IAL - Entry below IAF altitude

[blacksmith]

Approaching an IAF at an altitude above MSA/LSALT but below the initial approach altitude, can I enter that approach without climbing?

Example, Amberley ILS-Z RWY 15. Assuming I'm flying the full approach. Tracking 320 to the NDB at 4000 (above 10NM MSA) ready to commence the approach. Chart says must cross IAF not below 5100 however there is an immediate descent to 2500 before a procedure turn. Can I cross the IAF at 4000 and proceed outbound descending to not below 2500? Thoughts?

[hoss]

Yes, be adventurous and try 3400.
My chart makes no mention that I have to be at 5100.

[Bladeangle]

Thoughts?

Don't see any reason why not, the 5100 is the minimum surveyed height for the pattern.

Down to 2500, procedure turn at 8.8.

[alphacentauri]

Yes you can.

It comes down to the limitations of charting all available options on an approach plate. Basically we always try and design a procedure that starts at the highest MSA applicable for the approach. In this case its 5100ft, and that is what we chart. But if you are coming from another sector, or are established within 10nm, then (provided you stay within the area) you are protected at those heights.

In this case you can maneuver as required anywhere within 10nm at 3400ft...that includes starting the procedure.

Alpha

[waren9]

Chart says must cross IAF not below 5100

i've always known it as the procedure commencement altitude when shown on the lateral view. usually coincident with minimum height in the hold.

remember that the concept of a positive fix ohead, descending in the hold from enroute altitudes as required and timed outbounds was all they had back in the day before dme, gps, radar vectoring, controlled airspace, traffic info, 25nm msa's etc. approach design still has hangovers from then.

questions like yours arise because these scenarios are now safely possible with respect to terrain that technology didnt previously allow or the procedure rules hadnt even thought of, let alone cater for back then.

i wouldnt start the approach overhead below 5100 (unless under radar control) on a flight test if thats what youre getting at, especially octa. a last minute requirement for holding ohead will see you red faced.

trying to find a reference but i dont like my chances

[blacksmith]

Great thanks guys. That's my feeling - safe yes, but not for a flight test. Thanks for the feedback.

[hoss]

Absolutely, waren9 makes a lot of good points.

Legal versus Practical(safe).

I would expect to go over at an altitude closer to 10000' in a jet.

[Capt Fathom]

I would expect to go over at an altitude closer to 10000' in a jet.
That jet must have the descent profile of a brick!

[VH-FTS]

I no longer have a VTC to confirm, but if you're conducting this approach outside Amberley hours, consider the Brisbane control steps. From memory the control step was 4500', so the approach was started down at the MSA to remain OCTA while still being safe.

I can't see why it would fail a CIR test to commence the approach below 5100. This would be something I'd discuss with the ATO to gain his expectation of how it will be flown. I'd dare say he'd be more impressed about your application of IFR and local knowledge.

If AMB is active they might just vector your anyway.

[Capt Fathom]

FTS. Lets not overly complicate the original question!

[Capn Bloggs]

I would expect to go over at an altitude closer to 10000' in a jet.

7000ft....

[VH-FTS]

If anyone finds my reasoning complicated they shouldn't hold a CIR. The original post revolved around AMB, I gave an extra and relevant consideration.

[hoss]

I'll meet you in the middle at 8500' for the first attempt but I think we'll be 'dragging it in'.

Without checking the charts I was just relating it to Launy were we regularly go over the top around transition for the ILS reversal. Similar distances with a 80/260 turn.

Regards hoss

[Capn Bloggs]

I'll meet you in the middle at 8500' for the first attempt but I think we'll be 'dragging it in'.
27 track miles (2x12 + about 3 for the procedure turn), not allowing for the DME position.

Final offer, 7950ft. :)

[Wan]

Bloggs / Hoss - how do you get these numbers? I use the following rules of thumb: 3 x altitude for distance and 5 x groundspeed for rate of descent.

So for 27 miles, that would give 9000 feet (to threshold, I add a few miles if joining a circuit).

[Capn Bloggs]

Medium Jets 101: 9k/30nm, 7k/25nm, 5k/20nm.

or

3x altitude to lose + 5nm decel (+ a couple of miles for 10k slowup to 250)

Descent rate on final better: half the groundspeed (add zeros as required to make numbers nice). GS 140, sink 70 (0).

On that AMB ILS unless I was familiar, I'd be erring on the side of caution; lower than usual. Back to 7000ft over the top outbound!! :}