Staying high for quicker GS intercept

BrettInLJ

BrettInLJ

Well-Known Member
What are your thoughts on this? I hadn't flown instrument for a long time and was on a flight for my IPC. We were shooting the ILS at Oxnard, CA and intercepted the localizer at 4000 feet. The approach shows a glideslope intercept of 3400 feet, but the GS needle was alive so I planned to just stay at 4000 to intercept it early.

My instructor corrected me and had me decend further to 3400 feet and wait a little bit longer to intercept. She said that I should intercept the glideslope at that altitute because that is what was shown on the NOS chart. Can someone tell me what is wrong with waiting for the GS needle to center and then following it down to 3400 feet? I would still be decending before that 3400 intercept point, only I would happen to already be at the correct decsent profile for the rest of the approach. It has been years since I got my instrument rating, but I was under the impression that as long as I was not to far out, it was fine to intercept the glideslope from below a little bit early. Am I wrong?
 
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I would still be decending before that 3400 intercept point, only I would happen to already be at the correct decsent profile for the rest of the approach. It has been years since I got my instrument rating, but I was under the impression that as long as I was not to far out, it was fine to intercept the glideslope from below a little bit early. Am I wrong?

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Glideslope intercept altitudes may be a minumum, a maximum, mandatory (hard), or a recommended altitude. Procedurally, you must maintain glideslope intercept altitude (published or assigned) until intercepting the glideslope. When the GS intercept altitude is a recommended altitude, you must only comply with other IAP altitudes (FAF, for example), until established on the GS. Insure you crosscheck the GS check altitude published above the "lightening bolt" as you cross that point while on GS. The reason for this is protect against erroneous GS signals. Just remember, the GS is only to be used inside 10 NM.
 
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I would still be decending before that 3400 intercept point, only I would happen to already be at the correct decsent profile for the rest of the approach. It has been years since I got my instrument rating, but I was under the impression that as long as I was not to far out, it was fine to intercept the glideslope from below a little bit early. Am I wrong?

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Glideslope intercept altitudes may be a minumum, a maximum, mandatory (hard), or a recommended altitude. Procedurally, you must maintain glideslope intercept altitude (published or assigned) until intercepting the glideslope. When the GS intercept altitude is a recommended altitude, you must only comply with other IAP altitudes (FAF, for example), until established on the GS. Insure you crosscheck the GS check altitude published above the "lightening bolt" as you cross that point while on GS. The reason for this is protect against erroneous GS signals. Just remember, the GS is only to be used inside 10 NM.

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So what is the depiction for min vs. max vs. mandatory intercept altitude on the approach plate? In the case of OXR it has a line under 3400, so I would assume that would be a minimum, right? The intercept point is about 10 miles out, but by decending at a certain rate a little further out that happens to be along the glidesope path should be ok as long as I cross check everything and verifty that I am in the right place and altitude at that intercept point. Here is the approach:

http://download.aopa.org/iap/20050609/SW-3/oxr_ils_rwy_25.pdf
 
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So what is the depiction for min vs. max vs. mandatory intercept altitude on the approach plate? In the case of OXR it has a line under 3400, so I would assume that would be a minimum, right? The intercept point is about 10 miles out, but by decending at a certain rate a little further out that happens to be along the glidesope path should be ok as long as I cross check everything and verifty that I am in the right place and altitude at that intercept point. Here is the approach:



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Line under is a minimum altitude. Line over is a maximum altitude. Lines above and below the altitude number is mandatory.
 
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Line under is a minimum altitude. Line over is a maximum altitude. Lines above and below the altitude number is mandatory.

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You learn something new every day.
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Line under is a minimum altitude. Line over is a maximum altitude. Lines above and below the altitude number is mandatory.

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You learn something new every day.
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Maybe he uses Jepp charts (or isn't instrument rated).

Friggin' NOS and their stupid hieroglyphics... Jepps simply say, MAXIMUM, MINIMUM, RECOMMENDED, etc.

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It's also, all things being equal, to inercept the GS from below the GS because should you ever begin to fly couple approaches, most autopilots require an "underside" interception to capture.
-LC
 
For the OXR ILS (I shoot this particular approach about every other day) you were correct that you could have just intercepted the GS at 4000 at followed it down. In fact, that is the best way to do it, since it gives you more time to get stabilized and it simplifies the approach. adding the step-down is unnecessary and gives you one more thing to potentially screw up. Go teach that to your instructor. BTW, where do you fly out of?
 
In essence, the instructor is not wrong either... If you are cleared for the approach, you can go down to the next step down altitude and wait until the GS comes alive.
I think they are techniques, but neither one is right or wrong.
 
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In essence, the instructor is not wrong either

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I didn't mean to say that the instructor was wrong. It's just one of those things that I didn't learn until fairly recently and in this particular case the student's plan was better than the instructor. It's very likely that the instructor believes that you are required to do the step down, which just isn't the case.
 
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adding the step-down is unnecessary and gives you one more thing to potentially screw up.

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Simple answer.....don't screw it up. Flying a stepdown shouldn't add that much extra tasking, but I see your point too.....why make work for yourself?

Agree that both techniques are valid.
 
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For the OXR ILS (I shoot this particular approach about every other day) you were correct that you could have just intercepted the GS at 4000 at followed it down. In fact, that is the best way to do it, since it gives you more time to get stabilized and it simplifies the approach. adding the step-down is unnecessary and gives you one more thing to potentially screw up. Go teach that to your instructor. BTW, where do you fly out of?

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I fly out of Vista Air at Whiteman. To give you some background, this approach was as part of my IPC and the second flight I had done in over 18 months. The previous flight was my BFR, so needless to say I am very rusty on instrument flying, rules, procedures, etc. I flew the OXR ILS approach again yesterday, and this time the controller brought us in tight and had us descend to 3400. We ended up intercepting the localizer at NELLY, which is past the 3400 GS intercept so we were already above the glideslope. I ended up getting back on it and stabilized relatively quickly and the rest of the approach all the way down to minimums was great. The 172's don't have DME either so that adds to the workload a bit, but that's a good thing for training in my opinion. I still am a little frustraded because I feel like I would be overwhelmed if I was single pilot IFR and had to divert somewhere while fumbling with charts and plates while keeping the airplane right side up. My situational awareness is not quite there yet, and I hope I just need to get the cobwebs out. I wish there was a sim I could use.

I'm happy with Vista Air so far and my instruction there. As far as the right procedure, now I think she is just teaching me more exact flying, and even if it adds workload to descend to the glideslope altitude first, the more work the better while in training. After my commercial training is done I'm going to reward myself with a checkout in the G1000 equiped 182T they have, and shoot my first GPS approach.
 
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two words,

"delay vector"

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We didn't mind since it shaved off a tenth of hobbs time and we were VMC. Good to know for future reference though.
 
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I flew the OXR ILS approach again yesterday, and this time the controller brought us in tight and had us descend to 3400. We ended up intercepting the localizer at NELLY, which is past the 3400 GS intercept so we were already above the glideslope. I ended up getting back on it and stabilized relatively quickly and the rest of the approach all the way down to minimums was great.

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A word of caution I'm surprised noone else has mentioned here.........it's fine to intercept the glideslope further out/above the glideslope intercept *altitude* like mentioned before if the plate says you can. However, be careful about intercepting the glideslope from above like you did on that approach. False glideslopes can exist above the actual glideslope. If you intercept from above the glideslope, you run the risk of following one of these false glideslopes.

Also, as an aside, the controller is "supposed" to have you established at least 3 miles outside the FAF/GS intercept, per their rules. Sounds like this controller may have fudged that a bit.
 
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I flew the OXR ILS approach again yesterday, and this time the controller brought us in tight and had us descend to 3400. We ended up intercepting the localizer at NELLY, which is past the 3400 GS intercept so we were already above the glideslope. I ended up getting back on it and stabilized relatively quickly and the rest of the approach all the way down to minimums was great.

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A word of caution I'm surprised noone else has mentioned here.........it's fine to intercept the glideslope further out/above the glideslope intercept *altitude* like mentioned before if the plate says you can. However, be careful about intercepting the glideslope from above like you did on that approach. False glideslopes can exist above the actual glideslope. If you intercept from above the glideslope, you run the risk of following one of these false glideslopes.

Also, as an aside, the controller is "supposed" to have you established at least 3 miles outside the FAF/GS intercept, per their rules. Sounds like this controller may have fudged that a bit.

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Exactly what happened. When intercepting I determined that I was at the right altitude for where I was (NELLY) and the intercept went smooth, so I stayed with it. Good point though. Note that the FAF is not anywhere near the GS intercept though. I was well outside the FAF (more than 3 miles) but inside the NELLY.
 
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Also, as an aside, the controller is "supposed" to have you established at least 3 miles outside the FAF/GS intercept, per their rules. Sounds like this controller may have fudged that a bit.

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Come on down to the DFW area and shoot some practice ILS approaches. If you get vectored 3 miles out from the FAF/GS intercept, you're flying in the middle of the night. Most of the time, they vector you in, and you get the LOC and GS alive at the same time. It's happened to me everytime I shoot the AFW 16L ILS.
 
The truth is that false glideslopes are so steep that you would have to be pretty out of it not to notice that your descent rate is off the chart.

The only issue on intercepting the GS early, is that it is technically not useable outside the end of the "feather" on the Jepps. I forget what NOS uses to depict the useable volume, but I'm sure someone here knows.

I would say that not only is it ok to intercept the GS at what ever your altitude is (as long as it's inside the useable distance), but actually preferrable. If you're worried about false glideslopes, then check your GS crossing altitude at the OM. It is not only simpler and smoother to intercept it further out, but also safer -- more terrain clearance and more altitude in the event of a problem,such as a powerplant failure, etc.

It also is less likely that you'll descend too early.

I am quite sure that this is still the recommendation of the ALPA charting and instrument procedures committee -- at least it was when I was on it.
 
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