Yet Another DJ Near Miss

[RTB RFN]

KAPTAIN M thank you for your assumption regarding my knowledge of TCAS however my research regarding a particular airspace solution revealed that discretion with RA is not rare and is applied with various situations and with consideration of other knowns, appreciating the fact that there may be unknowns. Your opinion regarding uncompromising obediance to the instructions from the equipment is your right and often legislated for commercial operators (now work out who's left!).

This reminds me of an analogy with selection questioning for FLTENG in the 70's whereby only blind obediance to the captains intent permitted selection and any level of counter meant non acceptance. This has since been reversed during the eighties/nineties (CRM reared its ugly head). The human intelligence quotient was appreciated. What of Minimum Safe Altitude Warning and similar systems.

There have been many posts on PPRUNE that counter your opinion of absolutes with RA and they surely draw some merit, despite my own dubious knowledge. The principle of following SOP's is easily upheld by statistics however there will always be the case for intelligent human discretion. As the late Doctor Ratner said to me "its always smart to follow SOP's except when it is dumb to". Often this is only determined after the fact, after the smoking hole.

My primary point is that an RA disturbs the ATC equilibrium and may cause compounding hazards as a result of ATC action or inaction, adding additional complexities, requiring resequencing of any number of aircraft. In a normal system this is acceptable. However where the TCAS RA is depended upon as part of the normal system of separation the additional hazards may prove to be unacceptable. Consider a busy scenario with perhaps 30 aircraft within 30 nm's (work out where that happens in AUS) and tell me that any RA system can cope with such a dynamic environment with so many aircraft trying to electronically resolve compounding solutions. Has RA been tested in such an environment with such complexities. What of weather and restricted airspace (firing) etc - sure these are of secondary importance to avoidance of a collision but does the RA consider these? No - it considers only limited and immediate consequence; it does not look far ahead to ensure you are not placed into a dead end situation. Enter the human.

TCAS - it's not perfect however from my "scant" knowledge of TCAS I believe the captain must hold veto for an exceptional circumstance. BTW I personally watched the B737 try to dive in front of the E120 and I wondered if traffic had been provided and the aircraft were on the same freq. would the outcome have been any different (this was pre-2B so the prob. of other traffic is v. low).

This happened - Chopper departs on Christmas day no mode C. Switches it on and whadayerknow - 3,400 feet out.

So its a clear blue sky and your equipment says RA and you respond when you happen to notice the blooming of an aircraft in your RA directed position. Options - quickly review your Turning Rejoin - bug out procedures and slide smoothly beneath or blindly follow the RA just in case that's not the one!