CYMM ILS25 Question

This forum has been developed to discuss aviation related topics.

Moderators: lilfssister, North Shore, sky's the limit, sepia, Sulako, I WAS Birddog

Post Reply
A-Team
Rank 2
Rank 2
Posts: 64
Joined: Wed Oct 19, 2005 10:40 pm

CYMM ILS25 Question

Post by A-Team »

Since they moved PERVA off of the YMM VOR, this note "3400 from YMM VOR to PERVA FAF R-053 1NM" appeared on the ILS25 approach. What does it actually mean?

The P-Turn is 2800 and 25nm is 3900 so 3400 doesn't make sense.

Thanks in advance.
http://postimage.org/image/5iyv0qbn3/
Image
Image
---------- ADS -----------
 
arctic navigator
Rank 3
Rank 3
Posts: 189
Joined: Sun Feb 27, 2005 12:16 am
Location: Where the cold wind blows

Re: CYMM ILS25 Question

Post by arctic navigator »

It is giving you the location of PERVA so that you can safely transition onto the approach from the VOR without any type of RNAV/GPS capability as the VOR is not on the ILS track. For whatever reason they're allowing you to descend from the 25NM safe but the PT altitude is too low for obstacle clearance. Saying that altitude doesn't make sense is just like saying the DME arc safe altitude of 4000' doesn't make sense either with the 25NM safe of 3900'. Initial, intermediate, and final approach segments all have different obstacle clearance requirements as defined in the TERPS, but it could also be a function of radio reception or interference in the case of the arc altitude.

Here's a link that will take you to the FAA's TERPS document, have fun if you decide to dig into it further.

http://www.faa.gov/regulations_policies ... ntid/11698
---------- ADS -----------
 
atpl53
Rank 3
Rank 3
Posts: 157
Joined: Tue May 01, 2007 3:28 pm

Re: CYMM ILS25 Question

Post by atpl53 »

My reading of this plate would be that if I was approaching from the South, the TWR closed and planning on doing a full procedure approach, I would fly 4300 till the 10DME ARC, descend to 3900 till YMM VOR, pick up the 053 Radial from YMM while descending to 3400. At PERVA pick up the IMM LOC 075 Radial fly outbound, descend to 2800, complete the procedure turn and pick up the glide path.

Given that I will be at 2490 at PERVA inbound, 2200 if LOC only, crossing PERVA outbound at 3400 makes sense. It gives me lots of clearance from the high point at 1376 to the South of PERVA.
---------- ADS -----------
 
photofly
Top Poster
Top Poster
Posts: 11306
Joined: Tue Jan 18, 2011 4:47 pm
Location: Hangry and crankypated

Re: CYMM ILS25 Question

Post by photofly »

I don't get it either. The 25 mile MSA that applies between YMM and PERVA is 3300, so is the note about 3400 an additional restriction, or a permission? If it's a permission then it's redundant.
---------- ADS -----------
 
A-Team
Rank 2
Rank 2
Posts: 64
Joined: Wed Oct 19, 2005 10:40 pm

Re: CYMM ILS25 Question

Post by A-Team »

arctic navigator wrote:It is giving you the location of PERVA so that you can safely transition onto the approach from the VOR without any type of RNAV/GPS capability as the VOR is not on the ILS track. For whatever reason they're allowing you to descend from the 25NM safe but the PT altitude is too low for obstacle clearance. Saying that altitude doesn't make sense is just like saying the DME arc safe altitude of 4000' doesn't make sense either with the 25NM safe of 3900'. Initial, intermediate, and final approach segments all have different obstacle clearance requirements as defined in the TERPS, but it could also be a function of radio reception or interference in the case of the arc altitude.

Here's a link that will take you to the FAA's TERPS document, have fun if you decide to dig into it further.

http://www.faa.gov/regulations_policies ... ntid/11698
75 views before a reply... Glad I wasn't the only one scratching my head at this. :wink:
arctic navigator wrote:It is giving you the location of PERVA so that you can safely transition onto the approach from the VOR without any type of RNAV/GPS capability as the VOR is not on the ILS track.
But if you were between the 090-North-270 Radial, the 25NM Safe Alt situated off the VOR is lower @ 3300'. So why not 3300'? :rolleyes:
arctic navigator wrote:Initial, intermediate, and final approach segments all have different obstacle clearance requirements as defined in the TERPS
A lot like why a lot of the Outer-T approach altitudes are actually higher than your 25NM safe altitude.

http://postimage.org/image/cvcjj1u39/

Image
---------- ADS -----------
 
photofly
Top Poster
Top Poster
Posts: 11306
Joined: Tue Jan 18, 2011 4:47 pm
Location: Hangry and crankypated

Re: CYMM ILS25 Question

Post by photofly »

I guess what happened is that:

- The VOR is an IAF
- Navigation instructions have to be given how to get from each IAF to the FAF where the PT begins
- There's not enough room to show the leg on the chart so the instructions are included as a side note instead
- Each segment of the approach has to be given a minimum altitude
- the altitude is calculated by cranking the handle on the appropriate set of rules
- in this case the rules produce 3400.
---------- ADS -----------
 
55+
Rank 6
Rank 6
Posts: 437
Joined: Tue Jul 26, 2005 4:49 pm

Re: CYMM ILS25 Question

Post by 55+ »

The operational note you are referring to is a transition. For obstacle clearance the enroute criteria apply ie VHF airway which is 4-2-2-4. In other words primary obstacle clearance(1000ft ROC) is 4nm each side of center line followed by secondary 2nm. I assume there is obstacle issues within that transition that warrant 3400ft. Me personally as a designer, I wouldn't publish such a narrow 1nm transition - not worth it in such a small confined area, I would have utilized a terminal fix from the VOR source to the FAF(DME) reference with a radial.

:)
---------- ADS -----------
 
old_man
Rank 5
Rank 5
Posts: 319
Joined: Sun Aug 16, 2009 3:58 pm

Re: CYMM ILS25 Question

Post by old_man »

atpl53 wrote:My reading of this plate would be that if I was approaching from the South, the TWR closed and planning on doing a full procedure approach, I would fly 4300 till the 10DME ARC, descend to 3900 till YMM VOR, pick up the 053 Radial from YMM while descending to 3400. At PERVA pick up the IMM LOC 075 Radial fly outbound, descend to 2800, complete the procedure turn and pick up the glide path.

Given that I will be at 2490 at PERVA inbound, 2200 if LOC only, crossing PERVA outbound at 3400 makes sense. It gives me lots of clearance from the high point at 1376 to the South of PERVA.
???

Why would you not just fly the arc at 4000 until you intercept the Loc (255*), follow that in, and then descend on the slope?
---------- ADS -----------
 
old_man
Rank 5
Rank 5
Posts: 319
Joined: Sun Aug 16, 2009 3:58 pm

Re: CYMM ILS25 Question

Post by old_man »

A-Team wrote:
A lot like why a lot of the Outer-T approach altitudes are actually higher than your 25NM safe altitude.

http://postimage.org/image/cvcjj1u39/

Image

Actually no. If you notice that approach has LPV mins. That means if you have the right equipment you can follow a 'slope' down to those LPV mins. The reason for the Outer-T altitudes being so high is that you intercept that 3* slope far out enough to allow you to fly a stabilized approach down.
---------- ADS -----------
 
MRP
Rank 2
Rank 2
Posts: 58
Joined: Thu Sep 18, 2008 7:36 am

Re: CYMM ILS25 Question

Post by MRP »

This is a transition to the FAF for those unable to fly the ARC in a non-radar environment. They simply didn't have the space on the chart to place it on the diagram so it is written in the top corner. Assume no radar, no GPS, only 1VHF on YMM VOR and DME, and the other VHF on IMM localizer.

Approaching from the South East as an example, fly directly to the YMM VOR

1) Fly no lower than 4300 outside YMM 25 DME
2) No lower than 3900 within 25DME
3) after crossing the VOR and on R-053 to PERVA you may descend to no lower than 3400 to the FAF to commence a procedure turn
4) After crossing PERVA you would now disregard the VOR and fly the LOC for the procedure turn. You may now descend to 2800 untill established back inbound on the localizer
5) the rest you should be able to figure out.

Hope this helps.
---------- ADS -----------
 
Post Reply

Return to “General Comments”