Why are clearing turns supposed to be shallow bank?

Question

During my CFI training, my instructor relayed a story in which he had a mid-air collision while teaching (how to teach) clearing turns to two other CFI applicants. The other aircraft was underneath them and may have climbed into them. No one in his aircraft saw the other aircraft. They did not even know they had hit another aircraft until they heard the report of another crash nearby.

My question is (in the title) why is a shallow banked clearing turn considered better than a steep one? I feel like I get a much better view of everything (above, level, and below) in the direction of the turn if it is a steeper turn. The downside is that I'm changing direction more quickly...but I think seeing other aircraft wins over that. Furthermore, large, rocking wing movements tend to make the aircraft I am in easier to see as opposed to gentle, shallow turns.

Answer 1

Clearing turns solve two problems: seeing other aircraft and helping them to see you.

Banking will make you more visible to other aircraft, who may not have noticed you before. A lower bank angle (and thus turn rate) gives them more time to see and avoid you. But a very low bank angle also doesn’t make you as visible in the first place, so it’s a balance.

I was taught 20-30°, and I’ve never had anyone say later that was too much or too little. I also don’t have to worry much about losing altitude at moderate bank, so I can keep my eyes outside scanning for traffic—not checking the altimeter every few seconds like during “real” maneuvers.

Answer 2

Generally because one is actively looking out the window for other aircraft, not at the instruments or the horizon. This is a distraction that places the less experienced pilot (doing a clearing turn before practicing a maneuver) farther away from the safety of "straight and level". Much better to mistakenly turn a shallow turn into a steeper turn than to turn a steeper turn into an extreme bank.

However, too shallow a bank takes more time, and taking too long increases the chance of another plane entering the practice area undetected.

With two people (pilot and instructor), the turn can be fairly aggressive (more than 30 degrees), itself a practice maneuver, but an inexperienced pilot alone could quickly get into trouble by overbanking.

A good way to do a clearing turn is to slow down below cruise speed, which reduces the turn radius:

r = V$^2$/g x tangent(bank angle)

but we must be aware that the bank angle increases stall speed by:

turning stall speed = stall speed x square root(load factor)

Load factor in turn is calculated as:

1/cosine(bank angle)

Answer 3

That is a matter of personal preference. The FAA's Airplane Flying Handbook only states: "Pilots should always clear the area with two 90° clearing turns looking to the left and the right, as well as above and below the airplane." This article from Flying Magazine, "Clearing Turn Basics", also does not mention bank angles in clearing turns. Personally, I make shallow clearing turns, and then decide if I want to practice steep turns. Someone flying a biplane like a Pitts Special, for example, might have a different opinion.