Alternate minima

[Woodwork]

The diiference between Y and Z plates are the missed approach performance gradients.

Yes, that's quite perplexing. The two approaches seem otherwise identical. I can only presume the higher MAP gradient on the Yankee is designed to protect against more than just terrain.

[Capn Bloggs]

I can only presume the higher MAP gradient on the Yankee is designed to protect against more than just terrain.

Simple really. If you can hack a higher gradient during the Missed Approach, you can go down to a lower Minimum. The limiting obstacle is at a set distance away: the lower you are when you start the MA, the steeper gradient you have to achieve to get over that obstacle.

[PPbash]

That is an easy question. The flying school makes more money from you flying all the way to Canberra and back. With slight variations all ILS are basically the same so EN or AV are all you need to practice on. If the flying school wants you to practice at Canberra for whatever altruistic reasons then tell them you want to do it in a simulator or synthetic trainer. Saves a lot of money and is just as effective.

As if, do you really think a flying school in MB takes a student to CB for an ILS? Tee Emm, you’re not all related to that poor guy in a wheelchair from south park, timmy?

[Woodwork]

Simple really. If you can hack a higher gradient during the Missed Approach, you can go down to a lower Minimum. The limiting obstacle is at a set distance away: the lower you are when you start the MA, the steeper gradient you have to achieve to get over that obstacle.

I think you might have me confused. I'm not talking about why you have different gradients for different minima - that's self-evident. I'm wondering why two different approach plates are produced for exactly the same approach.

The ILS-Y SI minima, not adjusted for QNH, are 2440/2.3 for a 2.5% MAP, and 2170/1.2 for a 5% MAP. The ILS-Z minima are the same for a 2.5% MAP, and split the difference at 2300/1.5 for a 3.3% MAP. That is the only difference between the approaches. Surely the good folks at ASA could save a page in DAP and a few megs of memory in the flight bag by inserting the 3.3% MAP gradient into the ILS-Y plate, and decommission the ILS-Z? That's what's perplexing, why we bother with two plates that reproduce identical information.

That, in turn, got me thinking that perhaps ATC might need to clearly indicate they need a good, strong climb in the MAP to protect against nearby airspace or a STAR, but then now I think about it, ATC wouldn't know which climb gradient you're capable of achieving, so that was a silly thought.

Probably some rule somewhere that you can't have more than five minima fields per plate or something.

[newifr]

Thanks for all the posts. It has been very informative.

newifr

[brown_eyes]

Fixed Reserve.

Just returning to Oz after a few years overseas and was wondering if there has been any changes to the requirements on the Fixed Reserve.

1. Is the Fixed Reserve sacred or can it be used?

2. If it can be used under what circumstances?

[bentleg]

1. Is the Fixed Reserve sacred or can it be used?

2. If it can be used under what circumstances?

Answered in a separate thread