Like Jack, I just read the whole thread. 4 comments:

1. Remember, the most important glass in a glass cockpit
is above the instrument panel. I used to quote this
to airline pilots, but these days I find it appropos
for many gadget-oriented glider drivers.

2. If you're not seeing much traffic, you're just not
looking hard enough.

3. I tried the 10 point font 'o' at ten feet. Even
in light blue it was clearly visible. At age 46, it's
actually harder to see it at 10 inches! I see another
aircraft at 10 miles, I wish I could read my altimeter
to tell ATC where I am ;o)

4. The rules are see and avoid, and give way to the
glider. The PIC is responsible for knowing all pertinent
information about the intended flight. Adjusting speed
or flight path to avoid heavy glider traffic is not
just a good idea, it's the law.



At 04:42 01 September 2006, Glen Kelley wrote:
Ramy, I would agree. Mode A isn't completely worthless,
since at least the
airliner knows you are around. Clearly Mode C provides
more 'protection'.

Glen
'Ramy' wrote in message
roups.com...
Thanks Glen. I am not aware of any transponder equiped
glider not using
mode C. Seems like once you go through the hassle
and cost of
installing a transponder, the encoder is the easy
part. Mode A sounds
almost useless, more confusing then not. A mode A
transponder could
signal an alert to any airline crusing at 30K above.
Which baffles me - Why aren't modern transponders
already including
internal encoder??

Ramy

Glen Kelley wrote:
Ramy,

The problem is that TCAS will display you as a target
with altitude
unknown
(unless you have mode c with an encoding altimeter).
Therefore, TCAS
will
only call you out as traffic and display your position
without generating
a
Resolution Advisory (RA). We see this pretty often
as VFR traffic. We
will
be looking hard for the traffic, but won't necessarily
maneuver the
aircraft, since we can't see altitude/heading.

If in fact, the sailplane does have mode C with an
encoding altimeter,
then
the RA will be generated and you should see the big
bird maneuver to
avoid
the conflict. Note that a TCAS RA will direct maneuvering
in the
vertical
only, since TCAS azimuth is considered too innacurate
to generate
turn-based
avoidance. Typical RAs would be 'Climb,Climb, Climb
- Descend, Descend,
Descend - Reduce Climb - Reduce Descent, etc'.

I guess I figured most of the gliders with transponders
weren't using
Mode
C, so good catch.

Glen
'Ramy' wrote in message
ups.com...
Thanks for the excellent overview, Glen. Regarding
number 3, why would
a TCAS equipped airliner pilot need to see me if
the TCAS gives the
resolution? I'm pretty sure most of the airliners
vectored around me
never actually see me (although I always
wave ;-)

Ramy

Glen Kelley wrote:
A few additions to Kirk's excellent points - from
the background of
former
fighter pilot, current airline pilot, and current
glider pilot:

1. We often surprise each other in sailplanes with
how hard it is to
see
each other. Don't expect an airline pilot to be
any better at it!
The
fighter pilot at least will have good visual acuity
and is used to
looking
for small targets.

2. Airline pilots don't carry sectionals - at the
speeds we operate,
there
would be little time to use them anyway. Fighter
pilots will carry a
low
level map and will have thought about visual traffic
conflicts, wires,
terrain, etc in the planning stages. At the speeds
they operate, they
aren't looking at those maps very often, once airborne.

3. The busier glider operations are notam'd and often
referred to by
atc
controllers. If you have an operable transponder,
you will *normally*
be
called out by atc and if TCAS equipped, airline pilots
will be aware
of
your
location. They would still have to see you to maneuver
away from you.
(See
note 1.) Big airliners are not very maneuverable
(mine - the Boeing
737 -
is limited to 2.5 g!).

4. Fighters are a different case. They don't have
TCAS and only some
of
them have the ability to interrogate/detect transponder
targets. Some
of
them have air intercept radar capability, but sailplanes
are small
radar
targets and will often (usually!) be filtered out
because of their low
speeds and altitudes - like highway traffic. If
they are at low
altitude,
fighters usually operate at high speed (420 - 540
indicated, except
the
A-10). As Kirk pointed out they will almost never
be alone, but will
be
in
formations of 2 - 4. When low level (100 to 1500
agl, most commonly
300 -
500agl), they will normally *not* be receiving traffic
information
from
ATC.
When operating in a MOA, there may be intercept controllers
who can
call
out
glider traffic, but again, without a transponder,
it is unlikely. The
formations will vary, but most pairs of flight lead
and wingman will
be
laterally spread by 5000 to 10000 feet, for visual
lookout. The
flight
lead
will be spending quite a bit of his time looking
forward for threat
detection and navigation, but the wingman will be
spending less time
looking
forward because he must maintain formation. If they
see you, they
have
an
excellent capability to avoid you. Head on and tail
on, the sailplane
has
the tiny visual profile that fighter designers dream
of.... In other
words,
you are nearly invisible unless you have a wing up
in a turn/thermal.

5. As Kirk said, the primary threat is at 6 o'clock,
because it is
the
hardest to see - essentially, only the overtaking
aircraft has a
reasonable
chance of avoiding a collision. Therefore, if you
know you are
operating
in
a high threat area: MOA, low level route, approach
corridor, VFR
flyway,
near an airport etc, I would 'belly check' periodically,
depending on
the
nature of the threat. The timing is based on the
amount of time it
takes
for
the threat aircraft to close from outside visual
range to hitting me
from
the 6 o'clock position. I use visual ranges of 8nm
for airliners, 5
nm
for
small commercial jets (corporate and regional jets)
and fighters, and
3
nm
for light aircraft - adjust as your visual acuity
and experience
dictate.
I
use worst-case speeds as follows: airliner and small
jets - 4 nm/min,
fighters - 8 nm/min, and light aircraft - 2.5 nm/min.
Combing
detection
ranges and times, I calculate: airliners - 2 min,
small jets - 1 min
and
15
sec, fighters - roughly 40 sec, and light planes
- approx 1 min and 15
sec.
So... if you are straight and level for more than
these times, there
is
sufficient time for an aircraft to move from outside
(my) visual range
to
the same airspace as my (your) little pink body.
As you would probably
guess, fighters are the worst case because of their
relatively small
size
and high closure rate. On the positive side, there
are typically more
eyeballs with better acuity and better maneuverability
involved.
Interestingly, small jets and light aircraft are
not that far behind,
as
far
as detection time is concerned. In my experience
they are far less
likely
to see you than the fighters. The same is true for
airliners, but
because
of their size you have more time to see them coming...

6. How to do a belly check: No, I don't hack a
stopwatch, but I keep
the
above times in mind with respect to the likely threat
for my area. My
primary threat is small jet/light aircraft that operate
on various
highway/flyways and approach corridors. Away from
these specific
areas,
traffic density is extremely low. First clear your
'new six' - if you
are
going to turn left, look to the area behind to the
right 4 - 5 oclock
position - this will be your new blind spot. Next
clear your new nose
position - this is where you are going to roll out.
Finally make a 45
deg
turn to the left and visually clear your 'old six',
which is now at
your
left 7 to 8 o'clock. Often/usually, a belly check
can be incorporated
into
turns you are going to make anyway, for other reasons.
When you
visually
clear, make sure you focus on something on the horizon,
otherwise you
are
only visually clearing out to an arms length. If
I really need to
hold a
straight line, I do the belly check as a gentle 45
deg turn to each
side.

7. In a thermal, periodically check to the outside
of your term to
clear
your 'new six'. If there are other sailplanes with
you in the
thermal,
of
course they are the primary threats for midair, but
you still need to
check
for other aircraft. Fortunately, you are easier to
see while turning -
as
long as the other pilots are looking...

8. Proximity to clouds. You need to think about
what you are doing
when
you are near cloudbase, in proximity to likely IFR
traffic. If you
are
500'
below cloudbase (perfectly legal), and an airliner
descends out of the
cloud
at 250kt on his descent profile on collision course
(perfectly legal),
there
may be as little as 20 seconds to impact. If you
are tail on when
this
happens - good luck. I'm sure no one would ever
be right at cloudbase
on
a
nice day, because that would violate the FARs -
more importantly, you
are
'rolling the bones' every time you do this on a known
approach
corridor.

9. Conclusion. If you fly in a high airliner/small
jet threat area
and
can afford a transponder it will help other people
see/avoid you. If
your
primary threat comes from military operations in
MOAs, I would not
spend
the
money on a transponder unless I knew those fighters
have intercept/atc
controllers passing them information. The various
TPAS - type devices
will
help your see/avoid efforts and should help in the
case of fighters,
although the flight lead is likely the only one squawking
in the
formation.
Only you/your club knows the primary threats for
your particular
operating
area and you need to understand what they are. Taylor
your altitude
awareness/cloud avoidance and belly check frequency
to the nature of
your
local area. Don't cede visual lookout/avoidance
responsibility to
someone
else - ever. Sailplane right-of-way is a myth in
most situations and
a
comfort only to your survivors/legal counsel.

Hope this helps.

Glen