Hey Bob & Co,

Your online exam bank has been super helpful!

I've just run through the exams and had a few questions i thought I could get your advice on........

1. Refer Q28 (image attached)
The LDA from the ERSA for Wycheproof RWY 08/26 is 718m (~720m). The Bob Tait answer appears to use an interpolated value closer to 700m. I've plotted 718m several times and get a point that sits slightly higher which probably makes all the difference in the final answer. Refer Image 1 attached which is my version of where I think 718m should sit. Appreciate your review of this one! Maybe an LDA from an older version of the ERSA was used?

2. Refer Q27) (image attached)
The Bob Tait answer rounds down the 0.4% slope to 0% which drives the answer of 2830kg. I've found in using the actual slope (0.4% down), an answer closer to 2830m is obtained keeping all things equal.

3. Refer Image 2) (image attached)
What would you advise is the best way to interpolate accurately between two lines that aren't parallel (refer two red lines)?

4. Am I correct in my understanding that winds that are forecast shall be used as given in Take-off P-Chart Calculations? For Landing P Charts, I understand forecast winds are reduced to nil wind for conservatism in LDR and LDW calculations, except when more recent winds are obtained i.e via AWIS for instance.

I'm probably being a bit pedantic with Q27 and Q28 but without knowing how stringent the CASA exams will be, i'm a bit nervous!

Thanks a lot,

Shayaan

Shayaan
Regarding Questions 27 and 28, I can't fault your working so I'm sure you have nothing to worry about as far as the exam is concerned. Maybe our computer has very narrow margins for allocating full marks for type-in answers. We'll have a look at that.

Years ago there was a document called the Civil Aviation Orders (CAO), that concerned the use of take-off or landing performance charts. The requirement pertaining to the use of wind in a landing chart was as follows.

If you are establishing a maximum take-off weight by considering the maximum landing weight plus the weight of the trip fuel, then the maximum landing weight must be calculated using no wind.

It was considered that you were being too optimistic if the maximum take-off weight was based on the assumption that a particular headwind component would exist at the moment you crossed the fence at the destination aerodrome. (that would also be the common sense approach). Remember that, when you do the landing weight calculation, you are still flight planning at the departure aerodrome - you haven't left yet.

However, that sensible CAO requirement is no longer in force. CASA has indicated that, for the purpose of the exam, if a destination wind is given in a TAF, or in the text of the question, you should use that wind when establishing a maximum landing weight in those circumstances.

Bob

Bob, many thanks for the thorough reply. Please can I also get your thoughts on my 3rd question if you don't mind? I think this one's caught me out a few times!

+ 1 Question,

Refer attached Q8,

I understand requirement to arrive 10 mins before EOD although recommended is no longer mandatory (AIP 1.2-1 para. 1.1.3) ? The answer might've not caught up with the AIP change, but is it fair to say with a question like this that the legal answer (certainly not the safe answer) is 0722UTC

I think also the XW from B -> C has an impact on the ETAS, 9 degrees drift due 100% crosswind (25 KTs) gives roughly an ETAS of 158 KTS, anyhow minor in grand scheme of things to the final answer but just thought I'd flag given answer calls up TAS of 160kts on this leg.

I have changed the question text to say "if you allow 10 minutes for unexpected headwinds and an extra 5 minutes for a circuit and approach over C." that should make it clear. Thanks for your feedback.

Bob

When it comes to interpolating between converging guide lines, I don't think there is a simple way to make it easier. Perhaps you could try the ruler method as described on page 32 of the book.

If you skewed the ruler across the two guide lines in the region you are interested in that should be some help.

It really shouldn't be necessary to go to such lengths though. It was never the intention of the people who designed the P charts for you to go to those crazy lengths. There are generous margins built into the charts so that you should get a 'safe' answer making a careful 'guess'.

Of course I understand the concerns of students who have to come up with a 'type-in" answer, but it really is a shame that the use of P charts for exams should be so far removed from their practical application.