DEAR BOB,

I HAVE BEEN DOING SOME LONG READING ON THE CAO 20.7.4, AND I HAVE BEEN VERY CONFUSED ON THE ENTRY ARGUMENTS ON THE TAKE OFF AND LANDING WEIGHT AND DISTANCES CHARTS. I JUST WANT TO MAKE SURE THE BELOW DATA WHAT I AM THINKING IS RIGHT AND IS THE DATA THE RIGHT ENTRY ARGUMENTS TO BE USED IN THE CASA - CPL PERFORMANCE EXAM.

TAKE OFF AND LANDING WEIGHT - ONLY USE ACTUAL WIND AND USE THE SLOPE ONLY IF ITS EXCESS OF 1%

TAKE OFF AND LANDING DISTANCES - ONLY USE ACTUAL WIND AND USE LEVEL, SHORT DRY GRASS

SHOULD I BE USING THE ABOVE DATA FOR ANY QUESTIONS IN REGARDS TO THE CESSNA, PIPER AND ECHO TAKE OFF AND LANDING WEIGHT AND DISTANCES CHARTS IN THE CASA PPL & CPL (AEROPLANE) WORKBOOK - VERSION 1 - 01 SEPTEMBER 2014?

YOUR KIND RESPONSE WILL BE HIGHLY APPRECIATED FOR MY EXAMS AND I LOOK FORWARD TO HEAR FROM YOU.
THANKING YOU IN ADVANCE.

KIND REGARDS,
VENK.

And well might you be a little confused.

First, it is important to keep in mind that the old DCA format P-Charts (eg Echo) used for the exam predate the outcome of the Ron Yates report and relate to now-defunct regulatory requirements.. The 20.7.4 requirements, in effect, were transcribed from the now-cancelled CAO 101.22 so the charts are still OK so far as the requirements were/are concerned.

In respect of CAO 20.7.4.4.1.a,

(a) use the reported wind component. You will notice in the wind carpet of the chart that the distance between the lines changes at zero wind component. This reflects the requirement to use 0.5 of a headwind component and 1.5 of a tailwind component. That is, you enter actual wind component and the chart takes care of the factoring requirement.

(b) in respect of slope, the requirement is that slope must be accounted for if greater than 1 %. Unless Bob indicates that the examiner does not want slope accounted for if it is less than 1 % (and I would be amazed if that were the case) I would apply whatever slope you have for the runway.

In respect of CAO 20.7.4.6.2 you are expected to use an appropriate entry. The entries, while described as varying grass conditions, just apply different friction coefficients to the equations. The coefficients are representative of the nominated surfaces but, quite obviously, you should conduct real operations conservatively for other than short dry grass as the real world coefficients may not match those presumed all that well.

The above comments apply to the old DCA P-chart format. For other charts, I would need you to specify the chart and I can offer comment.

On a general note, though, in respect of CAO 20.7.4.6.3 be VERY wary of overseas NAA POH data for light aircraft as the data may not have the factors we have been used to locally. After all, those OEM manuals were prepared to meet overseas requirements, not Australian.

Also, don't fuss about whether you are trying to figure a distance limit or a weight limit .. all done the same other than for running the carpet lines a little differently.

As far as slope is concerned, I advise students to always use the slope if it is known. The wording in the CAO can be taken by some students to indicate that you are not permitted to use the slope if it is less than one percent. I am at a loss to understand why the one percent is mentioned at all.

I concur with Bob's thoughts.

The suggestion that 20.7.4.4.1.a should be interpreted as a requirement not to account for slope if slope is less than 1 % is logical nonsense. The intent is to require accounting for significant slope while permitting a concession for small slopes.

I don't have a copy of the old 101.22 to hand so a check there will have to wait until I have an opportunity to dig out an archived copy. I just can't recall what that document (which was the certification requirement) said about slope - too long ago since I last read it. However, it is reasonable to presume either that

(a) the 20.7.4 requirement followed from something in 101.22 or

(b) it was an purely operational assessment added to the 101.22 transcription.

When I can locate an old copy, I'll come back to threads such as this and clarify what the certification requirements were.

A little follow-up information.

In respect of the 1% slope matter, I have just been reading a rather old US conference paper on airline operational aircraft performance scheduling dating back to the 60s. In it there is a reference to the FAA's not requiring older design aircraft (eg DC3) to account for slopes less than 1%. I will need to do some further research to see if I can track down the regulatory basis for this but it is too coincidental not to be linked to the old DCA requirements discussed above.

If I have any success with the research exercise, I will add detail in due course. On another sideline consideration, if you have any interest in the FAA's history, you might run your eye over this link www.faa.gov/about/history/brief_history/#origins

Just a bit of FYI ...