Effectively the tower needs a radar standard between the arrival and the departure; so 3 minute spacing allows for a departure between each arrival. If the arrivals are more tightly spaced; i.e. 5NM apart on final (the normal rate) in such conditions due to not being able to sight the arriving aircraft the tower can’t ‘fire’ the departure. So you can arrive two closer than 3 minutes even in PRMs; but not get a departure away too.
During PRM approaches the general concept is, due to the huge length of final it’s inefficient; this isn’t actually the case; yes, it’s not as efficient as visual conditions but it’s better than full dependent ILS approaches; see more below.
So the other morning we were on 40 arrivals and 40 departures an hour = maximum capacity (by law).
However, CTMS was at play and on ground delays which are strategic by nature didn’t equal the arrival rate; the CTMS rate was 34. So we are ‘expecting’ 6 slots not fully utilised. Why? Well when the CTMS program was run at 0500; it looked like the capacity would have been 34 Arrivals an hour; 17 on each runway; this configuration happens when we use 16 Dependent ILS Approaches.
PRM in Sydney is only staffed for in an adhoc at call manner; i.e. we only use it when people agree to come in on their day off. So at 0500 it wasn’t likely that enough people were going to say yes (2 of them). So rather than running CTMS rate of 40 and only achieving 34; and costing heaps of tactical fuel burns they ran it at 34. The PRM consoles are independent positions; when PRM is open all 12 consoles in Sydney are open and the room buzzes; but what do I know about such things, I’m based in Melbourne. CTMS was re-calculated around 0700; but the extra slots created were not fully utilised.
This is where effectively we use a radar standard between arrivals operating to different runways; in the SY case there is less than 1NM between centre lines; so to establish them in a dependent stream it requires spacing such as this.
Dependent Approaches
PRM Approaches
The advantage of PRMs is that if required you can have arrivals tighter than the ‘nominate acceptance rate’ on the same ILS; possibly swapping a departure slot for an extra arrivals slot etc; without effecting what’s happening on the other runway with dependent approaches; what ever you do on one ILS in terms of spacing has an effect on the other runways spacing too.
So back to what I do. The sequence here.... Just talking about the RWY16R sequence.
I’ve taken the liberty to include the savings in time (due to high speed and track shortening) into account across the averages. Things to note; between 2017 and 2054 the runways is at effective maximum capacity; then the CTMS rate of 34 left a few holes, basically 3 nine minute gaps. From 2127 until 2151 again its a maximum capacity.
Another thing to consider is we deal in whole minutes for the purposes of MAESTRO and flow; but the realities of the beast is is we have 150 seconds (2.5 minutes) between arrivals or a rate of 48 arrivals an hour; we actually use this rate (or tighter at times). So early or late at a fix does transpose into the real sequence spaces not the flowed spaces.
The nuts and bolts about how this one happened: QFA42 was slowed to follow EA2202; VOZ401, VOZ809 and QFA730 were given 250Kts and a vector to follow QFA42. HVN783 was given DCT to RIVET with high speed to follow QFA730; as was JST761.
VOZ811 and QFA408 were actually vectored to follow JST761 for separation, even though it appears there was no delay. VOZ619 was given DCT RIVET with high speed. QFA412 was untouched and QFA130 joined in from BN sectors (using my runway); QFA586 was untouched and RXA514 was shortened up on the non-jet STAR.
Then there were the gaps and all aircraft got high speed descents. CPA023, CAL051 and CES561 joined the sequence via BN sectors. QFA414 was given a crew managed delay time for RIVET; i.e. “adjust speed to cross RIVET at 13 at 250K.” Note it’s 23 minutes from RIVET at 250K (45NM SY) via the PRM approach to touch down.
SIA231 was vectored at cruise and given slow speed on descent (250K) to make RIVET at time 19; but later it became apparent that they wouldn’t make 19 (cause they got low); so they were brought back to profile speed; QFA740, VOZ821 were vectored to follow SIA231 and descended at 250K.
QFA564 (Canberra Sydney) was given a ‘strategic’ slot for departure to make good a landing of 2150; they got away early so were estimating the field at 2145; but the delay was need to make a landing of 2151; so they got a vector at 250K.
We came off PRM approaches at 2151 and the folks that came in on their day off got to go home after about 3 hours work.
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