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card, probably because the cards themselves are usually out of date.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

(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

"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)

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

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)

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

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/