FAR 91.205(d)

NealRomeoGolf

NealRomeoGolf

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Here is a fun thought experiment (and real life example of my plane) with these new electric gizmos we have available.

My plane has a vacuum driven gyro attitude indicator, an electric attitude indicator with a slip-skid ball, and a G5 installed as an HSI.

IFR rules state you must have a rate of turn indicator unless you have 3 attitude indicators (it references 121.305(j) for setup).

My plane does not have a rate of turn indicator. The HSI can revert to an AI with a rate of turn indicator if I choose to.

Is my plane IFR legal, assuming I meet all other subsections of 91.205(d)? Does the fact that my third usable attitude indicator as discussed in 91.205(d)(3)(i) is not always displayed disqualify me from being IFR legal?

Discuss.
 
Are you saying dual G5’s with a vacuum AI in the TC spot? If not, what’s the primary electric AI you were mentioning?
 
Radar Contact said:
Are you saying dual G5’s with a vacuum AI in the TC spot? If not, what’s the primary electric AI you were mentioning?
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Nope. Only a single G5 installed as an HSI. Above the G5 is a vacuum driven AI. To the far left (two holes over - by the window) is an electric AI.
 
Here is a terrible picture of the panel for reference. I am trying to get ready for IFR training and need to be legal.

lance panel.jpg
 
So what do you have to indicate a standard rate turn? I understand the G5 can display that, but I don't think it would normally in its HSI mode?

I would think those three would count legally, but I'd sure want a rate of turn display of some kind. You spend a lot of time making standard rate turns.
 
NealRomeoGolf said:
Nope. Only a single G5 installed as an HSI. Above the G5 is a vacuum driven AI. To the far left (two holes over - by the window) is an electric AI.
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Gotcha. I’m GUESSING legal. It doesn’t say in 91.205 that you can’t toggle to it. :) Of course I’m an optimist.
 
Jim K said:
So what do you have to indicate a standard rate turn? I understand the G5 can display that, but I don't think it would normally in its HSI mode?

I would think those three would count legally, but I'd sure want a rate of turn display of some kind. You spend a lot of time making standard rate turns.
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Yes, this poses a problem. I dunno what you do then.
 
Radar Contact said:
First 2 digits of your TAS plus 5 is your bank for standard rate. Real world, if you’re hand flying at your speeds, 20 ish degrees of bank and call it a day. :)
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I saw someone else post something similar - 15% of TAS as your bank. At cruise for me that's about 23 degrees. What you said...
 
Radar Contact said:
First 2 digits of your TAS plus 5 is your bank for standard rate. Real world, if you’re hand flying at your speeds, 20 ish degrees of bank and call it a day. :)
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I would've said 10%, but thats because I spend a lot of time at 90, which breaks your formula lol. But that's what you do if your tc goes tu.

I will say that in my experience the ai lacks enough precision to replace the tc. 15 degrees is awful hard to tell from 11 or 19, and if you're not coordinated its worse. Probably doesn't matter in the real world, but it'd make timed turns harder. If you're not at a normal speed (like when mdw tower tells you to keep your speed up), then you're doing math, which I am literally incapable of while flying. I can barely add the 30 degrees to do a teardrop hold entry.

That said I haven't tried doing timed turns without the tc, I guess on the theory compound failures are rare. Might be no big deal. I'd be surprised though if you can find a CFII or dpe that will accept no tc. I'm interested to see what you find out.
 
Do not think I have ever seen an electronic HSI without a rate of turn arc across the top.

This is how the Aspen PFD dispays the ROT. Others I have seen are pretty much identical.

Screenshot_20200901-231129_Adobe Acrobat.jpg
 
Looks like the G5 puts it under the "Ball" and calls it a "Turn Rate Indicator"

Screenshot_20200901-231617_Adobe Acrobat.jpg
 
The g5 stc does not allow for removal of both the DG and turn rate indicator as it appears happened here. It’s one or the other.
 
Salty said:
The g5 stc does not allow for removal of both the DG and turn rate indicator as it appears happened here. It’s one or the other.
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What do you think of the AC I posted? Sure seems to cover the missing TC.
 
Not a legal expert, but years before the proliferation of electronic gyro displays (G5, Aspen, etc.), owners were replacing turn coordinators with electric powered AIs, that also had a slip-skid ball, like Castleberry, MidContinent, and so on, per the mentioned AC91-75. These units had battery backup, therefore providing redundancy even if the primary AI was electric.
 
Does being able to fly a "standard rate" turn really matter anymore in practical flying? I'd argue that it does not (I understand the OP is in training, so it's a different answer for him). Any close approximation will work for real flying.

A standard rate turn is only really necessary if you're using it to make a timed turn due to a DG failure and have no other instruments to tell you your direction. In almost all other situations, I can't see it mattering - use the estimate above and it will work good enough to get you turned in a reasonable amount of time, but not too quick that it's a steep turn. Even if all you have is an AI and a compass, you can still make decent turns to headings using the UNOS method, without any timing. But realistically, in that situation I'm telling ATC about my problem and will start flying GPS ground track instead of heading.

Heck, above about 200 ktas, a standard rate turn requires more than 30 degrees of bank, so almost nobody flies standard rate turns at those airspeeds.
 
RussR said:
Does being able to fly a "standard rate" turn really matter anymore in practical flying? I'd argue that it does not (I understand the OP is in training, so it's a different answer for him). Any close approximation will work for real flying.
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That is exactly what the AC @NealRomeoGolf referenced says:

5. RATIONALE FOR CHANGE.
a. Substituting a second attitude indicator (with a power source independent from the primary attitude indicator) for the rate-of-turn indicator will provide an increased level of safety. It will replace a gyro that only indicates direction and rate of turn with one instrument that presents turn direction, bank angle, and pitch attitude information. Also, a second attitude indicator will be less confusing during partial panel operations because it presents pitch and bank information in the same manner as the primary attitude indicator. The pilot’s scan and instrument interpretation during partial panel operations becomes easier because pilots will still be able to rely on an attitude indicator for pitch and bank reference just as they did during full panel operations. Recognition time that a failure condition exists will be equivalent to current system configurations.

b. Replacing the rate-of-turn indicator will mean losing an easy reference for standard rate turns. However, in today’s air traffic control system, there is little need for precisely measured standard rate turns or timed turns based on standard rate. Maintaining a given bank angle on the attitude indicator for a given speed will result in a standard rate turn. Pilots using this AC to substitute an attitude indicator for their rate-of-turn indicator are encouraged to know the bank angle needed for a standard rate turn. NOTE: The FAA preamble language for the 1970 amendment to section 91.33, re-codified to section 91.205, states: “[T]he FAA believes, and all other commenters apparently agree … the rate-of-turn indicator is no longer as useful as an instrument which gives both horizontal and vertical attitude information.”​
 
Timed turns are my preferred way to deal with partial-panel situations, at least in a "steam-gauge" airplane.
 
Jim Carpenter said:
Not a legal expert, but years before the proliferation of electronic gyro displays (G5, Aspen, etc.), owners were replacing turn coordinators with electric powered AIs, that also had a slip-skid ball, like Castleberry, MidContinent, and so on, per the mentioned AC91-75. These units had battery backup, therefore providing redundancy even if the primary AI was electric.
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That's what I have - a Castleberry. Sounds like I'm legal.
 
Palmpilot said:
Timed turns are my preferred way to deal with partial-panel situations, at least in a "steam-gauge" airplane.
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Sure. In the OP’s case, he’ll realistically never be to a level that timed turns matter. If he lost the vacuum pump(s), then the alternator(s), then the battery(s), he’s still have at least one AI with 4 hours to get him to VMC.
 
midlifeflyer said:
Gave up both timed and compass turns in favor of GPS track information.
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Right, because there's never been a GPS outage. I take it your favorite color is magenta.

No one flies a hold or a procedure turn anymore, just vectors to final and LPV on home? Must be nice
 
aftCG said:
Right, because there's never been a GPS outage. I take it your favorite color is magenta.

No one flies a hold or a procedure turn anymore, just vectors to final and LPV on home? Must be nice
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Thanks. It is so nice to see someone with the intelligence necessary to make big biased assumptions based on extremely little knowledge. Let's see if I can help:

I am quite capable of flying standard rate timed turns. They are very easy to do, although you are welcome to make fun of whatever in my brain makes it difficult for me to subtract an assigned heading of 060 from a current heading of 330. So I'm actually one of those strange ones who prefers compass turns to timed ones. But since neither method is as as accurate as a functioning HSI or DG or an current readout of GPS direction I can match with a normal rollout, yes, I prefer them.

My favorite color is orange.

I fly both holds and procedure turns with some regularity. Even give them on IPCs and instrument checkouts, along with less-than-common GPS tasks in a attempt to test whether my flight client understands how to best use the newfangled stuff while understanding the limitations and having the skills to cope if it fails.

And yes, new, quality equipment is nice to fly.
 
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holds are TLAR'd in the real world, good bad or indifferent. No gyro vectors are TLAR'd as well. Std rate turns thus become less relevant. Reading through the ACS it looks like they've acknowledged the change in environment (allows the use of MFD graphical depiction to maintain x-track in holds for instance). Even by the FAA's own stipulation, two AIs in lieu of a TC and AI is a safer and an encouraged setup. The subtext is that in the event of a PFD or electrical out degrade in IMC, ATC is generally tolerant of track deviations so long as you're an emergency, which you would be.

We've made changes to undergraduate training in the USAF in order to keep with changes to the operating environment. No more fix-to-fix [FAA won't allow them], no more RMI only approaches [mil equivalent to unslaved ADF stand-alone presentation], among others. There's always the argument to be made about the degree to which we "dilute" competency by shifting requirements, but I think that can easily become unnuanced and rank ancestor worship. Std rate turns are not a significantly relevant part of present day flying environment. The OP's equipment reflects that and the FAA encourages it. It would be inconsistent imo to chastise him on an IR evaluation for it. In any event, a passing tolerance of 3/4 deflection with the aid of an MFD and digital readout of x-track, I'd say that's already deep into the camp of TLAR anyways, so the issue is moot :D
 
NealRomeoGolf said:
That's what I have - a Castleberry. Sounds like I'm legal.
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FYI: As mentioned above, replacing TIs with AIs has been a common thing for a number of years per the AC you referenced. But considering this a new aircraft to you, you may want to review your records to ensure the installation of your electric AI meets the requirements of the AC and references the AC in the sign off.
 
Bell206 said:
FYI: As mentioned above, replacing TIs with AIs has been a common thing for a number of years per the AC you referenced. But considering this a new aircraft to you, you may want to review your records to ensure the installation of your electric AI meets the requirements of the AC and references the AC in the sign off.
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Castleberry was installed in 2006 and it references AC 91-75 in the install.

It's also when the Loran and ADF were removed. Sometimes it's fun reading through the history. And learning this stuff is very beneficial.
 
Here is the relevant STC information from the installation manual:

upload_2020-9-2_19-38-21.png
 
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