DME arc maximum speed?
PPRuNeaholic
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I see where you're coming from now Ojuka. I've never seen anything in Pans Ops that justifies the selection of a lead distance of 2 NM. Indeed, my examples on page 1 suggest that there should be some sort of statement about the speed because the optimum speed for the turn does not equate well with the range of speeds for Initial Approach, particularly for Cat C/D types.
And, of course, the speed situation is much worse if the altitude involved in the manoeuvre is above the 4,000 feet that I used in my examples.
It has to be said though, that the most common usage involves a transition between Initial and Final Approach. Thus, pilots really should anticipate the need to slow down, to be able meet the speed range for Final Approach by the time they pass the FAF. Following this logic, it is probably a bit unreasonable to try to execute the turn at speeds above about 180 knots, as you say.
We can probably design a turn that caters for a larger radius, but there'd have to put a note about it on the chart because it differs from Pans Ops criteria. If we do all that, how do we provide an opportunity for pilots to slow their aircraft down for final approach? The only way is to build extra track miles into the procedure somewhere - making it longer to fly, less convenient for ATC traffic flow and more costly for aircraft operators.
I guess that we can't please everyone.
And, of course, the speed situation is much worse if the altitude involved in the manoeuvre is above the 4,000 feet that I used in my examples.
It has to be said though, that the most common usage involves a transition between Initial and Final Approach. Thus, pilots really should anticipate the need to slow down, to be able meet the speed range for Final Approach by the time they pass the FAF. Following this logic, it is probably a bit unreasonable to try to execute the turn at speeds above about 180 knots, as you say.
We can probably design a turn that caters for a larger radius, but there'd have to put a note about it on the chart because it differs from Pans Ops criteria. If we do all that, how do we provide an opportunity for pilots to slow their aircraft down for final approach? The only way is to build extra track miles into the procedure somewhere - making it longer to fly, less convenient for ATC traffic flow and more costly for aircraft operators.
I guess that we can't please everyone.
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Very intersting thread..ill be watching..
Flew to Tabba,Egypt last night..the approach coming from the North was a 10 dme arc leading to a FAF at 7.6 dme(VOR DME).
Per boeing training 3 NM prior to FAF you have gear down flaps 15 150kts,2 nm prior flaps 25 140 kts,1nm prior falps 30 vref plus additive.
Our sop state that 3nm at the latest gear must be selected and flaps 15///
Coming from a 10 dm arc..it sounds dodjy...
VNAV was giving a arc speed of 220 kts..(minimum altitude is 4000ft at 10 dme..INCREASING to 6000ft at 12 DME!)
Here comes the question...
7.6 plus 10.6....when to select gear down..in the turn ?I agree open minded is also a quality...:-)
Doesnt Boeing stipulates that a circling (DME arc included?) max speed is 180kts?
Cheers,
M.85
Flew to Tabba,Egypt last night..the approach coming from the North was a 10 dme arc leading to a FAF at 7.6 dme(VOR DME).
Per boeing training 3 NM prior to FAF you have gear down flaps 15 150kts,2 nm prior flaps 25 140 kts,1nm prior falps 30 vref plus additive.
Our sop state that 3nm at the latest gear must be selected and flaps 15///
Coming from a 10 dm arc..it sounds dodjy...
VNAV was giving a arc speed of 220 kts..(minimum altitude is 4000ft at 10 dme..INCREASING to 6000ft at 12 DME!)
Here comes the question...
7.6 plus 10.6....when to select gear down..in the turn ?I agree open minded is also a quality...:-)
Doesnt Boeing stipulates that a circling (DME arc included?) max speed is 180kts?
Cheers,
M.85
I found the following useful advice from the booklet “From Take Off to Landing”. This is an unofficial guide to PANS-OPS and TERPS, but highly rated and reliable.
PANS-OPS:- “Lead radial (shown on approach chart) provides at least 2 NM lead for turn onto intermediate approach track.”
TERPS:- “When angle of interception of the intermediate course > 90 deg, a lead radial provides at least 2 NM lead for turn onto the intermediate approach course.”
The above is based on limiting the speed to that required (mandated) when flying the initial approach segment of any procedure; aircraft category:-
A: 90 - 150 kt
B: 120 - 180 kt
C: 160 - 240 kt
D: 185 - 250 kt
The obstacle clearance and procedure flight path are compensated for wind and altitude effects:-
Statistical or omnidirectional wind; 47 kt + 2 kt per each thousand of procedure altitude.
Bank angle. The lesser of 3 deg/s turn rate or 25 deg (the latter applies for TAS > 170 kt)
PANS-OPS:- “Lead radial (shown on approach chart) provides at least 2 NM lead for turn onto intermediate approach track.”
TERPS:- “When angle of interception of the intermediate course > 90 deg, a lead radial provides at least 2 NM lead for turn onto the intermediate approach course.”
The above is based on limiting the speed to that required (mandated) when flying the initial approach segment of any procedure; aircraft category:-
A: 90 - 150 kt
B: 120 - 180 kt
C: 160 - 240 kt
D: 185 - 250 kt
The obstacle clearance and procedure flight path are compensated for wind and altitude effects:-
Statistical or omnidirectional wind; 47 kt + 2 kt per each thousand of procedure altitude.
Bank angle. The lesser of 3 deg/s turn rate or 25 deg (the latter applies for TAS > 170 kt)
PPRuNeaholic
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M.85... sounds like someone in the company should've done some trigonometry for you, to support the SOP. In the case that you've mentioned, you're 10 NM from the VOR/DME and you need to find a point that is 3 NM prior to the required final approach radial.
Therefore, arctan(3/10) = 16.7 degrees. Call it 17 degrees. Thus, you'll be 3 NM from the final approach track with a radial set up that is 17 degrees prior to the final approach radial. Surely someone in the company could translate that to the required radial for this approach at Tabba?
Finding a distance of 2 NM is achieved the same way :-
arctan(2/10) = 11.3 degrees. Call it 12 degrees and your lead radial for that position is 12 degrees prior to the final approach radial.
The Pans Ops forumula results in slightly different numbers :-
3 NM = 17.2 degrees
2 NM = 11.5 degrees
But it's all close enough for practical purposes. Maybe you can convey this to the folks who write your SOPs? In any event, I'd have thought that the company would've done this for you anyway, so that you'd know whether the lead radial for the turn is at 2 NM or 3 NM, or some other distance - a case of every little bit of information being helpful.
alf5071h... Spot on, as always. That's a good summary of the design requirements.
Therefore, arctan(3/10) = 16.7 degrees. Call it 17 degrees. Thus, you'll be 3 NM from the final approach track with a radial set up that is 17 degrees prior to the final approach radial. Surely someone in the company could translate that to the required radial for this approach at Tabba?
Finding a distance of 2 NM is achieved the same way :-
arctan(2/10) = 11.3 degrees. Call it 12 degrees and your lead radial for that position is 12 degrees prior to the final approach radial.
The Pans Ops forumula results in slightly different numbers :-
3 NM = 17.2 degrees
2 NM = 11.5 degrees
But it's all close enough for practical purposes. Maybe you can convey this to the folks who write your SOPs? In any event, I'd have thought that the company would've done this for you anyway, so that you'd know whether the lead radial for the turn is at 2 NM or 3 NM, or some other distance - a case of every little bit of information being helpful.
alf5071h... Spot on, as always. That's a good summary of the design requirements.
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I've always used a lead point of 1% Groundspeed, for 90 degree turn...200 GS = 2 miles, 300 = 3 miles. On 15 DME arc (4 degrees per mile), at 200 GS use 8 degrees lead, at 300 GS use 12 degrees. On 12 DME arc, same formula yields 10 degrees for 200 GS, 15 degrees for 300 GS, interpolate for different speeds and arc DMEs.
Semaphore Sam, flying is meant to be simple. There are many good rules of thumb for cross checking safety, but they should not take precedence over the basic rules for safe flying. This means that you must have a good understanding of approach procedures and that they must followed as published. Your rule of thumb may be adequate for most procedures, but somewhere, someday, there will be an exception. If you do not turn at the stipulated position on the chart then you may not have the advertised obstacle clearance; then what rule of thumb do you have for that?
OzExpat, thanks for the comment, but the accolade for this work resides with Mr Olle Akerlind, a retired SAS ground school instructor who wrote “From Take Off to Landing”, and also to Honeywell Safety Systems who republished the document 3-4 years ago as a CFIT ALAR safety initiative.
OzExpat, thanks for the comment, but the accolade for this work resides with Mr Olle Akerlind, a retired SAS ground school instructor who wrote “From Take Off to Landing”, and also to Honeywell Safety Systems who republished the document 3-4 years ago as a CFIT ALAR safety initiative.
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alf5071h
I never meant to imply one should ignore published procedures, only to give a simple way to judge proper lead-points for a 90 degree turn from arc to course/radial. If the published turn-point is based on 180 GS, and your actual GS is 300, at least you can anticipate an overshoot. Also, many procedures don't have published lead-points. It's just a simple tool.
I never meant to imply one should ignore published procedures, only to give a simple way to judge proper lead-points for a 90 degree turn from arc to course/radial. If the published turn-point is based on 180 GS, and your actual GS is 300, at least you can anticipate an overshoot. Also, many procedures don't have published lead-points. It's just a simple tool.
Semaphore Sam, I understand your point, I did not mean to imply otherwise. However, sometime it is the simple rules that we have misconceived or are using inappropriately that lead us into trouble.
My earlier post indicates that a good procedure design will accommodate a range of ground speeds (wind and altitude effects), and provided the aircraft is flown within the range of the procedure speeds (IAS) there should not be any flythrough or severe undershoot. But note that there are still many poor procedures published, which although meet the design requirements (PANS-OPS, TERPS) they are complicated / difficult to fly or have pitfalls for the unwary. These should be identified before the charts are used, but we (the operating industry) rarely complain or seek changes for the seemingly inconsequential issues.
For those who require the challenge of an example, see the DME Arc procedure for Ajaccio Corsica; spot the potential for an error – it’s not at the turn it point.
The generic problem is that we (pilots) often make up our own rules of thumb to counter problems, which in reality do not exist. In creating short cuts, we open the possibility to other errors based on our assumptions. Thus, a little knowledge is a dangerous thing, but pilots rarely have all of the required knowledge for completely safe flight.
My earlier post indicates that a good procedure design will accommodate a range of ground speeds (wind and altitude effects), and provided the aircraft is flown within the range of the procedure speeds (IAS) there should not be any flythrough or severe undershoot. But note that there are still many poor procedures published, which although meet the design requirements (PANS-OPS, TERPS) they are complicated / difficult to fly or have pitfalls for the unwary. These should be identified before the charts are used, but we (the operating industry) rarely complain or seek changes for the seemingly inconsequential issues.
For those who require the challenge of an example, see the DME Arc procedure for Ajaccio Corsica; spot the potential for an error – it’s not at the turn it point.
The generic problem is that we (pilots) often make up our own rules of thumb to counter problems, which in reality do not exist. In creating short cuts, we open the possibility to other errors based on our assumptions. Thus, a little knowledge is a dangerous thing, but pilots rarely have all of the required knowledge for completely safe flight.
pitfalls for the unwary. These should be identified before the charts are used, but we (the operating industry) rarely complain or seek changes for the seemingly inconsequential issues.
When, in the Sim, we come across pitfalls, anomalies and even errors in procedures, I consider it my job to complain and seek changes. I have always had an excellent response from the procedure designers at CAA. And from the publishers of Plates, if that's where the error lies. So I'm making two points:
1. Sim instructors are the perfect people to identify and follow up procedure problems. That's why I follow threads like this one.
2. Changes and corrections can be done quickly and easily with just a phone call - in UK at any rate.
HTH
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'I have always had an excellent response from the procedure designers at CAA'
keithl - Would it be possible for you to post contact details for these guys as there are one or two questions I would dearly like to get an official answer on.
keithl - Would it be possible for you to post contact details for these guys as there are one or two questions I would dearly like to get an official answer on.
PPRuNeaholic
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Well thanks guys, you've just given me an idea that should've occurred to me ages ago. In this dark corner of the planet, we're still developing our website so I'm going to see how practical it'll be to have a page devoted to procedure design FAQ... so to speak! I think it might help to resolve a lot of the problems that have come up.
Pitfalls for the unwary – Ajaccio
The DME Arc procedure is at 11 nm from ‘AJO’, but at the point that you join the arc from approach or the holding pattern the aircraft is also at 11 nm from the ILS DME ‘AC’. Note the speed restriction for the procedure and the lead in radial. Thus, for those of you who like to pre-select the ILS and have dual DME displays be very careful as to which DME you use; if you inadvertently fly 11 DME from ‘AC’ you get very close to the hills as you fly through the ILS centreline.
You would not make that mistake? Someone already has; and, but for a GPWS warning and good crew reaction there would have been a fatal accident.
What a great approach to use for training! It's got so many traps & complex holds/final intercept/MAPt/missed app intercept. If I were teaching again I'd love to set this up on a sim for IR students. Even a PC would be good.
