QFA06.......1930................1945..........15
BAW015.....1937................1947..........10
SIA221.......1943................1949...........6
QFA32........1944................1951..........7
ETI450........1945................1954..........9
UAE412......1952................1956...........4
RBA193......1954................1958...........4
VOZ623......1954................2000..........6
QFA400......1955................2003..........8
JST601........1956................2005..........9
RXA453.......2001................2006..........5
EA2221.......2005................2008..........3
VOZ601......2012.................2012*........0
RXA774.......2013................2013*........0
So lets now explore this basic type of a sequence. QFA06 is number 1 but it’s the end of the curfew and the first arrival slot is 2000. In the above table the ETA_FF and STA_FF is for position RIVET for jets and WELSH for non jets; which is about 15 minutes flying time to the 16R threshold at 250K IAS. So QFA06 needs to cross RIVET at 1945 for a landing time of 2000. Also note at the end RXA453, EA2221 and RXA774 have less delay than looks necessary; this is because from the WELSH there is approximately 65NM still to go to touchdown which take a non jet an extra minute.
So what do we do to delay the aircraft?
All going well the ALOFT program has been calculated correctly and the enroute delay has been applied to the aircraft somewhere near 2 hours ago. ALOFT is a new system to achieve time based sequencing for the pre 0700 local time arrivals; this came about mostly due to the significantly more aircraft arriving at 0600 local time, than the aerodrome could handle; i.e. many aircraft want to get on the ground as close to 0600 as possible; this is an airline scheduling issue not an ATC one; but we have developed this tool to determine the landing order based on the estimates for Sydney calculated around 4am. Hopefully as a result of ALOFT pilots have made sufficient adjustments to absorb the majority of their delay prior to reaching the descent phase of flight.
But I’ll expand on this situation without ALOFT in use and the delays only ‘discovered’ with around 200NM to go.
The solution to absorb delay in the safest manner is through holding.
From the South West of Sydney we have 3 Jet holding patterns and 3 non jet holding patterns (with a red in-fill in the picture) for use to delay aircraft; all patterns are left hand patterns with the exception of TARAL which is a right hand hold; (to keep clear of the BIK holding pattern)
We treat CULIN and MAKKA as the same pattern and stack vertically within them, to feed the TARAL pattern; we do similar with KEDDY and NICKI, which are rarely used; but give us options when the BIK area is busy. Usually we stack aircraft vertically where number one in the sequence is at the lowest level; this doesn’t always happen because of the mix in cruising levels and aircraft types.
Normally at TARAL we stack jets at FL210, FL220, FL230 and use FL240 as a transition level, so this is used some times. Then we move back to fill CULIN and MAKKA. Treating those patterns as one, we stack at FL250, FL260 etc.
Normally the exit hold time at TARAL is 5 minutes before RIVET; so we manage the patterns at CULIN and MAKKA to fill the pattern at TARAL. The idea being that you hold in the outer patterns without it being time critical and are moved up to TARAL for more accurate delaying action. This usually only happens when delays exceed 15 minutes; but we do use both patterns at time with less delay than that due to not fitting enough aircraft in the TARAL pattern.
Now when to hold or not, is a very difficult decision. When the delays exceed 9 minutes, it’s a no brainer; holding is best and easiest to manage. Why 9 minutes, well 2 minutes for slow speed from TOD to the pattern, 6 minute holding pattern and another minute leaving the hold at reduced speed. Not totally accurate, but close enough for government work.
But look at the sequence above; 4 aircraft have at least 9 minutes to lose, but are mixing it with aircraft that don’t have that much. QFA06, BAW015 will hold, and perhaps JST601, but looking at the disposition of the others it looks like vectors and speed control to achieve the delays. (QFA400 is on the cusp, maybe a hold maybe a vector, but if holding not going slow into the pattern, which always seems to confuse the crews) If QFA400 and/or JST601 are held they will need positive vertical positioning to avoid the aircraft on vectors and speed control so the get into the pattern in an orderly manner and underneath the aircraft that will overfly them in the pattern.
We tend to manage exiting holding patterns through Stack Departure Times (SDTs) we want pilots to be very accurate with them, but there is a bit of give and take still in the sequence; as you’ve got the best part of 100NM to touch from TARAL, unless it’s RWY 07.
The pilot responsibility is to be anywhere between 30 seconds early and 1 minute late; it’s amazing how many times I see this buggered up. For example pilots approaching TARAL 2 minutes early and either saying good enough, or worse turning out for another pattern. Me being the vigilant bloke I am, I’m thinking a 2 minute orbit, not bloody likely unless you’ve only got boxes down the back; if you are too early ask for assistance, don’t manage it yourself. If you are late, no problem, depending on how late, expect higher speed or if too late expect a swap in slots.
Next time, vectoring and speed control; and how we ‘pick the order’; the old I was going to be number one but, *#%^& dumb controller...; scenario.
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