Question about ILS/DME

[Amish RakeFight]

...by the way there's also a marker sensitivity switch which should be checked along with the marker lights. Before executing the ILS, one of the checks is to ensure that each of the three markers light up. The markers are sometimes refered to as "fan markers" and only while above the marker will you hear the specific morse code identifier for each. By setting the sensitivity of the fan marker, you can adjust how long the dots and dashes of morse code go on for. A low sensitivity will allow for a shorter duration of the marker compared to the high sensitivty where the marker signal is picked up further away and sounds for a longer time as you traverse across each marker.

 

[Amish RakeFight]

A couple of other things.

The reason there are even markers are to provide you "milestones" along the approach as you descend on the ILS.

Normally, glideslope intercept is considered the FAF for the approach. This usually occurs before reaching the OM although one can theoretically intercept it at an altitude concurrent with the OM GS intercept altitude. On non-precision approaches, you'll use the OM as the point where you begin timing the approach and where you'll start a descent down to your MDA (minimum decision altitude).

For a CAT I ILS approach which allows for a 200' DH, the MM (middle marker) would correspond to this altitude. IOW, the MM tone can be used as a backup of when to commence the MAP or whether to continue on and land.

For a CAT II approach an inner marker might be installed between the landing runway and the MM. It would also correspond to the DH on this type of approach and make a distinct morse code informing you of your position along the approach.

 

[lawfly]

"DME lights"?

 

[nosehair]

"DME lights"?

Yeah, he means Marker lights - we think. Sort of a logical misstatement. The markers are at a known measured distance.

 

[nosehair]

...only while above the marker will you hear the specific morse code identifier for each.

Actually, there's not a morse code identifier. It's just a continuous series of dashes, or dot/dash, or dot/dot. The markers are also differentiated by tone and time between dashes and dots.

The Outer Marker: (low tone)Doh,..Doh,..Doh,..
The Middle Marker: (high-middle tone) Dah,Dot,Dah,Dot,
Inner Marker: (high pitched shriek!)Deet!Deet!Deet!Deet!

 

[Amish RakeFight]

Actually, there's not a morse code identifier. It's just a continuous series of dashes, or dot/dash, or dot/dot. The markers are also differentiated by tone and time between dashes and dots.

The Outer Marker: (low tone)Doh,..Doh,..Doh,..
The Middle Marker: (high-middle tone) Dah,Dot,Dah,Dot,
Inner Marker: (high pitched shriek!)Deet!Deet!Deet!Deet!

You're right, I should have been more specific.

Only [dashes], [dots] and [dots and dashes]... but they sound just like morse code!

 

[Amish RakeFight]

Yeah, he means Marker lights - we think. Sort of a logical misstatement. The markers are at a known measured distance.

Marker lights found on the panel that illuminate blue, amber and white corresponding to the marker one is presently traversing.

 

[Fedora]

The MB's were realy not put there as checklist reminders, so I wouldn't count on them being there.
In reality, they apply more to LOC only or VOR approaches, as the "decision" point for a go around or landing for an ILS is based on your altitude on the glide path and not a MB.
Good luck in your training!