trickijedi
Posts: 3201
Joined: Sun May 13, 2001 4:35 pm

"Capture The Localizer" - Specifics

Sun Sep 26, 2004 7:25 pm

Basic question here...

I understand that the localizer is a system involving a radio signal (frequency?) used for lining up an aircraft with its intended runway heading.

When an aircraft "captures" or "intercepts" the localizer, what cockpit indications are there that this has been achieved? Is the process the same when the glidescope "comes alive"?

Also, when landing using a visual approach, are the localizer and glidescope (despite being part of an ILS approach) still used for initial guidance?

Thanks!


Its better to be on the ground wishing you were in the air than be in the air wishing you were on the ground. Fly safe!
 
air2gxs
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RE: "Capture The Localizer" - Specifics

Sun Sep 26, 2004 8:26 pm

A driver can probably explain it better but, when you capture the localizer it means that the flight director and/or autopilot are using the localizer for guidance. The normal indication is the indicator (whether on the EADI or the APD, approach progress display), goes from yellow (armed) to green (captured).

The glideslope coming alive means that the needle has respobded to the radio signal (usually this indicates armed).
 
PhilSquares
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RE: "Capture The Localizer" - Specifics

Sun Sep 26, 2004 10:08 pm

The localizer signal is used to reference the runway extended center line. When you are given a vector to intercept the localizer, you are "established" when you have captured the localizer. I can't give you the "legal" definition for captured, but as a check airman, I look for the localizer centered. Then there are momentary deviations from center as the aircraft descends on the glidepath.

As for glide slope interception, it's the same. If you're using a flight director, then the pitch and bank steering bars (if you're using a dual cue F/D) should be centered.

For a visual approach, it's really a matter of technique. If you're visual, then it's up to you, but it doesn't hurt. If you have a glass cockpit then an acceptable technique is to extend the runway centerline and use the magenta line as a guide.
Fly fast, live slow
 
pilotpip
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RE: "Capture The Localizer" - Specifics

Sun Sep 26, 2004 10:40 pm

As for the visual part, you can use the ILS for guidance assistance. But, the important key of a visual approach is having the runway in sight. This is why most runways will have some sort of visual glideslope indicator. On a clear day, you can see an airport from many miles away.

DMI
 
SlamClick
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RE: "Capture The Localizer" - Specifics

Sun Sep 26, 2004 11:01 pm

You can say that the localizer and the glideslope are "captured" when the needles, or the flight director command bars begin to respond to them. This usually involves their tracking in suddenly from one side of the instrument, to the center (from the top for the glideslope) If the autopilot is engaged, the plane will begin to maneuver to maintain the centerline of these signals. It is captured.

Of course it is still up to the pilots to configure for landing and to use thrust to maintain the proper speed and rate of descent.
Happiness is not seeing another trite Ste. Maarten photo all week long.
 
trickijedi
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RE: "Capture The Localizer" - Specifics

Wed Sep 29, 2004 2:59 pm

Thanks for the explanations.

So on the following transmission...
"... descend and maintain three thousand, cross (name your fix) at three thousand, cleared for the ILS (name your runway) approach..."

Does cross mean intercepting the localizer? And is there any particular reason why ATC would specifically have to instruct the aircraft to do this? Traffic purposes? Lining them up?

Also, for commercial pilots, how often would you choose to land your aircraft completely VFR and without any guidance from your instruments? Or in other words, how often would you go completely old school?
Its better to be on the ground wishing you were in the air than be in the air wishing you were on the ground. Fly safe!
 
PhilSquares
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RE: "Capture The Localizer" - Specifics

Wed Sep 29, 2004 3:46 pm

All things being equal, I will do a visual anytime I am able. It's no real big deal at all and generally will get you on the ground a few minutes quicker.

As far as the clearance you are asking about, it would be great to see the approach you're talking about but here goes an answer. If you are on the localizer and have been cleared for the approach, you can either descend along the glideslope or you can do a descent to the cleared altitude and intercept the glideslope at the lower altitude. Personally, I will intercept the glideslope out wherever I can and then just follow it down from there.
Fly fast, live slow
 
tbanger
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RE: "Capture The Localizer" - Specifics

Wed Sep 29, 2004 7:21 pm

Does cross mean intercepting the localizer? And is there any particular reason why ATC would specifically have to instruct the aircraft to do this? Traffic purposes? Lining them up?

The emphasis on cross is not fly over or past the fix, it is on the altitude. Cross the fix at 3,000. Meaning, if you are descending, then don't descend below 3,000 UNTIL you have intercepted the glideslope....then continue descending. Cross the fix AT 3,000.....don't be above or below it.

 
PhilSquares
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RE: "Capture The Localizer" - Specifics

Wed Sep 29, 2004 9:15 pm

The thing to remember is when you are on a published segment of the approach and have been cleared for the approach then the published altitudes apply. If you intercept the g/s at 4000' for example and the outer marker altitude is 3000' you can descend to 3000 along the glide slope and continue the approach or descend down to 3000' provided that is the appropriate altitude for that segment of the approach.
Fly fast, live slow
 
sccutler
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RE: "Capture The Localizer" - Specifics

Thu Sep 30, 2004 10:40 am

A bit additional: when the clearance states that you are "Cleared for the approach," it means that you may proceed with all of the elements of the published instrument approach procedure without further instructions from the approach controller (i.e., once you are actually established on an approach segment, you may turn, descend, etc. as necesary to comply with the procedure without further clearance from the controller).

Many such clearances, for ILS or Localizer approaches, will ask that you "advise when established" on the approach and that typically means (as referenced above) when the localizer comes off of full deflection, i.e., you are within the relatively narrow beam transmitted by the localizer and in line with the runway.

At that point, they will usually then direct you to tower frequency (if the field is tower controlled), or authorize you to change to the common traffic advisory frequency (if the field is uncontrolled).
...three miles from BRONS, clear for the ILS one five approach...

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