VOR Check question

[Michael 182]

I was told by an avionics guy that if a plane has VOR's they must be
accurate to file IFR, even if I file /G.

FAR 91.171 says "(a) No person may operate a civil aircraft under IFR using
the VOR system of radio navigation unless the VOR equipment of that
aircraft..."

I'm not debating the logic of having VOR's that are accurate, and I'm
getting mine adjusted - but it seems to me if my means of navigation is an
IFR certified GPS I do not have a legal responsibility to pass the VOR
check. Am I right?

Michael

[Mark Hansen]

On 7/22/2005 12:01, Michael 182 wrote:

> I was told by an avionics guy that if a plane has VOR's they must be
> accurate to file IFR, even if I file /G.
>
> FAR 91.171 says "(a) No person may operate a civil aircraft under IFR using
> the VOR system of radio navigation unless the VOR equipment of that
> aircraft..."
>
> I'm not debating the logic of having VOR's that are accurate, and I'm
> getting mine adjusted - but it seems to me if my means of navigation is an
> IFR certified GPS I do not have a legal responsibility to pass the VOR
> check. Am I right?
>
> Michael
>
>

You are also required to have available in the aircraft equipment necessary
for navigation along your route, in the event GPS goes out. That sounds like
VOR to me.

--
Mark Hansen, PP-ASEL, Instrument Student
Sacramento, CA

[Guillermo]

if you go to the AIM: 1-19-1, d. 1.
(b) Aircraft using GPS navigation equipment under IFR must be equipped with
an approved and operational alternate means of navigation appropriate to the
flight.

So basically you MUST be able to complete the flight without GPS, so you'll
probably need a VOR (checked) to be able to comply with that.


"Michael 182" > wrote in message
...
> I was told by an avionics guy that if a plane has VOR's they must be
> accurate to file IFR, even if I file /G.
>
> FAR 91.171 says "(a) No person may operate a civil aircraft under IFR
using
> the VOR system of radio navigation unless the VOR equipment of that
> aircraft..."
>
> I'm not debating the logic of having VOR's that are accurate, and I'm
> getting mine adjusted - but it seems to me if my means of navigation is an
> IFR certified GPS I do not have a legal responsibility to pass the VOR
> check. Am I right?
>
> Michael
>
>

[Ron Natalie]

Mark Hansen wrote:

>
> You are also required to have available in the aircraft equipment necessary
> for navigation along your route, in the event GPS goes out. That sounds
> like
> VOR to me.
>

Not if you have the right GPS. But an unchecked VOR is technically not
airworthy, so unless you're going to follow the procedures for inop
equipment, it would be easier just to do it.

[[email protected]]

Ron Natalie wrote:

> Mark Hansen wrote:
>
> >
> > You are also required to have available in the aircraft equipment necessary
> > for navigation along your route, in the event GPS goes out. That sounds
> > like
> > VOR to me.
> >
>
> Not if you have the right GPS. But an unchecked VOR is technically not
> airworthy, so unless you're going to follow the procedures for inop
> equipment, it would be easier just to do it.

Not so. VOR is still the primary means of navigation in the NAS. Even the
latest and greatest airline aircraft with dual GPS sensors, dual FMSes, triple
IRUs, etc, cannot be dispatched without operate VOR receivers (in their case
two).

The presumption is that the GPS system can fail at any time; at least in a given
area. WAAS doesn't mitigate that whatsoever.

[Brien K. Meehan]

If you use the VOR for IFR navigation, 91.205(d)(2) makes 91.171 apply
to you.

.... but (contrary to popular belief) there is no requirement under Part
91 (or Part 135) that says you have to have a VOR receiver to fly IFR.

So, assuming you don't use it, you're right.

[[email protected]]

"Brien K. Meehan" wrote:

> If you use the VOR for IFR navigation, 91.205(d)(2) makes 91.171 apply
> to you.
>
> ... but (contrary to popular belief) there is no requirement under Part
> 91 (or Part 135) that says you have to have a VOR receiver to fly IFR.
>

It's an indirect regulatory requirement because by FAA policy the primary
means of IFR navigation in the NAS is by VOR.

[Brien K. Meehan]

Whoever told you it's an indirect regulartory issue was making it up.

[[email protected]]

"Brien K. Meehan" wrote:

> Whoever told you it's an indirect regulartory issue was making it up.

Well, okay, but I work with this stuff all the time.

Here is from the current FAA Order 8260.19C:

l. Dual Minimums. Enter dual minimums, when authorized. Do not publish
dual minimums unless a 60-foot operational advantage is obtained or a
reduction in visibility can be achieved. To avoid proliferation of dual
minimums, *all IFR aircraft are assumed to have at least one VOR
receiver*. Dual minimums based on a stepdown fix combined with local and
remote altimeter settings could result in four sets of minimums. When two
remote sources are used, treat the source resulting in lower minimums as
the "LOCAL" altimeter setting source in the following paragraphs.
Document only two sets of minimums. The combinations authorized are
minimums with and without a stepdown fix; or minimums with local and
remote altimeter settings.

The words between the asteriks are reflective of FAA Class I navigation
policy, which is a requirement to be a part of ICAO.

And, from the FAA's Instrument Procedures Hanbook (available in Summit's
Aviation Reference Library):

In the broad concept of air navigation, there are two major categories
of navigational operations consisting of Class I navigation and Class II
navigation. Class I navigation is any en route flight operation conducted
in controlled or uncontrolled airspace that is entirely within
operational service volumes of ICAO standard NAVAIDs (VOR, VOR/DME, NDB).
Class II navigation is any en route operation that is not categorized as
Class I navigation and includes any operation or portion of an operation
that takes place outside the operational service volumes of ICAO standard
NAVAIDs. For example, your aircraft equipped only with VORs conducts
Class II navigation when your flight operates in an area outside the
operational service volumes of federal VORs/DMEs. Class II navigation
does not automatically require the use of long-range, specialized
navigational systems if special navigational techniques are used to
supplement conventional NAVAIDs. Class II navigation includes
transoceanic operations and operations in desolate and remote land areas
such as the Arctic. The primary types of specialized navigational systems
approved for Class II operations include inertial navigation system
(INS), OMEGA, Doppler, and global positioning system (GPS). Figure 4-15
provides several examples of Class I and II navigation.

[Stan Gosnell]

wrote in :

> Not so. VOR is still the primary means of navigation in the NAS.
> Even the latest and greatest airline aircraft with dual GPS sensors,
> dual FMSes, triple IRUs, etc, cannot be dispatched without operate VOR
> receivers (in their case two).
>
> The presumption is that the GPS system can fail at any time; at least
> in a given area. WAAS doesn't mitigate that whatsoever.

Not only airliners - I have to have 2 (not just one, but 2) operable VORs
to dispatch offshore, where there are precisely zero VOR transmitters,
and I'm almost always out of range of any VOR. But both VORs have to be
operable to dispatch IFR.

Ain't bureaucracy wonderful?

--
Regards,

Stan

"They that can give up essential liberty to obtain a little temporary
safety deserve neither liberty nor safety." B. Franklin

[Brien K. Meehan]

Ah, cool, thank you very, VERY much for posting those references.

The FAA's policy subject to ICAO membership doesn't make it regulatory,
as the ICAO is a standards organization and holds no sovereignty. If a
DOT organinzation outside the FAA, or a department outside the DOT,
adopted those ICAO standards as regulatory, then the FAA would assume
an indirect regulatory role - even so, the equipment requirement would
be arguable (the equipment assumption is for the purpose of determining
minima, not actual navigation, and regulatory equipment requirements
are otherwise very precise). But, as far as I know, this is not the
case.

The second part describes Class I and Class II navigation, but doesn't
spell out an equipment requirement either. On the contrary, it says
that you don't automatically need equipment appropriate for the
corresponding class of navigation.

[[email protected]]

Stan Gosnell wrote:

> wrote in :
>
> > Not so. VOR is still the primary means of navigation in the NAS.
> > Even the latest and greatest airline aircraft with dual GPS sensors,
> > dual FMSes, triple IRUs, etc, cannot be dispatched without operate VOR
> > receivers (in their case two).
> >
> > The presumption is that the GPS system can fail at any time; at least
> > in a given area. WAAS doesn't mitigate that whatsoever.
>
> Not only airliners - I have to have 2 (not just one, but 2) operable VORs
> to dispatch offshore, where there are precisely zero VOR transmitters,
> and I'm almost always out of range of any VOR. But both VORs have to be
> operable to dispatch IFR.
>
> Ain't bureaucracy wonderful?

I suppose they feel you might need them on the leg back to shore?

[[email protected]]

"Brien K. Meehan" wrote:

> Ah, cool, thank you very, VERY much for posting those references.
>
> The FAA's policy subject to ICAO membership doesn't make it regulatory,
> as the ICAO is a standards organization and holds no sovereignty. If a
> DOT organinzation outside the FAA, or a department outside the DOT,
> adopted those ICAO standards as regulatory, then the FAA would assume
> an indirect regulatory role - even so, the equipment requirement would
> be arguable (the equipment assumption is for the purpose of determining
> minima, not actual navigation, and regulatory equipment requirements
> are otherwise very precise). But, as far as I know, this is not the
> case.
>

Indeed, ICAO is not regulatory. What the FAA accepts as navigation policy,
though, is subject to FAA regulation, ala 91.205(d)(2); i.e.
"appropriate." "Appropriate" serves to the benefit of the FAA, not the
pilot.

> The second part describes Class I and Class II navigation, but doesn't
> spell out an equipment requirement either. On the contrary, it says
> that you don't automatically need equipment appropriate for the
> corresponding class of navigation.

[Mike Rapoport]

> wrote in message ...
>
>
> Ron Natalie wrote:
>
>> Mark Hansen wrote:
>>
>> >
>> > You are also required to have available in the aircraft equipment
>> > necessary
>> > for navigation along your route, in the event GPS goes out. That sounds
>> > like
>> > VOR to me.
>> >
>>
>> Not if you have the right GPS. But an unchecked VOR is technically not
>> airworthy, so unless you're going to follow the procedures for inop
>> equipment, it would be easier just to do it.
>
> Not so. VOR is still the primary means of navigation in the NAS. Even
> the
> latest and greatest airline aircraft with dual GPS sensors, dual FMSes,
> triple
> IRUs, etc, cannot be dispatched without operate VOR receivers (in their
> case
> two).
>
> The presumption is that the GPS system can fail at any time; at least in a
> given
> area. WAAS doesn't mitigate that whatsoever.
>
>

I thought that WAAS was approved for sole means of navigation?

Mike
MU-2

[Stan Gosnell]

wrote in :

>
> I suppose they feel you might need them on the leg back to shore?

For what? Most of our bases have no VOR near them anyway, and no VOR
approach, so they don't do a lot of good.

--
Regards,

Stan

"They that can give up essential liberty to obtain a little temporary
safety deserve neither liberty nor safety." B. Franklin

[Stan Gosnell]

"Mike Rapoport" > wrote in
nk.net:

> I thought that WAAS was approved for sole means of navigation?

Not that I'm aware of. WAAS has nothing to do with reliability, other
than vertical accuracy. Its only function is to give enough vertical
accuracy to allow a semi-precision approach.

--
Regards,

Stan

"They that can give up essential liberty to obtain a little temporary
safety deserve neither liberty nor safety." B. Franklin

[Mike Rapoport]

My understanding is that WAAS has an integrety function and is able to
detect an inaccurate signal.

Mike
MU-2

"Stan Gosnell" > wrote in message
...
> "Mike Rapoport" > wrote in
> nk.net:
>
>> I thought that WAAS was approved for sole means of navigation?
>
> Not that I'm aware of. WAAS has nothing to do with reliability, other
> than vertical accuracy. Its only function is to give enough vertical
> accuracy to allow a semi-precision approach.
>
> --
> Regards,
>
> Stan
>
> "They that can give up essential liberty to obtain a little temporary
> safety deserve neither liberty nor safety." B. Franklin

[Steven P. McNicoll]

> wrote in message ...
>
> Not so. VOR is still the primary means of navigation in the NAS. Even
> the
> latest and greatest airline aircraft with dual GPS sensors, dual FMSes,
> triple
> IRUs, etc, cannot be dispatched without operate VOR receivers (in their
> case
> two).
>
> The presumption is that the GPS system can fail at any time; at least in a
> given
> area. WAAS doesn't mitigate that whatsoever.
>

So why is it presumed that the VOR system cannot fail?

[Steven P. McNicoll]

> wrote in message ...
>
> Well, okay, but I work with this stuff all the time.
>

That doesn't mean you understand it.


>
> Here is from the current FAA Order 8260.19C:
>
> l. Dual Minimums. Enter dual minimums, when authorized. Do not publish
> dual minimums unless a 60-foot operational advantage is obtained or a
> reduction in visibility can be achieved. To avoid proliferation of dual
> minimums, *all IFR aircraft are assumed to have at least one VOR
> receiver*. Dual minimums based on a stepdown fix combined with local and
> remote altimeter settings could result in four sets of minimums. When two
> remote sources are used, treat the source resulting in lower minimums as
> the "LOCAL" altimeter setting source in the following paragraphs.
> Document only two sets of minimums. The combinations authorized are
> minimums with and without a stepdown fix; or minimums with local and
> remote altimeter settings.
>
> The words between the asteriks are reflective of FAA Class I navigation
> policy, which is a requirement to be a part of ICAO.
>

FAA Order 8260.19C places no regulatory requirements upon pilots or the
operation of aircraft.

How are you doing with that reference for the timing tables on NACO charts
being IAS?

[Jose]

> So why is it presumed that the VOR system cannot fail?

I would assume (and I know the etymology) that VORs fail 1000 square
miles at a time, and GPS fails 3,000,000 square miles at a time. Or,
more to the point, there is more systemic redundancy in the VOR system.

Jose
--
Nothing takes longer than a shortcut.
for Email, make the obvious change in the address.

[Stan Gosnell]

"Mike Rapoport" > wrote in news:HZrFe.8543$dU3.6278
@newsread2.news.pas.earthlink.net:

> My understanding is that WAAS has an integrety function and is able to
> detect an inaccurate signal.

RAIM (Receiver Autonomous Integrity Monitoring) is available without WAAS,
and was available before WAAS was implemented.

--
Regards,

Stan

"They that can give up essential liberty to obtain a little temporary
safety deserve neither liberty nor safety." B. Franklin

[Steven P. McNicoll]

"Jose" > wrote in message
. ..
>
> I would assume (and I know the etymology) that VORs fail 1000 square miles
> at a time, and GPS fails 3,000,000 square miles at a time. Or, more to
> the point, there is more systemic redundancy in the VOR system.
>

The question was, "So why is it presumed that the VOR system cannot fail?",
not, "So why is it presumed that a VOR cannot fail?" The loss of a GPS
satellite would not render the GPS system unusable.

[Mike Rapoport]

"Stan Gosnell" > wrote in message
...
> "Mike Rapoport" > wrote in news:HZrFe.8543$dU3.6278
> @newsread2.news.pas.earthlink.net:
>
>> My understanding is that WAAS has an integrety function and is able to
>> detect an inaccurate signal.
>
> RAIM (Receiver Autonomous Integrity Monitoring) is available without WAAS,
> and was available before WAAS was implemented.
>
> --
> Regards,
>
> Stan


I'm aware of that. The WAAS signal was to contain another
intergrety/availiblity function.

Mike
MU-2

[Jose]

> The question was, "So why is it presumed that the VOR system cannot fail?",
> not, "So why is it presumed that a VOR cannot fail?" The loss of a GPS
> satellite would not render the GPS system unusable.

.... and my response addresses exactly that. The failure of a single VOR
(or even twenty) won't cripple the VOR system. But the (albeit
unlikely) failure of twenty satellites will cripple the GPS system.
There is more systemic redundancy in the VOR system, just by virtue of
there being more VORs, and by virtue of the fact that a single VOR
affects a relatively small area.

Jose
--
Nothing takes longer than a shortcut.
for Email, make the obvious change in the address.

[Clay]

Remember.
ALL FAR's are written to violate the pilot.

[Frank Ch. Eigler]

Stan Gosnell > writes:

> > My understanding is that WAAS has an integrety function and is able to
> > detect an inaccurate signal.
>
> RAIM (Receiver Autonomous Integrity Monitoring) is available without WAAS,
> and was available before WAAS was implemented.

Look up FDE "fault detection / exclusion" instead. This computation
is possible to perform without WAAS (the GNS430 does some now), but
WAAS carries satellite health flags that simplify it.


- FChE

[Brien K. Meehan]

91.205(d)(2) is exactly the point. If a pilot is using VOR ground
facilities, a VOR receiver would be appropriate. If he's not (e.g.
using TACAN or GPS), a VOR receiver would not be appropriate and
therefore not required.

Support for the anti-requirement is in 91.205(e), which specifically
accounts for flying IFR without a VOR.

[[email protected]]

"Steven P. McNicoll" wrote:

> > wrote in message ...
> >
> > Well, okay, but I work with this stuff all the time.
> >
>
> That doesn't mean you understand it.
>
> >
> > Here is from the current FAA Order 8260.19C:
> >
> > l. Dual Minimums. Enter dual minimums, when authorized. Do not publish
> > dual minimums unless a 60-foot operational advantage is obtained or a
> > reduction in visibility can be achieved. To avoid proliferation of dual
> > minimums, *all IFR aircraft are assumed to have at least one VOR
> > receiver*. Dual minimums based on a stepdown fix combined with local and
> > remote altimeter settings could result in four sets of minimums. When two
> > remote sources are used, treat the source resulting in lower minimums as
> > the "LOCAL" altimeter setting source in the following paragraphs.
> > Document only two sets of minimums. The combinations authorized are
> > minimums with and without a stepdown fix; or minimums with local and
> > remote altimeter settings.
> >
> > The words between the asteriks are reflective of FAA Class I navigation
> > policy, which is a requirement to be a part of ICAO.
> >
>
> FAA Order 8260.19C places no regulatory requirements upon pilots or the
> operation of aircraft.

Sure it does. It provides guidance for minimums, procedural data notes, etc,
which
are Part 97 imperatives when transmitted through the rule-making process onto
the
approach chart. Obviously, you don't know what you're talking about.

>
>
> How are you doing with that reference for the timing tables on NACO charts
> being IAS?

Those are "speeds." How you choose to use them is up to you. The regulatory
basis is the
distance from the FAF to the MAP. Nothing more, nothing less. Obviously, with
today's
equipment navigating to the MAP via RNAV is more accurate than a pilot attempt
to
convert IAS to TAS, then to G/S.

[Ron Rosenfeld]

On Sat, 23 Jul 2005 04:41:18 -0700, wrote:

>Not so. VOR is still the primary means of navigation in the NAS. Even the
>latest and greatest airline aircraft with dual GPS sensors, dual FMSes, triple
>IRUs, etc, cannot be dispatched without operate VOR receivers (in their case
>two).
>
>The presumption is that the GPS system can fail at any time; at least in a given
>area. WAAS doesn't mitigate that whatsoever.

Could you reconcile your statement with AIM 1-1-20 c.

"7. Unlike TSO-C129 avionics, which were certified as a supplement to other
means of navigation, WAAS avionics are evaluated without reliance on other
navigation systems. As such, installation of WAAS avionics does not require
the aircraft to have other equipment appropriate to the route to be flown."


Ron (EPM) (N5843Q, Mooney M20E) (CP, ASEL, ASES, IA)

[[email protected]]

"Brien K. Meehan" wrote:

> 91.205(d)(2) is exactly the point. If a pilot is using VOR ground
> facilities, a VOR receiver would be appropriate. If he's not (e.g.
> using TACAN or GPS), a VOR receiver would not be appropriate and
> therefore not required.
>
> Support for the anti-requirement is in 91.205(e), which specifically
> accounts for flying IFR without a VOR.

You're reading the regulation without the context of FAA policy. VOR is
still the primary en route nav aid. Write FAA Flight Standards in DC
and ask them if the regulation means what you think it means.

[Steven P. McNicoll]

> wrote in message ...
>
> Well, okay, but I work with this stuff all the time.
>

Prior to a recent discussion in this forum you believed the speeds in the
timing tables of NACO charts were IAS. Anybody that worked with this stuff
all the time would have known they were ground speed. It appears you're a
fibber.

[Steven P. McNicoll]

"Jose" > wrote in message
.. .
>
> ... and my response addresses exactly that.
>

No, it addresses the failure of a VOR and the failure of a GPS satellite.


>
> The failure of a single VOR
> (or even twenty) won't cripple the VOR system. But the (albeit unlikely)
> failure of twenty satellites will cripple the GPS system.
>

You're right, but you're now comparing the failure of about 0.1 to 2% of the
VOR system to the failure of about 69% of the GPS constellation.

[Steven P. McNicoll]

> wrote in message ...
>
> Sure it does. It provides guidance for minimums, procedural data notes,
> etc, which are Part 97 imperatives when transmitted through the
> rule-making process
> onto the approach chart.
>

But no regulatory requirements upon pilots or the operation of aircraft.


>
> Obviously, you don't know what you're talking about.
>

Is it? Let's test that. If you can provide a reference from FAA Order
8260.19C which places a regulatory requirements upon pilots then I don't
know what I'm talking about. If you can't provide that reference then you
don't know what you're talking about. Fair enough?


>
> Those are "speeds." How you choose to use them is up to you.
>

You said previously they are IAS, are they or aren't they IAS? Or are you
saying that IAS and groundspeed can be used interchangeably?


>
> The regulatory basis is the distance from the FAF to the MAP. Nothing
> more,
> nothing less. Obviously, with today's equipment navigating to the MAP via
> RNAV is more accurate than a pilot attempt to convert IAS to TAS, then to
> G/S.
>

So you're still maintaining that the speeds in the timing tables are IAS,
even after it was proven here that they cannot be anything other than GS?
That's incredible! And you think it obvious that I don't know what I'm
talking about!

Okay, fine. When I said the speeds in the timing tables were GS you asked
for a supporting reference. Since you "work with this stuff all the time"
it should be a simple matter for you to provide a reference indicating these
speeds are IAS. If you wish to retain what little credibility you have left
you'll do so.

[Steven P. McNicoll]

> wrote in message ...
>
> You're reading the regulation without the context of FAA policy. VOR is
> still the primary en route nav aid. Write FAA Flight Standards in DC
> and ask them if the regulation means what you think it means.
>

So is it FAA policy that the regulations mean what they say, or that the
regulations mean what FAA Flight Standards in DC say they mean?

[Jose]

> No, it addresses the failure of a VOR and the failure of a GPS satellite.

No, it doesn't =address= this, it =uses= this to =address= the original
point.

> you're now comparing the failure of about 0.1 to 2% of the
> VOR system to the failure of about 69% of the GPS constellation.

.... which is my point. A single VOR failure brings down 0.1% to 2% of
the VOR system. A single failure brings down 69% of the GPS system.
(your numbers - I don't believe the 69% part and haven't verified the
0.1% to 2% part though that sounds reasonable)

Jose
--
Quantum Mechanics is like this: God =does= play dice with the universe,
except there's no God, and there's no dice. And maybe there's no universe.
for Email, make the obvious change in the address.

[Paul Lynch]

Ah figures lie and liars figure. Actually you are comparing statistical
apples and oranges.

If a single VOR fails in your area, or worse on your approach, you have a
little to a big problem depending on the circumstances. If a single
satellite fails for the area you are operating you are not likely to even
know it because so many other satellites are still available to provide no
worse than about 60M accuracy.

PK

"Jose" > wrote in message
. ..
>> No, it addresses the failure of a VOR and the failure of a GPS satellite.
>
> No, it doesn't =address= this, it =uses= this to =address= the original
> point.
>
>> you're now comparing the failure of about 0.1 to 2% of the VOR system to
>> the failure of about 69% of the GPS constellation.
>
> ... which is my point. A single VOR failure brings down 0.1% to 2% of the
> VOR system. A single failure brings down 69% of the GPS system. (your
> numbers - I don't believe the 69% part and haven't verified the 0.1% to 2%
> part though that sounds reasonable)
>
> Jose
> --
> Quantum Mechanics is like this: God =does= play dice with the universe,
> except there's no God, and there's no dice. And maybe there's no
> universe.
> for Email, make the obvious change in the address.

[Jose]

> If a single VOR fails in your area, or worse on your approach, you have a
> little to a big problem depending on the circumstances. If a single
> satellite fails for the area you are operating you are not likely to even
> know it because so many other satellites are still available to provide no
> worse than about 60M accuracy.

Uncontested. But a small number of failures is sufficient to bring down
the entire GPS system. A small number of failures is not sufficient to
bring down the entire VOR system. And the issue is the robustness of
the -system-, not the robustness for any individual flight.

I do not claim that one is better than the other. I do claim that the
difference in failure modes is significant, and as you pointed out, can
play either way. That it can play one way does not mean it can't play
the other way, or that the other way isn't a significant factor.

Jose
--
Quantum Mechanics is like this: God =does= play dice with the universe,
except there's no God, and there's no dice. And maybe there's no universe.
for Email, make the obvious change in the address.

[Roger]

On Fri, 5 Aug 2005 18:07:49 -0400, "Paul Lynch" >
wrote:

A solar storm can render the GPS signals unusable for a period and
have at least once if not twice. It's a rare occurrence. OTOH it is
possible, but with a low probability of either meteor (dust size
particles), or a solar storm of enough magnitude, disabling a portion
of the satellite constellation.

Although the likely hood is very small, GPS is more likely to run into
a wide area failure than VORs. OTOH you can still fly via GPS with
only 2 satellites. With 3 it does a reasonable job of vertical nav.
I don't believe it'd be legal for approaches or you'd have enough
information for such, but it does show the *relative* immunity of GPS
to failures rendering the system unusable.

Both are good systems with GPS being far more accurate and less prone
to interference or failure.

GPS makes an excellent primary system, but as with any system for
serious work you always want a separate back-up. Your hardware can
fail, their hardware can fail, or some one could jam the system which
is true for any system. For emergencies even the old ADF and the
local AM broadcast station can get you in the vicinity of the airport.
It doesn't take much thinking to roll your own approach using an ADF
in an emergency.

If it's a true emergency you use what's available and sort out the
legalities later.

Roger Halstead (K8RI & ARRL life member)
(N833R, S# CD-2 Worlds oldest Debonair)
www.rogerhalstead.com
>Ah figures lie and liars figure. Actually you are comparing statistical
>apples and oranges.
>
>If a single VOR fails in your area, or worse on your approach, you have a
>little to a big problem depending on the circumstances. If a single
>satellite fails for the area you are operating you are not likely to even
>know it because so many other satellites are still available to provide no
>worse than about 60M accuracy.
>
>PK
>
>"Jose" > wrote in message
. ..
>>> No, it addresses the failure of a VOR and the failure of a GPS satellite.
>>
>> No, it doesn't =address= this, it =uses= this to =address= the original
>> point.
>>
>>> you're now comparing the failure of about 0.1 to 2% of the VOR system to
>>> the failure of about 69% of the GPS constellation.
>>
>> ... which is my point. A single VOR failure brings down 0.1% to 2% of the
>> VOR system. A single failure brings down 69% of the GPS system. (your
>> numbers - I don't believe the 69% part and haven't verified the 0.1% to 2%
>> part though that sounds reasonable)
>>
>> Jose
>> --
>> Quantum Mechanics is like this: God =does= play dice with the universe,
>> except there's no God, and there's no dice. And maybe there's no
>> universe.
>> for Email, make the obvious change in the address.
>

[Douglas Wood]

If you look at GPS notams, you will find a surprising number of area outages
that are small. They tend to be kind of conical in shape (small near the
ground and larger area as you increase in altitude. These seem to be due to
geometries for the satellite. If a satellite is out, this makes the
coverage even worse.

I fly in the east coast region (Wash DC ADIZ). There seems to be some areas
that have fairly permanent outage areas, perhaps jamming tests are done
there.

One should check GPS notams just as you would check VOR notams if you depend
on either navigation system.

Doug Wood

"Roger" > wrote in message
...
> On Fri, 5 Aug 2005 18:07:49 -0400, "Paul Lynch" >
> wrote:
>
> A solar storm can render the GPS signals unusable for a period and
> have at least once if not twice. It's a rare occurrence. OTOH it is
> possible, but with a low probability of either meteor (dust size
> particles), or a solar storm of enough magnitude, disabling a portion
> of the satellite constellation.
>
> Although the likely hood is very small, GPS is more likely to run into
> a wide area failure than VORs. OTOH you can still fly via GPS with
> only 2 satellites. With 3 it does a reasonable job of vertical nav.
> I don't believe it'd be legal for approaches or you'd have enough
> information for such, but it does show the *relative* immunity of GPS
> to failures rendering the system unusable.
>
> Both are good systems with GPS being far more accurate and less prone
> to interference or failure.
>
> GPS makes an excellent primary system, but as with any system for
> serious work you always want a separate back-up. Your hardware can
> fail, their hardware can fail, or some one could jam the system which
> is true for any system. For emergencies even the old ADF and the
> local AM broadcast station can get you in the vicinity of the airport.
> It doesn't take much thinking to roll your own approach using an ADF
> in an emergency.
>
> If it's a true emergency you use what's available and sort out the
> legalities later.
>
> Roger Halstead (K8RI & ARRL life member)
> (N833R, S# CD-2 Worlds oldest Debonair)
> www.rogerhalstead.com
>>Ah figures lie and liars figure. Actually you are comparing statistical
>>apples and oranges.
>>
>>If a single VOR fails in your area, or worse on your approach, you have a
>>little to a big problem depending on the circumstances. If a single
>>satellite fails for the area you are operating you are not likely to even
>>know it because so many other satellites are still available to provide no
>>worse than about 60M accuracy.
>>
>>PK
>>
>>"Jose" > wrote in message
. ..
>>>> No, it addresses the failure of a VOR and the failure of a GPS
>>>> satellite.
>>>
>>> No, it doesn't =address= this, it =uses= this to =address= the original
>>> point.
>>>
>>>> you're now comparing the failure of about 0.1 to 2% of the VOR system
>>>> to
>>>> the failure of about 69% of the GPS constellation.
>>>
>>> ... which is my point. A single VOR failure brings down 0.1% to 2% of
>>> the
>>> VOR system. A single failure brings down 69% of the GPS system. (your
>>> numbers - I don't believe the 69% part and haven't verified the 0.1% to
>>> 2%
>>> part though that sounds reasonable)
>>>
>>> Jose
>>> --
>>> Quantum Mechanics is like this: God =does= play dice with the universe,
>>> except there's no God, and there's no dice. And maybe there's no
>>> universe.
>>> for Email, make the obvious change in the address.
>>
>

[Roy Smith]

In article >,
Roger > wrote:

> A solar storm can render the GPS signals unusable for a period and
> have at least once if not twice. It's a rare occurrence. OTOH it is
> possible, but with a low probability of either meteor (dust size
> particles), or a solar storm of enough magnitude, disabling a portion
> of the satellite constellation.

Right. That's why redundancy is critical. Vacuum powered gyros have been
a part of aviation for half a century, I don't see any reason why vacuum
couldn't provide the same level of redundancy for naviads. Put a really
big vacuum pump at the end of the runway and any aircraft that gets close
enough gets sucked right to the threshold.

"Cessna 12345, cleared for the vacuum two approach. Report established in
the vortex".