[P7_TOM]

Posting for “K” today – who is under orders - ‘be there’- or else.

SR continuum.

‘Procedural separation’ (Class E ala Dick) was a topic at a recent BRB indaba.  Thought the BRB vote may be of some interest.

The need for 24/7 blanket coverage was dismissed as not required – 100% against.  The need for a system which could be ‘on –standby’ when ‘alternates’ where required and ATC was aware of more than three aircraft scheduled to arrive within ‘alternate’ buffer periods found much support; 78% thought it ‘sound’, a further 14% thought it should be made to happen.  That naturally led to some debate.  I will try to summarise:-

The weather across the inland is for the most part benign and traffic sparse; the chances of multiple arrivals, within a narrow time frame, in IMC are slim.  There are the exceptions but in the main, ATC would not be frequently called upon to take a hand.

Along the coastal areas and over the hills, the weather can be fickle and occasionally brutal, the OCTA airports do carry a fair bit of traffic and two or three aircraft arriving within a narrow time band is probable – but not high frequency.  A busy period where the RPT is scheduled, a charter or two due about the same time – perhaps a trainer in the circuit; in reasonable weather it is not a problem – except for extended circuits or even a short hold to allow safe separation.  Inefficient? sure, and operationally costly but not a situation for risk mitigation – in the form of positive separation by ATC.  Unless the required triggers are in place; weather at alternate minima; more than two IFR aircraft scheduled within 30 minutes of each other, i.e. within the time needed for an approach – missed approach and sort out.  Close proximity aircraft in this situation are at a higher risk level – (A) misses out and decides to head to the alternate, (B) now aware of the weather decides not to mess about and also decides to divert; depending on height, position, speed and selected alternate; without good communication, there is a chance the two could get fairly close, particularly when the same alternate is used and track height needs to be changed; this is routinely resolved by flight crew, but add a third or fourth aircraft and the risk matrix alters.    

When we look at the Hotham event – YHOT can be ignored 364 out of 365 days a year; there simply is not a traffic problem – but when an event which requires multiple arrivals and departures within a close time frame is flagged and the weather demands an alternate, even with the most meticulous planning things can and do go wrong – in fact, you could bet money on Murphy to win the race.  

So, solutions.  Given the triggers present on that day, would it have been feasible for ATC to provide a watching brief and ‘positive control’ – as the traffic piled up behind the lowest aircraft.  Stack ‘em and release ‘em when the way was clear?  They can do that, standing on their heads, they could also ask the question ‘intentions?’  On the other hand, good communication from the aircraft having difficulties would have assisted in the short term; but a helping hand from someone who had the whole picture would have been of great value.

If we put aside the costing, liability, rules and an inflexible, hidebound, draconian ATC ‘responsibility’ system; how good would it be to have a friendly voice chiming in “ABC – instrument approaches in progress, hold at 10 thousand expect 15 minute delay.  “DEF -*-*-*-*-“.  Is it worth all the trouble for a couple of hours a year?, probably not.  Except for 300 small feet – not even 92 meters, which separated two aircraft with a closing speed of about 500 kph.  Allowing for maximum tolerable instrument error, and within tolerance flying +100 for the lower aircraft; they could have been a bit further apart or, much closer.  Either way, it’s only the difference between two or three heartbeats.  

Risk analysis puts the percentile chance of a reoccurrence off the chart; but, can it be allowed to happen a second time?  It’s the same thing as the Mildura fiasco, infinitesimal chances of those holes lining up – but they did; more chance of winning the lottery, but people do.  

Aye, ‘tis a puzzle.  No blame on ATC, nor the system, which whilst not efficient, performs design function and separates aircraft.  The pilots and actions could stand some scrutiny, but that would, without all the facts, be subjective.  I guess we just got lucky – one more time.

Just a Sunday twiddle – food for thought if you will.  

Toot – I’ll be there directly dear – toot.