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I know that the turn coordinator has markings that allow you to turn at a particular rate, so you can use the TC and a clock or stopwatch to turn a particular number of degrees. Are you always supposed to turn with the wings on one of these marks, or is that only necessary when you need to use a clock to measure your turn?

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The Turn Coordinator index marks denote a standard rate turn. Standard rate is 3 degrees per second, meaning it takes 2 minutes to fly a full circle. It's also called a "2 Minute Turn" or "Rate 1 Turn".

The bank angle required to achieve a standard turn rate varies with true airspeed, and you can estimate it by dividing your TAS by 10, +7. So, at a TAS of 100 kt, a seventeen degree bank angle gives more or less a Rate 1 turn.

Rather than have to estimate the bank angle to use in your head, you just use the Turn Coordinator to tell you when you are at the required bank and save the mental formula for when the Turn Coordinator fails.

Generally, standard rate turns are used for IFR flying, most turns when on instruments being flown at the standard rate. On airplanes with Flight Directors, the FD will command bank angles that provide a standard turn rate at lower speeds, and the autopilot (which just does what it is told by the Flight Director) will turn the airplane at standard rate (at higher speeds and altitudes, turn rates are reduced due to bank angle limitations).

Outside of IFR flying, there isn't really any need to stick precisely to a standard rate turn if you're just blundering around on a nice day. An exception to this might be flying without a directional gyro, and you want make precise turns from one heading to another, and holding the standard rate in the turn allows you to time when to roll out of the turn and be reasonably close.

Timed turns is a skill that pilots taking instrument training have to master for flying "partial panel", where you have no directional gyro and are flying by wet compass only. When the compass is dancing and slewing every which way while turning, it's pretty much useless until you settle into level flight, and a stopwatch can come in handy. Even just counting "one thousand two thousand..." for the period of the turn will get you in the ballpark if you hold the standard turn rate and can count seconds with reasonable accuracy.

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    $\begingroup$ It’s an interesting one concerning IFR flight. In my experience, SOPs for 737s state limiting angle of bank (with the limiter) to 25°. Which actually is a lesser than rate 1 turn for practically all of the flight, including procedural instrument approaches (can be difficult to force deceleration to 180 knots). (Also bank angle limiter turned down to 10° for flight above FL300) $\endgroup$ May 30, 2023 at 11:57
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    $\begingroup$ I should have mentioned that this was for slower speeds. Yes FDs for jets will use much lower turn rates. $\endgroup$
    – John K
    May 30, 2023 at 12:04
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Fly the aircraft however you want to fly the aircraft... if you want a really slow turn, put in a few degrees of bank. If you want to crank it around, roll it to 60 degrees and enjoy the 2 G's. There's a time & a place for each of these, and everything in between.

If you have a need to ("are supposed to") fly a standard rate or a half standard rate turn, then use the marks on the turn coordinator. If that's not required, and usually it isn't, then there's no need to attempt to match that rate.

There are cases when a standard rate turn is desired; an ASR approach comes to mind, which is a little rare these days. There are probably others, beyond timed turns (which is also a valid example).

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  • $\begingroup$ Don’t all published procedural approaches assume standard rate turns, not just ASR? cf. PANS-OPS. $\endgroup$ May 30, 2023 at 11:52
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Are you always supposed to turn with the wings on one of these marks, or is that only necessary when you need to use a clock to measure your turn?

In the VFR context, no one ever feels compelled to limit turns to standard rate, and in practice turns are almost always conducted at a much higher rate.

I have completed a powered pilot's license as well a glider pilot's license in the USA, (private in each case) and I would be willing to bet large amounts of money that my total time engaged in turns at standard rate (or lower) throughout the entire duration of my training, as well as throughout additional flights after completion of training, does not exceed ten minutes.

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