IAL descent techniques
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IAL descent techniques
There are a couple of different procedures i know of that are taught in relation to how a descent is performed during a NPA. The ones I know of are:
1. Constant descent profile. ie work out your descent point in the approach and then descend at a predetermind rate of descent pretty much all the way to your MDA. The idea to avoid CFIT, inadvertantly descending through not below altitudes or MDA's.
2. The stepped profile where you descend quickly down to the step then level out until able to descend to the next step. The idea to become visual as quickly as possible.
What are everyones for and againsts for each of these techniques, and is there any other techniques out there that i don't know of?
1. Constant descent profile. ie work out your descent point in the approach and then descend at a predetermind rate of descent pretty much all the way to your MDA. The idea to avoid CFIT, inadvertantly descending through not below altitudes or MDA's.
2. The stepped profile where you descend quickly down to the step then level out until able to descend to the next step. The idea to become visual as quickly as possible.
What are everyones for and againsts for each of these techniques, and is there any other techniques out there that i don't know of?
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Well I'll bite....
What is the point of "getting visual as early as possible"?
I don't understand why that is a desireable outcome.
All the aeroplanes I have flown, flew equally well in cloud or in the dark as they did in 8k vis. Makes no difference to the aeroplane if you are tracking via the ADF or by looking out the window. You have to track to the MDA/DA or circling area anyway, so why make it harder for yourself?
Being an IFR pilot of only average ability, I prefer the constant descent.
The only time you need to be visual is (a) at the minima, aligned with the landing runway and in position to continue visually to the landing with buggerall change to your path or power/attitude, or (b) at or above the minimum descent altitude within the circling area and able to make a nice, straight forward circle and land.
A constant descent profile suggests...
- you have examined and planned the approach before you commenced it (good start)
- you don't put yourself unnecessarily close to the immovable objects on or connected to the earth's surface.
- you are making a minimum number of power and attitude changes during the approach, leaving you brainspace to monitor what you are doing.
- you have one method that will work, with minor changes, at any aerodrome, in any aeroplane, anywhere in the world.
The idea is to (a) have a plan (b) keep it simple and (c) fly accurately.
My 0.02c worth.
What is the point of "getting visual as early as possible"?
I don't understand why that is a desireable outcome.
All the aeroplanes I have flown, flew equally well in cloud or in the dark as they did in 8k vis. Makes no difference to the aeroplane if you are tracking via the ADF or by looking out the window. You have to track to the MDA/DA or circling area anyway, so why make it harder for yourself?
Being an IFR pilot of only average ability, I prefer the constant descent.
The only time you need to be visual is (a) at the minima, aligned with the landing runway and in position to continue visually to the landing with buggerall change to your path or power/attitude, or (b) at or above the minimum descent altitude within the circling area and able to make a nice, straight forward circle and land.
A constant descent profile suggests...
- you have examined and planned the approach before you commenced it (good start)
- you don't put yourself unnecessarily close to the immovable objects on or connected to the earth's surface.
- you are making a minimum number of power and attitude changes during the approach, leaving you brainspace to monitor what you are doing.
- you have one method that will work, with minor changes, at any aerodrome, in any aeroplane, anywhere in the world.
The idea is to (a) have a plan (b) keep it simple and (c) fly accurately.
My 0.02c worth.
Last edited by ITCZ; 6th May 2006 at 12:53.
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I'll just add one
Just one to add to ITCZ's list.
Having an idea of your average descent rate over the whole approach can very benificial if things don't seen to be right. If you need a much higher descnt rate to achive the next height/distance check, you may have a problem.
Eg GNSS RNAV Arrival and heading to the minima in the wrong 5 mile block.
Constant descent profile is the way to go.
Only comment is don't spend 5 minutes working the descent out to the last decimal place of a foot, there are too many chances for a mistake. Use an easy rule of thumb which will give you a good average, and use a logic test on it to confirm the result.
Around 140 KTS GS - 320 FP/NM - 700FPM your distance or time is displayed on the plate.
Richo
Having an idea of your average descent rate over the whole approach can very benificial if things don't seen to be right. If you need a much higher descnt rate to achive the next height/distance check, you may have a problem.
Eg GNSS RNAV Arrival and heading to the minima in the wrong 5 mile block.
Constant descent profile is the way to go.
Only comment is don't spend 5 minutes working the descent out to the last decimal place of a foot, there are too many chances for a mistake. Use an easy rule of thumb which will give you a good average, and use a logic test on it to confirm the result.
Around 140 KTS GS - 320 FP/NM - 700FPM your distance or time is displayed on the plate.
Richo
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I used to work for an aeromedical supplier who tried to bash the constant rate profile out of me. The local senior base pilot did the C&T and tought one should get visual as soon as possible so the approach could be abandoned, then fly a small circuit and deliver the patiant or doctor, stat!
Interestingly none of the other bases within the company had the same concept. (the ops manual was nonexsistant)
I argued a strong defence, including Flight Safety findings re NDB approaches, and night circling etc, but he wouldn't budge. So I would fly all the runway aligned approached I could find, and do what he wanted on the checks'.
I don't work for him anymore.
My view is that you'll use less fuel and spend more time further away from the ground on a constant rate descent profile. The figures Richo uses work well. I found over the top for a sector entry at 6500', and start the approach at around 4000' (pressurised turboprop).
fly safe
Leatherdog
Interestingly none of the other bases within the company had the same concept. (the ops manual was nonexsistant)
I argued a strong defence, including Flight Safety findings re NDB approaches, and night circling etc, but he wouldn't budge. So I would fly all the runway aligned approached I could find, and do what he wanted on the checks'.
I don't work for him anymore.
My view is that you'll use less fuel and spend more time further away from the ground on a constant rate descent profile. The figures Richo uses work well. I found over the top for a sector entry at 6500', and start the approach at around 4000' (pressurised turboprop).
fly safe
Leatherdog
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Getting visual as early as possible can be desirable (and is in fact recommended in the NZAIP) when conducting an instrument approach at an uncontrolled aerodrome after the completion of base turn as VFR traffic (especially if they're NORDO) may be operating in the vicinity of the airport just below the cloud base. Apart from that, I agree with the others.
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Fair chance that if the place has a published approach, its an MBZ, and the VFR aircraft that are operating just under the cloud would need to have a working radio to be there.
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Fair chance if you're flying into an airport frequented by scheduled airline traffic otherwise............. And then there is the trust that a pilot places in radio calls from PPL or microlight pilots (not having a go, just suggesting those with less experience) in a said MBZ particularly if they are operating in poor weather (probably with a high workload).
Besides, I think the MBZ comment is a moot point somewhat. It's see and be seen not hear and be heard.
Besides, I think the MBZ comment is a moot point somewhat. It's see and be seen not hear and be heard.
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Am I missing something? I guess you guys are talking about CTAF(R) in Aus. Not sure about NZ.
You'd think flying in cloud on an approach would sometimes be safer as there is no (shouldn't be) any VFR traffic to worry about while you are there. That along with good radio broadcasts should be safe enough if the VFR guys know what they're doing and are making broadcasts.
I'll support the constant rate profile as there are no major attitude changes hence minimal power lever movement ie a more stable approach as ITCZ has suggested. Why have more workload than you have to whilst flying an approach? There is an added bonus in twins if you have a buffer between the profile height and the minimum alt step if you have an engine failure in IMC, you could bust the obstacle clearance limit if your sitting on the step and have an engine failure. Just a thought.
You'd think flying in cloud on an approach would sometimes be safer as there is no (shouldn't be) any VFR traffic to worry about while you are there. That along with good radio broadcasts should be safe enough if the VFR guys know what they're doing and are making broadcasts.
I'll support the constant rate profile as there are no major attitude changes hence minimal power lever movement ie a more stable approach as ITCZ has suggested. Why have more workload than you have to whilst flying an approach? There is an added bonus in twins if you have a buffer between the profile height and the minimum alt step if you have an engine failure in IMC, you could bust the obstacle clearance limit if your sitting on the step and have an engine failure. Just a thought.
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There are lots of airports with Inst approaches that are not CTAF (R). I thought that CTAF (R) came from the old MBZ........... and in the long past these airports had a Flight Service Operator to talk to (What did we call that airspace back then??)
Just because most (or all) CTAF (R)'s have an instrument approach this doesn't go to say that all instrument approaches are at a CTAF (R).
In the last round of airspace there were airports having an approach and no CTAF Frequency at all...............
And with GPS NPA the number of approaches has grown considerably......
Just because most (or all) CTAF (R)'s have an instrument approach this doesn't go to say that all instrument approaches are at a CTAF (R).
In the last round of airspace there were airports having an approach and no CTAF Frequency at all...............
And with GPS NPA the number of approaches has grown considerably......
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Roger on the GPS NPA, thats a recent thing. Although, even If I was in the middle of the desert at a strip that was landed on once a year, I wouldn't even consider letting down on any approach, through cloud, until I had broadcast on both area and 126.7 or the place discreet frequency.
Once again, I wouldn't consider letting down without a broadcast, and the thing about IFR, is the lack of being able to see, or be seen. 
Besides, I think the MBZ comment is a moot point somewhat. It's see and be seen not hear and be heard.
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Spoilher. I guess a bit of both.
Couldn't agree more but I think the reason why it is stipilated in the NewZealandAIP is a valid one for some airfields. Was only trying to give an instance where not using a constant ROD profile MAY be beneficial as per the beginning of the thread. Easy Wiz!
NZAIP
Once again, I wouldn't consider letting down without a broadcast, and the thing about IFR, is the lack of being able to see, or be seen.
You'd think flying in cloud on an approach would sometimes be safer as there is no (shouldn't be) any VFR traffic to worry about while you are there.
It's the one's that "should'nt be there" who quite often are!
