no control over the separation loss. An element can be scored as elevated risk (15), some risk (10), minimal risk (5), or nil risk (1). When all elements are assessed, the collision risk is calculated by summing the element scores: Elevated risk of collision – score of 41 to 60 Some risk of collision – score of 26 to 40 Minimal risk of collision – score of 9 to 25 Nil risk of collision – score of 8 or less The tables show how each element is scored. Airborne LOS Elements Closure rate & proximity Evasive action Relative tracks Awareness & communication 15 Considering relative aircraft performance, <20 seconds to imminent collision Altitude +/- 250ft vertically between aircraft Laterally separated by <400m Necessary, or should have been to avoid an imminent collision Aircraft tracks are crossing, reciprocal or converging (critical) No awareness by ATS or flight crews of imminent collision Traffic alert (STCA or TCAS RA) as last line of defence 10 >20 seconds but <60 seconds to potential collision Altitude >250ft but <500ft vertically between aircraft Laterally separated by >400m but <1,000m Close conflict necessitating pilot or ATS action Aircraft tracks are crossing, reciprocal or converging (critical but not imminent) Loss of situational awareness by ATS or Flight Crews Ground based or aircraft traffic alert activation preventing potential collision High traffic, frequency congestion 5 >60 seconds to potential collision Vertical separation >500ft Lateral separation >1,000m Action required to re-establish separation standard (non-critical) or should have been taken Aircraft tracks are crossing, reciprocal or converging One aircraft of the other or ATS aware of both aircraft 1 Closure rate and proximity not a factor (aircraft were never going to collide) Evasive action not required ATS action not required to standard Diverging, parallel or same track Tracks did not cross ATS and all associated aircraft had situation awareness (technical LOS) critical)