Five Mile Final

[Guest pelorus32]

I've just being doing some thinking about five mile finals and what height you have to be at what point. The rules say that you need to be established on rwy centreline at 5 miles.

 

My rule of thumb calcs look like this. Please don't expect them to be exact - there's some rounding in them.

 

First a rough table:

 

FPM descent rate = GS (knots) X Factor.

 

Factors:

 

1 deg: 1.66

 

2 deg: 3.33

 

3 deg: 5.0

 

4 deg: 6.66

 

5 deg: 8.33

 

6 deg: 10

 

Then: Height/Distance x 60 = slope in degrees. Just use 6000 for a nautical mile.

 

So an example:

 

5 miles out 1700' AGL 90 kn GS = 450 fpm descent rate

 

that will get you to:

 

1 mile out 500' AGL 50 kn GS = 400 fpm descent rate

 

As you can see I've used nearly a 5 degree slope which is what I think we do in practice in an a/c like a Tecnam.

 

Note that we are talking GS - for this example I have used a 10 knot headwind as IAS on the Tecnam for final is 60 knots.

 

For me the information I need from my calcs is: what height should I be at when I'm at 5 miles and what sort of rate should I have to get me to my 1 mile point? From the 1 mile point it is your normal visual approach anyway but those are roughly the figures.

 

Also if you can see the runway clearly at 5 miles you can just use your normal aim point technique without any calculation.

 

I'd be interested in the comments of others.

 

Regards

 

Mike

 

 

[PaulN]

G'day Mike,

 

The mind boggles, where do you come up with all this technical stuff. Take it easy mate, most of us here are just simple pilots ;).

 

Of course, a STA should only be attempted with good visibility and comfortable terrain. Here at Cooma, the few times I do this I line myself up (more or less) 5 miles out at 2000' AAL with a GS of around 90kt and a 500fpm descent. This gets me at around 700' 1 mile out in time to set fine pitch, throttle back, flaps ext and normal late final. Different winds make for slight variations to this theme, otherwise it works fine in my little CT. I guess every a/c is different though.

 

Hope this helps.

 

Paul

 

 

[Guest pelorus32]

G'day Mike,The mind boggles, where do you come up with all this technical stuff. Take it easy mate, most of us here are just simple pilots ;).

 

Of course, a STA should only be attempted with good visibility and comfortable terrain. Here at Cooma, the few times I do this I line myself up (more or less) 5 miles out at 2000' AAL with a GS of around 90kt and a 500fpm descent. This gets me at around 700' 1 mile out in time to set fine pitch, throttle back, flaps ext and normal late final. Different winds make for slight variations to this theme, otherwise it works fine in my little CT. I guess every a/c is different though.

 

Hope this helps.

 

Paul

G'day Paul,

 

brain won't stop ticking. It's mostly the 1:60 rule.

 

I think your numbers marry very nicely with my calcs:

 

5 miles out at 2000' arriving at 1 mile at 700' = 1300' over 24,000' x 60 = 3.25 degrees slope. If you then check my factors (by interpolation) it's around 5.5 so 5.5 x 90 knots = 495 fpm descent. Just about what you do.

 

My idea was to get a rule of thumb to drive that 4 miles from 5 miles to 1 mile.

 

For instance if we were at 3000' AAL at 5 miles and at 90 knots GS then the ROD would be (for you with 700' at 1 mile) 2300/24,000 x 60 = 5.75 degrees so the factor is about 9.6. therefore 9.6 x 90 = 860fpm.

 

There is another way of course: 4 miles @ 90 knots GS = 4 miles /1.5 miles per minute = 2.66 mins. Therefore 2300'/2.66min = 864 fpm ;). In the cockpit I'd do that (2300/2.66) by inspection and say "a bit less than 1000fpm".

 

Should be flying:;)3:

 

Regards

 

Mike

 

 

[Guest pelorus32]

Aimlessly wandering further than this:

 

Imagine I'm planning my descent and I say "I'm happy descending at 400fpm and I will track inbound for the first 4 miles at 80 knots GS". What height do I have to be at at 5 miles to arrive at 500 feet at 1 mile?

 

The answer on the CR-3 is obtained by the following steps:

 

1) Line up the ^ index with 80 on the outer ring (for knots GS) then under 40 (for 4 miles) read off 30 (3 minutes) so you have 3 minutes inbound for 4 miles.

 

2) Line up the "10" in the black dot under 40 on the outer ring (for 400 fpm) and then go around to 30 (for 3 minutes) on the inner ring and read off 12 (for 1200 feet) on the outer ring.

 

3) Add 1200' to 500' (desired height at 1nm) to arrive at 1700' at 5 miles.

 

Off course that one could be done by inspection, others end up with greater pencil chewing if the number isn't a nice whole number like "3".

 

Indeed all the calcs can be done by CR-3 as it will add, divide, subtract and multiply.

 

Regards

 

Mike

 

 

[Yenn]

The method I prefer is to maintain altitude until I am on the engine out glide slope, which for me results in over 500' per minute. When the slope looks correct, I reduce power to idle and do my normal glide approach. If I have misjudged I may have to apply power, but I usually keep high anyway and have to slip somewhere in the last 700' or so. It is much like the IFR approach where the glide slope is intercepted from below.

 

 

[PaulN]

;) CR-3 :;)5:

 

Egads Mike, if I had to pull this out of my bag and attempt the calcs like you imply, I'd have to start the sums about 150 miles out :confused:.

 

Paul

 

 

[BigPete]

This works well for me. ;)

 

5 mile final commenced at circuit height - radio call - "downwind" checks completed by 3 mile fnal.

 

3 mile final = "turning base" - radio call, power off, carb heat, attitude, flaps, 70 knots, check for traffic etc.

 

1 mile final = "turning final" - radio call - full flap, carb heat to cold, reduce power etc.

 

regards

 

 

[vk3auu]

5 mile final

 

Assume you are flying a 1000 foot high circuit and you are still at 1000 foot when you turn base. If you have a glide ratio of 10 to 1 with whatever flap setting you have, you should need 10000 feet to get to the threshold of which half should be base and half should be final, so what the hell are you doing flying a 5 mile final anyway, just getting in the way of other planes.

 

David

 

 

[Guest brentc]

David, the reference to the 5 mile final is for a straight in approach with no circuit.

 

 

[vk3auu]

5 mile final

 

Point taken Brent, but where I come from, it isn't considered good airmanship to fly straight in approaches, even if it is legal and you do make the appropriate radio calls.

 

David

 

 

[Guest pelorus32]

G'day David,

 

It's not common where I come from either. Sometimes however they are appropriate, I could also see some circumstances where such an approach might be very desirable. I think that the issue of airmanship comes up when you start landing on the wrong runway or interfering with other a/c conducting full circuits - the rules require those on a 5 mile final to give way.

 

Just thinking also - whilst we don't commonly conduct straight in approaches they are very commonly conducted where I fly: Air Ambulance, Charter, the Premier, helicopters....

 

So the other question is when someone calls that they are established on five mile final for rwy 36 and you are 5 miles south of 36 it's worthwhile to know what sort of height they might be at as they often don't call height.

 

Bottom line is when I do want to do a straight in approach for whatever reason I wanted some rules of thumb to guide my setup of that approach just like with a normal circuit.

 

Regards

 

Mike

 

 

[vk3auu]

5 mile final

 

If you are coming straight in, I would suggest that it would be desirable for you to be somewhere around circuit height when you get into the circuit area. That would be between 1000 and 500 feet AGL, remembering that there are still people out there without radio who are just relying on see and avoid. These people tend to be flying slower "real" ultralights and in general they are draggy machines which come in fairly steeply on final. They also tend to fly fairly close in circuits, so you need to be looking for them to come in from above you when you are on short final.

 

Happy flying,

 

David

 

 

[Mazda]

The establishment on 5 mile final wasn't planned to be in the CTAF rules - it was something wanted apparently by airline pilots. Hopefully in future this will be changed back to the original plan, which will mean you won't need to be established that far out. A 5 mile final is fine if you are flying an airline jet but it isn't really necessary in a small aircraft!

 

At the moment though, the rules say we need to do it.

 

 

[Ross]

My copy of "Ultralight Basic Aeronautical Knowledge" by Des Rycroft has some information on "Flight Rules & Procedures" on pages 71 through to 78.

 

 

 

One of the points amongst others is on

 

"Entering the circuit

 

 

 

Circuit entry is by flying at least three legs, i.e. all or part of downwind, base and final. Entry height is usually 1500 feet AGL and circuit height usually 1000 feet AGL ......"

 

 

Are we still bound by these "Ultralight" rules although I know they have been modified to some extent with a least three circuit heights now in force plus the different climb out height before turning cross wind and the local requirements for fly friendly at various strips as listed in ERSA?

 

 

 

Regards

 

 

 

[Guest pelorus32]

Hi Ross,

 

My understanding is that we are, in this respect, the same as any other aircraft and are bound by the NAS2 (I think) changes that applied to airspace, circuits, CTAFs etc.

 

That provides for 3 circuit heights, 45 degree joins and straight-in finals.

 

I'd just like to make it clear that I wasn't advocating habitual use of S-I finals. Rather I was noting that you could use them and simply mulling over a rule of thumb to allow sensible performance of one if you wanted to.

 

As far as I can work out Ian in his CT is the only one entitled to a 1500 foot circuit ;-)

 

Regards

 

Mike

 

 

[Ben Longden]

Mike is right.

 

We are taught the rules of the air apply to ALL, and come from the one authority and that is CASA.

 

This is straight from their current VFG Guide, and CASA have these regulations "pending review" which means they are rules until they are changed.

 

Ben

 

 

 

 

[facthunter]

Straight-in approaches.

 

Ian's CT. should not be doing 1500' circuits as the 120 Kts. and above is the NORMAL DOWNWIND speed for the aircraft type.

 

Most RPT approaches are 3 degrees and the final descent point is usually 10 miles/ at just above 3000' AGL. This is just above 300'/mile. If you want a 5 degree slope ( more like what we would use) it becomes 500'/mile. 6 degrees becomes 600'/mile and so on.(this is a still air distance to maintain a constant angle approach the power will have to be increased in a headwind) Nobody so far has allowed for slowing down to extend flap/undercarriage or just to get back to the normal approach speed. This is best done by arriving at a fixed height ,below the final approach slope and holding that height to bleed off airspeed, reconfiguring the aircraft & judging the whole procedure in such a way that you intercept the one mile final on the slope that you planned for. This requires a fair bit of judgement to get it right, and you need to be familiar with your aircrafts performance. Nev...

 

 

[Guest pelorus32]

Aww gee Nev,

 

You've gone all serious on us...:) I had my tongue stuck well into my cheek with that comment about Ian's CT.

 

As for slowing the aircraft down, getting flaps and reconfiguring, that's why my initial example said among other things:

 

" 5 miles out 1700' AGL 90 kn GS = 450 fpm descent rate

 

that will get you to:

 

1 mile out 500' AGL 50 kn GS = 400 fpm descent rate"

 

I was only aiming for a rule of thumb but set it up in two chunks with a decelerate phase at around circuit final height. The idea being to accomplish the first phase (4 miles) of the 5 miles at some reasonable pace and then to slow to the depressingly slow flaps speed for the Tecnam of 67 knots for flaps 1 and 60 knots for everything else.

 

Good point about decelerating and reconfiguring the aircraft on final, rather than on the base turn and about being able to stay "on slope" as you decelerate and reconfigure. I've done a bit of practice on that in other circumstances. When it's done correctly it's quite Zen.

 

Regards

 

Mike

 

 

[facthunter]

Slowing up.

 

Yes, sorry Mike ,but you never know ,someone may take you literally. I have tried to give real simple formulas that enable you to have a fairly good idea of where the other traffic might be. I myself need simple formulas because I reckon my brain goes to about half speed when I get in an aeroplane. Perhaps it's like that all the time.

 

The exaggerated plateau ( level flight to reduce speed ) is needed because of the very restrictive flap extend speeds most of these aircraft have, and to which you have referred, even though it makes the approach untidy. Often the speed will not come back if a descent is maintained. Nev..

 

 

[Yenn]

You are all talking of distances out and heights to be at, but what I would like to know is how do you know how far out you really are, and that is before you take wind into consideration. I believe it should all be done by visual sighting using experience.

 

Concerning the 3 different circuit heights I don't like them for use at non controlled airports as you can have slow traffic coming into the area to let down on the dead side at the same height as fast traffic in the circuit. You can also be letting down into helicopter circuit height while on base or downwind. Not too bad if you are high wing but deadly for a low wing plane.

 

 

[Guest pelorus32]

Hi Ian,

 

In the circuit area of a known airfield I find I develop geographical markers that allow me to estimate fairly accurately my distance from the field. On a new airstrip I tend not to conduct straight ins, but assess my distance if necessary off the WAC against identifiable features.

 

I suppose the technological amongst us probably use the GPS.

 

I take your point about doing it visually - ID the aimpoint and go for it. For much of the summer however there is not 5 miles clear vis so it makes it hard - smoke, haze etc.

 

I agree with you about circuit height, I'd be interested in other comment but it seems to me that if you are conducting a 500' circuit you have to join at worst mid-field crosswind or downwind. If you cross the strip beyond the midpoint you are at risk of hitting an aircraft on upwind climbout.

 

Regards

 

Mike

 

 

[Ben Longden]

On my Nav check ride with Matt, he taught me that its fine to use geographical markers for a familiar strip, but when at a new location, to firstly ensure correct height, then use the geometry of the plane to align with airstrip features.

 

So, after joining crosswind he would say to look over your left shoulder and once the tail plane has crossed the strip, to then turn downwind. This has always placed me in an ideal situation for turning base, which should be on about a 45 degree angle from the end of the runway.

 

For me that has helped set up my best landings.

 

As a double check, in the Tecnam cruising downwind, I look to the left, and find that the flap hinge 'aligns' with the runway, as well.

 

Ben

 

 

[Guest pelorus32]

Good stuff Ben,

 

my reference to geographical markers was in response to Ian's question about "how do you tell that you are 5 miles out anyway" (or words to that effect). I don't use them in the circuit.

 

Regards

 

Mike

 

 

[Mazda]

Yenn, there are a few ways to estimate distance. Obviously GPS will help.

 

Remember though that navigation can be done with a watch, so if you have calculated an estimate for your arrival and are aware of groundspeed, that will give you a good idea of when you SHOULD be 5 miles out.

 

You will develop a bit of a "feel" for distance, but it has to be an estimate if you don't have DME or GPS.

 

When you are close enough to see the runway, remember too that the runway is a known length, so you can also use that length to help to judge distance. It's still an estimate though!

 

 

[facthunter]

Estimating distances.

 

I think that we are all pretty much agreed on the straight -in approach only being used at the appropriate time, ie you have radio, you know the wind direction, and you won't just bore into the circuit, if it's full of traffic, and you have some familiarity with the aerodrome. This could be an extensive briefing, or personal experience. If you don't do a straight-in remember that others may (RPT, & charter) You should be aware of them because of their radio calls. The best way to adjust for traffic in the circuit is by extending the downwind leg. Speed adjustments are not very effective and jeopardise safety.

 

Regarding the 5 mile estimate, I think you are supposed to be aligned with the runway BY 5 miles. as to estimating that distance, I feel without DME or GPS you really only having an enlightened guess, unless you are familiar with a known feature on the ground. I'm not against the straight-in approach as it reduces the number of aircraft cluttering up the circuit. Hopefully everyone knows the rules and keeps a good lookout and listens on the radio. Throw glider operations on a contra-circuit, on an adlacent strip, in and you really have a workload. no time to be checking up on the ERSA as you enter the circuit. Keep ahead of your aircraft Nev..