(USA) NTSB issues recommendations to the FAA and the SSA regarding transponder use in gliders

Mike Schumann wrote:
The failure to provide separation services between VFR and IFR traffic is
the way the system has been run since day one. The rules haven't been
changed to account for increases in aircraft speed and traffic density. VFR
altitude encoders, while not meeting the standards of IFR systems designed
for reduced separation environments, still have to meet FAA standards. Any
lack of accuracy should be reflected in the separation provide to the IFR
traffic.

My understanding is it's not the lack of basic accuracy of the encoders,
but the lack of confirmation that the encoder is working properly. An
IFR aircraft is in contact with ATC, and ATC knows it's altimeter and
encoder show the same pressure altitude. ATC is not in contact with the
VFR aircraft, and can not do this cross-check of the altimeter and
encoder readings.

--
Eric Greenwell - Washington State, USA
* Change "netto" to "net" to email me directly

* Updated! "Transponders in Sailplanes" http://tinyurl.com/y739x4
* New Jan '08 - sections on Mode S, TPAS, ADS-B, Flarm, more

* "A Guide to Self-launching Sailplane Operation" at www.motorglider.org

So just because there is a chance that the encoder on a VFR aircraft is not
working, you go ahead and let an IFR aircraft head right towards the
target??? That certainly doesn't make sense. If there is a legitimate
concern that the VFR encoder is not accurate, the logical conclusion would
be to make sure you have extra separation vertically between the IFR
aircraft than you otherwise might.

Mike Schumann

"Eric Greenwell" wrote in message
news:_SUgk.205$oU.75@trnddc07...
Mike Schumann wrote:
The failure to provide separation services between VFR and IFR traffic is
the way the system has been run since day one. The rules haven't been
changed to account for increases in aircraft speed and traffic density.
VFR altitude encoders, while not meeting the standards of IFR systems
designed for reduced separation environments, still have to meet FAA
standards. Any lack of accuracy should be reflected in the separation
provide to the IFR traffic.

My understanding is it's not the lack of basic accuracy of the encoders,
but the lack of confirmation that the encoder is working properly. An IFR
aircraft is in contact with ATC, and ATC knows it's altimeter and encoder
show the same pressure altitude. ATC is not in contact with the VFR
aircraft, and can not do this cross-check of the altimeter and encoder
readings.

--
Eric Greenwell - Washington State, USA
* Change "netto" to "net" to email me directly

* Updated! "Transponders in Sailplanes" http://tinyurl.com/y739x4
* New Jan '08 - sections on Mode S, TPAS, ADS-B, Flarm, more

* "A Guide to Self-launching Sailplane Operation" at www.motorglider.org


** Posted from http://www.teranews.com **

On Jul 21, 6:14*am, "Mike Schumann" mike-nos...@traditions-
nospam.com wrote:
*If there is a legitimate
concern that the VFR encoder is not accurate, the logical conclusion would
be to make sure you have extra separation vertically between the IFR
aircraft than you otherwise might.

In a system where the transponder and encoder are separate units, the
encoder to transponder altitude interface is typically implemented by
multiple ground/open discretes. Something as simple as a dirty
contact may result in a discrete being assumed open instead of ground
state. A single bit error may result in an encoder reporting an
altitude several thousands of feet in error. The Gilham Grey code
used for altitude encoders has no parity check and, with few
exceptions, no other means of error checking except correlation with
the pilot's altitude report. One exception is transponders that
display the reported altitude and allow the pilot to check it.
Nevertheless the controller has no way to know the reported altitude
is accurate unless verified against a pilot altitude report.

In this context accurate does not mean plus/minus 200 feet (the
resolution is only 100ft) but perhaps plus/minus 5000ft or more.

Of course the same non error checked, low integrity, transponder/
encoder systems are the basis for TCAS conflict resolution.

ref http://www.airsport-corp.com/dot_faa_ct-97_7.pdf

"The results of this study indicate that most of the transponders
carried
by GA aircraft fail to meet all of the performance criteria specified
in national
standards documents, and that a number of these failures may be
serious enough
to significantly affect their performance with secondary surveillance
radar
systems and TCAS collision avoidance equipment. In addition, the data
showed
that performance failures on key transponder parameters were unrelated
to the
time that had elapsed since a transponder had received its last
biennial
inspection."

Anyone ready for ADS-B yet.

Andy

ADS-B is definitely the way to go. But this ignores the most basic problem,
which is that the FAA is ignoring the data that they already have. Even if
they get have VFR ADS-B target that they know is accurate, their current
procedure is to give the IFR traffic an advisory, but generally not any
deviation to avoid the known traffic.

Mike Schumann

"Andy" wrote in message
...
On Jul 21, 6:14 am, "Mike Schumann" mike-nos...@traditions-
nospam.com wrote:
If there is a legitimate
concern that the VFR encoder is not accurate, the logical conclusion would
be to make sure you have extra separation vertically between the IFR
aircraft than you otherwise might.

In a system where the transponder and encoder are separate units, the
encoder to transponder altitude interface is typically implemented by
multiple ground/open discretes. Something as simple as a dirty
contact may result in a discrete being assumed open instead of ground
state. A single bit error may result in an encoder reporting an
altitude several thousands of feet in error. The Gilham Grey code
used for altitude encoders has no parity check and, with few
exceptions, no other means of error checking except correlation with
the pilot's altitude report. One exception is transponders that
display the reported altitude and allow the pilot to check it.
Nevertheless the controller has no way to know the reported altitude
is accurate unless verified against a pilot altitude report.

In this context accurate does not mean plus/minus 200 feet (the
resolution is only 100ft) but perhaps plus/minus 5000ft or more.

Of course the same non error checked, low integrity, transponder/
encoder systems are the basis for TCAS conflict resolution.

ref http://www.airsport-corp.com/dot_faa_ct-97_7.pdf

"The results of this study indicate that most of the transponders
carried
by GA aircraft fail to meet all of the performance criteria specified
in national
standards documents, and that a number of these failures may be
serious enough
to significantly affect their performance with secondary surveillance
radar
systems and TCAS collision avoidance equipment. In addition, the data
showed
that performance failures on key transponder parameters were unrelated
to the
time that had elapsed since a transponder had received its last
biennial
inspection."

Anyone ready for ADS-B yet.

Andy


** Posted from http://www.teranews.com **

Mike Schumann wrote:
ADS-B is definitely the way to go. But this ignores the most basic problem,
which is that the FAA is ignoring the data that they already have.

The FAA isn't ignoring any data, they just aren't using it the way you
think they should. They do give the information to the IFR pilot, who
can request a new vector if the pilot thinks the present one is unsafe.

You aren't getting the detailed reasoning or procedures from RAS that
you seem to be looking for, so I suggest you discuss the situation with
a controller as the next step. That should get you the procedures, but
not necessarily the reasoning, for which you will likely have to dig
further.

Practically speaking, the current procedures seem to work well. If you,
as a transponder equipped VFR pilot, want to improve upon them, you can
contact ATC so they can confirm your altitude. You can also request
flight following. Contacting ATC will usually help even if you are not
transponder equipped.

Even if
they get have VFR ADS-B target that they know is accurate, their current
procedure is to give the IFR traffic an advisory, but generally not any
deviation to avoid the known traffic.

We are at the beginning of the transition to ADS-B. The procedures will
change as it's use expands, and I don't think even the FAA knows what
the detailed procedures will be 10 or 20 years from now, but no one
suggests they will the same.

--
Eric Greenwell - Washington State, USA
* Change "netto" to "net" to email me directly

* Updated! "Transponders in Sailplanes" http://tinyurl.com/y739x4
* New Jan '08 - sections on Mode S, TPAS, ADS-B, Flarm, more

* "A Guide to Self-launching Sailplane Operation" at www.motorglider.org

We are at the beginning of the transition to ADS-B. The procedures will
change as it's use expands, and I don't think even the FAA knows what
the detailed procedures will be 10 or 20 years from now, but no one
suggests they will the same.

--
Eric Greenwell - Washington State, USA


When is ADS-B going to be implimented?

Do you think it will be any better for gliders from the power/size/
cost standpoint?

Perhaps the FAA /SSA can help fund/steer development of ADS-B for use
in gliders
to meet our specific limitations and concede on some points for
Gliders not using them below some agreed upon
altitude to conserve power. It could simply be desinged to turn on
automatically at the preset altitude.

Im sure we could get these things made to mil spec by some Chineese
company at a greatly reduced price.

Ray

On Jul 22, 2:14*pm, jb92563 wrote:
Perhaps the FAA /SSA can help fund/steer development of ADS-B for use
in gliders

Your questions are answered in this month's and last (or a bit older)
month's issues of Soaring.

-Tom

The NTSB report on the mid-air over Minden indicates that there are quite a
few TCAS advisories being generated between IFR traffic and transponder
equipped VFR aircraft, both powered and gliders. This indicates that the
system is NOT working well. A TCAS advisory should be considered just as
serious as a runway incursion. The reason that we are getting all of these
TCAS advisories is because we are relying on see and be seen for IFR traffic
to avoid VFR aircraft, instead of having ATC automatically vector IFR
traffic around known targets.

Mike Schumann

651-208-3791

"Eric Greenwell" wrote in message
news:Kgnhk.323$oU.266@trnddc07...
Mike Schumann wrote:
ADS-B is definitely the way to go. But this ignores the most basic
problem, which is that the FAA is ignoring the data that they already
have.

The FAA isn't ignoring any data, they just aren't using it the way you
think they should. They do give the information to the IFR pilot, who can
request a new vector if the pilot thinks the present one is unsafe.

You aren't getting the detailed reasoning or procedures from RAS that you
seem to be looking for, so I suggest you discuss the situation with a
controller as the next step. That should get you the procedures, but not
necessarily the reasoning, for which you will likely have to dig further.

Practically speaking, the current procedures seem to work well. If you, as
a transponder equipped VFR pilot, want to improve upon them, you can
contact ATC so they can confirm your altitude. You can also request flight
following. Contacting ATC will usually help even if you are not
transponder equipped.

Even if they get have VFR ADS-B target that they know is accurate, their
current procedure is to give the IFR traffic an advisory, but generally
not any deviation to avoid the known traffic.

We are at the beginning of the transition to ADS-B. The procedures will
change as it's use expands, and I don't think even the FAA knows what the
detailed procedures will be 10 or 20 years from now, but no one suggests
they will the same.

--
Eric Greenwell - Washington State, USA
* Change "netto" to "net" to email me directly

* Updated! "Transponders in Sailplanes" http://tinyurl.com/y739x4
* New Jan '08 - sections on Mode S, TPAS, ADS-B, Flarm, more

* "A Guide to Self-launching Sailplane Operation" at www.motorglider.org


** Posted from http://www.teranews.com **

Mike Schumann wrote:


The reason that we are getting all of these TCAS advisories
is because we are relying on see and be seen for IFR traffic
to avoid VFR aircraft, instead of having ATC automatically
vector IFR traffic around known targets.


Mike,

Are you just venting, or are you willing and able to offer a suggestion
about how that could be done?


Jack