Hi guys sat performance and flight planning today and failed with 63%, devastated considering it was my last CPL exam. Anyway i stumbled on a few questions regarding ETP and PNR. it seemed that CASA want you to do a little more working out yourself rather than just getting told the if its headwind or tailwind from A to B. They give you a wind e.g. 250/20 knots and the say the track from A to B is 037 degrees so i take it that you need to use the whizz wheel to work out what your actual TAS is, is that correct?

Other questions that i stumbled on was when you had to work max takeoff using the graphs and they give you the TORA and TODA. I used the TODA but now come to think of it should i have used the TORA as I'm aware thats actually the length of the runway without a clearway.

Any help is much appreciated and just wondering if i could get some help in regards to working out ETP/PNR as stated in the question above.

Guttered but will collect my thoughts and have another crack.

I do have an example in the book of PNR/ETP where the headwind component has to be calculated given a FPT and wind. Maybe I should include a few more.

As far as the take-off chart is concerned, don't change your approach. The take-off charts are based on using TODA not TORA. If you have a look at the distance box, you will see that TODA is printed on the scale. So whatever you did wrong, it wasn't using TODA, that's what you should use.

As Bob indicates, TODA is the relevant figure for light aircraft calculations.

However, there is a sideline caveat re TORA/TODA. It probably would only present a potential problem if the takeoff is commenced from an inappropriate intersection on a long runway with significant declared clearway.

TORA has no certification relevance to light aircraft.

It certainly has for heavy aircraft where the two declared values (TORA and TODA - the difference being the declared clearway) are used to make sure that the aircraft is off the ground before it gets into the clearway (which usually includes surfaces not suitable for an aircraft's ground roll). To ensure this is addressed, the takeoff calculations involve checking the TORR (takeoff run required) from AFM data, whether explicitly or implicitly. As a note, the term TORR is a bit of a misnomer .. the requirement is that the air distance to 35ft (we use 35ft for heavies rather than the 50ft for lighties) may only have the latter half over the clearway to ensure a bit of a pad (the factor was smaller - 1:2 rather than 1:1 - for older British certifications but those aircraft gradually are disappearing from the scene so the figure to remember if you are looking to go onto ATPL training is one half).

The aerodrome standards allow the declared clearway to be up to half the declared TORA so, for a longer runway, one could see quite a long declared clearway length.

As a ball park figure, the light aircraft air distance to 50ft is going to be less than around 300 metres without an engine failure - in the OEI case, all bets are off for most light aircraft operations.

It follows that, on a longer runway with a takeoff commencing from an upwind intersection inappropriately close to the runway head, one could find the aircraft still on the ground at the end of the TORA .. depending on what is in the area under the clearway, that may, or may not, be a good idea.

Just something to keep in the back of the mind. For those who wish to read further, PPRuNe has a few discussions on clearway, eg www.pprune.org/tech-log/393405-effect-cl...l?highlight=clearway and www.pprune.org/questions/600618-vodka-bu...l?highlight=clearway

.. better luck for the next run through the exam, Mark. I wouldn't worry too much .. the great majority of folk have a failed exam or two along their way to the various licences.

Hi Bob, thanks for the quick response considering it is a Sunday. I have the latest perfomance book and i can not seem to find it in the book hence how i had no idea how to tackle that question in the exam yesterday.

Thanks John, thats an interesting read and glad that i choose the correct distances to plot on the graph. not to sure what i had done wrong then. there were a few take off weight question where you had to write the answer to the closest decimal rather than pick an answer from the ones given. Not to sure what the tolerance was but i thought i was pretty spot on with all my answers, It came as a little shock when i seen 63%

Hello guys just wondering if anyone could help me with the above questions in regards to working out ETP/PNR with a given wind and FPT as I have re booked my exam for a little over a weeks time and would love to be able to practice these.

Many Thanks

At the bottom of page 122 you will find 'ANOTHER EXAMPLE OF PNR/ETP CALCULATIONS'.
I think that is what you are after. The example is fully worked on the opposite page.

Thanks so much Bob, exactly what i was after.

Always appreciate the support you provide us within this forum.

Many thanks..

Hi Bob, While i remember i came across a question where i had to figure out max takeoff weight or or max take off distance can't really remember which one it was and in the question the gave the grass as UNRATED. Would you be able to tell me which reference line do you go down to in that case.

Many thanks Bob.

There is no reason to believe that 'unrated' means that the surface is going to be a problem. It simply means that the surface has never been rated for tyre pressure tolerance. It would not be a problem for any GA aircraft.



By the way, the surface descriptions on the P charts are often not much help in the real world. What about a sandy surface like many islands? What about a surface with long grass at one end and gravel at the other? What about a surface that is wet at one end and dry at the other? What about a surface that has a high spot in the middle? You just have to use you common sense and experience.

Most pilots would use the rule 'when in doubt, take the worst case'. Examiners find it difficult to phase questions relating to those scenarios.