G'day guys,

I'm using the July 2011 version of the instrument rating study guide. On page 4.8 it says that you should use the RNAV[GNSS] approach at Kempsey to get the lowest altitude requirement to return to Kempsey following an engine failure on VH-OZY, in IMC after take-off.

The answer to revision exercise 4, question 17 says we can't use the 06 GNSS at Blackall for our return because OZY has a TSO 129 GPS.

I'm confused - how come we can use it at Kempsey but not at Blackall... they seem like the same type of approach.

I'm probably missing something very simple but I've been studying for too long & can't see the forest for the trees

I'm sitting IREX on Monday so I hope you can get back to me over the next couple of days. Thanks very much!

Paul

That's all been changed in the latest print of the book. The AIP now says that, unless you have a GPS TSO C145a or C146a, you cannot do an RNAV GNSS approach unless another approach is available. So you can no longer plan on an RNAV GNSS approach in the event of an engine failure after take-off.

See AIP EEN 1.5 para 8.5.5.4 table RNAV GNSS centre column item 4

The book has been amended to reflect that. Thanks for your feed back.

G'day guys,

I have been really confused with this one too just seeking some clarification. Are they saying we can't plan a GNSS approach unless we have GPS TSO C145a or C146a if theres only a GNSS approach available?

Also are they saying we can plan to come back on a GNSS approach using TSO 129 as long as theres also another approach available? Or if there is another approach available are we expected to use that approach and ignore the GNSS approach altogether?

Thanks guys!

There is nothing to stop you planning to do a GNSS approach with a C129 GPS. But, if it's the only aid available, you must have enough fuel to go to an alternate if the equipment fails. Remember there is no problem with the accuracy of a C129, it's as good as a C145/6. The only issue is the integrity. You must always plan for the possible failure of the equipment, so you must always have 'plan B', that is, either an alternate aerodrome or another aid at the destination aerodrome.

If you intend to return in the event of an engine failure after take-off, you can still do the GNSS approach when you get back, but you cannot take off unless the weather conditions will allow the use of the other 'conventional' aid. In other words, you must always say "What if" when planning to use a GNSS approach with a C129 GPS.

Thanks for that Bob!