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I was reading my Aircraft general knowledge book, and noticed something peculiar that was written.

The book described that the turn and slip indicator works as a back-up in case of a malfunctioning artificial horizon / attitude indicator.

From my perspective this seems strange to me because of the following:

  • An attitude indicator shows pitch information.
  • A turn and slip indicator shows: "no pitch information".

Therefore the usage of a Turn and slip indicator as a back-up for the attitude indicator is not logical from my (probably narrow) point-of-view.

My Questions:

Is it true that a Turn and slip indicator is a valid back-up for the attitude indicator?

To what extent is a turn and slip indicator a back-up for the attitude indicator?

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Is it true that a Turn and slip indicator is a valid back-up for the attitude indicator?

Partially, but it would need to be used in conjunction with one or more other instruments if the Artificial Horizon is inoperable.

  • Change in the DI and/or compass will indicate a turn.
  • Change in altitude on an altimeter will indicate a climb or descent. Usefulness of the VSI is limited in this sense.

To what extent is a turn and slip indicator a back-up for the attitude indicator?

With every one of the instruments on an aircraft there are backups. Sometimes this may be an entire second stack (eg Radio may have a complete second system, AoA sensors may be duplicated) other times you need to use a combination of more than one other instrument. In the case of a Turn/Slip indicator the latter is true. You use a combination of DI, VSI, altimeter as described above to get a picture of your attitude when the Attitude Indicator itself is inoperable

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The most common killer of inadequately trained pilots who fly into clouds is a spiral dive, caused by the aircraft entering a steep bank without the pilot realizing it or understanding the direction of turn. Eventually the aircraft is destroyed due overspeed or excess G-load.

A magnetic compass is generally useless whenever an aircraft is banked and turning, so forget about trying to use that to keep the wings level, except in some very particular circumstances. Hence the importance of a turn rate indicator or attitude indicator.

Many pilots have flown sailplanes in clouds with a turn rate indicator as the only gyroscopic instrument present. Charles Lindbergh did a great deal of cloud-flying during his 1927 Atlantic crossing, and a turn rate indicator was his only gyroscopic instrument. So the general answer to your question is "yes, a turn rate indicator is a valid backup for an attitude indicator". But read on for more--

The turn rate indicator can tell you which direction you are banked, and can give you a clue as to how steeply you are banked. However, with no attitude indicator, it can be challenging to manage the aircraft's pitch attitude. Lots of practice in safe conditions is needed. Flying with the turn rate indicator as the only available gyroscopic instrument is called "partial panel" flying, and pilots practice this in safe conditions outside of the clouds by covering up all the other gyroscopic instruments and donning a blind flying hood to block the view out the windows.

So how is pitch attitude controlled in "partial panel" flying?

If the airspeed is changing, that is a valuable cue to pitch attitude. Inside a strong updraft or downdraft, you can't rely on the vertical speed indicator, or changes in the altimeter reading, to tell you the aircraft's pitch attitude. Therefore you could argue that the airspeed indicator and the turn rate indicator are best pair of instruments to serve as a backup for attitude indicator, if you can only choose two and need to stay right-side-up in turbulence. Of course the heading indicator also gives some clue of the turn rate and therefore the bank angle, and it also gives you heading, so that's a very nice instrument to have as well. In some conditions, the heading indicator plus the airspeed indicator might be the best choice for a pair of instruments to stand in for the attitude indicator.

The relationship between airspeed, pitch attitude, and vertical speed will depend on aircraft performance as well as updrafts and downdrafts. A pilot flying a fast jet might have better results relying primarily on the altimeter for control of pitch attitude even in significant turbulence, while a pilot flying a light plane in the same conditions might have better results relying primarily on the airspeed indicator for control of pitch attitude.

Don't forget that the airspeed indicator can fail due to ice in the pitot tube, unless the pitot tube is heated. That would be a bad thing to happen if your life depended on it.

If you are trying to use ONLY the turn rate indicator (or ONLY the heading indicator) to substitute for the attitude indicator-- i.e. if you are trying to fly using no pitch information of any kind, not even from the airspeed indicator or altimeter-- then you had better be flying a very pitch-stable, well-trimmed aircraft. This has been done, but it has not always ended well.

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  • $\begingroup$ Future edit: last paragraph could be modified to make it clear I am talking about flying in clouds, not VMC! $\endgroup$ – quiet flyer Nov 29 '19 at 20:17
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It's called "partial panel" flying and if you ever advance to a commercial license, you will have to demonstrate proficiency at partial panel during training and on the commercial check ride. On my commercial check flight in the late 70s I even had to demonstrate recovery from an unusual attitude (diving spiral) on partial panel under the hood because my examiner thought it would be fun. Not sure they still make you do that these days.

Partial panel is maintaining controlled flight in IMC with only one gyro instrument, the turn and slip/turn coordinator, and pitot static instruments (you may be allowed to use the Directinal Gyro). In a light aircraft the gyro horizon and Directional Gyro are normally vacuum operated and the turn and slip is electric. So if the vacuum pump goes south, there you are with only turn and slip and pitot/static instruments (which is why the turn indicator is electric; to have an independent energy source).

In partial panel, the turn indicator is your primary roll source, airspeed + altimeter is your primary pitch source, and heading control is using compass and (assuming no Directional Gyro) stopwatch.

Because if its lagging indication, VSI is useless in partial panel work as a primary pitch source except as an indication of the longer term condition you are in, going level, up or down.

So, it's roll inputs to keep the turn indicator/coordinator centered, and pitch inputs to keep airspeed and altitude constant, compass to know your heading while in level flight, and stopwatch to change heading by timing the duration of the standard rate turn. When you roll out of the timed turn, more or less in the ballpark on heading, you can then make very fine heading adjustments on the compass alone in little baby steps.

It takes finesse (make a small input and wait, make a small input and wait) and good skill at exploiting trim to fly well on partial panel, although once you get good at it, in a way it's easier because you have less instruments to scan.

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I openend a flight sim (X Plane 10) to check for similarities and differences between the turn and slip indicator and the attitude indicator.

Horizontal flight If the airplane is horizontal then the airplane symbol on both instruments: turn and slip indicator and attitude indicator display similar data.

Soft turn to the left In a soft turn to the left, the airplane symbol on turn and slip indicator is tilted to the left. It almost reaches it's maximum. The airplane symbol on the attitude indicator tends to the "ground" on the left side.

Sharp turn to the left In a sharp turn to the left, the airplane symbol on turn and slip indicator is also tilted to the left. But, it reaches it's maximum. The airplane symbol on the attitude indicator reaches the first white line on "ground" on the left side.

Almost putting the airplane vertically If the airplane is almost vertically, then the airplane symbol on turn and slip indicator is also tilted to the left. It doesn't deviate more then the maximum. The airplane symbol on the attitude indicator reaches the second white line on "ground" on the left side.

Conclusion: the turn and slip indicator and the attitude indicator show more or less the same angle on the roll axis. The differences are: turn and slip indicator is limited to a specific angle, the attitude indicator works beyond this angle.

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  • $\begingroup$ I really don't see how this answers your own question at all. You've mentioned nothing at all about pitch, or how to use other instruments to back up a failed AH. $\endgroup$ – Jamiec Dec 5 '19 at 14:01
  • $\begingroup$ I guess I was asking the wrong question in the first place. I just wanted to see the difference and similarities between those two instruments... my bad. Anyway, your answer is the best answer to the question. I'll mark it as the best answer. $\endgroup$ – Julian Dec 5 '19 at 14:04

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