ILS approaches and stepdowns

[FL420]

OK, back to the original topic. Anyone want to explain why it's legal to intercept and track the localizer beyond 18 nm miles out as issued in many an approach clearance?

I can't speak strictly to the "legality" of it but be aware that some localizers are flight-checked and certified to have a service volume beyond 18 miles. I don't know offhand how a pilot can readily find that information. Perhaps from the navaid section of airnav.com?

 

[FL420]

Personally, on a localizer only or even a VOR, why drop like a rock to the MDA? Just set your VSI at a decent rate to where you arrieve at the MAP over the end of runway. Like 120kias you need about 550 fpm decent. This makes for a smoother ride.

Not a good idea, especially in higher performance aircraft or in aircraft operated under 121 or 135. If you don't get to the MDA before you get to the MAP on a NP IAP, you will likely not be in a position to land in the designated touchdown zone or the first third of the runway without performing an unstabilized approach with an excessive rate of descent.

 

[A Squared]

Not a good idea, especially in higher performance aircraft or in aircraft operated under 121 or 135. If you don't get to the MDA before you get to the MAP on a NP IAP, you will likely not be in a position to land in the designated touchdown zone or the first third of the runway without performing an unstabilized approach with an excessive rate of descent.

Yep, what he said.

If you did this in part 135 or 121 ops, you would never land legally, or alternately, every landing would be a violation. Remember that under those parts, you must use a normal descent and touch down in the touchdown zone. Now, I'll admit to being a little hazy on the exact definition of "touchdown zone" but I seem to recall that it's the first 1/3 of the runway. If we go with that definition, and add the fact that a "normal descent" is about 3 degrees, it would take 4470 ft to descend from 250 feet above the threshold (Standard location of the MAP on a straight in approach is directy over the threshold) at a "normal descent", so you could never land legally on a runway shorter than 14,310 ft using this technique. Next time you're out doing some discretionary flying, level off at 250 feet above the touchdown, and fly directly over the threshold of the runway. Notice how high you are and how steeply you'd have to descend to get down from this altitude to the runway.

Anyone got a reference for the definition of "touchdown zone" ???

 

[SSDD]

The first 3000' of the runway, or half the length if less than 6000'.

 

[A Squared]

The first 3000' of the runway, or half the length if less than 6000'.

Thanks, got a source for that?

 

[VNugget]

P/CG:

TOUCHDOWN ZONE - The first 3,000 feet of the runway beginning at the threshold. The area is used for determination of Touchdown Zone Elevation in the development of straight-in landing minimums for instrument approaches.

 

[Fedora]

Outside the FAF, you need to heed the stepdown altitudes. Riding the GS can take you below these and result in a violation. (has happened on the Paradise arival into LAX.) The step downs keep you clear of both VFR coridor and crossing trafic to the north side runways. Riding one dot high keeps you legal on the step down altitudes until reaching the FAF (tail of the feather)

 

[nosehair]

I've seen this question a lot, but cannot recall if such an approach exists. Step down minimum altitudes which are higher than the glidslope.
Anybody got a copy of one?

 

[Seadogrun]

I've seen this question a lot, but cannot recall if such an approach exists. Step down minimum altitudes which are higher than the glidslope.
Anybody got a copy of one?

I'm not sure there should be one.

It would take some math to figure out if the stepdowns are actually below the GS as the profile views are not in scale.

It would be interesting if someone could find one.

 

[Say Again Over]

I don't have the plate handy, but I heard this is true at KLAS also, whereby the G/S goes below the floor. Just a rumor.