Reading the whiskey compass

[Ben Jackson]

When you're flying partial panel, to what precision do you read the
mag compass? To the nearest 5 degrees? Estimate to the nearest
degree? How long do you go between readings and rely only on timed
turns?

For that matter, do you ever try to apply values from the correction
card? In IMC or even VMC?

--
Ben Jackson
>
http://www.ben.com/

[Bob Gardner]

Unless you are flying in unnaturally calm conditions, precision with the wet
compass is hard to come by. IMHO compass turns should be eliminated from
instrument training and timed turns emphasized.

In my experience, few pilots pay any attention to the compass correction
card, probably because the cards themselves are usually out of date.

Bob Gardner

"Ben Jackson" > wrote in message
news:3wZ_b.54783$Xp.264494@attbi_s54...
> When you're flying partial panel, to what precision do you read the
> mag compass? To the nearest 5 degrees? Estimate to the nearest
> degree? How long do you go between readings and rely only on timed
> turns?
>
> For that matter, do you ever try to apply values from the correction
> card? In IMC or even VMC?
>
> --
> Ben Jackson
> >
> http://www.ben.com/

[Michael]

(Ben Jackson) wrote
> When you're flying partial panel, to what precision do you read the
> mag compass? To the nearest 5 degrees? Estimate to the nearest
> degree? How long do you go between readings and rely only on timed
> turns?
>
> For that matter, do you ever try to apply values from the correction
> card? In IMC or even VMC?

With a whiskey compass, it is my opinion that in smooth air +/-3
degrees is about the best you can hope for. Further, even a tiny
deviation from wings level is going to make the reading worthless.
Therefore, I ONLY read the compass when I've been maintaining level
flight for at least 3 seconds. I do not attempt compass turns - I
rely on timed turns at all times, even for small corrections.

In light chop, +/-5 degrees is about the best attainable. Anything
worse, and your guess is as good as mine. Off-field NDB approaches
with a whiskey compass in moderate turbulence are basically exercises
in dead reckoning - if you break out within a mile of the field, you
did pretty good.

With a vertical card compass with good damping, you can consistently
do a whole lot better. I find that I can effectively read heading
+/-2 degrees, at which point using the correction card becomes
somewhat worthwhile. This is not significantly degraded by light chop
because of the damping. In moderate turbulence, the solution

I'm not really sure why anyone who has a modern (flat) DG messes with
a whiskey compass anyway. With a barrel DG, it made some sense - you
wanted both instruments to read the same way to reduce confusion.
These days few pilots have even seen a barrel DG, never mind flown
instruments with one, so I really have no clue why anyone would
tolerate a whiskey compass in an IFR airplane.

Michael

[Dan Luke]

"Michael" wrote:
> I really have no clue why anyone would
> tolerate a whiskey compass in an IFR airplane.

In my case, it's because I know of two occasions where VCC installations
failed. In each instance the hysteresis error of the compass sometimes
exceeded 10 degrees and none of the fixes proposed by the mfr. helped.

I hate whiskey compasses. If you have any insights into how to achieve
happiness with a VCC, I would be interested to read them.
--
Dan
C172RG at BFM
(remove pants to reply by email)

[John R. Copeland]

There's a good reason why NDB visibility minima are a mile or more.
You need to be able to see the airport when you get somewhere near it.
---JRC---

"Bob Gardner" > wrote in message =
news:M0a%b.56799$Xp.269573@attbi_s54...
> True story: The Boeing 747 building is east of the approach end of =
runway 16
> at Paine Field. The NDB approach is based on a beacon nine miles away. =
On my
> ATP checkride, the FAA examiner had me shoot the NDB 16 approach, and =
I did
> my very damndest....but when I called "missed approach" and he told me =
to
> lift the hood, the Boeing building was to my right...my approach was =
that
> far east of the runway. "Good approach," he said.
>=20
> As an instructor, when a student shot an NDB with an off-field beacon =
and
> ended up looking right down the runway, I assumed that he or she had =
cheated
> somewhere along the way. Too many variables for an NDB approach to be
> perfect.
>=20
> Bob Gardner
>

[Teacherjh]

>>
There's a good reason why NDB visibility minima are a mile or more.
You need to be able to see the airport when you get somewhere near it.
<<

I don't buy that. If you can't see it, you go missed. If you can see it, you
land. Shooting an NDB with poor visibility may lead to more missed approaches,
and perhaps that's their thinking (why tempt a pilot into attempting an
approach that's likely to fail and leave him looking for his alternate) but
OTOH, this should also be trained into pilots, and then the visibility thing
becomes moot.

It might be that, since you will be farther from the airport, you need to see
more to avoid terrain, but again, you don't see the runway, you go missed.

Jose

--
(for Email, make the obvious changes in my address)

[Matthew S. Whiting]

Bob Gardner wrote:
> True story: The Boeing 747 building is east of the approach end of runway 16
> at Paine Field. The NDB approach is based on a beacon nine miles away. On my
> ATP checkride, the FAA examiner had me shoot the NDB 16 approach, and I did
> my very damndest....but when I called "missed approach" and he told me to
> lift the hood, the Boeing building was to my right...my approach was that
> far east of the runway. "Good approach," he said.

Yes, I had a similar experience on my check ride. It was a very windy
(10G15 on the surface and 40+ at 4,000') and bumpy day when I took my
instrument ride. The examiner didn't require a PP NDB approach, but
even with a full panel it was hard to set the DG accurately with the
compass dancing a jig. ELM is in a valley probably 3/4 - 1 mile wide.
The DE told me not to look outside upon reaching the MDA, but to wait
for his call. When he said to look for the field, I was probably a good
1/4 mile off the runway, maybe even farther. I thought that was the end
of the ride, but he said "good approach, you kept us between the
mountains!" and we continued on. It convinced me though that I'd never
fly an NDB in IMC to an airport in a valley unless it was the last
option I had ... even though I believe the MDA at ELM is slightly above
the tops of the surrounding mountains.


Matt

[Andrew Sarangan]

Bob
I guess I have a different opinion. I have no trouble using the
compass even in light turbulence. Moderate turbulence is a different
matter. Perhaps this is because the airplanes at my FBO have bad DGs
that need to be reset every 5 minutes, and we just got used to reading
the compass in bumpy air. Regarding timed turns, they will only get
you to the approximate heading. For example, even if you are only 5%
off from a standard rate turn (which is hard to tell on the TC), you
will be about 10 degrees off after a 180-turn. In order to fine tune
that heading, one needs to know about compass errors. I've seen
students zig zag their way along a north heading because they didn't
understand how to compensate for the banking errors.

I do agree that the correction card is often overlooked because the
card is out of date or the numbers are simply impossible to read.
However, most of the correction cards I've seen are rarely more than 2
degrees off, which is well within the tolerance for flying approaches.




"Bob Gardner" > wrote in message news:<WR5%b.56390$Xp.268321@attbi_s54>...
> Unless you are flying in unnaturally calm conditions, precision with the wet
> compass is hard to come by. IMHO compass turns should be eliminated from
> instrument training and timed turns emphasized.
>
> In my experience, few pilots pay any attention to the compass correction
> card, probably because the cards themselves are usually out of date.
>
> Bob Gardner
>
> "Ben Jackson" > wrote in message
> news:3wZ_b.54783$Xp.264494@attbi_s54...
> > When you're flying partial panel, to what precision do you read the
> > mag compass? To the nearest 5 degrees? Estimate to the nearest
> > degree? How long do you go between readings and rely only on timed
> > turns?
> >
> > For that matter, do you ever try to apply values from the correction
> > card? In IMC or even VMC?
> >
> > --
> > Ben Jackson
> > >
> > http://www.ben.com/

[Teacherjh]

>>
For example, even if you are only 5%
off from a standard rate turn (which is hard to tell on the TC), you
will be about 10 degrees off after a 180-turn. In order to fine tune
that heading, one needs to know about compass errors.
<<

No, you do another timed turn. It will be shorter, and (in the above example)
you'll only be off by half a degree. That's plenty good.

Jose

--
(for Email, make the obvious changes in my address)

[Bob Gardner]

The wet compass will only give you an approximate heading as well.

This is the scenario I use against compass turns: You are flying at night,
in turbulence, in the clouds, picking up ice, and your vacuum instruments
fail. Your kids are crying, your wife is bombarding you with questions, and
the mag compass looks like a washing machine. Would you use a compass turn
or a timed turn? If your answer was a timed turn, then you are guilty of
suiting the procedure to the situation, which doesn't pay off too well in an
emergency.

(I tried to put that scenario into the Instrument Flying Handbook, but it
didn't get past the FAA editors.)

Bob Gardner

"Andrew Sarangan" > wrote in message
om...
> Bob
> I guess I have a different opinion. I have no trouble using the
> compass even in light turbulence. Moderate turbulence is a different
> matter. Perhaps this is because the airplanes at my FBO have bad DGs
> that need to be reset every 5 minutes, and we just got used to reading
> the compass in bumpy air. Regarding timed turns, they will only get
> you to the approximate heading. For example, even if you are only 5%
> off from a standard rate turn (which is hard to tell on the TC), you
> will be about 10 degrees off after a 180-turn. In order to fine tune
> that heading, one needs to know about compass errors. I've seen
> students zig zag their way along a north heading because they didn't
> understand how to compensate for the banking errors.
>
> I do agree that the correction card is often overlooked because the
> card is out of date or the numbers are simply impossible to read.
> However, most of the correction cards I've seen are rarely more than 2
> degrees off, which is well within the tolerance for flying approaches.
>
>
>
>
> "Bob Gardner" > wrote in message
news:<WR5%b.56390$Xp.268321@attbi_s54>...
> > Unless you are flying in unnaturally calm conditions, precision with the
wet
> > compass is hard to come by. IMHO compass turns should be eliminated from
> > instrument training and timed turns emphasized.
> >
> > In my experience, few pilots pay any attention to the compass correction
> > card, probably because the cards themselves are usually out of date.
> >
> > Bob Gardner
> >
> > "Ben Jackson" > wrote in message
> > news:3wZ_b.54783$Xp.264494@attbi_s54...
> > > When you're flying partial panel, to what precision do you read the
> > > mag compass? To the nearest 5 degrees? Estimate to the nearest
> > > degree? How long do you go between readings and rely only on timed
> > > turns?
> > >
> > > For that matter, do you ever try to apply values from the correction
> > > card? In IMC or even VMC?
> > >
> > > --
> > > Ben Jackson
> > > >
> > > http://www.ben.com/

[Teacherjh]

>>
If your answer was a timed turn, then you are guilty of
suiting the procedure to the situation, which doesn't pay off too well in an
emergency.
<<

Isn't that the whole point - to suit the procedure to the situation?

Jose

--
(for Email, make the obvious changes in my address)

[Michael]

"Dan Luke" > wrote
> > I really have no clue why anyone would
> > tolerate a whiskey compass in an IFR airplane.
>
> In my case, it's because I know of two occasions where VCC installations
> failed. In each instance the hysteresis error of the compass sometimes
> exceeded 10 degrees and none of the fixes proposed by the mfr. helped.

Ouch. Was the compass on a rigid or flex mount? I've seen some of
them stick when they were hard-mounted into the panel or put on a
rigid mount, but I've yet to see one stick when it was on a rubber
flex mount. Of course the rubber part has to be replaced every few
years, but this is about $2.

Michael

[Barry]

> I guess I have a different opinion. I have no trouble using the
> compass even in light turbulence. Moderate turbulence is a different
> matter. Perhaps this is because the airplanes at my FBO have bad DGs
> that need to be reset every 5 minutes, and we just got used to reading
> the compass in bumpy air. Regarding timed turns, they will only get
> you to the approximate heading. For example, even if you are only 5%
> off from a standard rate turn (which is hard to tell on the TC), you
> will be about 10 degrees off after a 180-turn. In order to fine tune
> that heading, one needs to know about compass errors. I've seen
> students zig zag their way along a north heading because they didn't
> understand how to compensate for the banking errors.

I fly and teach partial panel using timed turns for a heading change of 60
degrees (20 seconds) or less, and the compass for longer turns. In both
cases, but especially with the compass, you can expect to fine tune the
heading with a second timed turn. One big mistake I see with both timed and
compass turns is that the pilot looks at the compass too soon after the turn.
I teach my students that after they begin the roll out, based on either time
or compass lead/lag, they should ignore the compass completely for the next
few seconds. The main priority after roll out is to stabilize the airplane
using the turn coordinator and VSI. After that, check the altimeter, then go
back to the TC and VSI. This allows you to verify that pitch is OK, and also
gives the compass the time it needs to settle down. Students who "zig zag
their way along a north heading" do so not because they fail to compensate for
compass errors, but because they don't give the compass time to settle down
after turning.

One item on the Instrument Rating Practical Test Standards that's often
overlooked is the turn coordinator calibration (Area IV, Task E4). People
who've never done this should try it sometime. You might be surprised at how
far off the instrument can be.

I have one other comment, not directly relevant to the compass question. All
pilots should be careful to use the correct descriptions of turbulence given
in the AIM (para.7-1-23). Moderate turbulence is pretty bad:

"Unsecured objects are dislodged."

In my experience a lot of GA pilots report Moderate turbulence when it's
really just Light ("Unsecured objects are displaced slightly"). I usually
keep my kneeboard loose on my lap, not strapped down. If it doesn't leave my
lap, the turbulence is no worse than Light.

Barry

[Bob Gardner]

Everybody to their own taste, as the lady said when she kissed the cow. In a
real emergency, pilots should not have to sort through a laundry list of
possible procedures to find the one that fits...they should learn a
procedure that works in all situations and train for that. In the instant
case, absent failure of the turn coordinator, timed turns always work.

Bob Gardner

"Teacherjh" > wrote in message
...
> >>
> If your answer was a timed turn, then you are guilty of
> suiting the procedure to the situation, which doesn't pay off too well in
an
> emergency.
> <<
>
> Isn't that the whole point - to suit the procedure to the situation?
>
> Jose
>
> --
> (for Email, make the obvious changes in my address)

[Dan Luke]

"Michael" wrote:
> Ouch. Was the compass on a rigid or flex mount?

IIRC, the club changed compass mounts as one of the attempted fixes, but
I don't know if they went from rigid to flex or vice versa. Apparently
the compass requires *some* vibration to work properly - don't remember
where I read that.

I still would love to have a (working) VCC. I googled up this bit of
troubleshooting experience yesterday:
http://www.avionicswest.com/articles.htm (scroll down a ways)

I'm not giving up. Others besides you (Jay Honeck, for one) have
reported good luck with their VCCs.
--
Dan
C172RG at BFM
(remove pants to reply by email)

[Judah]

It seems to me that timed turns are easier to do, but require more
iterations for accurate results. Wet Compass turns are easier to get more
accurate results, and involve an instrument that one would be using
anyway (for heading performance absent a DG) but require slightly more
attention and concentration.

It also seems to me that there is a situation where timed turns
absolutely do not work - electrical failure. No TC, and possibly no
clock. So the timed turn procedure does not work in all situations as you
so describe.

So, you see, sometimes you MUST manage the situation. And there clearly
is a valid reason to train both techniques. Redundancy is a popular word
among pilots, and I can't imagine anyone being admonished for having it
in a plane - even when it comes to technique and training...



"Bob Gardner" > wrote in
news:lmq%b.418281$na.808957@attbi_s04:

> Everybody to their own taste, as the lady said when she kissed the cow.
> In a real emergency, pilots should not have to sort through a laundry
> list of possible procedures to find the one that fits...they should
> learn a procedure that works in all situations and train for that. In
> the instant case, absent failure of the turn coordinator, timed turns
> always work.
>
> Bob Gardner
>
> "Teacherjh" > wrote in message
> ...
>> >>
>> If your answer was a timed turn, then you are guilty of suiting the
>> procedure to the situation, which doesn't pay off too well in an
>> emergency. <<
>>
>> Isn't that the whole point - to suit the procedure to the situation?
>>
>> Jose
>>
>> --
>> (for Email, make the obvious changes in my address)
>
>

[David Brooks]

My first attempt to fly that approach had me over the coastline, about a
mile to the west. But at least I was parallel with the threshhold.

Then I had to do it again on my checkride, partial panel, picking up a
little ice (normally the PP approach would be the VOR one, but the VOR was
OTS). I dialed in a "that feels about right" for the wind, and held it. I
was *not* peeking; in any case, most of what you can see out of the corner
of the hood is water.

Damned if I didn't end up about 20 feet off the centerline. I don't know how
I did it, especially because I'm sure I didn't look at the compass (which
would have involved peeking). Dumb luck, definitely.

-- David Brooks

"Bob Gardner" > wrote in message
news:M0a%b.56799$Xp.269573@attbi_s54...
> True story: The Boeing 747 building is east of the approach end of runway
16
> at Paine Field. The NDB approach is based on a beacon nine miles away. On
my
> ATP checkride, the FAA examiner had me shoot the NDB 16 approach, and I
did
> my very damndest....but when I called "missed approach" and he told me to
> lift the hood, the Boeing building was to my right...my approach was that
> far east of the runway. "Good approach," he said.
>
> As an instructor, when a student shot an NDB with an off-field beacon and
> ended up looking right down the runway, I assumed that he or she had
cheated
> somewhere along the way. Too many variables for an NDB approach to be
> perfect.
>
> Bob Gardner

[Andrew Sarangan]

"Barry" > wrote in message >...

>
> One item on the Instrument Rating Practical Test Standards that's often
> overlooked is the turn coordinator calibration (Area IV, Task E4). People
> who've never done this should try it sometime. You might be surprised at how
> far off the instrument can be.

Very true. I have seen TC that were indicating standard rate when it
took a lot longer than 1 min to complete a 180 turn. In another case,
I've seen a TC that did not move beyond standard rate. I could be at
2x standard rate but still showing 1x standard rate on the TC.

[Teacherjh]

I don't get it. You'd use the same procedure for a fire in the cockpit as you
would for a gear malfunction? There are no procedures that work "in all
situations", even limiting ourselves to PP work. (which P of the P?) In any
case, your saying "...timed turns always work" goes against what I was
complaining about (using a timed turn is suiting the procedure...)

What am I missing?

(and yes, in this case I'm top-posting.)

Jose

=========

Everybody to their own taste, as the lady said when she kissed the cow. In a
real emergency, pilots should not have to sort through a laundry list of
possible procedures to find the one that fits...they should learn a
procedure that works in all situations and train for that. In the instant
case, absent failure of the turn coordinator, timed turns always work.

Bob Gardner

"Teacherjh" > wrote in message
...
> >>
> If your answer was a timed turn, then you are guilty of
> suiting the procedure to the situation, which doesn't pay off too well in
an
> emergency.
> <<
>
> Isn't that the whole point - to suit the procedure to the situation?
>
> Jose
>
> --
> (for Email, make the obvious changes in my address)

--
(for Email, make the obvious changes in my address)

[Bob Gardner]

The FARs and AIM do not address multiple failures such as you posit...vacuum
pump failure plus electrical failure. No procedure can be written for a Part
91 piston pilot that will always work under those conditions, and no
examiner would expect an applicant to have a solution at hand.

In an emergency (and loss of vacuum instruments IS an emergency), accuracy
is secondary...aircraft control is primary. Who cares if you are five
degrees off of the heading the controller gave you...after you have said the
E word, anything goes.

I remember reading about a pilot and his daughter plunging to earth solely
because they had lost their vacuum instruments and couldn't fly without them
(and there is the Carnahan case of recent memory).

Don't worry about dead-on accuracy, bank as little as possible (in your
scenario you have no bank instruments, of course), and pray a lot.

Bob Gardner

"Judah" > wrote in message
...
> It seems to me that timed turns are easier to do, but require more
> iterations for accurate results. Wet Compass turns are easier to get more
> accurate results, and involve an instrument that one would be using
> anyway (for heading performance absent a DG) but require slightly more
> attention and concentration.
>
> It also seems to me that there is a situation where timed turns
> absolutely do not work - electrical failure. No TC, and possibly no
> clock. So the timed turn procedure does not work in all situations as you
> so describe.
>
> So, you see, sometimes you MUST manage the situation. And there clearly
> is a valid reason to train both techniques. Redundancy is a popular word
> among pilots, and I can't imagine anyone being admonished for having it
> in a plane - even when it comes to technique and training...
>
>
>
> "Bob Gardner" > wrote in
> news:lmq%b.418281$na.808957@attbi_s04:
>
> > Everybody to their own taste, as the lady said when she kissed the cow.
> > In a real emergency, pilots should not have to sort through a laundry
> > list of possible procedures to find the one that fits...they should
> > learn a procedure that works in all situations and train for that. In
> > the instant case, absent failure of the turn coordinator, timed turns
> > always work.
> >
> > Bob Gardner
> >
> > "Teacherjh" > wrote in message
> > ...
> >> >>
> >> If your answer was a timed turn, then you are guilty of suiting the
> >> procedure to the situation, which doesn't pay off too well in an
> >> emergency. <<
> >>
> >> Isn't that the whole point - to suit the procedure to the situation?
> >>
> >> Jose
> >>
> >> --
> >> (for Email, make the obvious changes in my address)
> >
> >
>

[ross watson]

For those of us who practice with it extensively, it's piece of mind.
fwiw
************************************************** **************************
****
"Michael" > wrote in message
om...
> (Ben Jackson) wrote
> > When you're flying partial panel, to what precision do you read the
> > mag compass? To the nearest 5 degrees? Estimate to the nearest
> > degree? How long do you go between readings and rely only on timed
> > turns?
> >
> > For that matter, do you ever try to apply values from the correction
> > card? In IMC or even VMC?
>
> With a whiskey compass, it is my opinion that in smooth air +/-3
> degrees is about the best you can hope for. Further, even a tiny
> deviation from wings level is going to make the reading worthless.
> Therefore, I ONLY read the compass when I've been maintaining level
> flight for at least 3 seconds. I do not attempt compass turns - I
> rely on timed turns at all times, even for small corrections.
>
> In light chop, +/-5 degrees is about the best attainable. Anything
> worse, and your guess is as good as mine. Off-field NDB approaches
> with a whiskey compass in moderate turbulence are basically exercises
> in dead reckoning - if you break out within a mile of the field, you
> did pretty good.
>
> With a vertical card compass with good damping, you can consistently
> do a whole lot better. I find that I can effectively read heading
> +/-2 degrees, at which point using the correction card becomes
> somewhat worthwhile. This is not significantly degraded by light chop
> because of the damping. In moderate turbulence, the solution
>
> I'm not really sure why anyone who has a modern (flat) DG messes with
> a whiskey compass anyway. With a barrel DG, it made some sense - you
> wanted both instruments to read the same way to reduce confusion.
> These days few pilots have even seen a barrel DG, never mind flown
> instruments with one, so I really have no clue why anyone would
> tolerate a whiskey compass in an IFR airplane.
>
> Michael