VOR/DME Approach Chart

[Errajane]

I've not seen an approach chart like this before, since coming to Asia so I'm wondering if I have interpreted the chart correctly. My question lies in when the timing of 2.5 minutes actually begins before turning inbound. This is how I have interpreted the chart. (I fly category B aircraft)

1. After over MIA VOR, track outbound on 001 deg and commence descent from 3000 ft (at an arbitrary 500 ft/min).

2. On reaching 2200 ft, maintain this altitude and start timing for 2.5 minutes. At a groundspeed of 120 knots, this will give a distance of 8.2 NM from the VOR. (3.2 NM during the descent at 500 ft/min, and 5 NM during the 2.5 min level segment)

3. When 2.5 minutes timing is up, commence the turn to intercept the inbound course 166 deg. Maintain 2200 ft until 6.4 DME from MIA, and then commence the descent to the MDA.

4. If no visual contact by 1.7 DME, commence the Missed Approach Procedure.

http://i.imgur.com/ikstWWy.jpg

The ambiguity lies in when the 2.5 minutes timing begins. Where I come from and where I've been trained, we usually commence the timing overhead the VOR station outbound, but that obviously isn't the case with this procedure as that would not give you sufficient distance to commence the inbound descent at 6.4 DME.

Have I interpreted this chart correctly? Your thoughts appreciated.

[Nightstop]

Timing starts from over the VOR outbound. The relevance of 2200' is that you must not descend below it until 6.4 DME inbound on the final approach course. If you're really smart you can fly a CDA to reach 2200' at the 6.4 DME point inbound without actually levelling off, that saves fuel and keeps the environmental noise down.

[TopBunk]

NS is correct, the 2.5 minutes are timed from the VOR overhead.

The descent from 6.4d and 2200ft to the MDA/MAP at 1.7d is a nominal 3deg path as shown on the chart. What you may be missing is that the chart is drawn showing altitudes, and the runway threshold is 286ft, so your 6.4d at 2200ft is actually about 1900ft above the threshold.

[BOAC]

What others are 'missing' is the question!:ugh: It cannot be flown as advocated by you two. Is 2.5/1.5 minutes enough time to reach 6.4DME outbound? That requires more than 250kts procedure speed outbound for Cat C/D and 155kts for Cat A/B and that gives no room to intercept the radial either. Everyone happy with that? I can see errajane's logic in flying the 'turn' but more terrain info is needed. Since there is no 'do not exceed xx DME outbound' warning one HOPES there is no terrain problem!

Why on earth the turn point is not defined on DME I cannot fathom! Not a chart I would be happy with and I would probably turn at about 8D like errajane to give track intercept space. Back to company for a decision, errajane, I think!

[ChickenHouse]

Strange map, never seen such before. If you have to start turn 2.5 min. after MIA on 001 and have to reach 166 inbound at 6.4 DME, then this would be no constant turn, but would require turn with increasing bank? Any more enlightening in the textual part of the procedure?

[BOAC]

If you have to start turn 2.5 min. after MIA on 001 and have to reach 166 inbound at 6.4 DME, - this apart from the fact that you cannot do it?

[compressor stall]

FWIW, the VYMD AIP entry (not Jepp) has the same outbound timing labelled so that it is unambiguous that the timing starts passing MIA (not that was really in any doubt).
http://www.ais.gov.mm/files/pdf/VYMD.pdf
That does not, however, solve the issue that you go outbound in a cat C aircraft at 240kts=4nm/min*1.5mins you'll only get 6nm…..

[BOAC]

It would appear to be a wise precation to go to Mandalay on the road?

[AerocatS2A]

My guess is that you turn at the time from MIA. If you didn't have any great tail wind or anything you end up turning inside 6.4D and can descend below 2200 as soon as you are established on final. On the other hand if your timing took you beyond 6.4D due to a high tail wind or whatever then you must wait until 6.4 D on final before descending below 2200'. Clear as mud.

[compressor stall]

Possibly, but if you did it by the book at your maximum category speed for initial approach, you'll be rolling out inbound with the descent point for the 3° slope half a mile behind you….

As for how far out the design could have been drawn to take you out safely at 2200, well Google earth shows some reasonably high hills starting at 10DME - just off the map north of the rivers' junction. Photo from them looking south to the airport. Panoramio - Photo of Sagaing - View from the top of Sagaing hill ???? (http://www.panoramio.com/photo/44962985?) these are probably the limiting factor.

[OzExpat]

Initial Approach speed is essentially used to determine splayed angle between outbound and inbound track. This often results in different outbound courses for a common final approach track. Let me say, right here, is that I hope that I'll never have to fly with a pilot who doesn't have the first clue where outbound timing commences

Okay, the splay angle (aforementioned) is based on the outbound max IAS for category and a max bank angle of 25 degrees. This is done because the procedure designer, regardless of his or her flying experience, cannot predict the point at which a pilot will reach the point at which a lower IAS is required. Prior to final approach in a non-precision approach, the design speed and bank angle are assumed under Pans Ops - and TERPs, for that matter.

But you better be at the appropriate speed for final approach when passing the FAF!

Now then, you don't go below 2200 until established on final approach. Period. If you want to*make*a CDA approach, you'll find a few airports where obstacles have been placed, seemingly without regard for a 3-degree approach. That's life and it happens so suck it up and deal with it professionally.

If it means that you can't reach MDA at your precious 3-degree approach then, hey, YOUR MDA will be higher. Your company procedures should account for that in SOPs - in some countries, there's actually a legal requirement for this. There's an expression that covers this situation admirably - Proper Prior Planning Prevents Poor Performance.

[BOAC]

May I inject some realism to this discussion? - not unless you understand the original question:ugh:

Where is aterpster when you need him? Does Jepp carry this chart? If it is the same, how does Jepp reckon we fly it?

[Amadis of Gaul]

I'd just declare an emergency and go somewhere with an ILS.

[JAR]

Why would you be at 240 kts?

[Amadis of Gaul]

'Cause at 230 he goes into a panic attack?

[de facto]

JAR Why would you be at 240 kts?

On my type,(catC) a procedure turn is to be flown at 170 kts.

[MarkerInbound]

BOAC that is the Jepp chart. And there is also an ILS to 17.

[BOAC]

So we need to hear from the Jepp man......

[aterpster]

OK465:

There are RNAV fixes FF17 and MA17 associated with this approach, so it is coded in somebody's onboard nav database somewhere.

I can see loading this approach and receiving the "TILT" warning message.

It's coded in the Garmin database as two procedures: one for the A/B turn and one for the C/D turn.

The coding flies outbound to 6.4 DME then turns inbound to FF17.

This is a DME required procedure so the timing makes no sense whatsoever. Seems like either a poor implementation of PANS-OPs or a poor rendering on the AIP chart.

[FlightDetent]

Hi,

I believe the defenition of the procedure is very clear, timing starts overhead. Positioning of the text box in the profile view section of the chart is fairly common, and is just a matter of graphical layout, with no real substance.

I agree that with the speed range* for A/B or C/D aricraft, the geometry just would not work.

First thing to do is check AIP and see, wheter or not Jepp ommited something and they very rarely do.

http://www.ais.gov.mm/files/pdf/VYMD.pdf

Hmm. Same story. :ugh: Problem seems to be with the source of the data, and not the delivery boy.

Best course of action, in my opinion, is to bring the issue up within the airline to people who may send some e-mails / make phone calls.

2OP: Errajane WELL SPOTTED!! :D

* PANS-OPS for initial approach

[aterpster]

FlightDetent:

But it is a VOR/DME approach.

Timing is not supposed to be an element of a DME-required approach.

[FlightDetent]

FAF is defined with DME. Why is the DME not also used for the outbound leg in the design of this particular procedure I do not understand. And the timing interval seems just plain incorrect.

[aterpster]

FlightDetent:

As I replied to OK465 Jepp has coded the turn on the base leg at 6.4 DME.

[Tinstaafl]

Maybe, in the dim & distant past, this was once a 'VOR or VOR/DME' approach? As time moved on, corporate memory failed, and ICAO played silly buggers with approach naming conventions (again) the 'VOR' just happened to get dropped?

[OzExpat]

According to the source document - the actual chart produced by the regulatory authority - the procedure is ICAO (ie Pans Ops) not TERPs. Using some of the Pans Ops calculations that I've used over a period of about 26 years, I found :

1. The base turn splay angle for Category A/B, based on 180 knots at the highest MSA, 4600 feet, should be 17 degrees for 2.5 minutes outbound, not 15. The nominal outbound distance would be around 8.2 NM, which would be enough to permit the inbound turn without too much of an excursion beyond the final approach track.

2. The base turn splay angle for Category C/D, based on 250 knots at the same MSA should be nearly 40 degrees for 1.5 minutes outbound, not 30 degrees. The nominal outbound distance would be 6.87 NM or thereabouts, which would be okay for a reversal to reach the FAF, but the splay angle seems manifestly inadequate to accommodate the turn.

Personally, I've never had a problem with declaring an outbound timing for a procedure that defines the FAF by means of a navaid or fix. The procedure can still be called VOR/DME but, with a titling change to ICAO charts, the procedure should be identified as VOR RWY 17 with information in another box to identify the other aids that are required by the procedure. I'm not convinced that's the right way to go but it seems to be more related to database recording than actual chart usage.

I was going to include an image of the final approach course, runway alignment and navaid locations, but couldn't be bothered with the trouble of placing the image online first. Anyway, I used the coordinates for navaids, ARP and thresholds to try to figure out why the MAPt is located at 1.65 DME MIA (according to the source chart).

What I found was that the actual intercept point for final approach course and runway centreline occurs about 1.9 DME, or thereabouts. The location at 1.65 DME MIA appears to be the very latest point at which the runway approach splay is intercepted by the final approach course. It's legal in Pans Ops but not especially satisfactory for the pilot flying a Cat. D aeroplane that might have to use the procedure.

It was interesting to note that the chart publishes a decent gradient of 5.2% between FAF and MAPt. I'm guessing that it would've been a tad steeper if the MAPt had been at 1.9 DME.

According to the source chart, the procedure has existed since a publication date of 1 January 2011 (and perhaps longer?). Either there's been no complaints because the approach has never been used, or complaints have been made and ignored.

It seems like a good chart to use for SIM work though! :}

Perhaps it's time for those who use, or plan to use this approach, to refer the issue to their company experts, who can make enquiries with the national regulatory agency. I doubt that an enquiry to Jeppesen would be any more helpful because it would seem that all they've done is to reproduce the chart for their own customers.

[BOAC]

EJ - as I said in post #4,
"Back to company for a decision, errajane, I think!" - do you have any feedback? This is not a 'safety' issue since the worst that will happen is a session of missed approaches, so that avenue is closed, but your company NEEDS to take this up with the CAA to get it sorted. Nothing to do with 'splay angles' - just cock-up. I'd be interested in what one of your shiny TRE's has to say about it.

[aterpster]

OzExpat:

Personally, I've never had a problem with declaring an outbound timing for a procedure that defines the FAF by means of a navaid or fix. The procedure can still be called VOR/DME but, with a titling change to ICAO charts, the procedure should be identified as VOR RWY 17 with information in another box to identify the other aids that are required by the procedure. I'm not convinced that's the right way to go but it seems to be more related to database recording than actual chart usage.

I can't speak to PANS-OPS, but with TERPS when DME is mandatory for the final approach segment DME goes in the title. When DME is not mandatory for the final approach segment, but for some other part of the procedure then DME Required goes in a note.

In any case, timing makes no sense when the FAF requires DME.

As to Jeppesen "copying" the AIP chart that is all they are permitted to do.

[Errajane]

Thanks all for your feedback. I'm glad I'm not the only one who is confused about this approach.

[BOAC]

--- so, EJ - what answer do you have from company?