ILS query
Joined: Jun 2005
Posts: 390
Likes: 0
From: London
Not sure what you are getting at. Until you're on the localiser, trusting or not trusting the glideslope is irrelevant.
Unless you're talking about CDA. In which case, I find that it depends on the aircraft. On the 737NG I found that the G/S indication was pretty reliable on an intercept angle. But on the A320 the indication seems to fluctuate up and down considerably so I use the projected level off arrow to judge what V/S I need to avoid levelling off before the G/S.
P
Unless you're talking about CDA. In which case, I find that it depends on the aircraft. On the 737NG I found that the G/S indication was pretty reliable on an intercept angle. But on the A320 the indication seems to fluctuate up and down considerably so I use the projected level off arrow to judge what V/S I need to avoid levelling off before the G/S.
P
Joined: Mar 2005
Posts: 1,338
Likes: 1
From: Uh... Where was I?
Miles to go and height.
G/S can be very misleading, although I believe it makes you feel low while you are on base. not because of the G/S plane which, if I recall correctly, tends to bend up to the sides. But because in base you are going to fly more miles than the distance to the runway. Many follow it and later realise they are low.
At 4 NM though with 30º interception, things can be different because the track miles and direct distance miles are practically the same, so G/S should be a good reference to use along with height-miles.
That is a pretty tight vector I wouldn't accept in IMC, except maybe if I don't feel pushe by anyone, with a low enogh radar minimum vectoring altitude is low, I have "the beast" under control in speed, configuration and profile so as to be stabilised by 1,000, checklist read and trying not to forget to obtain the landing clearance. Personally I think that if such manoeuvre is not planned, there is little or no saving at all compared to a 6 NM final, for instance.
G/S can be very misleading, although I believe it makes you feel low while you are on base. not because of the G/S plane which, if I recall correctly, tends to bend up to the sides. But because in base you are going to fly more miles than the distance to the runway. Many follow it and later realise they are low.
At 4 NM though with 30º interception, things can be different because the track miles and direct distance miles are practically the same, so G/S should be a good reference to use along with height-miles.
That is a pretty tight vector I wouldn't accept in IMC, except maybe if I don't feel pushe by anyone, with a low enogh radar minimum vectoring altitude is low, I have "the beast" under control in speed, configuration and profile so as to be stabilised by 1,000, checklist read and trying not to forget to obtain the landing clearance. Personally I think that if such manoeuvre is not planned, there is little or no saving at all compared to a 6 NM final, for instance.
Joined: Jun 2009
Posts: 17
Likes: 0
From: out west
Use of ILS glidepath signals outside designated area
From a formal aspect.......
ICAO Annex 10 details the limitations on the use of an ILS.
Under ICAO regulations the signal is only assured useable within the appropriate designated area of coverage.
For the glidepath the lateral area is within 8 degrees of the centreline and then only to a range of 10 miles from the threshold. There is a vertical constraint as well.
The glidepath signal is formed in space by bouncing the radiated energy off the ground in front of the antenna and has several anomalies and variables. Signals within the designated coverage areas will have been flight checked.
The radiated signal will, of course, extend much further so beware using it - that will probably not have been examined.
As an aside, the loalizer also has quite strict areas of coverage, the azimuth covrage is only +/- 35 degrees at 17 miles from the localizer. and 25miles within 10degress of C/L.
ICAO Annex 10 details the limitations on the use of an ILS.
Under ICAO regulations the signal is only assured useable within the appropriate designated area of coverage.
For the glidepath the lateral area is within 8 degrees of the centreline and then only to a range of 10 miles from the threshold. There is a vertical constraint as well.
The glidepath signal is formed in space by bouncing the radiated energy off the ground in front of the antenna and has several anomalies and variables. Signals within the designated coverage areas will have been flight checked.
The radiated signal will, of course, extend much further so beware using it - that will probably not have been examined.
As an aside, the loalizer also has quite strict areas of coverage, the azimuth covrage is only +/- 35 degrees at 17 miles from the localizer. and 25miles within 10degress of C/L.
Joined: Oct 2000
Posts: 436
Likes: 0
From: N. Europe
The underside of the GP typically droops at the sides, and the sensitivity and structure tends to change as well.
The coverage, as far as signal levels go, goes out to eight degrees azimuth to either side, but the GP will often not be pretty that far out, even if it is usable. This is highly site dependent.
Even though the GP should be checked to safeguard GP interception all the way out to the coverage limits, I'd make sure to follow the book and be on the LOC before descending below MSA on the glide.
The coverage, as far as signal levels go, goes out to eight degrees azimuth to either side, but the GP will often not be pretty that far out, even if it is usable. This is highly site dependent.
Even though the GP should be checked to safeguard GP interception all the way out to the coverage limits, I'd make sure to follow the book and be on the LOC before descending below MSA on the glide.
