When to turn from crosswind to downwind to base in a circuit?

Question

I was told by my instructor that my circuit spacing is inconsistent. I do not know how to look at the runway and use it to judge when to turn downwind and base. As a result, my base leg is sometime high and sometime low.

How do you determine when to turn at different leg in a circuit?

Answer 1

Like almost everything (aviation or otherwise), this is just something you learn with practice!

I was taught to turn downwind to base when the threshold was between 4 & 5 o'clock (in a RH circuit).

Here's a good graphical representation in a LH circuit.

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At the end of your downwind leg, when you once again reach a 45° angle to the runway, do a medium 30° turn onto base.

_{(Image & Text source: http://www.ppl-flight-training.com/circuits-briefing.html)}

As for the base leg being high or low - it shouldn't be a problem. You can easily correct this.

Too high:reduce power 50-100rpm, lower the nose slightly to maintain speed
Too low: Increase the power slightly.

As was commented, it is also worth considering the wind direction before you depart. On a perfect day, the wind will be directly down the runway towards you on final. Consider the effect of this on your circuit? I find it useful to draw the circuit, and an arrow with the wind direction. Then consider when to turn early/late as appropriate.

Finally remember the GOLDEN rule: You can ALWAYS go around. (Assuming you have a fan up front!)

Answer 2

What it entails is developing the "sight picture" in your mind of what the runway looks like from the air when you are 45 degrees off the threshold at the nominal turn point.

It's my own personal opinion, but I think that for a brand new student the best method is to start off using a predetermined landmark on the ground to locate yourself precisely for the turn, and concentrate on internalizing the runway sight picture you see from that location.

As quickly as you can, you start to replace dependence on the landmark with judging the sight picture of the runway, until you can ignore the landmark but get reasonably close to it by runway eyeballing alone.

You must not develop a reliance on landmarks at your local airport as a crutch, because as soon as you go to another airport you're back to square one, but you need a starting point somehow. You will need to be able to locate your turn reasonably well without depending on ground land marks before you can solo, so try to develop the correct sense as fast as possible.

One way to help with judging the 45 degree aspect of a runway with a well defined threshold edge is to study the apparent angles of the runway edge closest to you and an imaginary line extending along the threshold's edge, relative to the horizon. They should form a "level" V as shown below.

Answer 3

At least you've eliminated fast or slow, which (because energy is proportional to the square of your speed) makes it much more complicated. Trimming to approach speed after turning to base makes it a question of high (reduce power/add flap) or low (add power).

Because of wind, landing patterns will never be perfect, but improvements can be made to make them more consistent. It is the distance from the runway on your downwind that needs to be worked on first. Landmarks and old saws such as "half way up the spar" help train your eye, as well as your speed and AGL.

Landing can be done in stages (example Cessna 172):

1. Enter downwind at consistent speed (around 100 knots), AGL, and distance from runway.
2. At a chosen point along the runway reduce power and drop to approach speed. Add flaps 10. Work on establishing your best spot to do this.
3. Turn to base and trim to 65 knots, look high or low?
4. Use power and/or flaps to adjust rate of descent to set up your final.

If you do this consistently, it should make your approaches much easier. "Good patterns make good landings".