PPRuNe Forums - View Single Post - BASI "Limitations of See & Avoid" ??
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Old 7th Aug 2003, 20:44
  #16 (permalink)  
Join Date: Jun 2003
Location: Awstraya
Posts: 194
**WARNING - longwinded, may cause eyes to glaze over and inhibit scan **

To go back to the start of the post re: limitations of "see & avoid"

For those who fly in A & C only - not really an issue until someone with their transponder and radio off wander into their tracks outside primary radar cover;

For those who fly in D,G & E -

a. for radio broadcasts to be effective you need parties with operating radios listening on the same frequency delivering information on ACTUAL position and intentions - I think that all three requirements for this to be a consistently helpful defense are frequently not met;

b. for ATC broadcasts to be effective - ditto plus requirement to be radar visible and/or known traffic;

c. for TCAS - need a TCAS unit in your ACFT and operating transponders in the other ACFT - not mandatory outside class E (below 8500 at this stage) or ACFT without electrical systems, thus frequently not effective - what do the RPT guys do from 8500' (transponder mandatory in E) down to 5000' (radio mandatory in MBZ)? Cross their fingers, trust TCAS, slow down to look out the window, speed descent to minimise exposure or know that the big sky will protect them?;

d. alerted see & avoid - how many times have you been given info on traffic at 2 miles +/- 1000' at x o'clock and still not been able to see them? If you are on frequency though, at least you can arrange some mutual agreement on altitudinal separation....;

e. unalerted see and avoid - en route, this is virtually the same as big sky and occurs when the other defenses above are not present (which is frequently);

f. see and avoid approaching the circuit area (where most midairs occur) - at least we do slow down, look in the areas most likely to yield traffic as well as perform a general scan for traffic and we are hypervigilant - a state that we can maintain for the short period of time of joining circuit and landing, but not for the long periods of en-route. See and avoid is more likely to be successful in this environment but is not infallible. Only positive control down to ground level can improve on this, but is not affordable/practical outside major centres

g. Big sky - the statistical improbability that two ACFT will occupy precisely the same volume of airspace at precisely the same time protects us a lot more often than we think

My point is not that airmanship will save us, but that:
1. there are already frequent large gaps in the defenses available to us for prevention of en-route midairs,
2. that we do not really know or have quantified the relative or additive contributions that each of these defenses actually make;
3. that see and avoid (alerted or not) is very fallible as BASI indicates, and especially en-route;
3. that despite these current real gaps we don't have a tradition of en-route collisions;
4. we don't really know what effect that things such as withdrawing common radio communications outside controlled space will have - we just have opinions, which are like fundamental orifices... but I certainly agree with Icarus that the issue of emergency comms has not been adequately addressed

To interpret US vs Aust statistics on mid-airs we really need to consider en-route rates (not absolute numbers) only and factors such as traffic density. (I don't know about you, but I find the ATSB site frustrating to get any meaningful statistical information on this or many other topics..... ).

Sentiment and the way I've been trained (often based on instructor's/check pilots habits and training, not always based on logic! ) lean me to supporting the status quo rather than NAS but I'm open minded enough to to consider alternatives, and that NAS may even *possibly* be safety neutral relative to the current airspace in view of the above remarks.....but by God, the silence from the ARG is deafening

Fly safely

NOtimTAMs is offline