need for dial altimeter?

On Sep 26, 7:52*am, Peter Purdie wrote:
Transponders give Flight Level (assuming they are working properly), so
will give the altitude ATC are intereted in. *That's how they know what
FL you are at when not talking to them.

The controller see your transponder altitude CORRECTED for the local
pressure. So don't give them the number off the transponder display
unless the current pressure is 29.92

That's why the altimeter must be calibrated when you calibrate the
transponder. You must be able to set the altimeter to the current
(not what it was several hours or hundreds of miles away) before
talking to ATC, and that is why they will give you an altimeter
setting on initial contact unless you indicate you have current ATIS
info.

-Tom

On Sep 26, 9:43*am, 5Z wrote:
On Sep 26, 7:52*am, Peter Purdie wrote:

Transponders give Flight Level (assuming they are working properly), so
will give the altitude ATC are intereted in. *That's how they know what
FL you are at when not talking to them.

The controller see your transponder altitude CORRECTED for the local
pressure. *So don't give them the number off the transponder display
unless the current pressure is 29.92

That's why the altimeter must be calibrated when you calibrate the
transponder. *You must be able to set the altimeter to the current
(not what it was several hours or hundreds of miles away) before
talking to ATC, and that is why they will give you an altimeter
setting on initial contact unless you indicate you have current ATIS
info.

-Tom

Actually this is a common misconception, (one of several reported
recently in the Safety Corner in Soaring magazine). The encoder/
transponder/altimeter system is checked as a part of an install and
you must also do this if the static system is touched during
maintenance. Subsequent checks for aircraft operating VFR are only
required to test the transponder RF/signal properties and do not need
to check the altitude calibration. IFR calibration do. See FAR 91.413
appendix F (RF/signal properties only) and Appendix E (install/static
maintenance and IFR checks).

Back to the original question, I would not want to fly any aircraft
without the ability to reliably (i.e. when the battery dies) know and
be able to report pressure altitude.

Darryl

Back to the original question, I would not want to fly any aircraft
without the ability to reliably (i.e. when the battery dies) know and
be able to report pressure altitude.

Darryl

If your battery dies, wouldn't you lose your ability to report
anything to anybody?

I'm not suggesting we fly around without an altitude readout of some
kind, but does it have to be the big, old 80mm round dial? Why can't I
use the pressure altitude displayed in double height on the home page
of my SN-10. Keep the black cursor on it, so my altitude can be read
at a glance. If I should have the SN-10 on another page, I can always
read pressure altitude to the nearest 100 feet off my transponder. If
for some reason I'm unable to use any of the above, I can always read
pressure altitude off the GPS (model 20).
Most of us have two batteries so we can switch if the primary goes
dead.
JJ

JJ Sinclair wrote:

I'm not suggesting we fly around without an altitude readout of some
kind, but does it have to be the big, old 80mm round dial? Why can't I

No it hasn't to be 80mm, mine is 57mm. Aside from this, yes it has to:
More than once I was happy to be able to continue my flight under a
class C ceiling despite of two flat batteries.

Besides, many contries reqire gliders to be equipped with a certificated
altimeter.

On Sep 27, 7:51*am, JJ Sinclair wrote:
Back to the original question, I would not want to fly any aircraft
without the ability to reliably (i.e. when the battery dies) know and
be able to report pressure altitude.

Darryl

If your battery dies, wouldn't you lose your ability to report
anything to anybody?

I'm not suggesting we fly around without an altitude readout of some
kind, but does it have to be the big, old 80mm round dial? Why can't I
use the pressure altitude displayed in double height on the home page
of my SN-10. Keep the black cursor on it, so my altitude can be read
at a glance. If I should have the SN-10 on another page, I can always
read pressure altitude to the nearest 100 feet off my transponder. If
for some reason I'm unable to use any of the above, I can always read
pressure altitude off the GPS (model 20).
Most of us have two batteries so we can switch if the primary goes
dead.
JJ

Yes, assuming the backup handheld dies as well, then I'd just be
talking to myself.

I fly a certified glider so I have no choice but to follow the
equipment list. You tell us J.J. what is the requirements for
homebuilt/experimental and racing/exhibition/experimental.

Darryl

I fly a certified glider so I have no choice but to follow the
equipment list. You tell us J.J. what is the requirements for
homebuilt/experimental and racing/exhibition/experimental.

Darryl

Alas, yes they both require old fashioned dial altimiters. With todays
glass cockpits, I'm wondering if this requirement isn't outdated?
JJ

On Sep 27, 2:57*pm, JJ Sinclair wrote:

Alas, yes they both require old fashioned dial altimiters. With todays
glass cockpits, I'm wondering if this requirement isn't outdated?
JJ

JJ - Can you, or anyone else, reference a regulation on altimeters
that includes the word DIAL.

91.205.b.2) requires for VFR flight an "altimeter"

91.205.d.5) requires for IFR flight "a sensitive altimeter adjustable
for barometric pressure".

Neither requires a dial and neither requires a mechanical instrument.

Andy

On Sep 27, 3:51*pm, Andy wrote:
On Sep 27, 2:57*pm, JJ Sinclair wrote:

Alas, yes they both require old fashioned dial altimiters. With todays
glass cockpits, I'm wondering if this requirement isn't outdated?
JJ

JJ - Can you, or anyone else, reference a regulation on altimeters
that includes the word DIAL.

91.205.b.2) *requires for VFR flight an "altimeter"

91.205.d.5) requires for IFR flight "a sensitive altimeter adjustable
for barometric pressure".

Neither requires a dial and neither requires a mechanical instrument.

Andy

I am also building a homebuilt sailplane and talked with the DAR
(designated airworthiness representative) about the instrumentation.
The answer I got was that it's pretty much up to him. I can have a
compass out of a child's toy if that's what I want and he's willing to
sign it off. Ditto for most of the other instruments.

Good point, Andy.....................maybe we can use one of the many
altitude displays available. As you may have guessed, I removed the
big dial altimeter about a year ago when I installed a transponder. I
set field elevation on the SN10 which is on the first (custom) page
and set-up to be displayed at twice normal height. When not otherwise
being used I leave the black cursor on altitude.................works
like a charm! Yes, my flight manual says I need an altimiter approved
for use on certified aircraft, but it also says I must use the Prandtl
tube, but I'm using a triple probe instead. The guy that's sign'n off
my annual condition inspections doesn't sweat the little stuff.
JJ

Andy wrote:
On Sep 27, 2:57�pm, JJ Sinclair wrote:

Alas, yes they both require old fashioned dial altimiters. With todays
glass cockpits, I'm wondering if this requirement isn't outdated?
JJ

JJ - Can you, or anyone else, reference a regulation on altimeters
that includes the word DIAL.

91.205.b.2) requires for VFR flight an "altimeter"

91.205.d.5) requires for IFR flight "a sensitive altimeter adjustable
for barometric pressure".

Neither requires a dial and neither requires a mechanical instrument.

Andy