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FMS and STARs - ATC perspective

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FMS and STARs - ATC perspective

Old 17th Jun 2007, 10:02
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FMS and STARs - ATC perspective

G'day all,

A quick question about FMS capabilities and a pilot's perspective on STARS. Most who have flown into YMML, YSSY or YBBN will be familiar with the 'cross xxxxx at time 53 then 250kts' given by ATC for sequencing. I understand the different capabilities with regards to on-track speed losses. What I was wondering is about time out of holding patterns.

For example, the LIZZI STAR into Melbourne, the holding patteren is at BULLA. ATC use 7 minutes for the time from BULLA to LIZZI for aircraft out of the hold to cross LIZZI at the right time. Personally, I tell the aircraft to adjust their pattern to depart BULLA at required LIZZI time - 7 minutes. I have heard people also say to adjust their pattern departure time to cross LIZZI at time xx.

My question is: what is easier for both aircrew and for the various FMS capabilities out there?

For ATC, we use a standard time from hold to feeder fix, but this needs to be adjusted for wind, and is sometimes hard to pick. The FMS can usually do it better than we can, but can they adjust the the pattern to meet a time given at the next point too?

Hope I've made it as clear as mud. Thanks in advance for the replies.

Cheers,

NFR.
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Old 17th Jun 2007, 10:28
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Thumbs up

The RTA function on the FMC is generaly pretty good if asked to achieve a solution within the parameters it considers realistic. The ATCO needs to have a ball-park idea of what is achieveable under the current conditions.

The following sounds cumbersome from both an FMC programming and a mental DR point of view:

I have heard people also say to adjust their (BULLA) pattern departure time to cross LIZZI at time xx
The following is easier from FMC and mental DR points of view:

Personally, I tell the aircraft to adjust their pattern to depart BULLA at required LIZZI time - 7 minutes.
I presume you do the maths for the them??? (XX:XX - 7min)

Remember, at this stage of the approach, many airlines' SOPs dictate less heads-down (ie FMC programming) time and more heads-up.

Personally I would prefer to be given time to depart the next waypoint I am due to cross. If it is during the hold, then it's easy to use mental DR to adjust the pattern so as to turn inbound to pass the next fix on time. Seems to work.

A good reason to have a pass in mathematics???

The FMC RTA (Required Time of Arrival) function works well over long distances and the Set Course time (or whatever it's called - for holding, etc) is something I don't usually bother with as I'd rather be looking out the window or otherwise maintaining SA, flying the airplane, etc.

PS: While we're at it - please no more "Descend at 250 knots", five seconds after we've nosed over at TopD!!!
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Old 17th Jun 2007, 10:49
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PS: While we're at it - please no more "Descend at 250 knots", five seconds after we've nosed over at TopD!!!
Hear hear. Talking 717 in this case, not often as BN/SY/ML but every day into CS, PH and DN.

The FMS in our bus draws a path BACK from the runway to the TOPD, based on known and forecast winds (TOPD, intermediate levels, and surface conditions), aircraft weight, configuration, and speed requirements (ATC and/or aircraft).

We are trained to have the winds and ATIS is in the box by TOPD-40nm. A speed reduction means that the aircraft will be descending close to, or at, its best lift/drag ratio. Therefore it needs a flatter, earlier descent.

A "best speed to field, cancel speed restrictions below A100" is best achieved by telling our machine to descend at .78/320 with all restrictions cleared. It will push the TOPD closer to the field, staying higher for longer, keeping the TAS high and achieving the lowest ETI to the field.

If you tell us your speed requirement at around 140nm to run, we can comply very efficiently. If you tell us at about 100nm, it is usually too late to do the slowdown efficiently.
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Old 17th Jun 2007, 11:04
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My question is: what is easier for both aircrew and for the various FMS capabilities out there?
When we 717 folk are asked this at YBCS, we have an estimate displayed for each and every waypoint in the arrival.

If we didn't consider Human Performance and Limitations along with the capabilities of the FMS, I would suggest telling us the constraint for the waypoint that is your constraint (LIZZI in this case) We can edit FMS speed or Cost Index until we have something that matches.

However from a human factors point of view, I would suggest that it is better to issue a time or altitude constraint related to the holding fix, if you have instructed us to hold.

Reason being that our attention will be focussed on to the holding fix, BULLA in your example. The phenomenon is known as "anchoring," and it is not peculiar to pilots. We create the hold in the FMS flight plan by doing a "lateral revision" off BULLA, describing the hold (left, right, timing, inbound course) or accepting the standard hold if it is a charted holding fix.

If you have us holding at one fix, and put a time/speed/altitude constraint at another point, it is very human to (a) request you to repeat the clearance and/or (b) put the time/speed/ or altitude constraint on the wrong waypoint.

================
Agree with the above, RTA (required time of arrival) function is an enroute function, need to be about 500-700nm to the RTA waypoint or it is next to useless.

================
Here's one for you, NFR -- when it comes to exiting a holding pattern, pilots might have this in mind:

AIP ENR 12.4 "..... A pilot should endeavour to leave the holding fix on time, but one (1) minute ahead of time is acceptable."

I've flown with some eager beavers that stopped editing their speeds once they got to the hold fix requirement speed -1min, even though it was clear ATC was trying to slow us down by at least the time they specified.

Problem, or insignificant in the scheme of things?

Last edited by ITCZ; 17th Jun 2007 at 11:20.
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Old 17th Jun 2007, 11:15
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If you tell us at about 100nm, it is usually too late to do the slowdown efficiently.
That's what extra track miles are for; two benefits, more miles to meet your VNAV and increased speed due to the extra miles.

Seriously if it is a problem say so, I'll happily give you what ever speed you want; 320 285 265 etc; just let me know and if I can make it work I will. Usually when I make the offer of increased speed and more miles in lieu of 250K I usually get we can do 250K.

Usually we work on 250K vs 300K = 2 mins more from TOD to the STAR Feeder Fix (the fix to cross, ie Lizzi, Rivet etc.); so we are looking for 2 mins on descent and usually another 1 to 2 mins from the Feeder Fix to the STAR 250K below A100 kicking in.

Of course if there is a stream i.e. more than one aircraft in the sequence via your fix it's a little trickier re giving you what you want; unless we can all get along.

We don't apply the 250K for pleasure and if we knew it before your ToD we would actually tell you; trust me

I've flown with some eager beavers that stopped editing their speeds once they got to the hold fix requirement speed -1min, even though it was clear ATC was trying to slow us down by at least the time they specified. Problem?
Would prefer you came out 1 late not early as I can speed you up to catch up the minute; otherwise more than likely you will be too tight and it's vector time; unless of course the one ahead came out 1 min early too.
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Old 17th Jun 2007, 11:24
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Would prefer you came out 1 late not early as I can speed you up to catch up the minute; otherwise more than likely you will be too tight and it's vector time
I'm good with that

While I'm here, what about Category speed limits (ie Cat C airspeeds 160-240kt inside the IAF) when we have been given "make best speed/no STAR speed restriction below A100" in a radar environment?

If I string a STAR into an ILS, I can clear the 250kt/10000', but the IAF has a 240KIAS limit, and in some cases the IAF is 20 or 25 miles remaining to the field.

At all but highest landing weights, our machine can hold 320kias to 20nm/6000' AAL and comfortably slow down, no cowboy stuff, to be landing config and stable by 1000' AGL.

If you want me faster, are you worried about the 240kt limit at the IAF?

Last edited by ITCZ; 17th Jun 2007 at 11:34.
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Old 17th Jun 2007, 11:34
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Speaking of Speeds

My pet beef at present is when I see controllers give 250K on descent (ie when flying on IAS not mach number) and the pilot says (at FL370) we can't go that fast, we'll do our best or variations there-of; we get it already! Fly your mach into 250K... purrrrlease! When this happens usually gives us a net present gain of 0 minutes; so vector time it is...

Also the pilots that insist on having a Feeder Fix time vice a speed for descent; it just doesn't always work that way; separation first then sequencing...

and, while I'm here...

We give a feeder fix time and the pilot says 'can't make it'; we say do 250K on descent and we end up speeding them up; cause they will be late... How does the FMS get the winds?; is it "actuals on climb up"/"forecast BOM product"/"capture when last here" Is any data shared (uploaded) across company fleets/types/frames etc.
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Old 17th Jun 2007, 12:20
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How does the FMS get the winds?; is it "actuals on climb up"/"forecast BOM product"/"capture when last here" Is any data shared (uploaded) across company fleets/types/frames etc.
Blockla, thank you for the question!!!

All things being equal, a 717 pilot in our operation will enter forecast winds and temps for the climb, for each enroute waypoint, and for the descent prior to engine start at the departure point. The ATIS is used for the surface wind and temp at the departure point, and the SPFIB winds derived from BoM GRIB data are used for climb, enroute and descent.

You might tell it something like this...

Climb Forecast page
F340/270/80
F265/300/45
F185/310/30
YBXX/095/10 +22C

ITSMA
F385/290/115 F340/-42
F340/280/95
F300/260/82
F265/200/42

PARTI
F385/280/120 F340/-43
F340/275/102
F300/255/92
F265/210/50

Descent Forecast
F300/260/85
F265/195/44
F100/080/30
YBYY/060/22 +15C


Once the engines are started, the Honeywell FMS interpolates the winds for all levels, and calculates a vertical profile from takeoff to touchdown, based on these winds, weight, cost index, and flight planned cruise level.

Once airborne, the aircraft 'knows' the actual wind and temperature affecting it where it is, right now, from it Air Data and Inertial/GPS solutions.

It then "blends" the actual wind with the forecast winds. Eg in the climb winds above, climbing through 8,500 feet, it gives 100 percent weight to the FL185 forecast.. It uses the actual wind for where it is right now. It blends the actual and forecast winds for intermediate levels, that is, 2,500 above, the blend is 75/25 actual/forecast. 5k above, 50/50. 7,500' above, 25/75 actual/forecast. This happens automatically, and is updating several times a second.

After the calculated TOPC, or in the cruise, it blends vertically, and ahead.

Approaching TOPD, it looks down 10,000', and blends the actual/forecast winds in the same ratios as the climb.

The only 'wind' that we enter after departure, is the surface wind and temperature at the destination, when we are within range of the ATIS. Then it is usuall the OAT at YBYY that will make a change in the TOPD, sometimes eight miles for a 10C variation from ISA.

This means....

          Last edited by ITCZ; 17th Jun 2007 at 12:37.
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          Old 17th Jun 2007, 12:38
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          If you come out of hold 1 min late with 40 to run, most of the aircraft can't make it up. Come out 1 min early is fine, it's easily fixed with reduced speed or small vector, sometimes the 1 in front of you is a bit early and I don't need to do anything
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          Old 17th Jun 2007, 12:49
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          So topdrop/SM4, what you are saying is -- be accurate and I won't be stuffed around!
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          Old 17th Jun 2007, 22:36
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          Thanks heaps for the replies - interesting reading. Looks like easiest for crew/FMS is the hold departure time given to meet a time at the next point.

          I really didn't want this to get into a sequencing slanging match. 250kts at TopD - sorry, sometime sh!t happens. We know it's not the ideal thing to do, but one cannot predict go-arounds, WX diversion, MED1 traffic etc etc. We try our hardest - we want you out of our airspace ASAP! And standard speeds for descent for types would be great, but we understand that's out of your hands, just like a lot of circumstances are out of our hands.

          So here's one for you lot - no more 'why are we being delayed?' What a stupid bloody question! You are being delayed because you are the only plane in the sky and we don't like the tone of your voice, of course!

          Cheers,

          NFR.
          No Further Requirements is offline  
          Old 17th Jun 2007, 22:51
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          Sprucegoose
           
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          A good reason to have a pass in mathematics???
          I assume you are talking about at grade 3 level, cause don't know about you, but by then I had a good grasp on addition/subtraction!
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          Old 18th Jun 2007, 01:59
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          You are being delayed because you are the only plane in the sky and we don't like the tone of your voice, of course!
          That answers my question!
          Or if in Perth, "because there is a Fukker 50 within 300nm...
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          Old 18th Jun 2007, 02:05
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          Interesting thread!
          But if the flightplan says BE35 - it is not a Beech 350 (as I was called the other day) and I do not have access to all this fancy FMS gear.
          I do have some toys up front and I was pretty good at maths (although completely cr*p at mental arithmetic), so it takes me a few minutes to work out how to "adjust speed to cross XXX at time YYY", ....... and when I stick the nose down I will accelerate (and overtake the Dash 8 in front of me) unless told to do otherwise.
          I can hold 160 kts to 1000'/5nm and still turn off at the first taxiway.
          Cheers
          Dr
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          Old 18th Jun 2007, 02:57
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          Sprucegoose
           
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          Once over heard on a visit to approach....

          ATC: "Peckerhead 69 (heavy) you are on a nine mile final at 5000, can you make it in from there or do you require extra track miles?"

          Pilot: "AFFIRM, we can make it"

          ATC: "Cleared visual approach straight in runway 29"

          ATC: "Peckerhead 69 you are now 5 miles and 3000 can you still make it in from there?"

          Pilot: "AFFIRM"

          A short pause, then...

          Pilot: "Err, ATC doesn't look like we can make it in from here!"

          ATC: "Turn right zero, nine, zero" (releases PTT) "for NO apparent reason"...

          Offending aircraft then taken to a 15 mile final! Still makes me smile...
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          Old 18th Jun 2007, 06:34
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          Unfortunately H, in the feel-good world of magenta line (horiz and vert) flight this is what will increasingly happen. Get off the line and they're stuffed.
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