DME Step descents

[flying ginge]

Interested in people's thoughts about DME step descents. Does it seem to anybody that there is potential for ultimate balls up when in a non-radar environment the tower controller clears you "descend DME steps to 3000ft" for example? I think it would be way to easy to automatically set 3000ft on the alerter/assigned indicator if one wasn't focused, totally forgetting about intermediate steps. Especially going into somewhere unfamiliar. Why not say "descend via the DME steps". May seem insignificant to some but am interested in what others think. Any ATCers out there?

FG

[flyby_kiwi]

Because descend DME steps to 3000ft means excactly that......... To descend VIA the steps do a limiting height of 3000'.

Remeber that it is YOU who is resposible for your terrain clearance and the controller is not in a postion to sort out your terrain clearance unless under radar terrain which will not be the case in somewhere like NZGS.

Agree - could be a bad day if you misread the step.

[No Further Requirements]

Also, if there is someone at 2000ft that the ATCer was separating you with, that's why 3000ft would be the descent issued. If you wanted to let someone descend all the way to the deck, the ATC would say (in Oz anyway) "cleared DME arrival".

Just as an aside, if you do a localiser approach, the ATC doesn't step you down, or a VOR/DME, so what stops people stuffing that up?

Cheers,

NFR.

[Chimbu chuckles]

The easiest way to fly DME steps is using a constant profile which you have calcuated before you ever leave the ground and written in pencil on your chart...should be easy in NZ...what do you have 10-15 airports with DME arrivals?

Use a profile that relates to your aircraft type...for instance 3 x DME dist=altitude in a slow or pressurised aircraft.

Just say for instance that the DME steps are, in reverse order, 2000' until 6 DME, 3300 until 10 DME , 4800' until 16 DME, 7000 until 25 DME. Your aircraft descends on a 3 x profile under normal circumstances....i.e it loses 1000' every 3nm or 300'/nm (a baron for instance descending at 180 GS/1000' per min)

To work out the 'limiting step' (which one you will cut on your normal descent) multiply each DME distance x 3.

6x3=1800' (3x + 200')
10x3=3000' (3x + 300')
16x3=4800' (3x)
25x3=7500' (3x)

If you descend on your normal 3 x profile you will be below the 6 DME step by 200' and the 10 DME step by 300'.....so the 10 DME step is your 'limiting step'.

Your descent point now becomes a function of your profile...cruising at 9000' your descent point would be 29 DME....29x3=8700'...and all the way down, every few miles at convenuant numbers, you do a little math. 25 DME should be at 7800', cool....20DME should be at 6300', spot on...15 DME should be at 4800'...hmm 100 low so I'll just make a slight reduction in ROD (say 200'/min) ...12 DME 3600', ok again (return to original ROD-100'/min)..10 DME 3300' and level at 3000'...it will happen at 9 DME.

So when given a clearance (in Oz) "descend 3000' not below DME steps" you can happily set 3000' in the window and descend concentrating on flying the aeroplane without constantly glancing down at the chart trying to read (in the dark with your torch?) what it says.

You can use exactly the same methodology for working out the limiting steps on a VOR/DME app or a LOC/DME approach...write the profile on the applicable chart in pencil and fly them the same way...safe in the knowledge you'll break no altitude limits....VOR/DME app minima is 2DME/750'? That's 3x + 150'....if that profile keeps you above any other altitude limits on the whole approach fly the whole approach at 3 x DME dist +150 = altitude. If another alt/dme limit further back in the approach is + 200 fly that profile until that limiting step and then 'lose' the extra 50'.

Just say for arguments sake the profile was 3x-200'... you could fly the whole approach at that profile and arrive at the minima about 1.2nm early...3x3.2 =960(-200)=760'....then fly level for a mile take a look and if not visual GA....or you could ignore the 3x-200 profile and fly the whole thing at 3x+150 and arrive at the minima at the MAP, which is SOP in most companies.

If your companies SOP is add 50' to MDA to get a company 'DH' don't forget to do that too...and then we would have a profile of 3x+200'...and away we go...:ok:

Runway profiles?...why not! You can calculate a rough one by eyeballing where on the aerodrome chart the DME is...far end of a 12000' runway? 12000' is roughly 2nm and we descend at 300'/nm...roughly speaking the runway profile would be 3x -600'....far end of a 6000' runway (or halfway down a 12000' one) would be 3x-300'...at the arrival threshold straight 3x (actually probably +50 or so feet because your correct touchdown point is passed the DME :OK:

Or you can do a quick calc on finals and compare DME distance/altitude when on papi/vasi and then make a note on the landing chart. This is really usefull when on base on a pitch black (or all black :ok: ) night so you can see where you at...remember though on mid base at say 2.5 DME you'd want to be a little high because you're descending while not pointed straight at the runway...if you're exactly on profile on early/mid base you'll be low turning finals.

Practice this in day VMC until you are completely comfortable.

Chuck

[pakeha-boy]

flying ginge...good question mate,but stray from from the "thoughts" thing...decent profiles(STARS)whether they be in radar contact or not,treat them with golden gloves.These profiles are aimed at one thing and one thing only...Terrain clearance !!!

I fly into Mexico/Honduras/Guatamala on a regular basis..ie ..below transistion altitudes(and they vary just like downunder) there is no radar,no atis, no loving care.As previous posts have said ....its your dollar,spend it wisely...unless you have GWPS/EGWPS,like I have(the idiot factor) then you are on your own(in a non-radar).Use normal rates of decent,3 degree glide paths(unless other-wise stated).

These profiles/notes etc are their for a reason,does the controller give a sh@t,sure they do,but its sort of hard when they cant see you....comply with all restrictions,they are there for a reason,especially if you are not familiar with where you are.........now I know why my a$$hole hurts every time I go somewhere new:eek: ......moepapa

[Ready Immediate]

Not sure what happens in NZ or if this is less ambiguous but I say "Decend to 3000 not below the DME steps".

RI

[ravan]

As Ready Immediate said, "Descend to 3000' not below DME steps" is unambiguous. I get it all the time around SE Queensland both in training and charter and find the instruction perfectly clear in its intent. :ok:

[DirtyPierre]

"Descend to 3000' not below DME steps" This is the way we train the controllers in Brisbane to give descent outside radar coverage.

Or "leave controll airspace descending not below the DME steps" is a common instruction for descending into places like Coffs when the tower is closed.

[Binoculars]

Does it seem to anybody that there is potential for ultimate balls up when in a non-radar environment the tower controller clears you "descend DME steps to 3000ft"

In twenty+ years I've never heard that phraseology. I wouldn't blame you for being confused, but pray tell, just where did you hear it? It's meaningless.

[Capt Claret]

flying ginge

That's not a phrase I've heard in Aus and I suspect it's an NZ thing.

However, if when cleared to "descend DME steps to 3000ft" one can't grasp that there are limits on the descent to 3000, then perhaps one shouldn't be flying.

It's not much difference to being cleared to climb or descend with a requirement to be at/above/below a particular level by a specified time/distance. In fact, it's no different, just expressed differently.

[pakeha-boy]

C.C. ....dont think its a kiwi thing at all...just like pilots,controllers use (on occassion) non-standard phraseology.In the non radar environment you would think that would be at least more careful.

If you are cleared(to decend) via an arrival(star) you are cleared to descend to the lowest altitude on that arrival,and comply with all restrictions on that arrival.If a STAR is not availble,to which I am familiar,controllers will give you a decent profle using DME/ALTITUDE restrictions.

The onus is on you to comply Any clown,like myself would check ,MEA,s,MOCAs,etc etc,before even thinking of decending non radar .If you dont understand the clearance,dont accept it.

Nothing worse than breaking out and wondering why there is a goat(rider) standing on that cloud :{ hahake

[Chimbu chuckles]

:hmm: I think you missed the point of my post...and I wasn't arguing the correctness or otherwise of the phraseology :ok:

[pakeha-boy]

C.C...didnt miss it at all ,it was a great post,well thought out as well.......the error is on my part,it was directed at Capt C.....the piss is on me.......aroha mai(apology)

[Cloud Cutter]

Binos

That's the standard here in NZ, straight out of MATS. "Descend DME steps to 3000 ft" - There is nothing ambuguous about it. It is a shorthand version of "descend in accordance with the DME steps to not below 3000 feet"

Ginge

In response to you question, most operators adopt a proceedure of writing the clearance altitude on the nav log, and setting MSA and the DME step altitude in the allerter as they are passed - so there is almost zero chance of getting it wrong even at the end of a 12 hour day after a late night:ok: As mentioned it is good airmanship to adopt a constant profile based on the highest part of the DME step.

eg. approaching GS from DABIP (or RO):
MSA 6400
20-30 DME 5700
14-20 DME 4600
0-14 DME 3000

If you draw a little picture you will see that 4600 at 14 DME is the highest pont on the steps, so plan your descent to be 4600 (or say 5000) at 14 DME. Of course it's different if you're anticipating visual, in which case it may be wise to get to the step and level out.