Square circuits or rounded circuits?

[iflyforpie]

Everybody seems to teach and examiners all want to see square circuits.

I can't remember the last time I did one. I find things go so much better with rounded ones.

Why do we teach square circuits?

Let the debate begin!

[AuxBatOn]

rounded circuit? racetrack you mean?

[AUGER9]

IMHO, with traffic in the circuit I think the rectangular pattern would be more organized.

[AuxBatOn]

If you're talking about a racetrack pattern (continuous turn from take off to downwind) I could argue both sides. Here's my take:

On a low performance aircraft, your turn rate will be slow. THerefore, you will spend a lot of time belly up to the downwind side. What if someone is rejoining and you didn't see/hear him and he didn't see you? That can be some sort of conflict. WHen I do patterns, I always roll out for a second, take a look, roll in for the downwind turn. I do this when I rejoin to initial or set up for a straight in approach.

Now, having said that, we also do what we call "Closed patterns". From take off, accelerate then a climbing turn to downwind, configure and right into a 180 degree turn to short final. Mind you, we do have the power to climb up 1500' in a hurry and the performance to turn 180 degrees in no time too.

So, for a Cessna type airplane or any normal type pattern (ie: setting up for a normal final), I would advise against it, since you'll be belly up to potential incoming traffic for an extented period of time.

[MichaelP]

I don't like being in a high wing Cessna in a gentle turn at all!

Oval - racetrack circuits are fun, especially low level but they are not always accommodating to other traffic. I do them sometimes when ATC asks me to "keep it close to stay ahead of traffic over the gas stations", and often when the weather is poor and no-one else wants to fly.

For student pilots getting to grips with doing their checks, making radio calls, and trying to spot traffic, concentrating on doing a turn is just too much.
Instructors who teach their students to orbit prior to doing a diversion, or even do continuous turns in the forced landing procedure are not doing them any favours.
Straight flight can be trimmed, and the aeroplane 'not flown' while other details are attended to.

We all have to accommodate each other and so the rectangular circuit is best for all.

[Hedley]

the rectangular circuit is best for all

Er, no. If you're flying an aircraft with restricted
visibility forward, the very last thing you want to
do, is fly a straight-in final.

A two-star (retired) USN Admiral once landed his
Pitts on top of a 182 which pulled out in front
of him on (straight-in) final.

If the idea of mid-air collision doesn't bother you,
sure, fly a straight-in final all the time in all
aircraft.

Budd Davisson, of Scottsdale AZ refers to a
straight-in final as the "black zone". Don't
go there.

Plenty of aircraft that I fly have the problem
of restricted visibility out the front ... the
Pitts S-2B (x4), Pitts S-2C (x2), Ryan, Stearman,
even the Harvard from the back seat. Not far
from here are plenty of similar aircraft (spitfire,
P-51, hurricane, corsair, P-40, etc) which have
the same problem.

And none of which I would fly a rectangular
pattern in.

[MichaelP]

Does flying a rectangular circuit mean you have to do a long straight in final?

I don't think so.

You fly the crosswind, downwind and part of the base leg square, but you can always do a curved approach from base without affecting the other traffic.
Like you I have flown aircraft with restricted forward visibility, but I've almost always managed to fit in.

The one time I didn't was landing at Redhill in the War FW190 and that was because I needed 70KIAS minimum on finals and the slow Cessna's were in the way.
One instructor saw the situation and gave way to me... Some people at least have situational awareness combined with courtesy.

Unfortunately for us the majority of aircraft have to fly a rectangular circuit. We have to fit in with the majority.
But as I say the final approach can still be curved.

[Hedley]

The only way I can fly a straight-in final in the Pitts
is if I keep the speed over 180 mph, so I have some
hope of being able to see forward. I'm not sure that
approach technique fits in very well with other traffic
who are chugging along at 70 mph.

Another approach I can fly, straight-in, is the Gerry
Younger approach, where you stay incredibly high
on final, then sideslip at 10,000 fpm (no typo) to
touchdown. Not sure that fits in very well with
other traffic, either.

Best approach I've come up with is a slant final -
around 15 degrees off a straight-in. Even if
ATC clears me straight-in, I still set up a slant
final.

This allows me to actually see some of the
runway prior to touchdown. As you approach
the runway threshold, you simply dip a wing to
line up with the runway centerline, set the landing
attitude, and you are completely blind out the
front during the entire flare, touchdown and
rollout.

Various people - generally low-time private
pilots with only experience on cessna and piper
trainers - often get quite upset that unusual
airplanes have to fly unusual approaches.

Sorry, people. At my home airport, for a large
part of the year we have air cadets stationed
right at the edge of the runway, with people
continuously running back and forth across
the runway, and there is absolutely no way
I am going land without making sure that the
runway is clear

[Doc]

I'm with Hedley. Round out your circuits. Better visibility, and more fuel efficient as well. Don't know who invented square circuits. Perhaps the Germans?

[MorganAirCFI]

I would say its situation dependant. Considering aircraft type, traffic, pilot ability, configuration, terrain, etc. For most new students square pattern works best for judgement of glidepath, traffic, etc. Once proficient, give new scenarios where square pattern doesnt work, ie a mountain strip.

You can teach a monkey to fly, but you can't teach him to think.

[Hedley]

I don't care what exact shape your circuits are.

What matters is: If you lose power, can you
make the runway?

People like to fly HUGE circuits so that if they
lose engine power, they are assured of landing
in the bush or houses surrounding the airport,
instead of landing safely on the runway.

This is an odd choice.

Sure, when you are starting out, a large circuit
helps the student not get behind the aircraft,
esp with the tremendously long checklists FTUs
are fond of, and which the poor student has to
try to complete somehow on downwind, with
his head down in the cockpit.

But the objective should be, over time, to shrink
the circuit, so that if the engine fails, you are
NOT power-dependent - you can glide to the
runway.

A friend of mine lost engine power turning base.

Thankfully he was not flying one of the HUGE
circuits that are so popular today - he just landed
on the runway.

I know, at a towered airport, ATC will try to make
you fly a 5 mile final. If you can, suggest a 360
on downwind, abeam the numbers.

[iflyforpie]

By round I do mean racetrack.

Mine are climb straight out to 500 (or a bit higher if in a lethargic aircraft), shallow turn (crosswind) to downwind but reaching altitude before entering it (for traffic), fly a parallel downwind. Descending turn to about 1/4 mile final (if at all) from abeam the threshold.

The thing I hate about square circuits is first of all, they aren't square unless you snap into a knife edge turn at each corner.

And if you have definite straight crosswind and base legs (corrected for drift) and 30 degree bank turns, the circuit either winds up too large (try a forced from late downwind), or people wind up overshooting final. Then it is drag it in with lots of power (no configuration changes below 500ft right?) which further aggravates approach speed.


Visibility in a Cessna is not a big deal since the wings are on top and the turns are shallow enough that there is good visibility for low wings as well. Also being closer in allows you to scan final from above just as you are ending the downwind.

Remember AuxBatOn, the planes we fly turn slower, but they also travel slower, and therefore don't require high bank angles to do a small radius turn (at 30 degrees my turn radius is about 1000 feet). A pin prick isn't going to be a canopy full of airplane in 30 seconds.

I can do a curved approach with no power or trim changes from late downwind to final using rate of turn and flaps to control approach angle.

I think this would be easier for students to do since it doesn't require power or trim changes and it teaches them forced approach techniques as well.

[iflyforpie]

But the objective should be, over time, to shrink
the circuit, so that if the engine fails, you are
NOT power-dependent - you can glide to the
runway.

Another reason why I do circuits like I do. You should be able to make the field (or at least the general area of it) without power at any point in the circuit from crosswind to final.

One guy I checked out not only couldn't make the runway from late downwind, but none of the 54 fairways surrounding the airport either.

[AuxBatOn]

Remember AuxBatOn, the planes we fly turn slower, but they also travel slower, and therefore don't require high bank angles to do a small radius turn (at 30 degrees my turn radius is about 1000 feet). A pin prick isn't going to be a canopy full of airplane in 30 seconds.

The issue isn't the radius, but the time you spend belly up to potential incoming traffic. Roll out a second (litterally) to look out then keep on turning.

1000 ft radius means that in calm winds, you'll be 2000 ft abeam the runway. You can't aford to roll out for even 1 or 2 seconds??? (lets assume 80 kts, it adds 300-500 ft to your distance from the runway). Again, I think it depends on the type you fly.

[iflyforpie]

My circuits are about 1/2 mile, so I am actually doing a much shallower turn than 30 degrees. I am also scanning as I turn.

It is quite unlikely that a plane is going to sneak up to me NORDO in the last 20 degrees of my turn. In most cases aircraft cross midfield before joining at uncontrolled aerodromes (ATF).

[MichaelP]

I see nothing in the original question about the size of the circuit!
I think everyone would agree that we should, except on the initial climb out, at all other times be able to glide to the runway in the event of an engine failure.
The long straight in approach is not a function of flying a rectangular circuit... (I think a 'square' circuit would mean being out of gliding range downwind).

But let's go back to training... A student needs the calm of the straight and level downwind to do checks and radio call and for the instructor to impart information as required.
I have done low level fast circuits with students to speed them up and this is good practice and fun, but we can't do it when there's four in the circuit, several queued up at the holding point, and several joining from elsewhere.

The rectangular circuit is not everyone's ideal but it is the best compromise.

I still spend a lot of time flying with little or no forward vision, I sit in the back of the Citabria or the Decathlon.
In the Citabria we have to do different things to accommodate everyone else and so the rectangular circuit has a few modifications in its closeness and altitude.

The curved approach from base works really well and does not affect anyone else's circuit.

I agree with Hedley with respect to the long straight in finals, but I do not know the answer to the low and slow, power on approaches some instructors insist on teaching.
Sometimes ATC says "I'll call your base turn to allow for departures". If no-one is behind I slow down, right down, and stay high until the runway is made.
With people behind, I still stay high until I know I can get in, I like my options.

[Spokes]

Headly,

If vis is a problem, can't you just fly final inverted?

[Panama Jack]

How about . . . "Law of Primacy" as an arguement? Unlearning incorrect procedures (or bad habits) is always more difficult than learning the correct procedures in the beginning.

For those student pilots aspiring to airline wings and gold braid, it may be interesting to note that Boeing and Airbus SOP's (including that of the A340 I fly) are for square visual traffic patterns are the method used. In the airline world there isn't all that much room for individual technique.

[mashowski]

I prefer rounded circuits but level my wings briskly on base for a traffic scan, and so others can see me. My plane is very small.
Speaking of square circuits, how is this for square; the Katana trainers at my home field are often flying downwind at 2 to 2 1/2 miles parallel offset from the runway. I know the exact distance because I measured it with the odometer on my car when I drive under them on the way to the airport.
The instructor said this is because of the slow climb rate, I said turn crosswind at 800' feet or so and keep your downwind 1 mile or less. He said that you MUST turn crosswind at 500' because those are the rules. Sigh...

[Hedley]

Katana trainers at my home field are often flying downwind at 2 to 2 1/2 miles parallel offset from the runway

Is this for the purpose of logging cross-country time?

He said that you MUST turn crosswind at 500' because those are the rules

Er, no. There is no Canadian Aviation Regulation which requires that.

Sometimes, I might crosswind at 250 feet, and level off at downwind
at 500 feet. In fact, under some circumstances, this IS legally
required by the Canadian Aviation Regulations - can anyone think
of the circumstances?

[iflyforpie]

There is no rule to turn a crosswind at 500 feet. If you are doing circuits in Kelowna, Penticton, or Vernon where the circuit is more than 1000 feet above the aerodrome and you will either be joining downwind too low or extending the crosswind/base legs out too far by turning at 500.



And as far as using a square circuit for primacy for going into the airlines? Well, airliners don't usually do circuits. Visual approaches are specific instructions on a plate, not really open to interpretation. If a pilot cannot follow the landmarks/navaids and the arrows on the plate telling him or her where to go by the time he or she is flying an airliner there is something wrong.

For 727 training circuits at YLW it was square at one end, rounded at the other, to allow for terrain and so the circuit wouldn't be ridiculously big (downwind was still over 4 miles from the field).

[Panama Jack]

Well, geez gosh iflyforpie.

I am simply quoting it out of my manual Airbus A340 FCOM 3.03.20 Pg 3 (Rev 14). It's actually a cool little diagram.

Yes, I know we don't do these things very often (I personally prefer radar vectors to the ILS-DME regardless of the weather), but if we do a visual circuit (rarely), then this is the procedure the Company expects us to do it.

I remember this being the square patterns being the trained technique also on the A320, the 737, the DHC-8, and the Citation. If you get the book, Fly the Wing, it is the same profile they show for visual patterns.

The reason for my arguement is that, since Instructors are professionals and provide a service, that one reason for square patterns is to set up students for an industry-standard way of flying.

Yes, curved patterns have their purpose too, depending on terrain and conditions, and in my opinion a skilled pilot should be proficient on both maneuvers. Flying a curved pattern is a great building block towards flying circling approaches . . . but then again, many airlines prohibit circling approaches.

Hedley, back when I was flying GA airplanes, in the US I was taught to climb straight out to 700 or 800 feet prior to turning cross wind. The idea was to be level at Traffic Pattern Altitude before turning down-wind (you didn't want to be climbing or descending in the downwind leg-- where arriving traffic was also joining).

It wasn't until Canada that my instructor insisted that I must turn crosswind at 500'. I never understood the logic and never felt entirely comfortable with it.

[KnownIce]

Sometimes, I might crosswind at 250 feet, and level off at downwind
at 500 feet. In fact, under some circumstances, this IS legally
required by the Canadian Aviation Regulations - can anyone think
of the circumstances?

Are you asking us for an instance where it is legally required or for an instance where you might do it?

re 1: SVFR?

re 2: any time TC is not watching and you want to look awesome?

[iflyforpie]

I guess it is a different procedure in the 747 'cause when I flew to Honolulu, we did a constant turn from downwind to final over Barber's Point

[Hedley]

The funny thing is that Transport, which used to be
the fiercest advocate of square circuits (anyone else
remember the "MOT Rectangle"?) is now, guess
what, pushing the circling approach as a technique
for the most often-flunked maneuver on the flight
tests (the forced approach).

Current doctrine is to overfly the runway threshold
in the direction of landing at say 1600 AGL, which
is calculated as:

(2 minutes x 700 fpm) + 200 feet fudge

assuming that you descend at 700 fpm with
the throttle all the way back, and you do a
continuous, gentle, rate one turn all the way
around, descending in a circle, to touch down.

Apparently (and amazingly) CPL candidates are
also flunking in droves the new PFL on downwind (!!)
which you might think would be a good candidate
for this circling-descent technique.

re: downwind at 500 AGL

re 1: SVFR?

Close. Try controlled airspace - where you must be
500 feet vertically from cloud - and the cloud is at
1000 AGL. Better be doing your circuits with only
500 on downwind, or you ARE contravening CAR
602.114(c):

602.114 No person shall operate an aircraft in VFR flight within controlled airspace unless

(c) the distance of the aircraft from cloud is not less than 500 feet vertically and one mile horizontally

http://www.tc.gc.ca/CivilAviation/Regse ... tm#602_114

re 2: any time TC is not watching and you want to look awesome?

Heh. TC can come out and watch all they want -
there is nothing illegal about a 500 AGL downwind.

When I'm in an underpowered aircraft in hot wx,
rather than wasting the student's time, and getting
'way out of gliding distance from the runway, I
will frequently do circuits at 500 AGL so that the
student gets more landings per hour.

Why do circuits at 1,000 AGL? If you wanted to,
you could climb to 10,000 AGL on downwind
every circuit, too. But I don't think it would be
a good use of the student's hard-earned money.