Why Fly Square Circuits?
 

Can anybody tell me why most flying schools teach a large, square circuit flown at almost cruise power. Apart from maximising enviromental bother the chances of making the runway if the engine quits is almost nil. I reckon it's purely to increase the amount of time each circuit takes - therefore more money for the flying schools.

Have we lost sight of why we are flying a circuit in the first place?

As an instructor who teaches square circuits , i felt i had to respond to this post. Square circuits are flown to maximise lookout and reduce blind spots. If an oval circuit is flown in a high winged aircraft, the runway would be out of site as would other traffic. However i agree that a lot of circuits are too wide. Where I work we always teach that the airfield should be within gliding range at all times, this is not the case with all FTOs. Definatley a case of maximising their revenue, to the students cost. So a plea must go out for people to think about where they are going if the engine stops.

To be honest I was being a bit provocative with the square circuit thing! I personally find an oval circuit quite difficult to fly as well as having a poor view - however - the main thrust of my inquiry was to find out why such large circuits tend to be flown & why they are flown with high power?

I do not believe the argument that says "students need the time to get the checks done". I cannot think of an instance where a large circuit is better.

M14P,

I think that accusing the schools of teaching square circuits simply to squeeze a bit more money out of proto-PPLs is a wee bit out of order.

The civilian square circuits have helped PPLs to pick their way around an airfield without bumping into each other. It's also convenient for ATC or A/G as it allows all and sundry to visualise where an aircraft actually is, or should be.

If we move on to ovals, then what do we call? "G-XX, at 120 degrees". "Roger, G-XX, call when at 265 degrees". Nah.

I'm aware that military circuits are oval, but then again a lot of military procedures are different. A run and break might be fun in a Yak 52, but probably a bit silly in a C150, don't you think?

A major reason why the civilian square circuit seems to work is that everyone is (or should be) following the same procedure. What really worries me is that some in the warbird community are beginning to follow military-style procedures (i.e. run and break) in the same circuits as merely mortal traffic. This can't be good for the health.

It seems to me that, if there's a problem with the civilian circuit, it's the fact that it's getting wider and wider.

TW

Touchy Touchy!

I am not condoning oval circuits and I think that a run & break at a civillian airfield - particularly by a singleton and especially in a non-jet aircraft - is downright silly & dangerous.

The simple fact is if the 'average' club 150's engine quit downwind at either of the clubs near me they'd be in a field. Extra risk, extra damage and a load of bad press.

What about the noise issue?

As a student would you rather do an hours' flying with five landings or ten? I'd take a wild guess at the student who'd be more competent as the one with the most landings

I'm an Oval circuit (or to give it's proper name, constant aspect circuit) fan myself. It gives better visibility of traffic ahead on finals, is quicker, allows you to reach the right touchdown point more accurately, and reduces the bank angle used in the circuit.

It also lends itself well to separation of traffic flying at different speeds (and sometimes heights) on the same runway.

A run and break, if flown, has to be combined with a constant aspect approach, but the converse is not true. All the same joins used in a rectangular civil circuit can still be flown.

G

[This message has been edited by Genghis the Engineer (edited 24 April 2001).]

M14P,

Touché, touché? Moi? Mais non, Mon Ami!

I was busily composing whilst you were busily back-tracking on your 'provocative' first post. If you really intended this thread to be a discussion on lose circuits, then perhaps a different title and post would have been a better idea? Ah well, onwards:

I guess that we both agree that the average circuit flown is too large. All we need is a quick land-away on the downwind and then we can all save pots of dish by doing our circuits and navs at the same time. There are plenty of stories around of people getting lost whilst doing circuits. In poor visibility, I grant you, but still...

What happens if the donkey quits? What about the neighbours, bless 'em? What on earth does that J3 Cub think it's doing under-taking in like that?

The trouble is that the same argument I used above (everyone doing the same thing) means that any anarchist mad enough to do safe, tight circuits will be censured by all and sundry for under-taking.

TW

This is all true!

However, the best way of encouraging a discussion is by being deliberately provocative. If you read a random selecton of AAIB bulletin reports the vast majority are landing accidents of the 'bust the nosewheel off' variety. Surely this means that for all this supposed good circuit discipline described by Jude what is really needed is some proper instruction and lots of landings - not beetling around the pattern logging long-haul time.

I cannot help but think the one (poor circuits) probably leads on to the other (dodgy arrivals)

Must say I'm with Ghengis on the curvy patterns - quicker, safer, and very easy to spot all the other traffic. Mind you that could just be the superior brainwashing skills of UAS QFIs : ) Also concur on the silliness of run & break arrivals in a busy civvy environment in a piston single.

M14P's broader point is a valid one, I feel. Having spent plenty of a PPL course trucking round a square circuit the fact that as the circuit gets busier it almost always gets larger is to my mind a real problem. Cross-country style downwinds ensue, and all the previously highlighted issues surface. Jude - do you imply a square circuit is desirable simply because 152s are high-wing? And why do so many studes not get taught to keep patterns tight and simply go around again if they get baulked? Sorry to sound narky but some of the bomber circuits flown at my local club recently have caused much wailing and gnashing of teeth on my part.

[This message has been edited by RoughRunning (edited 24 April 2001).]

An interesting topic. Sorry to be picky, but do we all actually mean "square" circuits, or are we talking about rectangular circuits?

Personally, I've always been taught to fly rectangular circuits, and although I can't say I've ever flown a circular one, I think I'm more happy with the rectangle.

I can't imagine why square circuits would ever be flown! Is there any reason why the crosswind and base legs have to be the same length as the downwind?!
I have completed most of my training at PIK, can you imagine me extending the crosswind to the same lenght as the runway!

"G-BOAH, report overhead GLA" :)

For me flying rectangular circuits gives a very clear definition between the legs. For example, I've always been taught that as soon as you roll out on base leg, reduce the power and add 2 stages of flap. Although this could still be done whilst flying a circular pattern, I think it's easier for a low hour pilot (like me!) to clarify these things exactly.

Four 90* turns is easier in my opinion, than maintaining a continual bank angle.

But I'm always open to suggestions!

FJW.

Hooray!

RoughRunning gets the point - there isn't enough common sense out there (sorry to generalise but we are all guilty of it from time to time)

If you really want to clean the circuit up the best way is to pick your touchdown spot so as to minimise time on the runway (on long runways with finite turnoffs). The student who practises many landings can start to absorb this airmanship through a greater exposure to the bit of the circuit that tends to be most critical.

Go on chaps, give it a go and try to fly a little tighter, maybe a little steeper and in a much more thoughtful way.

FJW - by square I think it's safe to assume we all mean squared off. I am the first to admit that a totally oval pattern is incompatible with everyday life but a shorter crosswind leg will keep you in a better position in the event of an engine failure. Whilst learning by wrote (as you describe) is a good first step it becomes impossible to deal with contingecies as they arise. What if - due to other traffic your base leg is further out than normal? The resultant descent rate and configuration of your aircraft will not be satifactory for the rest of the approach.

In general datums (such at base leg and two stages of flap) are a good way, I feel, to approach the circuit but must not be applied robotically. Perhaps the robotic method of teaching is the root cause of ever larger circuits.

[This message has been edited by M14P (edited 24 April 2001).]

Fast Jet Wannabe,

Unless you can fly a geometrically precise rectangle, that would have made Pythagoras proud, then you are being picky. My circuits look more like seventy sided polygons, truth be told.

TW

The comment about a robotic approach to teaching circuits is interesting. When doing my wobbly prop conversion some months after getting my PPL, my instructor told me to stop flying "numpty PPL stude circuits" and tried to get me to approach the circuit as an exercise in progressive energy management (starting from when you join or level off from the climb out). Doing it this way, the power setting can often be a lot lower a lot earlier, but I can appreciate that in aircraft with little power to spare it may be thought best to keep the power a bit higher.

If people are following slower aircraft but still religiously flying all the numbers they were taught, they may end up over extending and enlarging the circuit, rather than slowing down and keeping tight by, eg a power reduction and even a stage of flap early on.

To this it might be said that you shouldn't be encouraging students or low hours PPLs to fly slowly at 1000 feet or lower, but I'm not talking about dangerously critical airspeeds or angles of dangle, and being able to chug along at (say) 80 knots instead of 95 ought to be something the average PPL could handle as a result of his/her training.

Of course none of this takes account of the loony circuits imposed by noise constraints. Quick straw poll of how many GA airfields have circuits which are "standard" on all or main runways? North Weald? Duxford? What others?

Just thought I'd lobb in my two 'pennorth.....When I have flown in the US, a frequent clearance from ATC was to fly a "Close Pattern" This involved a circuit which was VERY compact, and meant that as soon as 600 feet was reached, a climbing turn was made straight onto downwind at 1000 feet. As soon as the numbers were 45° behind the shoulder, power off first stage flap, and descend onto base, and thence onto finals. It makes some circuits I've seen here look like mini cross countrys.

Tailwinds

When aircraft first flew they could turn on a sixpence so the rectangular circuit was borne. The oval circuit followed primarily because forward vision was obscured nescessitating a curved approach. As the performance of military aircraft increased, an oval circuit was the only realistic option.

The average PPL student and many PPL holders require thinking time, an oval circuit correctly flown simply overloads them and does not provide them with the necessary time. A rectangular circuit therefore provides more time and a better lookout for the inexperienced.

That said, lets keep them a sensible size, Runway on the wingtip downwind, and not more than 45 degrees past the threshold for a Normal circuit.

Much hot air on this thread - only Jude has got it right.

Square circuits reduce 'blind time' for high wing ac; the military does not use high wing ac for training, hence they can safely use the standard racetrack circuit which optimises the look-out for low wing ac - particularly those which fly at high AoA around the final turn. In civilian flying training there is a mixture of both low and high wing ac; hence a compromise circuit pattern is required - this is the 'square' circuit.

There is no intrinsic reason why ac flying a 'square' circuit should be out of gliding range for the aerodrome - that's basic airmanship. Although tarnished by local nosie-moaners perhaps.

[This message has been edited by BEagle (edited 24 April 2001).]

I'd like to see a combination of oval and rectangular circuits as the pattern/traffic/ATC dictates. As a Controller at a very busy class G airfield, there is nothing more infuriating than having all your circuit traffic outside the ATZ because the Cessna who was number one when he turned downwind ended up on a three mile final at 65kts with an Arrow, a Robin and a Seneca behind him...it happened last weekend...and it happens regularly! but at the other end of the spectrum, a 'constant-aspect' type cutting up a £300 per hour IR trainer (despite having been told twice "Number two, follow...") causing him to break off his Instrument approach is just as annoying for all concerned. A potential problem with keeping circuits too tight, however, is finding time and space to get departures off. The point I think I'm trying to make is that pilots will encounter a different circuit pattern almost every time they fly...I always seem to.... so they need to be prepared to deal with every eventuality..short apporaches, slow flight and constant aspect approaches should be taught to everyone, early in their careers

My input on circuit size: try getting more than 3 in an oval circuit, when the active runway requires a backtrack, and they are low-time students on post-solo consolidations. I rest my case.

BEagle - I think you might be grasping the wrong end of the stick a little. As RoughRunning mentioned the logical conclusion of Judes argument is that we should adjust everybodys circuit behaviour just for high winged aircraft which is simply nuts.

I say again - to fly a sensibly sized rectangular circuit is one thing but to burn up miles of sky simply to arrive back a the same point is just clunky and nonsensical.

If the aircraft in front on downwid has just left the ATZ before managing to turn base what would you do? I suggest that he's no longer in the circuit and is a prime candidate for overtaking but airmanship may dictate your being a little more circumspect than that. If the chap has just spent more than three miles flying away from the field he may not even be aware of your presence. Thoughts?

[This message has been edited by M14P (edited 24 April 2001).]

I don't agree with this high wing / blind time theory being banded about. A properly flown constant aspect circuit uses a very shallow bank angle, and since you're mostly either in a climbing or descending turn , the traffic in front is always more-or-less ahead, and above the coaming. With a rectangular circuit the Viz of traffic ahead is fine in the climbout, but non-existent in most high-coaming aircraft on finals. The wing is irrelevant where aircraft you could interfere with are concerned.

A genuinely tight circuit has to be constant-aspect, unless you are planning to use 60°+ bank in the circuit turns, which wouldn't be very clever. But, the airfields where people routinely fly circuits that require a chart, drive me up the wall, even if flying square circuits. Having said that, it's usually the fault of individual pilots, not the airfield itself.

At BDN we used to regularly mix everthing from a Vigilant to Tornado in the same circuit (23L usually), constant aspect, with heights and distances from the runway altered for each aircraft to maintain a constant circuit duration (about 5 minutes) and position. I don't recall it ever causing us a significant problem.

Also, a constant aspect approach is the only (in my opinion) sensible approach to flying a PFL. John Stewart-Smith's article on the subject in FSB sums it up without me going into it more. And if you're going to use it for a PFL, why not practice it at home!

G

Personally, I prefer the racetrack circuit. However, that requires a lengthy shallow AoB turn onto downwind during which time a high wing aircraft is blind towards the active side of the circuit. In contrast, a 'square' circuit requires 2 short duration larger AoB turns between periods of straight flight. Hence the total 'blind time' is less. Low wing or high wing aircraft can cope with this together, hence it is, unfortunately, probably the better compromise for mixed civil light ac traffic.

Anybody flying beyond the normal visual circuit should be considered to have left that circuit; I suppose you could say "G-XX is visual with the traffic departing downwind and is turning left base" or something similar. Probably not in CAP413, but that assumes that people fly correctly! For example, the last time I went to Kidlington I was told to position behind the PA34 on final. Seeing one crossing the threshold I started to do so; however, I was told that I was turning inside the traffic. A quick reverse and I saw a dot on the horizon which was indeed a PA34 on hugely, enormously long final!! (Not my favourite aerodrome for many reasons - I was also very unimpressed to be waiting 'ready immediate' for departure only to be overtaken on the wrong side by some bizjet elbowing his way past the queue under some form of local priority system which does not appear in the AIP or Pooleys' and which no-one had briefed me about).

[This message has been edited by BEagle (edited 25 April 2001).]

I agree with you BEagle about the consideratons for those beyond the ATZ, however, I tried this a few times and occasionally got a huffy response from the 152 (despite being 500 yards clear of the runway when he was in the flare)

I guess if you're going to do it prepare to accept flak from the dingle you've just 'overtaken'.

Hoorah, sensible words Noggin, wingtip along the runway and turns when at 45degrees. Just how we try to teach them. Rectangular circuit within gliding range of the airfield. Its the landings that are important, not x country flying at this stage. Even when mixing it with 737s, this works, with just the odd orbit downwind for spacing. Admittedly it can be difficult if the aircraft ahead is flying cross country circuits, but a request for a right hand circuit instead of left hand normally allows a sensible circuit to be flown, provided noise abatment aspects permit. In reply to the comment about throwing things away when an approach goes pearshaped, definatly something we advocate, but it would be nice if we weren't charged for go-arounds.

Just like to make a couple of points as a military pilot who flies a lot of GA as well.

Noggin makes a good point about keeping the circuit to a sensible size, and running the wingtip down the runway is a good idea (if you're in a low wing aircraft); as is using the 45 degree point to turn finals (as a Jet Provost QFI we picked a point 45 ahead and on the extended centre line as a roll out point.

The main problem I see a lot is not the actual size or shape of the circuit (love those oval ones though), it's the fact that sometimes you get half a dozen aircraft flying half a dozen different sizes.

Run in an breaks - a quick method of a getting an aircraft down on the ground if you're coming in at 250kts+. not much use in a C152.

Interestingly, the Americans fly rectangular "patterns" but usually crank in approach flap at the end of the runway downwind and then start the descent, reducing power if necessary, turning on to a closer base leg.

This results in a tighter pattern, with the field "made" if the engine stops, but seems to be frowned upon in the UK.

Any comments from Jude or the other FI's?

[This message has been edited by Final 3 Greens (edited 25 April 2001).]

I think it very much depends on the type of aircraft flown. I used to teach it on some types where the first stage of flap was a relatively small deflection but gave a lower nose attitude thereby improving the view for the turn from downwind to finals. Also, the reduced speed makes for a tighter radius of turn thus allowing a lesser bank angle for the same rate of change and the increase in spanwise flow associated with flap application improves aileron effectiveness on most types.

All in all I would say that it is a valid procedure if it fits for the aircraft you usually fly.