Hi all
I'm cranking up for the IREX in 2 weeks time and working through any practice questions i can get my hands on.
The last CASA sample question is:
You are conducting the KUNNUNURRA, WA (YPKU) NDB procedure in IMC. At the commencement of the final segment of the approach, and at 1900 feet, the ADF indicator fluctuates +/- 15 degrees continuously about the expected bearing to the station. The "ident" of the aid continues to be satisfactory. In these circumstances which of the following approach procedures should you adopt?
Nothing in ERSA on KU NDB errors. On final you would be well within 30 NM rated coverage
ENR 1.5-1.10b says a missed approach must be executed if the performance of the radio aid becomes suspect
To my mind the azimuth fluctuation is enough to call a missed approach, even if the ident is still stable.
Can't find anything in the AIP on this, except the above.
Is there any definite guidance on this anywhere?
Another thing I'm not sure about is how you would go about the missed approach. Without the NDB, you could only navigate to the MAPt by DR. Climb to 3100 MSA and turn away from the high ground, I guess.
Sorry if it's a dumb question, or its been covered elsewhere in the forum. I find some of these grey area questions difficult.
Finding the IREX forums a great resource, thanks guys
Mike

It's not a dumb question Mike but it does require some interpretation. The tolerance for tracking on an NDB is +/- 5°. If your ADF is not stable within that tolerance you could not continue with the approach so you would have to initiate a missed approach. Although you have given up on doing the approach, you could still use the ADF to help maintain a track to the station - failing that you would have to resort to DR.

DR is quite safe since, even if you maintained the final approach track as your heading (with a guess at drift), the distance is so short you would at least end up in the circuit area.

You would commence climbing immediately so you would probably be a couple of thousand feet above MDA when you got to the DR position for the aid. Also the ADF would still give some indication of station passage.

Bob

Thanks Bob
I had considered the +/- 5 degree tracking limit, but had not connected that to the variation in the tracking displayed on the ADF. Two sides of the same coin I think.
If this was private or airwork, and you did not have another ADF or any other airborne radio navigation system (VOR or GNSS), and did not have an alternate because there were no other OPR when you were flight planning, what would your options be?
thanks again
Mike

You would be in big trouble! Remember that being legal does not guarantee that you can't have an accident. Nobody ever said that.
PVT/ AWK flights are permitted to take that risk.

Bob

That's what I thought.
Many things in Pvt/Awk Ops seem to get down to acceptable risk management, and the pilot's personal comfort level with the degree of risk.
Thanks again Bob, you're a legend!
Mike

Hi - I also have another question off the CASA website -

ERC L2 refers.
You are flying at night from WARRACKNABEAL, VIC (YWKB) (S3619 E14225) to HOPETOUN, VIC (YHPN) (approximately 37 nm NNW of YWKB). Nearing YHPN you sight and identify the aerodrome lighting for Runway 01. GPS RAIM is available. What distance from the aerodrome would be the earliest that you may descend below the route LSALT?

I want to answer - not until within circling area, but am wondering if doing so means I've missed where in the AIP it talks about 5/7/10nm - Hopetoun has LIRL so does this effect my answer?

Thanks guys,
Dee

ERSA and DAP indicate that Hopetoun has no navigation aids. You would have to use the NGT VFR circling area of 3nm. Had there been an instrument approach at Hopetoun, you could have used the associated MSA at 25nm. I suspect that when the question was written, there was an aid there so the original answer would be 25nm. The 5/7/10nm argument only applies to VASIS, PAPI or ILS equipped aerodromes, so it is not a consideration here.

Bob