ILS Procedure question

[COFlyBoy]

What causes a false glide slope signal?

Any radio antenna has side lobes. These are areas off the sides of the intended transmission direction where a bit of radio energy sort of leaks out. RF engineers try to minimize the side lobes when designing antennas, but it impossible to remove them completely. For the GS there are side lobes at multiples of the glideslope angle.

So at 6 degrees you can pick up the side lobe of the GS antenna and this is the false GS.

 

[gismo]

The PTS would disagree, as it tells the examiner to fail you if you don't maintain the published altitude +/-100 feet outside the FAF on a SIAP. The published altitude after the PT is 6600. I believe there's a similar reference in the IPH, but I'm too tired to look it up right now.

OK. Might be "improper" on a checkride but not contrary to FARs. That said I must admit I'm surprised that deliberately flying at a legally and safely acceptable GS intercept altitude on an ILS approach would generate a pink slip.

 

[John Collins]

The PTS would disagree, as it tells the examiner to fail you if you don't maintain the published altitude +/-100 feet outside the FAF on a SIAP. The published altitude after the PT is 6600. I believe there's a similar reference in the IPH, but I'm too tired to look it up right now.

There is a slight semantic difference in what the PTS says:

Prior to beginning the final approach segment, maintains the desired altitude ±100 feet, the desired airspeed within ±10 knots, the desired heading within ±10°; and accurately tracks radials, courses, and bearings.

So, I complete the procedure turn 3.4 miles from BUFFS and decide to descend from 7000 feet to 6600 at 318 feet/NM which for my approach speed of 120 Kts, that is 636 feet.minute. I will arrive at 6600 feet a few 10ths of a NM from BUFFS at the GS intercept point. Even though I have been cheating and have been following the GS since 7000 feet, I have not violated any PTS standard.

 

[poadeleted20]

OK. Might be "improper" on a checkride but not contrary to FARs.

That's why I chose that word in the earlier discussion.

That said I must admit I'm surprised that deliberately flying at a legally and safely acceptable GS intercept altitude on an ILS approach would generate a pink slip.

I'm not sure anyone's proven that flying above the depicted GS intercept altitude on an ILS is necessarily legal and/or safe in all conditions. OTOH, flying it "by the book" guarantees both. In any event, the practical test is about flying to specified standards, and this is the published standard for that test -- if you can't or won't do it, you don't pass.

 

[poadeleted20]

So, I complete the procedure turn 3.4 miles from BUFFS and decide to descend from 7000 feet to 6600 at 318 feet/NM which for my approach speed of 120 Kts, that is 636 feet.minute. I will arrive at 6600 feet a few 10ths of a NM from BUFFS at the GS intercept point. Even though I have been cheating and have been following the GS since 7000 feet, I have not violated any PTS standard.

This particular case is such that the difference in where you start the letdown is very small -- unless you go a very long way out beyond BUFFS, you'll be very close to GS intercept when you finish the PT. But as a matter of general procedure, if you remain at the PT altitude for a significant amount of time after completing the PT before beginning your descent to the published segment altitude, you aren't doing it "as published." In addition, if you start following the GS from outside the GS service volume, you'll need to crosscheck that you don't go below the GS intercept altitude before entering the GS service volume.

 

[midlifeflyer]

The PTS would disagree, as it tells the examiner to fail you if you don't maintain the published altitude +/-100 feet outside the FAF on a SIAP. The published altitude after the PT is 6600.

Is it? I thought the published "minimum" altitude was 6600 with no published maximum.

In a situation like the GXY ILS, I would tend to head down to the published minimum but I'm in no rush to do so and if I happen to intercept the GS on the way down... Do pretty much the same with approaches with multiple stepdowns.

 

[midlifeflyer]

I'm not sure anyone's proven that flying above the depicted GS intercept altitude on an ILS is necessarily legal and/or safe in all conditions.

True - you might hit that tower in which they put the big hole at the published altitude for airplanes to fit through - stay too high and you'll hit it .

If it's not legal/safe to be above a certain altitude, there is a published maximum. The approaches into KORL are good examples, where there are published maximums to remain below KMCO approaches. See for example the ILS or LOC 7 http://aeronav.faa.gov/d-tpp/1112/00305IL7.PDF and the published maximum at BUVAY

 

[Palmpilot]

I'm not sure anyone's proven that flying above the depicted GS intercept altitude on an ILS is necessarily legal and/or safe in all conditions.

We all know that flying legally does not always guarantee safety, but how could staying above a minimum altitude on an approach plate, which is incorporated into the regulations by reference, be illegal?

OTOH, flying it "by the book" guarantees both.

What descent profile is specified by the book when you're above a minimum altitude?

In any event, the practical test is about flying to specified standards, and this is the published standard for that test -- if you can't or won't do it, you don't pass.

What descent profile is specified by the PTS when you're above a minimum altitude?

 

[gismo]

This particular case is such that the difference in where you start the letdown is very small -- unless you go a very long way out beyond BUFFS, you'll be very close to GS intercept when you finish the PT. But as a matter of general procedure, if you remain at the PT altitude for a significant amount of time after completing the PT before beginning your descent to the published segment altitude, you aren't doing it "as published." In addition, if you start following the GS from outside the GS service volume, you'll need to crosscheck that you don't go below the GS intercept altitude before entering the GS service volume.

FWIW, I can think of a couple scenarios where postponing the descent would have an operational advantage. One is when you're currently above ice laden clouds and want to remain there as long as it's still possible to complete the approach safely. Another would be the same cloud deck but no ice, just turbulence that you'd rather avoid.

 

[John Collins]

The PTS would disagree, as it tells the examiner to fail you if you don't maintain the published altitude +/-100 feet outside the FAF on a SIAP. The published altitude after the PT is 6600. I believe there's a similar reference in the IPH, but I'm too tired to look it up right now.

I had a long conversation on this subject with a DPE that I have a very high opinion of, he is very competent, both as a pilot and examiner. He doesn't agree with your interpretation of the PTS.

 

[HPNPilot1200]

I had a long conversation on this subject with a DPE that I have a very high opinion of, he is very competent, both as a pilot and examiner. He doesn't agree with your interpretation of the PTS.

My CRJ700 sim instructor is a DPE and believes you can do it either way as long as you do not descend below the minimum published altitude. Think of the glideslope outside the final approach segment as advisory VNAV. You still have to make all the stepdowns.

 

[poadeleted20]

FWIW, I can think of a couple scenarios where postponing the descent would have an operational advantage. One is when you're currently above ice laden clouds and want to remain there as long as it's still possible to complete the approach safely. Another would be the same cloud deck but no ice, just turbulence that you'd rather avoid.

Agreed. Just make sure the technique you use doesn't violate any altitude restrictions or put you above the GS when it comes in.

 

[poadeleted20]

My CRJ700 sim instructor is a DPE and believes you can do it either way as long as you do not descend below the minimum published altitude. Think of the glideslope outside the final approach segment as advisory VNAV.

That's a good way to think of it. No excuses if the approach is fouled up as a result of following an unreliable GS outside the GS service volume or busting a published min/max altitude.