The document discusses the application of a legal case methodology to the development of ACAS XA. It provides background on the author's experience working on TCAS II and ACAS X. It summarizes that applying the legal case methodology did not reassure the author and undermined their confidence in the legal process. The document also notes that while the methodology could determine liability risk, it does not evaluate accident probability or likelihood of a case being brought. There is no possibility of using the legal case methodology in the ACAS X concept of operations. The only seen use is to transfer risk between actors.

2. Application of legal case
to ACAS XA

3. Background in ACAS X
• Worked on TCAS II for 28 years
– SARPs for ACAS II
• Chairman of EUROCAE WG-75
• Currently under contract to the FAA
– developing ACAS XA and ACAS XU

4. User Group Experience
• Joined at quite a late stage
• Fascinating but not reassuring
– Undermined my confidence in legal process
– No longer trust it to reach sensible decisions

5. Results from test application
• For whom? Methodology or ACAS X?
• w.r.t. methodology, it demonstrated that
the process can indeed be applied to ACAS
– Determines the exposure of each actor to the
risk of being found liable for an accident
– but it does not evaluate the probability of the
accident, nor of the case being brought
– nor does it seek to determine who is liable

6. Use in Concept of Operations
• Already reported: ACAS XA =TCAS II
• There no possibility of use in ACAS X ConOps
• But that would be the best place to use
anything that can be used

7. Use in design of ACAS XA
• I agree it is essential to define procedures
– Saying procedures must be defined does not help
• We know it
• Deep prejudice in favour of providing information
• There are other systems that just show tracks
– Track and TA will aid visual acquisition
• In the USA pilots are expected to rely on visual evidence,
in Europe EASA warns against that

8. Use in design of ACAS XA
• So – give them an RA
– Again, I happen to agree
– Not going to happen because endangers timescale
– Significant work involved
– Comments about maturity and encryption misplaced
• The technology is mature
• We want ADS-B to be open – that is the point of it
• Design of ADS-B not under control of ACAS X team

9. Final comments
• The application of well-meaning disciplines is
not always beneficial
– “The road to Hell is paved with good intentions”
• Already required to be safe and effective
• The only use I can see for the Legal Case is to
help transfer the risk between actors
– to avoid litigation by ensuring that those against
whom there is a credible case cannot pay