Hi All,

I am confused about a question in one of the practice exams.

For the DEVONPORT TAS NDB approach procedure, the minimum obstacle clearance provided by the circling minima for category B aircraft by night is -

1. 1000 ft
2. 300 ft
3. 400 ft
4. 600 ft

The answer is 300 ft

I understand that by day once you have reached the circling area and you are visual, you can descend below the MDA as long as you maintain 300 ft clearance from terrain, etc. But at night, the MDA is the MDA, surely it is designed to give you greater clearance than 300ft from obstacles that you can't see.
I would have thought that if the MDA only gave you 300 ft obstacle clearance to start with, then you couldn't descend below it even in the day.

Is there a reference for this in AIP? What am I missing?

Thanks
Sarah

For CAT A and B aircraft, the circling minimum gives you 300 feet above the highest obstacle in the circling area.

By day, because you can see where you are going, you can descend below the circling minimum providing you ensure that you remain not less than 300 feet above any obstacle that you fly over, remain within the circling area and maintain visual contact with the runway environment e.g. the approach lights or the runway threshold with visibility along the intended flight path not less that that specified for circling. This could well be much lower than the circling minimum altitude which is based on the highest obstacle in the circling area.

At night, you can't see what is below you or what is ahead of you, so you must remain not below the published circling minimum and within the circling area until you have intercepted the normal approach gradient for your aircraft type.

RAC OPS 1.5 para 1.7.6 and notes 1,2 and 3

Thank you Bob. That clears it up for me.

Now I have another question from the practice exams

You are the pilot of an IFR charter flight with passengers from Perth to Carnarvon with a landing at Geraldton. On the threshold of Runway 06 at Perth, with the Local QNH correctly set, one altimeter reads 70 ft and the other reads 125 ft. At Geraldton, with the local QNH correctly set at the threshold of Runway 03, the first altimeter reads 110 ft and the second altimeter reads 170 ft.

Select the correct statement -
1 this flight may continue as an IFR flight providing the second altimeter is placarded as unserviceable and the maintenance release is endorsed
2 this flight may continue as an IFR flight providing you ignore the indications of the least accurate altimeter
3 this flight may not continue as an IFR flight
4 this flight may not continue as an IFR or VFR flight

Answer 3 is correct.

According to ERSA the elevation of Perth is 67 ft which would make the ADF reading 125 ft out by 58 ft.
Geraldton is 121 ft which would make the ADF reading 170 ft out by 49 ft.
Neither of these errors are "in excess of 60 ft", yet the flight may not continue. Why?

Thanks
Sarah

Sarah

The elevations you should use for the altimeter check are the actual runway threshold elevations given in the aerodrome diagrams in DAP - not the aerodrome elevation given in ERSA.






That makes the second altimeter 67 feet out at Perth and 72 feet out at Geraldton. It has been more than 60 feet out on two consecutive occasions so it is out of limits for IFR operation.

Bob

Ahhhhh! Thank you again.
Sometimes this IREX makes me feel a bit stupid. But I'm getting there.
My exam is this Wednesday and I am passing the online practice exams, so hopefully I can pull it off on the day!

All the best with it Sarah! Let us know how you go........