Reading the whiskey compass

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/

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card, probably because the cards themselves are usually out of date.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/

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card is out of date or the numbers are simply impossible to read.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/

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)

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/

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)

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)

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

"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.

(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