Flying the ILS - any good advice?

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Great Ozzie
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Re: Flying the ILS - any good advice?

Post by Great Ozzie »

Oracle427 wrote:In all cases we're being taught to descend at to the next lower altitude at a rate of 800FPM. The idea being that you will not benefit from remaining higher for a longer period of time in non precision approach which naturally has higher minimums than the precision approach. Not saying any other way is wrong, but that is the reasoning.
Hey Oracle... since you alluded to this: not sure if the topic of "Dive and Drive" has come up here... it was something I was taught years ago, but thinking has changed regarding getting down to MDA as quickly as possible.

Good FAA advisory circular: AC: 120-108 Continuous Descent Final Approach (FAA's website)

An AOPA blog by Max Trescott on No more ‘dive and drive’ instrument approaches.

If you google "FAA Dive and Drive" there is a pdf "Jepp Briefing" (June 2001 by James Terpstra) that I found interesting - talks about "Dive and Drive" and "the Stablizied Approach"
Oracle427 wrote:Always plan ahead and manage your risks. :)
"Always have an out." :P
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Re: Flying the ILS - any good advice?

Post by Oracle427 »

Yep, better said as "always have an out."

Thanks I'll check those when I get home. Dive and drive is the method being taught.
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Re: Flying the ILS - any good advice?

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Oracle427 wrote:Yep, better said as "always have an out."
Well then, you can thank Bob Buck (Weather Flying). That phrase from him really stuck with me.
Oracle427 wrote:Thanks I'll check those when I get home. Dive and drive is the method being taught.
Kind of thought that (sort of sounded that way)... hope you find the above links useful.
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Re: Flying the ILS - any good advice?

Post by William Hughes »

Stabilized approach for a non-precision is what is being taught at the school near me. The plates are all being revised to support it, with little tables to cross reference ground speed against.

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Nick - A2A
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Re: Flying the ILS - any good advice?

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Rob - I found some of the comments in the Max Trescott blog you linked above very interesting. Clearly this is a divisive issue irrespective of FAA advice. I can certainly see that "getting down to the MDA as quickly as possible" is a recipe for busting MDAs and worse.

However, from my layman's perspective, flying a stabilised constant V/S non-precision approach seems to entail more workload than either the 'dive and drive' approach or a precision approach on the ILS. This is purely because it seem to be more of a struggle to recognise any significant deviation from the target glidepath without the benefit of vertical guidance.

In other words, if I was flying an old-fashioned VOR/DME approach, I'm sure I'd find it easier to maintain straight and level flight after a sensible descent (lets not call it a dive) to the MDA than I would to fly/monitor that constant vertical path. I really need to try both properly in the sim though...
William Hughes wrote:The plates are all being revised to support it
This seems like a fundamental point with respect to the shift from 'dive' and drive' to the 'stabilised approach'. I guess I tend to associate VOR/DME approaches etc. with that 'stepped' vertical profile you'd see on the approach plates.

I'm afraid I feel rather ill-qualified to join in these discussions, even on a flight-simming forum, so hope you'll excuse my confused thinking... :wink:

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Re: Flying the ILS - any good advice?

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Nick M wrote:However, from my layman's perspective, flying a stabilised constant V/S non-precision approach seems to entail more workload than either the 'dive and drive' approach or a precision approach on the ILS. This is purely because it seem to be more of a struggle to recognise any significant deviation from the target glidepath without the benefit of vertical guidance.

In other words, if I was flying an old-fashioned VOR/DME approach, I'm sure I'd find it easier to maintain straight and level flight after a sensible descent (lets not call it a dive) to the MDA than I would to fly/monitor that constant vertical path. I really need to try both properly in the sim though...
Hi Nick,

Have a look at that Advisory Circular (AC 120-108). There are a couple examples in the appendix that illustrate it well. You don't have to mess with adjusting power, trim etc (because there won't be any level offs). You set things up and have at it. Another point... the descent does not have to be "exact" like flying the glideslope. You know what descent rate you want and hold that rate... it will not need to be "perfect".

Because when you fly down to the MDA, you don't fly to that altitude (if still in the clag) but will fly to MDA plus something - that AC refers to it as a "Derived Decision Altitude" or DDA (I think I used to use 75feet). So you get to DDA and can descend if landing requirements are met (and the continuous descent approach is going to aid in putting you in a good position) or go-around. Reach the altitude and (basically) it's decision time.

I have not tried a "CDFA" in Actual conditions (IMC) but I know that it can be a bit tricky to hold altitude and at the same time being concerned with not busting the MDA while "waiting" for either the runway to come into view or time to expire.

I think this simplifies the procedure. Maybe Oracle will try both (since he's doing the one now) and report back what he thinks. :P

-Rob
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Re: Flying the ILS - any good advice?

Post by Oracle427 »

I have done both because the G1000 makes it so easy to do. It paints an advisory glide slope next to the altimeter and you can follow it down with ease. I haven't found it difficult to manage the level offs and power changes, but I can certainly understand the reasoning for recommending the use of the stabilized approach over dive and drive. I'll have a chat with my instructor about it.
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Re: Flying the ILS - any good advice?

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Oracle am curious what are you using as your "buffer" (how much altitude) above MDA?
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Re: Flying the ILS - any good advice?

Post by Oracle427 »

When you say buffer above the MDA, do you mean where I begin my level off? I start reducing my descent rate at 100 feet above the MDA and then I hang out about 20 feet above MDA. I have been descending at 800 FPM unless the altitude change is small on a leg or requires a faster descent over a short distance.
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Re: Flying the ILS - any good advice?

Post by Great Ozzie »

Yes, what altitude above MDA. So basically the same as I remember (phew btw).

Thanks!
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Re: Flying the ILS - any good advice?

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Great Ozzie wrote:You don't have to mess with adjusting power, trim etc (because there won't be any level offs). You set things up and have at it. Another point... the descent does not have to be "exact" like flying the glideslope. You know what descent rate you want and hold that rate... it will not need to be "perfect".
Rob - thanks for that. Put that way, it sounds a little less daunting! I'm afraid I'm coming at this in a rather erratic way as I've tended to neglect non-precision approaches in FS in favour of the ILS. (Perhaps a common failing for simmers - especially those like me who have 'graduated' from flying airliners badly to - hopefully - flying GA stuff a little better... :wink:) However, from one-or-two instrument rating syllabuses I've looked at, ILS approaches would be taught before VOR, NDB or circling approaches (and RNAV GPS stuff) anyway?

Perhaps a more structured approach is what I need, and this well-written and entertaining website seems like quite a good place to start: Flight Simulator Navigation.

It's already answered a couple of questions I had, but was afraid to ask. :oops: (For example, what's the bit in brackets in the minima section on approach charts? Answer: military stuff which I don't need to worry about!) Also the following paragraph helps me put into perspective why I was having so much trouble with staying on the glideslope as I approached the DH: "How sensitive is the glide slope? It's much more sensitive than the localizer. At the Outer Marker, each dot of glide slope deviation equals about a 50-foot excursion from the prescribed glidepath. At the Middle Marker, the sensitivity is an astounding eight feet per dot."

Cheers,
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Re: Flying the ILS - any good advice?

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Oracle427 wrote:When you say buffer above the MDA, do you mean where I begin my level off? I start reducing my descent rate at 100 feet above the MDA and then I hang out about 20 feet above MDA.
Dang I misread that... only 20' above MDA? You must be loaded with midi-chlorians to hold that close of tolerance. :D
Nick M wrote: However, from one-or-two instrument rating syllabuses I've looked at, ILS approaches would be taught before VOR, NDB or circling approaches (and RNAV GPS stuff) anyway?
In the training program I was in, there was a lot of work with the VOR, ADF, simulated instrument, partial panel etc. And ground sim time... a lot of work especially on such instrument exercises like that "Pattern-A" and the Vertical-S stuff etc. That all before what was termed the instrument rating course.

In terms of an actual training syllabus... I am not sure I even have the ones from the ground sim. However, I do have the one from the final flight course which (mentioned previously) was a combined wrap-up for the Commercial License & Instrument rating. It started off with basic instrument flying maneuvers. Then went to the VOR work / VOR approaches, ADF approaches, then to ILS.

Point being tho... there was quite a bit of basic instrument & navigation work done before actually getting into approaches.

Regarding that Gleim pub on the Vertical-S(s), Pattern-A etc., they are very good drills in preparation for flying instrument approaches. I hope you have taken some time to practice them - that is if you haven't already! Believe me... I know they are work and they can be tedious / boring... even frustrating. But I believe they are worth the effort. It's sort of like going to the gym. Sometimes I don't want to go, I get there and I know I am going to work hard... but I *never* say after a workout, "wow... stupid of me to come here today". So, I am a huge believer in getting the fundamentals down - e.g. in this case pitch / power settings in various phases of flight & aircraft control (tight ± tolerances on heading / altitude / airspeed). And the reason being it will translate directly to flying a tight approach.
Nick M wrote:Also the following paragraph helps me put into perspective why I was having so much trouble with staying on the glideslope as I approached the DH: "How sensitive is the glide slope? It's much more sensitive than the localizer. At the Outer Marker, each dot of glide slope deviation equals about a 50-foot excursion from the prescribed glidepath. At the Middle Marker, the sensitivity is an astounding eight feet per dot."
I appreciate you sharing that - I see that useful in helping to explain "the funnel". I don't think I ever knew the feet. I see Thomas Horne (AOPA) discussed that in an article Precision Approaches. I thought the Instrument Flying Handbook would have it (as it has a very good visual representation on page 9-36,37) but it just states it this way:

The glidepath is normally 1.4° thick. At 10 NM from the point of touchdown, this represents a vertical distance of approximately 1,500 feet, narrowing to a few feet at touchdown.
Nick M wrote:It's already answered a couple of questions I had, but was afraid to ask.
I wouldn't sweat that. Seriously. Yes, there is value in working on trying to research the answer. But if you get stuck on something... ask. I feel a bit fortunate in this area because, if I don't know or don't remember, I have a pretty good idea where I can go to get the answer. Once, not very long ago, I cold-called an author of a Flight Training article to discuss a related topic regarding an accident investigation (to see if my understanding aligned with his). Guy seemed happy to talk with me and it was good conversation. You know there's a lot of people here willing to discuss their experience - we all like to talk aviation and this a very civil place to do that.

The A2A forum / community has become a favorite of mine as a place of "iron sharpening iron" wrt our understanding of aviation subject matter.
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Re: Flying the ILS - any good advice?

Post by Oracle427 »

Great Ozzie wrote:
Oracle427 wrote:When you say buffer above the MDA, do you mean where I begin my level off? I start reducing my descent rate at 100 feet above the MDA and then I hang out about 20 feet above MDA.
Dang I misread that... only 20' above MDA? You must be loaded with midi-chlorians to hold that close of tolerance. :D
Really? Unless it is gusting the airplane pretty much does this by itself. If the winds are pitching me around I'll bump it a little higher to be safe. I like to be precise. :) I would be interested in seeing my eyes during the scan on final. I must look like I have googly eyes!
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Re: Flying the ILS - any good advice?

Post by Great Ozzie »

Well... it's half of ATP standards, which is fantastic. And I certainly agree with being precise. No point imo e.g. in holding altitude to ±100', when with some work one could improve to ±50'. I have no clue how close I could hold altitude "in my prime". Been too long for me to remember. I do remember sweating bullets... from time to time. :P
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Re: Flying the ILS - any good advice?

Post by Nick - A2A »

Great Ozzie wrote:Point being tho... there was quite a bit of basic instrument & navigation work done before actually getting into approaches.
Hey Rob - yeah, I'm definitely guilty of trying to run before I can walk here. Truth be told, after glancing over those instrument rating syllabuses, I haven't done half of the 'ground work' before graduating myself to approaches! :wink: A little more discipline* is called for here perhaps, and on this note: no - I'm afraid I haven't practiced those Gleim manoeuvres yet sir! :oops: (I will get round to it at some point - I promise!)
Great Ozzie wrote:The A2A forum / community has become a favorite of mine as a place of "iron sharpening iron" wrt our understanding of aviation subject matter.
Yes indeed! Although I don't have much in the way of 'iron' to bring to the table, I've learnt a tremendous amount from discussions such as this one, and I've definitely been inspired to address some of the sloppy habits I've picked up during years of unsupervised simming!
Oracle427 wrote:I start reducing my descent rate at 100 feet above the MDA and then I hang out about 20 feet above MDA.
Yup - with respect to holding altitude, I'm afraid I'm nowhere near this level of precision. :wink: That'll be my joystick's fault again... And don't even talk to me about 'gusting' winds yet!

Cheers,
Nick

*P.S. Talking of discipline, what is this 'gym' thing you speak of Rob? :mrgreen:
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