Stabilised Approaches

[Guest pelorus32]

In the spirit of throwing a rock into this pond from time to time I though I'd pose some questions on this subject for discussion and views:

 

1. What is a stabilised approach in an RA aircraft? How is it defined?
    
    
   
2. Is a stabilised approach important and if so why?
    
    
   
3. How do you get one of these beasties?
    
    
   
4. Where do they start?
    
    
   
5. What are the things that you should be doing/seeing in the cockpit in order to deliver one of these things?
    
    
   
6. How do you tell that you haven't got one and what do you do?
    
   

 

Go your hardest...

 

Kind regards

 

Mike

 

 

[Barefootpilot]

In a stabilised approached you should have a constant angle of decent and constant airspeed with very little adjustment to power (conditions depending)

 

The easist way to set one up in the begining is to start on a long final at 1000' trim the aircraft get the target airspeed and start you decent keeping the airspeed and decent angle constant and using power to control decent and elevator to control airspeed. (I know that last point will cause some discussion!)

 

As they always say the key to a good landing is a good approach!

 

 

[Ultralights]

and a good approach begins with a good circuit!

 

 

[facthunter]

Stabilised approaches.

 

... A stabilised approach embraces the following conditions, put simply.

 

You have achieved ,

 

1 the approach profile desired ( angle & aiming point ) in...

 

2 the final approach configuration. ( flaps ,gear, power setting) at ...

 

3 the correct approach speed.

 

I consider this to apply to ALL aircraft not just RAAus.

 

Is it important to have it? Yes . If the approach is not stabilised, at some point ,the approach should be discontinued as a fundamental prerequisite for a safe landing does not exist. This is in a disciplined environment as a concept for normal operations.

 

How do you get one?... You create it as a result of the training you have been given.

 

where do they start? How long is a piece of string? On route descent point, perhaps? More appropriately in circuit work, at the base turn, the first real judgement point, that you should get pretty right,if it's going to look nice. Enough for now . N....

 

 

[Ben Longden]

Quote Adam; As they always say the key to a good landing is a good approach!

 

Thats what Nathan, Tristo, Sue and our CFI Matt keep telling me.... I think ive managed it once.. by sheer fluke... with Matt on board...

 

Ben

 

 

[facthunter]

Bit surprised this thread appears to have run out of steam. There's a fair bit in it. When I fly with someone who does it really well, I get the feeling that the landing will automatically be good. Nev

 

 

[Guest pelorus32]

OK, I threw the original pebble into the pond and so I'd better respond to Nev's challenge that there's still a fair bit in this - I agree.

 

For me a stabilised approach (definition later) arises in the context of solid and organised flight. If the flight is pressured and chaotic then you can be sure that the circuit will suffer and so it goes.

 

Let's imagine that I'm arriving in the circuit and I am going to join crosswind. The elevation of the strip is 500 feet and I'm 10 miles out on the dead side at 4,500 feet, airspeed 100 knots and I know the strip in use and that the field is open so I intend to join midfield crosswind.

 

It will take me 6 minutes to reach overhead and I have 3000 feet to lose. So I throttle back and establish a 500 fpm descent. This is the beginning of the whole process for me. I like to be able to establish that descent, trim it and then not touch anything until I add power as I come overhead at circuit height. That is the first of my Zen exercises. If this goes well I feel that things will come together. If I'm joining midfield crosswind I generally do my "downwind" checks as I finish the xwind leg - have them out of the road before I settle on downwind.

 

On downwind I want the aircraft trimmed and stable at exactly circuit height, drift allowed for and slowly decelerating so that I enter the base turn at 80 knots. Abeam the numbers I now turn my attention for the first time to my aim point and check that all is clear and that the picture looks right. This now becomes my reference point. As I turn base I reduce power to idle and use the turn to decelerate to exactly 60 knots as I roll out. Just as I roll out I take first stage flaps, increase power and trim nearly full back for 60 knots descending at 500 fpm. I always do a brief hands-off here. I want to know that the a/c is trimmed neutral for the configuration and it also makes me relax.

 

I want to roll into the final turn at 600 feet and roll out 500 feet (AGL), but I'm no longer interested in altitude off the dial. I want the sight picture now. I only have 4 things in my scan: Attitude, Aspect, Aimpoint, Airspeed. If any of those things starts an excursion then I contemplate a missed approach. Airspeed 60 knots (+3 knots tolerance, - zero), attitude (+- a very few degrees), aimpoint nailed in the same spot on the screen, aspect neither flattening nor steepening (by aspect I mean the way the strip looks - vertical and horizontal - that's what gives me a picture of "am I low or high" and "am I on the centreline"). I know I may have to use power but in so doing I want to limit the range of power I have to add or reduce and I want to anticipate the effect on attitude so that I dampen it.

 

I want roughly 450 fpm descent and if it is greater than that then my sight picture will tell me something is astray and so I snatch a look at the VSI. That's a 6 degree approach slope. I'm not dragging it in, the obstacles are safe from me and yet it is well controlled.

 

Late final (over the fence) I reduce my airspeed to 55 knots (+5, -zero), trim and power to match, nothing else changes until I transition and then flare.

 

My circuit plan includes my own personal briefing for a missed approach. The only variance I will tolerate to my stabilised criteria is slightly high. I know that the aircraft will come down if we have hit some lift on final so I tolerate a slightly higher profile and therefore a slightly greater descent number for a short period early final.

 

My missed approach criteria include:

 

• airspeed excursion not immediately stabilised;
   
   
  
• attitude excursion not immediately stabilised;
   
   
  
• aspect not immediately stabilised - except for the point above;
   
   
  
• aimpoint if sliding either way and not immediately stabilised - except for the point above;
   
   
  
• not on the ground by a predetermined point;
   
   
  
• runway incursion of any sort;
   
   
  
• a bounce of more than minor scale;
   
   
  
• excursion from centreline during flare;
   
  

 

I know when I have it stabilised because the aircraft is sliding on rails and time seems to have stood still - it is entirely Zen. I know that I am going to arrive at the aimpoint with little or no need to tend to attitude or power and that a passable landing will ensue.

 

Having said all that the most usual circumstance is that I am having to tend to attitude and power - thermals, wind gradient, turbulence, sink...but my responses are so nearly anticipatory that my stabilised approach criteria aren't breached. That is still Zen, I just wish that Zen feeling happened every time!

 

The earliest point I have decided to make a missed approach was mid base where I knew it was all astray and so I just turned final for form. That was on my first solo nav. The latest was where I had 20 knots of headwind evaporate completely just over the threshold, airspeed decayed rapidly - we touched a wheel as I reached full power and continued the go around.

 

For me the notion of a stabilised approach relies entirely on your willingness to call a missed approach. It is an irrelevant concept without the willingness to go around.

 

I'm sure this is not complete but it will do for now.

 

Regards

 

Mike

 

 

[Guest Roger]

Mike, I am certainly not an authority on this but that looks the goods. ;)

 

Also IMHO to sit beside a competent pilot and watch him do half a dozen circuits is a great way of improving your own - especially if you are in your first 100hrs.

 

Anyway it works for me...

 

Roger

 

 

[facthunter]

Mike ,I'm not going to sit in judgement of that. It's pretty comprehensive, and would result in a planned ,safe operation. I feel that a set of parameters are aimed for & if the're not achieved, you act accordingly. That is a discipline. You set a standard for yourself, and retain control.

 

I didn't want to open this up too much as the only place where I have seen it spelled out is in Airline (Jet ops.) where the lowest height by which a stabilised approach HAS to be established is stipulated at 400 feet AGL.( in this case)

 

The parameters to be met.

 

1. On slope (glideslope or Vasis)

 

2. Sink rate not above 800 fpm

 

3. Target threshold speed established. (approach speed ).

 

4. Aircraft configured for landing, Land .flap.extended/ Gear down & locked.etc.

 

5.Thrust at normal for type of approach.

 

6.Able to maintain centreline of runway without savage bracketting turns being required.

 

While this is not relevent in the detail , a little thought shows that the principle is the same.

 

( How would this have affected the Garuda arrival ?) Nev...

 

 

[Guest micgrace]

Hi

 

Just a bit of a diversion, but still relevant, the use of flaps in a circuit. Have had these 2 different approaches in circuits for use of flaps.

 

Instructor 1., first stage flap set on downwind, second stage flap on final.

 

Instructor 2., First stage and second stage set on final only.

 

I personally find instructor 1. approach leads to an easy, stabilized approach., Instructor 2 method rather hurried and somewhat more unstable approach, if a bit quicker.

 

What does everyone think?

 

Micgrace.

 

 

[Guest pelorus32]

Hi Mic,

 

this is an interesting issue. For me it boils down to this: Vfe on the Tecnam I fly is 67 knots. I can't see that you make friends by flying downwind at that speed or less in a circuit which is busy and has GA aircraft in it. It would be different if the aircraft had circuit speeds closer to 65 knots but most of them are up in the 90+ knots on downwind.

 

So bottom line for me is flaps on base - first stage and then as needed on final. But I absolutely hear what you say about more time and more stability. I'd love to grab flaps 1 on downwind at say 85 knots and then more as needed.

 

Regards

 

Mike

 

 

[Guest micgrace]

Hi

 

Good point.

 

Instructor 2 approach was in a Texan at rather busy Recliffe, with it's ridiculously low height ceiling, thanks to Brisbane controlled airspace. This is necessary, as the circuit is extra busy with many quick a/c.

 

I wanna Texan. Micgrace

 

 

[facthunter]

Flap extension

 

I personally reckon that the flap extend speeds are so restrictive on most of the aircraft that we fly that PARTICULAR care should be taken that the flaps are not extended at above the permitted speed(s) which is often 60 knots A very deliberate speed reduction needs to be performed to achieve this, usually requiring that the aircraft be flown level. This is probably best done on downwind, rather than make a wider base turn. Normally the aircraft should descend steadily after the base turn is completed. The whole thing becomes a bit messy, just because the flap speeds are too restrictive. I imagine that the designers mean the figure that is stated should be observed, so there is no fat there.

 

Incidently, I've never seen a mention of flap assymmetry anywhere in our material .It will happen one day, so don't put flaps out above the limit speed. If a roll commences as the flap is extended, stop the flaps, and be prepared to use a lot of aileron and even the rudder till you sort it out. Nev...

 

 

[slartibartfast]

I'm a noob, but I have nothing else to do so I will respond to your kind invitation Micgrace.

 

BTW Mike, I loved your break-down of a stabilized approach. Very useful.

 

Although, I find in a Jabiru (both LSA and J160) that I have a lot of leeway on final with glideslope. If I'm too high, I can side-slip back to intercept the ideal - or even all the way to 40' if required. Your other criteria for go-around are fair enough. This is because (and to respond to Micgrace's invitation) I prefer a glide approach.

 

I started in gliders 30 years ago, and I still try to turn every landing into a power-free experience. To me this means if the engine fails on downwind, base or final, it just becomes another log book entry. No drama.

 

On turning base, I wash off the last 20 knots and come out of the turn selecting my desired flap setting (usually full) as the speed drops below VFE and power at idle.

 

Once trimmed and stabilized I will then adjust power and trim to what I think will be needed to intercept the glide point at mid-final. From there it is a glide to the aim-point - add power for sink or shear, allow aim point to extend a certain distance from threshold for lift. If max aim-point is going to be exceeded - side-slip or go around (hasn't happened yet - although I have had to go around for an accidental lesson in PIOs).

 

If I have full flap and the power fails on base or final, I can still put some flap away if short - provided I have some height left to allow for initial sink.

 

As I said I'm a noob (about 70 hours powered now), but I want to contribute. I also want to continue to learn and refine my style, so feel free to point out any flaws. Not that you guys need an invitation to do that. :;)4:

 

Ross

 

Edit: the point about expediting the landing was made while typing. I agree that there are times when you should hustle and leave the setup for final. I did this at Narromine because it was busy. Normally I have flown at very quiet strips.

 

 

[Guest pelorus32]

I probably should have been clearer and said that I'd love an aircraft with a Vfe of, say, 85 knots so that I could grab flaps 1 on downwind.

 

I, like Nev, think that we should pay particular care to Vfe.

 

As for assymetric flaps. Part of the FAR Part 23 flight test regime requires demonstration of a/c controllability with assymetric flap extension. Our a/c of course are not FAR Part 23 certified so do not have to demonstrate that!!

 

Regards

 

Mike

 

 

[Guest micgrace]

Hi

 

Interesting about flap assymetry. I find a lot more use of rudder is required with reduced use of aerilon, increasing on each stage of flap. The max flap extension cannot be ignored of course. Most aerilons or flap structures I've seen couldn't take much before a structural failure.

 

Can actually feel the assymetry when banking. (likes to "tighten up") esp in the Allegro. So, possibly, should be something about such effects in training.

 

In the Allegro at speed, use of rudder is preferred to lead in with just a hint of aerilon. The Texan, I found was the opposite, aerilon with just a hint of rudder. (No, not mixing paint) The effect reverses with flaps. Now, i think, that could give some trouble (smoking hole) if no adjustment to rudder/aerilon technique is made with flaps.

 

Micgrace

 

 

[Guest Juliette Lima]

Hi Slartibartfast,

 

What is a Noob?...and how does that relate to 30 years in gliders.....I think that experience might trump a few years in powered aircraft.

 

As a matter of interest, your landing technique is the perferred option of Leighton Collins, author of the brilliant classic, 'Takeoffs and Landings...The Crucial Maneuvers and everything in between.'

 

..Available from sporty's USA and not to be confused with Sporty's DVD on Takeoffs and Landings.

 

This book would seem to be mandatory reading for those interested in an analysis of every aspect of the title topics.....The author considers many styles of takeoff and landing techniques and gives commentary on the pros and cons relative to his extensive experience, and more importantly, relative to accident statistics known to have accompanied various takeoff and landing errors....and even safe assumptions.

 

At the risk of throwing a pebble into the pond of perfect landings.....something I have yet to acheive with consistiency, there is a rather interesting section in the book on 'Throwing the wind a curve'

 

Essentially (for this technique) if there is a crosswind, takeoff and landings start at the downwind edgeway of the runway, headed at a point 100 metres ahead on the upwind side of the runway....curving toward the cetre as the takeoff and landind roll is commenced..... Benefits are discussed.

 

I've read of this in 'Mountain Flying' articles from the US where the practice is commonplace.

 

It works.

 

Cheers

 

JL

 

PS. I can elaborate on this landing technique (as written) if anyone is half inclined.

 

 

[slartibartfast]

Thanks JL.

 

Feels right and sensible to me.

 

I was chuffed at Narromine when I took Biggles1 for a first light flight (now there's a poetic phrase). On turning base he immediately said "oh, so you're a glider pilot. This is how all landings should be."

 

I think that's what you said Jim

 

Anyway, a noob is a contraction of newbie, which is regarded as someone new to something. It's roots may go back as far as 1605 as follows from answers.com :-

 

"Newbie probably owes some connection in its construction to Wannabe (1981) and freebie (1942) and even the much older used-to-be (1853) and wouldbe (1605). The spelling still varies between newbie and newbee, though the pronunciation is the same in either case."

 

I would love for you to elaborate on the "throwing the wind a curve" technique. Damn sneaky wind.

 

Saves me buying the book.

 

Ross

 

Oh yeah - I don't have 30 years experience. I flew gliders for about 1 year before taking up hang-gliding. Again only about a year before other family pressures took over.

 

 

[Guest Juliette Lima]

HI Slartibartfast,

 

will follow up soon...away flying,

 

Cheers

 

JL

 

 

[Ben Longden]

Also IMHO to sit beside a competent pilot and watch him do half a dozen circuits is a great way of improving your own - especially if you are in your first 100hrs. Anyway it works for me...

 

Roger

It works for me as well.

 

I was the lucky b'stard who sat in the right seat of Nathan Muller (Air Shepparton) as he flew his Navajo into and from Avalon. That was such a huge, positive learning experience, and what he had been teaching me gelled at that moment.

 

Ben

 

BTW; Ask John Frew about his Bushby Mustang 11 and approach speeds... it comes in over the fence at 95 Knots, and the flaps are more of an air brake than anything...

 

 

[Guest Biggles1]

Right on Startibartfast, the next flight I did at Narromine was interrupted as I turned base, by an a/c on finals, he/she was on finals, down in the trees and about 2kms out asking if I had he/she in sight. Into a setting sun the a/c might as well been a stealth aircraft.

 

I like the old system of glide approaches, and I have heard several instructors advocating them. It becomes comfotable to do it the same every time. As a glider pilot you would be aware of getting the field into perspective, so that you could make a forced landing from any part of your cicuit.

 

On my last flight check, which I like to do if I haven't flown for 4 weeks or more, I said to the instructor whilst on finals "this part of the flight always seems to go on forever". I now know from reading the comments that it only does once you are "in the groove"

 

Regards

 

Biggles1

 

 

[Guest pelorus32]

Approach Criteria

 

The attached document is designed for the heavy metal, but change the numbers to suit yourself and it aligns pretty closely with what we have been talking about.

 

Also this link is to a good PowerPoint - again for heavy metal - but the principles still hold.

 

http://www.flightsafety.org/ppt/managing_threat.ppt

 

 

 

Another point that hasn't been discussed in this thread is (to quote someone else):

 

 

 

In addition a stabilized approach is one of the primary means of wind shear recognition. When you are on localizer, glideslope and “on speed” it is easy to recognize any variations. Early recognition is critical to successful wind shear avoidance and recovery.

 

Again forget on localizer and replace it with your own criteria.

 

Regards

 

Mike

 

alar_bn7-1stablizedappr.pdf

 

alar_bn7-1stablizedappr.pdf

 

alar_bn7-1stablizedappr.pdf

[slartibartfast]

Thanks Mike. They were very useful.

 

Ross

 

 

[IanR]

Have just had a quick look through this thread - seems to be a variety of opinion on stabilised approaches. What is being taught these days ? I have always been taught that the type of stabilised approach that the commercial jets use where there are specific requirements re altitude, distance out, etc is not really suitable for light single engine aircraft. Main reason is that once set up in one of those stabilised approaches you are behind the drag curve and need significant power to maintain the glideslope. This is a very easy and predictable way to land as long as everything goes well but what happens if you have an engine failure in that configuration ? You normally don't really have much choice if flying an ILS but for normal landings I prefer to have a bit of a safety margin - a planned approach rather than fully stabilised.

 

 

[eastmeg2]

Just from watching "Air Crash Investigation" on the pay tv, have seen an instance when a twin engine passenger jet had already lost one engine and let down to 6000ft 40Nm from the airport as per normal procedure and what happened when the other engine failed was most predictable.

 

They didn't make it did they.

 

Had they maintained altitude until they were within glide of the airport their chances would have been far better.