Discussion:
ILS transmitters
(too old to reply)
Rob
2010-03-06 14:25:03 UTC
Permalink
I am interested in rules governing the proximity of
buildings to ILS transmitters and propogation interference.
Having googled can't seen to find anything. Can anyone assist ?
bin me
2010-03-07 15:47:42 UTC
Permalink
The "rules" are the whole ILS must conform to regs. Glideslope is more
critical than localiser, as the frequency is higher. The effect of
fixed objects, like buildings, can often be adjusted out to get the
system within spec. Movable objects, like A/C at the departure end
waiting a turn for T/O, can't be accounted for. Hence the much larger
hold short area for Cat 2 or 3 ILS working - assuming a single runway.

The whole ILS is flight checked 2 or 3 times per year (depends on
maintenance history) to ensure it meets standards. Was involved about
10 years ago, out that loop now.

Alan

In message <***@mid.individual.net>, Rob <***@fishin.com>
writes
I am interested in rules governing the proximity of buildings to ILS
transmitters and propogation interference.
Having googled can't seen to find anything. Can anyone assist ?
--
Alan
Rob
2010-03-07 23:19:37 UTC
Permalink
Post by bin me
The "rules" are the whole ILS must conform to regs. Glideslope is more
critical than localiser, as the frequency is higher. The effect of fixed
objects, like buildings, can often be adjusted out to get the system
within spec. Movable objects, like A/C at the departure end waiting a
turn for T/O, can't be accounted for. Hence the much larger hold short
area for Cat 2 or 3 ILS working - assuming a single runway.
The whole ILS is flight checked 2 or 3 times per year (depends on
maintenance history) to ensure it meets standards. Was involved about 10
years ago, out that loop now.
Alan
I am interested in rules governing the proximity of buildings to ILS
transmitters and propogation interference.
Having googled can't seen to find anything. Can anyone assist ?
Thanks for that. I am hoping to extend a light a/c parking
area approx 150m (90 degrees) from the array. Just wondered
whether there were some parameters somewhere which referred
to obstacle proximities.

Rob
bin me
2010-03-08 13:36:49 UTC
Permalink
In message <***@mid.individual.net>, Rob <***@fishin.com>
writes
Post by bin me
The "rules" are the whole ILS must conform to regs. Glideslope is more
critical than localiser, as the frequency is higher. The effect of fixed
objects, like buildings, can often be adjusted out to get the system
within spec. Movable objects, like A/C at the departure end waiting a
turn for T/O, can't be accounted for. Hence the much larger hold short
area for Cat 2 or 3 ILS working - assuming a single runway.
The whole ILS is flight checked 2 or 3 times per year (depends on
maintenance history) to ensure it meets standards. Was involved about 10
years ago, out that loop now.
Alan
I am interested in rules governing the proximity of buildings to ILS
transmitters and propogation interference.
Having googled can't seen to find anything. Can anyone assist ?
Thanks for that. I am hoping to extend a light a/c parking area approx
150m (90 degrees) from the array. Just wondered
whether there were some parameters somewhere which referred to obstacle
proximities.
Rob
Glideslope or localiser? Hope I'm not teaching granny to suck eggs, but
the localiser array is at the end of the runway and the glideslope array
is around (lots of variables) one third of the way down the runway, but
always adjacent to the TDZ marked on the runway.

Would the new parking area be in front of or behind the array, or
exactly 90 degrees to it? Understand its 150m away. I'm trying to
picture it in my mind - not being awkward!

Software is used to "model" the situation. If it looks OK, then
permission is given to provide the parking, then a final flight check of
the ILS takes place. That's a much simplified version of events but
gives the general picture.

Alan
PS. If you want to email me, replace binme2 with my name, using the
rest of the email address "as is".
--
Alan
brian whatcott
2010-03-11 12:47:28 UTC
Permalink
/snip/
the localiser array is at the end of the runway and the glideslope array
is around (lots of variables) one third of the way down the runway, but
always adjacent to the TDZ marked on the runway. /snip/
Alan
A better guide for glideslope antenna positioning is around 1000 ft from
the runway end, near the PAPI and VASI sites, for obvious reasons.

Brian W
bin me
2010-03-14 14:55:41 UTC
Permalink
Post by brian whatcott
/snip/
the localiser array is at the end of the runway and the glideslope
array is around (lots of variables) one third of the way down the
runway, but always adjacent to the TDZ marked on the runway. /snip/
Alan
A better guide for glideslope antenna positioning is around 1000 ft
from the runway end, near the PAPI and VASI sites, for obvious reasons.
Brian W
TDZ is the place for the G/S aerial by International agreement, and
practical considerations. Might be a few exceptions, like the old 13
approach at Kai Tak @ Hong Kong (wasn't a true ILS anyway, its was a IGS
approach aid). TDZ is the "aiming point" for pilots carrying out an ILS
approach. Look at all the rubber on the tarmac at the TDZ for a typical
commercial use R/W, that is the aiming/landing point. The PAPI and VASI
can be useful for non IMC flight rules, but for IMC flight rules the TDZ
is the place to land and that is the place the G/S intersects the runway
surface.
--
Alan
brian whatcott
2010-03-17 22:43:37 UTC
Permalink
Post by bin me
Post by brian whatcott
/snip/
the localiser array is at the end of the runway and the glideslope
array is around (lots of variables) one third of the way down the
runway, but always adjacent to the TDZ marked on the runway. /snip/
Alan
A better guide for glideslope antenna positioning is around 1000 ft
from the runway end, near the PAPI and VASI sites, for obvious reasons.
Brian W
TDZ is the place for the G/S aerial by International agreement, and
practical considerations./snip/
Quite. Just about never "a third the way down the runway" in fact.

Brian W
bin me
2010-03-21 20:43:58 UTC
Permalink
Post by brian whatcott
Post by bin me
Post by brian whatcott
/snip/
the localiser array is at the end of the runway and the glideslope
array is around (lots of variables) one third of the way down the
runway, but always adjacent to the TDZ marked on the runway. /snip/
Alan
A better guide for glideslope antenna positioning is around 1000 ft
from the runway end, near the PAPI and VASI sites, for obvious reasons.
Brian W
TDZ is the place for the G/S aerial by International agreement, and
practical considerations./snip/
Quite. Just about never "a third the way down the runway" in fact.
Brian W
Brian,
As I said earlier in the thread, "the glideslope array is around (lots
of variables) one third of the way down the runway". I did not say it
was "a third of the way down the runway".

It depends on many factors, mainly designed for commercial transport
standards. To make it absolutely clear, it can be well into the runway
with a third being around the typical maximum with lots of variables,
(but somewhere in the world, including Farnborough in the UK, it
is/could be more than a third). It will always give an undershoot area,
the length of that area is again variable. As I also stated in the same
post, I have been out that loop for more than 10 years and things do
change.

Take some examples, all using very old date, but it does show the point.

London City 28 (5.5 degree), overall length is around 4948ft. 3962ft
available from TDZ. That is about 20% in.

Coventry 23 (3.0 degrees) is 5988ft overall, 4396ft available from TDZ.
That is 27% in.

Sumburgh 27 (3.0 degrees) is 3871ft overall, 2796ft available from TDZ.
That is 28% in.

Edinburgh 24 (3.0 degrees) is 8399ft overall, 5997ft available from TDZ.
That is 28.5% in.

Waterford, Ireland 21 (3.33 degrees) is 4701ft overall, 3201ft available
from TDZ. That is 32% in.

Isle of Man 08 (3.0degrees) is 5755ft overall, 3861ft available from
TDZ. That is 33% in.

Bournemouth 08 (3.0 degrees) is 7451ft overall, 4996ft available from
TDZ. That is 33% in.

Farnborough 24 (3.0 degrees) is 8005ft overall, 5011ft available from
TDZ. That is 37% in.

The conclusion is many factors are taken into account when designing an
ILS. The glideslope aerial/TDZ is one variable which is/can be, used to
ensure an A/C following the ILS will arrive at the TDZ if all procedures
are followed. You will often find the aerial position gives a 55ft
runway threshold crossing height - but not always.

Every ILS is "tailor made" to suit the circumstances for the field it is
installed on. Hence, every approach has a different approach plate
which lists some of the variables, mainly the important variables for
pilots.

Hope that clarifies matters.
--
Alan
brian whatcott
2010-03-23 23:21:13 UTC
Permalink
Hi, bin me:

I am going to suppose your old data for these UK fields is correct.

And I am going to suggest that a current DAFIF database will show the
great majority of (US) ILS glideslope transmitter placements is about
1200 feet from the runway threshold.

It may be helpful to review ILS instrument approach plates, which show
height above threshold, when on the glideslope.
This is normally around 55 foot elevation at the threshold.

If you recall that the usual glideslope angle is 3 degrees, I think you
will be able to work out the distance from threshold to the glideslope
that this elevation represents, with elementary trigonometry.
That's 50 / (tan (3 deg) feet.

Regards

Brian W
Post by bin me
Post by brian whatcott
Post by bin me
Post by brian whatcott
/snip/
the localiser array is at the end of the runway and the glideslope
array is around (lots of variables) one third of the way down the
runway, but always adjacent to the TDZ marked on the runway. /snip/
Alan
A better guide for glideslope antenna positioning is around 1000 ft
from the runway end, near the PAPI and VASI sites, for obvious reasons.
Brian W
TDZ is the place for the G/S aerial by International agreement, and
practical considerations./snip/
Quite. Just about never "a third the way down the runway" in fact.
Brian W
Brian,
As I said earlier in the thread, "the glideslope array is around (lots
of variables) one third of the way down the runway". I did not say it
was "a third of the way down the runway".
It depends on many factors, mainly designed for commercial transport
standards. To make it absolutely clear, it can be well into the runway
with a third being around the typical maximum with lots of variables,
(but somewhere in the world, including Farnborough in the UK, it
is/could be more than a third). It will always give an undershoot area,
the length of that area is again variable. As I also stated in the same
post, I have been out that loop for more than 10 years and things do
change.
Take some examples, all using very old date, but it does show the point.
London City 28 (5.5 degree), overall length is around 4948ft. 3962ft
available from TDZ. That is about 20% in.
Coventry 23 (3.0 degrees) is 5988ft overall, 4396ft available from TDZ.
That is 27% in.
Sumburgh 27 (3.0 degrees) is 3871ft overall, 2796ft available from TDZ.
That is 28% in.
Edinburgh 24 (3.0 degrees) is 8399ft overall, 5997ft available from TDZ.
That is 28.5% in.
Waterford, Ireland 21 (3.33 degrees) is 4701ft overall, 3201ft available
from TDZ. That is 32% in.
Isle of Man 08 (3.0degrees) is 5755ft overall, 3861ft available from
TDZ. That is 33% in.
Bournemouth 08 (3.0 degrees) is 7451ft overall, 4996ft available from
TDZ. That is 33% in.
Farnborough 24 (3.0 degrees) is 8005ft overall, 5011ft available from
TDZ. That is 37% in.
The conclusion is many factors are taken into account when designing an
ILS. The glideslope aerial/TDZ is one variable which is/can be, used to
ensure an A/C following the ILS will arrive at the TDZ if all procedures
are followed. You will often find the aerial position gives a 55ft
runway threshold crossing height - but not always.
Every ILS is "tailor made" to suit the circumstances for the field it is
installed on. Hence, every approach has a different approach plate
which lists some of the variables, mainly the important variables for
pilots.
Hope that clarifies matters.
brian whatcott
2010-03-24 02:24:13 UTC
Permalink
Hmmm...perhaps I was too ready to accept your inputs.
Take Baginton (That's Coventry Airport, one of my haunts from long ago.)

If I download Google Earth, and take a look at runway 05/23 there, I see
there are displaced thresholds. It looks like you are counting the
unusable lengths in your computations. Remember, the issue is not
length of runway past the touch down point, its the placement of ILS
glideslope transmitters from the threshold. Don't take my word for
it, look for yourself.
Manchester airport looks good - it has ILS. Take a look.

Brian W
Post by brian whatcott
I am going to suppose your old data for these UK fields is correct.
And I am going to suggest that a current DAFIF database will show the
great majority of (US) ILS glideslope transmitter placements is about
1200 feet from the runway threshold.
It may be helpful to review ILS instrument approach plates, which show
height above threshold, when on the glideslope.
This is normally around 55 foot elevation at the threshold.
If you recall that the usual glideslope angle is 3 degrees, I think you
will be able to work out the distance from threshold to the glideslope
that this elevation represents, with elementary trigonometry.
That's 50 / (tan (3 deg) feet.
Regards
Brian W
/snip/
Post by brian whatcott
Post by bin me
Coventry 23 (3.0 degrees) is 5988ft overall, 4396ft available from
TDZ. That is 27% in.
/snip/
bin me
2010-03-25 01:41:44 UTC
Permalink
Brian,
I used very old approach plates. I assumed the runway length quoted on
the chart was the usable runway length, (in between any displaced
thresholds - I can't see a pilot generally being interested in runway
length he can't use for that landing calculation i.e. before the
threshold), that is why I used the quoted length. The plate gives the
distance from TDZ to the runway end (including past any displaced
threshold at the localiser end if its designated as a stop way, as far
as I know).

I will have a look at the week-end to see if I can find the chart
symbols/definitions. I accept if it is the "entire paved length" and
not as I assumed between any displaced threshold(s) the maths would be
wrong.

Alan
Post by brian whatcott
Hmmm...perhaps I was too ready to accept your inputs.
Take Baginton (That's Coventry Airport, one of my haunts from long ago.)
If I download Google Earth, and take a look at runway 05/23 there, I
see there are displaced thresholds. It looks like you are counting the
unusable lengths in your computations. Remember, the issue is not
length of runway past the touch down point, its the placement of ILS
glideslope transmitters from the threshold. Don't take my word for
it, look for yourself.
Manchester airport looks good - it has ILS. Take a look.
Brian W
Post by brian whatcott
I am going to suppose your old data for these UK fields is correct.
And I am going to suggest that a current DAFIF database will show
the great majority of (US) ILS glideslope transmitter placements is
about 1200 feet from the runway threshold.
It may be helpful to review ILS instrument approach plates, which show
height above threshold, when on the glideslope.
This is normally around 55 foot elevation at the threshold.
If you recall that the usual glideslope angle is 3 degrees, I think
you will be able to work out the distance from threshold to the
glideslope that this elevation represents, with elementary trigonometry.
That's 50 / (tan (3 deg) feet.
Regards
Brian W
/snip/
Post by brian whatcott
Post by bin me
Coventry 23 (3.0 degrees) is 5988ft overall, 4396ft available from
TDZ. That is 27% in.
/snip/
--
Alan
Alan
2010-03-25 00:35:32 UTC
Permalink
Post by brian whatcott
I am going to suppose your old data for these UK fields is correct.
And I am going to suggest that a current DAFIF database will show the
great majority of (US) ILS glideslope transmitter placements is about
1200 feet from the runway threshold.
Post by bin me
Post by brian whatcott
Quite. Just about never "a third the way down the runway" in fact.
I was giving a few examples of where "just about never" did not apply.
The examples were around or greater than 1/3 of the way along the
runway. I was not suggesting this was the normal situation, its just
one of many variables used to ensure an ILS meets specification.

As you quote USA documentation, I hope you are familiar with the FAA
publication AIM. The current online version is here:
www.faa.gov/air_traffic/publications/atpubs/aim/Chap1/aim0101.html#1-1-9

I quote:
2. The glide slope transmitter is located between 750 feet and 1,250
feet from the approach end of the runway (down the runway) and offset
250 to 650 feet from the runway centerline. It transmits a glide path
beam 1.4 degrees wide (vertically).

The FAA use this as the basic guidance as the CAA do. However, it does
not mean in either Country it can't be varied to suit conditions. In
the USA generally, more land (real estate) is available for airport use,
and the approach can usually be accommodated with a GS position 750 -
1200 feet into the surface. In the UK with less land available, the
approach on occasions has to be modified to accommodate obstacle/terrain
clearance (lots of other reasons) which change the GS position - as
shown in the list in the last post.

Similarly, the FAA use (or in the past did, not sure about now with GPS)
marker beacons, while in the UK we tend to favour DME. DME takes up
less land, also maker beacons (all same frequency, different modulation
for type, OM, MM etc) are less precise in areas with close by airports
with ILS approaches. An accident occurred in the UK over pilot
confusion. The pilot was approaching airport A but was a little off
course and picked up airport B OM and started the descent - straight
into a hill. Since then, the UK favoured DME. Our airports can be
closer together, hence the reliance on DME when land is more difficult
to obtain. Another example of how the "general arrangement" is modified
to suit local conditions.
Post by brian whatcott
It may be helpful to review ILS instrument approach plates, which show
height above threshold, when on the glideslope.
This is normally around 55 foot elevation at the threshold.
If you recall that the usual glideslope angle is 3 degrees, I think you
will be able to work out the distance from threshold to the glideslope
that this elevation represents, with elementary trigonometry.
That's 50 / (tan (3 deg) feet.
Again from AIM, Fig 1-1-7 ILS: gives the 55ft (+/- 5ft) runway
threshold crossing height.

Again, this is not a limiting factor! It is a "general arrangement" -
it will be modified somewhere to take account of local conditions.

As this group is UK_rec_aviation, I hope nobody takes offence to the
frequent USA references.

Regards
Alan
Post by brian whatcott
Post by bin me
Post by brian whatcott
Post by bin me
Post by brian whatcott
/snip/
the localiser array is at the end of the runway and the
glideslope array is around (lots of variables) one third of the
way down the runway, but always adjacent to the TDZ marked on the
Alan
A better guide for glideslope antenna positioning is around 1000
from the runway end, near the PAPI and VASI sites, for obvious reasons.
Brian W
TDZ is the place for the G/S aerial by International agreement,
and practical considerations./snip/
Quite. Just about never "a third the way down the runway" in fact.
Brian W
Brian,
As I said earlier in the thread, "the glideslope array is around
(lots of variables) one third of the way down the runway". I did not
say it was "a third of the way down the runway".
It depends on many factors, mainly designed for commercial transport
standards. To make it absolutely clear, it can be well into the
runway with a third being around the typical maximum with lots of
variables, (but somewhere in the world, including Farnborough in the
UK, it is/could be more than a third). It will always give an
undershoot area, the length of that area is again variable. As I also
stated in the same post, I have been out that loop for more than 10
years and things do change.
Take some examples, all using very old date, but it does show the point.
London City 28 (5.5 degree), overall length is around 4948ft.
3962ft available from TDZ. That is about 20% in.
Coventry 23 (3.0 degrees) is 5988ft overall, 4396ft available from
TDZ. That is 27% in.
Sumburgh 27 (3.0 degrees) is 3871ft overall, 2796ft available from
TDZ. That is 28% in.
Edinburgh 24 (3.0 degrees) is 8399ft overall, 5997ft available from
TDZ. That is 28.5% in.
Waterford, Ireland 21 (3.33 degrees) is 4701ft overall, 3201ft
available from TDZ. That is 32% in.
Isle of Man 08 (3.0degrees) is 5755ft overall, 3861ft available from
TDZ. That is 33% in.
Bournemouth 08 (3.0 degrees) is 7451ft overall, 4996ft available
from TDZ. That is 33% in.
Farnborough 24 (3.0 degrees) is 8005ft overall, 5011ft available
from TDZ. That is 37% in.
The conclusion is many factors are taken into account when designing
an ILS. The glideslope aerial/TDZ is one variable which is/can be,
used to ensure an A/C following the ILS will arrive at the TDZ if all
procedures are followed. You will often find the aerial position
gives a 55ft runway threshold crossing height - but not always.
Every ILS is "tailor made" to suit the circumstances for the field
it is installed on. Hence, every approach has a different approach
plate which lists some of the variables, mainly the important
variables for pilots.
Hope that clarifies matters.
--
Alan
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