Compass turns revisited

In a glass cockpit Cirrus (at least the one I flew) it is the only
plan. A PFD failure leaves you with ASI, electric AI, Altimeter - and
two Garmin 430's without CDI's (the only CDI is built into the HSI
presentation on the PFD).

Don't the 430's still have the CDI on the "Default NAV page"? Or did Garmin
change the interface for the Cirrus?

Michael,

I think you need to brush up on your Garmin GPS's. In the Cirrus, I
believe, the Garmins drive the Avidyne display. One of the navigation pages
on the Garmin displays a CDI that scales properly to approach sensitivity.
That is much more accurate than following the magenta line for a backup
approach.

Ron


"Michael" wrote in message Well, that's
a defeatist attitude. I would like to think that I would
come up with some method they could handle.

Just turning until the little picture of the airplane is pointing in
the same direction as the purple line might just be a reasonable plan

with today's cockpits.

In a glass cockpit Cirrus (at least the one I flew) it is the only
plan. A PFD failure leaves you with ASI, electric AI, Altimeter - and
two Garmin 430's without CDI's (the only CDI is built into the HSI
presentation on the PFD). The only approach you can shoot after PFD
failure is a GPS, and you can shoot it ONLY by turning until the little
picture of the airplane is pointing in the same direction as the purple
line. I suppose you could use a compass, but I'm not sure what the
benefit would be.

I think you need to brush up on your Garmin GPS's. In the Cirrus, I
believe, the Garmins drive the Avidyne display.

Which is the PFD. The guidance in the latest revision of the PTS calls
for a non-precision approach to be performed without the PFD if the
aircraft is capable, and this one is.

One of the navigation pages
on the Garmin displays a CDI that scales properly to approach
sensitivity.

Sure - but it still only works for the GPS, not the VOR/LOC. You're
still limited to GPS approaches only.

That is much more accurate than following the magenta line for a
backup
approach.

This is not correct for three reasons.

First, the accuracy of the data is not affected by the presentation.
It is a function of satellite geometry and the underlying algorithms.
You're talking about precision, or resolution.

Second, you can zoom the map to a view of only a few hundred feet, and
if you so choose, you can configure the 430 to auto zoom as you get
closer. Your effective precision in this case is about 25 feet, which
is better than you can do with the CDI. This is better than the 430
can consistently do. In other words, you have accessible to you a
display with a level of precision not justified by the underlying
accuracy.

And finally, using the CDI only gives you information about your
position relative to the FAC. This is inherently wrongheaded. VOR/LOC
work that way because that's all the information you have, but the GPS
also has track information. The map display presents the same position
information as the CDI, with the same accuracy and any practically
usable precision, and it also presents the track information
graphically, such that the pilot can almost immediately see whether he
is converging with the FAC, diverging from it, or paralelling it -
without having to estimate this by monitoring the movement of the CDI
over time. This will allow the pilot to more consistently track the
course.

Thus, while I will grant you that there is indeeed a plan other than
watching the little airplane and its position and direction relative to
the courseline, it's a clearly inferior plan since it will yield
inferior results while requiring all the same equipment.

Michael

The interesting question is whether an examiner would insist on setting
up a situation, however improbable, that would require the student to
do partial panel flying without the GPS.

What do you mean "improbable"? The student gets his rating in a Cirrus,
rents a 172 on vacation, it has no GPS, and it loses vacuum.

Jose
--
Get high on gasoline: fly an airplane.
for Email, make the obvious change in the address.

On 4 Apr 2005 14:48:26 -0400, (Roy Smith) wrote:

Michael wrote:
Fortunately I've never had a student who couldn't deal with either
method. I'm not sure what I would do then.

I think the answer needs to be "not sign them off for the checkride".
The ability to turn to and maintain a heading without a working DG is
an essential skill. Somehow you need to be able to do it.

Just turning until the little picture of the airplane is pointing in
the same direction as the purple line might just be a reasonable plan
with today's cockpits. Unfortunately, I'm not sure you would convince
an examiner of that.


Why would you have to convince an examiner of anything?

The PTS doesnt require that one look at a specific device. It says
only that the applicant must complete a maneuver to a certain standard
with (or without) certain equipment.

The PTS determines what equipment is or is not available to the
applicant, not the examiner.


Back when all our airplanes had ADF's in them, just setting the ADF to
a distant AM radio station made a decent DG replacement.

Do you get the Designee Update? Good stuff in the April edition in the
context of this thread. Go to the AFS-600 page and click on Designee Update.

Bob

"Michael" wrote in message
oups.com...
The examiner has some degree of latitude in deciding just what a
"basic instrument flight maneuver" is...but no one is going to get a
pink
slip with "Timed turns to headings" on it.

However, the full procedure partial panel non-precision approach is
still in place, and in order to do that you will need to do compass
turns or timed turns to headings. The change allows you to do what
works best for you. Over time, I've discovered that what works best
depends on the student and the equipment.

Some students just don't get math. For them, the mental math required
to figure out how many seconds the turn needs to be is too much to do
while flying under the hood. For others, the jumping around, lead, and
lag of the compass is too difficult to deal with - they prefer to time
the turn, the check the compass only in level flight.

I personally belong to the latter camp. I am a strong believer in only
looking at the compass when I know it will be accurate, and using time
for turns when the heading gyro is not available. I've taught some
students that method, and they've done well with it. Others hated it,
and wound up just looking at the compass anyway. If they slow the rate
of turn to half-standard-rate when getting close to the heading, it
works reasonably well. Fortunately I've never had a student who
couldn't deal with either method. I'm not sure what I would do then.

Michael

"Michael" wrote in message
oups.com...
Some students just don't get math. For them, the mental math required
to figure out how many seconds the turn needs to be is too much to do
while flying under the hood. For others, the jumping around, lead, and
lag of the compass is too difficult to deal with - they prefer to time
the turn, the check the compass only in level flight.

For some reason, despite two 'A' levels in maths, I have brain failure with
my three times table when trying to figure out timed turns. So long as I
take a few seconds to double-check your multiplication, though, and I sanity
check it (e.g. if you're turning 120 degrees it should take less than a
minute, not more) it's not a problem.

I personally belong to the latter camp. I am a strong believer in only
looking at the compass when I know it will be accurate, and using time
for turns when the heading gyro is not available.

Seconded. The two aircraft I spent most of my learning hours in had
compasses that were pretty grim (mainly around North and South, of course)
unless you were flying absolutely straight, which made even checking the DI
a bit of a chore. There wasn't really an alternative to a timed turn if you
wanted to end up pointing even vaguely the right way.

D.

"David Cartwright" wrote in message ...
"Michael" wrote in message
oups.com...
Some students just don't get math. For them, the mental math required
to figure out how many seconds the turn needs to be is too much to do
while flying under the hood. For others, the jumping around, lead, and
lag of the compass is too difficult to deal with - they prefer to time
the turn, the check the compass only in level flight.

For some reason, despite two 'A' levels in maths, I have brain failure with my three times table when trying
to figure out timed turns. So long as I take a few seconds to double-check your multiplication, though, and I
sanity check it (e.g. if you're turning 120 degrees it should take less than a minute, not more) it's not a
problem.


I think its easier just to do it on the dg (or even an obs if your dg has failed and is covered up)-- as
Gardner said, count 10 seconds per "numbered" heading, even if it means putting your finger physically on the
numbers as you count from your current heading to your desired heading...

Cheers,
John Clonts
Temple, Texas
N7NZ

On Wed, 06 Apr 2005 03:21:03 GMT, "John Clonts"
wrote:

I think its easier just to do it on the dg (or even an obs if your dg has failed and is covered up)-- as
Gardner said, count 10 seconds per "numbered" heading, even if it means putting your finger physically on the
numbers as you count from your current heading to your desired heading...

Cheers,
John Clonts
Temple, Texas
N7NZ


Excuse me, but my irrepressible ego requires me to point out that it
was I who suggested this technique to Mr Gardner, as an alternative
to doing mental arithmetic.

wrote in message ...


Excuse me, but my irrepressible ego requires me to point out that it
was I who suggested this technique to Mr Gardner, as an alternative
to doing mental arithmetic.


Sorry about that...