Magnetic Compass a primary bank instrument???

[labbadabba]

Why in the world would the whiskey compass be a primary instrument for anything much less for bank?

With compass turning errors especially when turning East from North I would think that it could lead to some serious SD errors if used as a primary instrument. I've seen this in the Instrument Flying Handbook and have gotten this question wrong on my practice written tests.

The magnetic compass is pretty useless in my mind other than cross-checking your heading indicator. Any idea why the IFR gods deemed this to be a primary bank instrument??

 

[bobmrg]

Page 6-7 in the Instrument Flying Handbook includes the wet compass among the primary bank instruments with the qualifying words "when used in conjunction with the heading indicator." No publication that I can find recommends using it as THE primary bank indicator.

Bob Gardner

 

[MauleSkinner]

You'd be amazed what you can do with the whiskey compass when you understand what it does. At one time, I was able to do a lot with needle, ball, and airspeed sans needle and ball.

IME, a lot of pilots misunderstand it enough that they're really not able to cross check the DG with it, either. There's a certain entertainment value in watching an instrument student correct the DG 10 degrees right, then a couple minutes later correct it 10 degrees left...then right...then left...then....:wink2:

 

[Howard Wilson]

You'd be amazed what you can do with the whiskey compass when you understand what it does. At one time, I was able to do a lot with needle, ball, and airspeed sans needle and ball.}

Yup. Watching which way the ring dips and the rate of it's rotation can keep you right side up, if you know how to interpret it. I've not practiced it enough over the last forty years since that lesson to explain it though. My instructor for that lesson had been a fighter pilot in the Luftwaffe.

 

[MauleSkinner]

I used it whole towing gliders in that milk bottle air that's Maryland summertime...legally VFR, but the only place I could see the ground was behind me.

 

[DMD3.]

The primary bank indicator for level flight is the heading indicator. If the heading indicator has malfunctioned, the magnetic compass would be the primary bank instrument for level flight. The attitude indicator is primary for establishing a turn, and the turn coordinator is primary for maintaining it.

 

[Checkout_my_Six]

Page 6-7 in the Instrument Flying Handbook includes the wet compass among the primary bank instruments with the qualifying words "when used in conjunction with the heading indicator." No publication that I can find recommends using it as THE primary bank indicator.

Bob Gardner

even without vacuum?

 

[coloradobluesky]

If the compass isn't turning, neither are you. When it starts indicate right turn, you turn back left etc Good luck trying to do that! (you're gonna need it)

 

[frfly172]

Learned to fly in the early days before RNAV ,GPS,spent a good bit of time flying the compass. Keep the compass steady ,so is the airplane.

 

[poadeleted20]

If the compass isn't turning, neither are you. When it starts indicate right turn, you turn back left etc

Except that sometimes when it starts to turn right, you need to roll right to stop the turn. The reality is that the mag compass cannot, due to its inherent characteristics, be considered a primary bank instrument, and if you read the IFH, you see that the FAA agrees with tht position. Heading indicator (I.e., one which is gyro stabilized), yes; unstabilized mag compass, no.

 

[dtuuri]

Why in the world would the whiskey compass be a primary instrument for anything much less for bank?

By definition, there's always a "primary" bank instrument. The mag compass is self-powered, so to speak, a rather desirable attribute.

The magnetic compass is pretty useless in my mind other than cross-checking your heading indicator. Any idea why the IFR gods deemed this to be a primary bank instrument??

When your CFI fails your heading indicator, what instrument will tell you a heading change is called for?

dtuuri

 

[jesse]

By definition, there's always a "primary" bank instrument. The mag compass is self-powered, so to speak, a rather desirable attribute.


When your CFI fails your heading indicator, what instrument will tell you a heading change is called for?

dtuuri

Compass, but in reality, course updated a few times a second on a GPS display that most people have these days is a damn good option.

 

[poadeleted20]

Compass, but in reality, course updated a few times a second on a GPS display that most people have these days is a damn good option.

I know several DPE's who will fail you on judgment if you do not use any available GPS (including a handheld) to get good course/track data after losing your HI on the Primary Flight Instrument Inoperative task on the IR ride. And I have yet to see one who simulates a double failure (i.e., vacuum pump and loss of satellites) on that Task - nor have I ever hears of anyone actually simultaneously losing both for real, so I don't feel it's unreasonable to consider whatever GPS you have to be your primary backup for the HI and not worry much about having to revert to mag compass turning skills.

BTW, the fact that you use the mag compass for heading data with the HI out does not mean the mag compass becomes primary for bank in the primary/supporting system upon loss of the HI. From the IFH:

Primary Bank​

When flying in IMC, pilots maintain preplanned or assigned​

headings. With this in mind, the primary instrument for bank​

angle is the heading indicator. Heading changes are displayed​

instantaneously. The heading indicator is the only instrument​

that displays the current magnetic heading, provided that​

it is matched to the magnetic compass with all deviation​

adjustments accounted for.​

​

​

​

[Figure 6-32]​

There are supporting instruments associated with bank as​

well. The turn rate trend indicator shows the pilot when the​

aircraft is changing heading. The magnetic compass is also​

useful for maintaining a heading; however, it is influenced​

by several errors in various phases of flight.

Note that mag compass is not mentioned as primary for bank, only under supporting instruments as "useful for maintaining a heading".

 

[Checkout_my_Six]

wow Ron....you're easy. My guy gives me the DEFCON I treatment....

 

[jesse]

I know several DPE's who will fail you on judgment if you do not use any available GPS (including a handheld) to get good course/track data after losing your HI on the Primary Flight Instrument Inoperative task on the IR ride. And I have yet to see one who simulates a double failure (i.e., vacuum pump and loss of satellites) on that Task - nor have I ever hears of anyone actually simultaneously losing both for real, so I don't feel it's unreasonable to consider whatever GPS you have to be your primary backup for the HI and not worry much about having to revert to mag compass turning skills.

Same. I fail both sometimes during instrument training to ensure they can get by without a GPS incase they don't have one in a future airplane. But most of the failures I don't.

I've also never had an examiner fail both the vacuum system and GPS. I also never fail both on IPCs as long as they fly with both.

 

[TMetzinger]

When I was partial panel (no AI or DG), my primary instrument for keeping the wings level was my TC. My primary instrument for navigation at that time was of course the compass. Even then, I'd be level, then use timed standard rate turns to change headings, and then finally fine tune the heading with the compass.

I tend to think of instrument flying as having two goals - one is basic aircraft attitude control, and it's the most important thing - getting the pitch and bank under control so you don't die - aviate. The second goal is once you have the airplane under control, make it do what you need so that you can get the airplane where it needs to be - navigate. For me the compass is quite important for the second goal, not so much for the first.

 

[dtuuri]

BTW, the fact that you use the mag compass for heading data with the HI out does not mean the mag compass becomes primary for bank in the primary/supporting system upon loss of the HI. From the IFH:

Primary Bank
When flying in IMC, pilots maintain preplanned or assigned
headings. With this in mind, the primary instrument for bank
angle is the heading indicator. Heading changes are displayed
instantaneously. The heading indicator is the only instrument
that displays the current magnetic heading, provided that
it is matched to the magnetic compass with all deviation
adjustments accounted for.
[Figure 6-32]

There are supporting instruments associated with bank as
well. The turn rate trend indicator shows the pilot when the
aircraft is changing heading. The magnetic compass is also
useful for maintaining a heading; however, it is influenced
by several errors in various phases of flight.

Note that mag compass is not mentioned as primary for bank, only under supporting instruments as "useful for maintaining a heading".

I don't know why you'd ignore other IFH statements or how you can even conclude from what you quoted that a magnetic compass can never be a primary bank instrument according to the FAA. Here's more of what the FAA says about the compass:
Chapter 6--

Bank Control
Bank control is controlling the angle made by the wing and
the horizon. After interpreting the bank attitude from the
appropriate instruments, exert the necessary pressures to
move the ailerons and roll the aircraft about the longitudinal
axis. As illustrated in Figure 6-11, these instruments include:
• Attitude indicator
• Heading indicator
• Magnetic compass
• Turn coordinator/turn-and-slip indicator

And on page 5-19--

Heading Indicators
A magnetic compass is a dependable instrument used as a
backup instrument.

The compass is a bank instrument which is used as a backup. It's known in most circles, in fact, as a "standby compass". If the heading indicator is inop and was the primary bank instrument for the phase of the maneuver at hand, it seems pretty obvious the compass substitutes as the primary bank reference.

dtuuri

 

[poadeleted20]

I don't know why you'd ignore other IFH statements or how you can even conclude from what you quoted that a magnetic compass can never be a primary bank instrument according to the FAA. Here's more of what the FAA says about the compass:
Chapter 6--

And on page 5-19--

The compass is a bank instrument which is used as a backup. It's known in most circles, in fact, as a "standby compass". If the heading indicator is inop and was the primary bank instrument for the phase of the maneuver at hand, it seems pretty obvious the compass substitutes as the primary bank reference.

dtuuri

I ignored nothing-- the question was mag compass as primary bank, and all of those agree with the IFH in calling it supporting or backup, not primary.

 

[Checkout_my_Six]

this.....This is how I view it. :wink2:

When I was partial panel (no AI or DG), my primary instrument for keeping the wings level was my TC. My primary instrument for navigation at that time was of course the compass. Even then, I'd be level, then use timed standard rate turns to change headings, and then finally fine tune the heading with the compass.

I tend to think of instrument flying as having two goals - one is basic aircraft attitude control, and it's the most important thing - getting the pitch and bank under control so you don't die - aviate. The second goal is once you have the airplane under control, make it do what you need so that you can get the airplane where it needs to be - navigate. For me the compass is quite important for the second goal, not so much for the first.

 

[dtuuri]

I ignored nothing-- the question was mag compass as primary bank, and all of those agree with the IFH in calling it supporting or backup, not primary.

Once again you're just making stuff up. For those who don't know, a "primary" instrument is a moving target, depending on the task and even the phase of that task. If available, an attitude indicator is primary while transitioning, but then becomes supporting for example. Under the primary/supporting system only pitch, bank and power (not navigation) are defined. There's room for some personal preference as to which instrument at any given time is primary--except when taking an FAA written test. Then, you'd be smart to choose an answer that reflects the personal opinion of the FAA test authors. Here's a sample question from their test bank in the past:

The gyroscopic heading indicator is inoperative. What is the primary bank instrument in unaccelerated straight-and-level flight?
A: Magnetic compass.
B: Attitude indicator.
C: Miniature aircraft of turn coordinator.
​

A “primary” instrument relates to the current objective and is the instrument that measures whether the objective is being met at that instant. If the heading indicator, when it is primary, becomes inoperative, the stand-by compass comes off the bench to substitute as the primary.

dtuuri

 

[labbadabba]

I guess for me from a practical standpoint, if my DG fails, I can check my wet compass to make sure it stays steady. If it starts to move then I can cross-check my AI and Turn Coordinator to see whats going on.

But if my wet compass starts to turn to the right (depending on attitude and direction of flight) I cannot trust it necessarily to tell me that I'm turning right. I guess that's why I'm baffled as to why it would be a primary bank instrument.

It's basically saying, you're turning but I can't tell you for certain which direction you're turning.

 

[MauleSkinner]

It may not be indicating a turn, either...could be an acceleration or deceleration. But if you've got a good handle on your compass errors, you can start to make a determination, or at least figure out where to look next.

 

[labbadabba]

It may not be indicating a turn, either...could be an acceleration or deceleration.

Exactly why I think it's dumb. Yes, a person can get a handle on compass errors but apart from the DG there are already 2 other instruments that can tell you if you're banking and in which direction.

I suppose if someone were to fly a Piper Cub into the clouds this might prove useful be from a practical sense I don't see where this would be plausible.

 

[MauleSkinner]

Exactly why I think it's dumb. Yes, a person can get a handle on compass errors but apart from the DG there are already 2 other instruments that can tell you if you're banking and in which direction.

1. Are the other two instruments powered by the same source, or something different? If it's a power source failure rather than an instrument failure, you may or may not have one or both of the other instruments.

2. If different, how do you determine where the failure is, so you can transition away from the "dead" instruments to the good ones?

There may be times in a well-equipped airplane where you need to understand and follow your compass until you get things figured out. It never ceases to amaze me how many pilots make the wrong choice in which instruments to believe in fail-down scenarios because they don't or can't believe something as basic as a compass.

 

[Captain]

Nobody uses mag compass to SET a bank...ergo, it ain't primary.

 

[labbadabba]

1. Are the other two instruments powered by the same source, or something different? If it's a power source failure rather than an instrument failure, you may or may not have one or both of the other instruments.

In this case the AI is vacuum powered and the turn coordinator is D.C. electric.

2. If different, how do you determine where the failure is, so you can transition away from the "dead" instruments to the good ones?

Assuming I have a dead heading indicator, I could already have a vacuum failure. I would still have my Turn Coordinator which I could use to very clearly see whether or not I'm in a bank. If I had a full vacuum failure in IMC then I would use the compass for navigational purpose only but due to the errors in the compass itself I would be very uncomfortable using this as a primary bank instrument.

To me, if a vacuum failure happens and I lose my DG and AI. My primary bank instrument becomes my turn coordinator (primary) which I confirm the bank/heading change against the movement of the compass (supporting).

 

[dtuuri]

I guess for me from a practical standpoint, if my DG fails, I can check my wet compass to make sure it stays steady. If it starts to move then I can cross-check my AI and Turn Coordinator to see whats going on.

That's not how to use a compass. Your heading is the mean between the average extremes as it swings back and forth.

But if my wet compass starts to turn to the right (depending on attitude and direction of flight) I cannot trust it necessarily to tell me that I'm turning right. I guess that's why I'm baffled as to why it would be a primary bank instrument.

The primary instrument is the one that measures whether you're meeting your objective in either pitch, bank or power. If you're measuring whether or not you are holding a heading, "primary bank" would be a compass, DG or magnetic. If you want to measure whether your wings are level, but don't care if you're in a flat turn, primarily use your attitude indicator. If you want a standard rate of turn, the turn coordinator is the primary reference.

dtuuri

 

[MauleSkinner]

Assuming I have a dead heading indicator, I could already have a vacuum failure. I would still have my Turn Coordinator which I could use to very clearly see whether or not I'm in a bank. If I had a full vacuum failure in IMC then I would use the compass for navigational purpose only but due to the errors in the compass itself I would be very uncomfortable using this as a primary bank instrument.

To me, if a vacuum failure happens and I lose my DG and AI. My primary bank instrument becomes my turn coordinator (primary) which I confirm the bank/heading change against the movement of the compass (supporting).

Define "dead"...failures take many forms, and until you can actually confirm the failure, you're going to want to be able to use all of the tools you have to identify it.

 

[labbadabba]

Well, not to get too semantic here...

My point is, not that the WC is useless, especially when checking for failures in other instruments; but rather that I think it's silly that it's a primary bank instrument. Even if you have a full vacuum failure there are more reliable back-up instruments that more accurately indicate bank.

 

[MauleSkinner]

Well, not to get too semantic here...

My point is, not that the WC is useless, especially when checking for failures in other instruments; but rather that I think it's silly that it's a primary bank instrument. Even if you have a full vacuum failure there are more reliable back-up instruments that more accurately indicate bank.

Remember that a "primary bank instrument" is in reference to a specific condition. DG or compass is primary for bank only in level flight. "Are we wings level? Compass not turning, we are." Or "Are we wings level? Compass is turning, we are not. We now have to transition to the appropriate primary bank instrument for what we want to do," and the compass ceases to be our primary bank instrument until we're back in level flight. Our general goal when straight and level is to fly a heading, and so heading indication naturally becomes primary for bank in that situation, because it tells us whether or not we're meeting our goal.

 

[TMetzinger]

Remember that a "primary bank instrument" is in reference to a specific condition. DG or compass is primary for bank only in level flight. "Are we wings level? Compass not turning, we are." Or "Are we wings level? Compass is turning, we are not. We now have to transition to the appropriate primary bank instrument for what we want to do," and the compass ceases to be our primary bank instrument until we're back in level flight. Our general goal when straight and level is to fly a heading, and so heading indication naturally becomes primary for bank in that situation, because it tells us whether or not we're meeting our goal.

Yes, this is true, and reflects the FAA logic.
Unfortunately unless the plane is on the ground, it's always rolling a little bit if you're in IMC, whether due to air or pilot motion. Which means that when you're in partial panel, you're most likely using the TC to maintain a close approximation of straight and level, and the Mag compass to maintain a close approximation of course flown.

 

[MauleSkinner]

Yes, this is true, and reflects the FAA logic.
Unfortunately unless the plane is on the ground, it's always rolling a little bit if you're in IMC, whether due to air or pilot motion. Which means that when you're in partial panel, you're most likely using the TC to maintain a close approximation of straight and level, and the Mag compass to maintain a close approximation of course flown.

Correct. "Primary" instruments are not the focus of our fixation. We still scan supporting instruments, and primary and supporting roles change with the needs of the moment.

 

[labbadabba]

Thanks guys, my replies were not meant to be a challenge to anyone's knowledge (other than my own). Thank you for crafting thoughtful responses.

 

[kgruber]

The whole concept of "primary and secondary" instruments is an example of the FAA's delusion of instrument training. It serves no purpose other than to fill the agenda of some government fool.

It reminds me of the "new math" heaved on high school students in the 60's that destroyed the joy of mathematics for millions of students.

 

[dtuuri]

The whole concept of "primary and secondary" instruments is an example of the FAA's delusion of instrument training. It serves no purpose other than to fill the agenda of some government fool.

It reminds me of the "new math" heaved on high school students in the 60's that destroyed the joy of mathematics for millions of students.

Speak for yourself, I like it because it's easy, peasy. You simply read whatever instrument gives the information you need at the time. It's hard to go wrong. It works on partial panel too, unlike the more complicated control/performance method which requires an attitude indicator.

dtuuri

 

[kgruber]

Speak for yourself, I like it because it's easy, peasy. You simply read whatever instrument gives the information you need at the time. It's hard to go wrong. It works on partial panel too, unlike the more complicated control/performance method which requires an attitude indicator.

dtuuri

Of course you do. That is what every instrument pilot does. Don't have to rethink the process with nonsense.

 

[MauleSkinner]

Of course you do. That is what every instrument pilot does. Don't have to rethink the process with nonsense.

Unfortunately most instrument students don't have your innate gift of instrument interpretation. They need some sort of "formula" to learn how to read and interpret their scan.

 

[kgruber]

Unfortunately most instrument students don't have your innate gift of instrument interpretation. They need some sort of "formula" to learn how to read and interpret their scan.

You drank the FAA koolaid.

 

[MauleSkinner]

You drank the FAA koolaid.

Of the three brands I'm aware of, the Faa koolaid, Stark's koolaid, and your Nike koolaid, I've found yours to be the least effective.

 

[eetrojan]

Page 6-7 in the Instrument Flying Handbook includes the wet compass among the primary bank instruments with the qualifying words "when used in conjunction with the heading indicator." No publication that I can find recommends using it as THE primary bank indicator.

Bob Gardner

I thought of this thread as I ran across a related test question in preparing for the written.

In particular, one of the FAA questions on the IR knowledge exam says that if the gyroscopic HI goes belly up, the magnetic compass becomes the primary bank instrument in unaccelerated straight-and-level flight: