What is the standard rate of turn for heavy aircraft?

Question

I have heard and read many times that for "heavy aircraft", they use a standard rate of turn which is 1.5° per second (4 minute turn), but I have never found an official source which addresses this. Although... I'm actually not even sure where the normal 3° per second (2 minute) standard rate turn is defined either.

The wikipedia entry on ROT (Aviation) says:

Light aircraft are equipped with 2-minute turn indicators while heavy aircraft are equipped with 4-minute turn indicators.

I don't see why "heavy" would have anything to with turning rate, but airspeed certainly does. So, I'm wondering if this is true, or just something they think is true because airplanes often use half-rate turns at airspeeds above 250 knots and bank limiting prevents them from making a standard rate turn at airspeeds above ≈ 200 knots?

Answer 1

I'm only able to find the following about bank angles, which specifically refers to turns while in a holding pattern:

AIM 5-3-86.(b):

(b) Make all turns during entry and while holding at:

(1) 3 degrees per second; or

(2) 30 degree bank angle; or

(3) 25 degree bank provided a flight director system is used.

NOTE-
Use whichever requires the least bank angle.

This is also in the Instrument Procedures Handbook which under *High Performance Holding on page 3-25 says that a flight director has a bank angle limit of 25 degrees.

If we use the above guidelines, then a flight director will use 3 degrees per second or 25 degrees of bank, whichever is less. My calculations give us the following bank angles and associated rate of turns¹:

        Standard Rate      Actual        Rate
TAS      Bank Angle      Bank Angle     of turn
80         13.17           13.17         3.00
120        19.34           19.34         3.00
160        25.08           25.00         2.99
200        30.33           25.00         2.39
240        35.07           25.00         1.99
280        39.31           25.00         1.71
320        43.10           25.00         1.49
360        46.48           25.00         1.33
400        49.48           25.00         1.20
440        52.15           25.00         1.09
480        54.54           25.00         1.00

As you can see, a jet travelling at 480 Knots TAS (not uncommon at altitude) would require almost a 55 degree bank angle to make a standard rate turn, which would be an amount considered by almost anyone as excessive.

When limited to 25 degrees of bank, this would result in a rate of turn of 1 degree per second (or a 6 minute turn). Anything over 160 Knots TAS would be less than a standard rate turn, and once past 320 Knots TAS it wouldn't even be a 1/2 standard rate turn.

As far as the 1/2 Standard Rate, they often use the 1/2 BANK autopilot mode at high altitudes. This would result in a rate of turn approximately halved, so a 360 degree turn would take 12 minute at the same 480 Knots TAS. ATC expects the normal bank in the terminal environment though, so it isn't used at lower altitudes.

As others have said, transport category jets don't even have a rate of turn indicator (it isn't required by 14 CFR 25 if you have a third attitude indicator) and they simply fly bank angles. Normal hand flying is limited to 30 degrees, which would allow a standard rate turn at a slightly higher airspeed, but then starts to taper off just the same.

That being said, the Instrument Flying Handbook does include this little tidbit in the section on turn indicators on page 5-21:

The dial of these instruments is marked “2 MIN TURN.” Some turn-and-slip indicators used in faster aircraft are marked “4 MIN TURN.” In either instrument, a standard rate turn is being made whenever the needle aligns with a doghouse. A standard rate turn is 3° per second. In a 2 minute instrument, if the needle is one needle width either side of the center alignment mark, the turn is 3° per second and the turn takes 2 minutes to execute a 360° turn. In a 4 minute instrument, the same turn takes two widths deflection of the needle to achieve 3° per second.

So maybe at some point in the past it was more common (or maybe faster but-not-quite-as-fast-as-todays-jets) but you just don't see that anymore. (It could be where all of the references to 1/2 standard rate turns come from though.)

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¹ Math adapted from the formulas here.

Answer 2

Standard Rate of Turn for Heavy Aircraft?

Standard rate turn is, well, standard. The standard is 3 degrees (of heading change) per second. So a 360 turn takes 2 minutes at the standard turn rate. Didn't say anything about the aircraft ....

Every aircraft type has a specific bank angle at which it is turning at the standard rate. It's all due to the design of the aircraft. Further that bank angle yielding a standard rate of turn changes with airspeed.

2 minute turn indicator

Means "line me up and it will take you 2 minutes to do a 360 turn." This happens to be a standard rate turn, not co-incidentally.

4 minute turn indicator

Means "line me up and it will take you 4 minutes to do a 360 turn." This just happens to be half standard rate. We know this because it takes 4 minutes for a 360. It make the arithmetic simpler than say, a 7 minute turn indicator.

Why bother with one of these, never mind 4 vs 2?

Compass problems? Roll into a standard rate turn and hack a watch. Now you can time yourself to reasonably accurate heading changes.

Why a 4 instead of a 2?

Allow the aircraft to do a timed turn but with less bank.

Huge, lumbering aircraft don't roll so quickly - turn timing is affected. Heavy & huge means for any bank angle it's more of a control issue. And, passenger comfort considerations.

Answer 3

Many airliners, heavy or otherwise, don't even have turn indicators anymore. Airliners don't worry about rate of turn, they just go to a given bank angle, typically 25-30 degrees, and are done with it.

That said, it's true that rate of turn doesn't depend on weight, but heavy aircraft usually fly faster, hence having a slower rate of turn. Pretty much all airliners go too fast to make a 3 minute turn practical unless in the terminal area and slowed down.

Answer 4

Like Ralgha said, larger aircraft with EFIS typically, don't have turn indicators or turn and slip. Best judgment and flight director is use what one would use to make turns. I'd have to dig into my manuals to make sure, but I think that a bank angle for standard rate is calculated up to a certain bank angle (I think less than 30 degrees) for pax comfort. Standard rate at 300kts is going to be a pretty bank angle.

Answer 5

Time for a 360 turn at 30 degree bank angle is TAS/60:

120 knots 2 minutes 180 knots 3 minutes 210 knots 3.5 minutes (airliner, clean) 240 knots 4 minutes ("heavy" airliner clean) 480 knots 8 minutes (airliner in the cruise at altitude)

Times will be slightly longer at 25 degrees. You can't fly a rate one turn in a commercial aircraft these days.