inner marker = 100 agl?

[taseal]

right?

I was talking about this with my inst and another inst student... they were pretty sure its 50 agl, but I insisted it was 100 agl. (the MAP for CAT II)

I looked around (aim too) and it says that it is at the DH of a CAT II landing. Which is 100 agl.

so is it 50, or 100?

[BuickCFI]

i thought it was just runway threshold? marker beacons are for distance information, not altitude info. if you happen to hit the DH at the MM then that is coincidence

[taseal]

Originally Posted by BuickCFI

i thought it was just runway threshold? marker beacons are for distance information, not altitude info. if you happen to hit the DH at the MM then that is coincidence

yes. This is considering you are on glideslope. Forgot to mention that, sorry!

[BuickCFI]

considering the 3* glideslope and the IM is normally at the threshold. i get 50ft at threshold to touchdown at the touchdown zone (300ft/nm divided by 6 for the 1000ft zone)

just remember the beacons are for distance. so even if the DH for a CatII approach is 100` arriving at the IM may just be coincidence.

then again i am very tired now and i could be wrong (i don't think so though)

[Fly4Pay]

According to AIM 1-1-9 f 2 c:

The IM will indicate a point at which an aircraft is at a designated decision height (DH) on the glide path between the MM and landing threshold.

So which decision height--50' or 100'? I've seen it listed (as in Wikipedia) as:

The inner marker, when installed, shall be located so as to indicate in low visibility conditions the imminence of arrival at the runway threshold. This is typically the position of an aircraft on the ILS as it reaches Category II minima.

To me, this would depend on what they are calling the "threshold." The actual threshold of the runway should have a threshold crossing height of approximately 50 feet. The overrun would have a crossing height of about 100 ft...

We do it all off of radio altitude, so it's never been a factor...

[casey]

Originally Posted by Fly4Pay

We do it all off of radio altitude, so it's never been a factor...

there are CAT II approaches that arent authorized for RA mins, and in those cases the IM is the decision point.

[Fly4Pay]

Originally Posted by casey

there are CAT II approaches that arent authorized for RA mins, and in those cases the IM is the decision point.

Yeah, I know... but my point was that we do all RA....

[LarryinTN]

The Cat II DH is less than 200' and not lower than 100'. 100' is most common. The IM will coincide with the Cat II DH, whatever that may be. On approaches with an IM you are at the Cat II DH when either the RA reaches the published RA minimum or you begin receiving the IM--whichever comes first.

[PeanuckleCRJ]

A CAT II approach's mins are never based upon your hearing of the IM. They are based on either a radio altimeter altitude or barometric altitude.

The IM will coincide with the minimums if on glideslope, but it is not utilized in the decision of landing.

[LarryinTN]

Originally Posted by PeanuckleCRJ

A CAT II approach's mins are never based upon your hearing of the IM. They are based on either a radio altimeter altitude or barometric altitude.

The IM will coincide with the minimums if on glideslope, but it is not utilized in the decision of landing.

Not according to our OpSpecs...

[taseal]

sounds like I have brought up a pretty interesting topic!

[B767Driver]

Originally Posted by casey

there are CAT II approaches that arent authorized for RA mins, and in those cases the IM is the decision point.

Per our ops specs...if the RA in not authorized for the approach, we are not permitted to conduct a CAT 2 with only the marker beacons. You cannot fly the approach.

[B767Driver]

Originally Posted by PeanuckleCRJ

A CAT II approach's mins are never based upon your hearing of the IM. They are based on either a radio altimeter altitude or barometric altitude.

The IM will coincide with the minimums if on glideslope, but it is not utilized in the decision of landing.

In Delta's Ops specs the DH used to be either the Baro or Radar altitude, whichever came first. Now for Cat 2s and 3s it's RA only. They actually set the Baro bug to field elevation for both approaches.