Hi guys,

Came across the following question in one of the practice cyber exams. Went through the chart about 3 times and every time i got an answer somewhere between 1025 and 1050kg. Is there a limit imposed that I'm missing?

Just a quick look at the P-chart on the screen.

Did you check both the runway and climb limited weights ? I suspect you might have overlooked the climb limit ? The latter looks to be suspiciously close to 1000kg.

Hmmm note 1 at the bottom of the chart states the gross weight at take-off shall not exceed the lessor of (A) and (. (A) seems to be around 1010kg and i think B is the 5 knot tail wind reference line. As 1030kg is above (A), is the weight now limited back to that reference?

Now, what your comments tell me is that you have either -

(a) not been taken through the correct chart use methodology and philosophy (or, perhaps, missed some of it along the way) if you did a classroom course, or

(b) have missed a few things if you have done a correspondence/on-line course.

First off - there is always a variety of separately overlapping potential limits for a takeoff calculation. For a lightie (such as to which this question relates) they are pretty simple .. for big iron, there is a whole bunch of considerations to review, any one of which will be the eventual limiting matter on the day. Main thing is the philosophical procedure is the same, regardless of which bird we might be looking at - run each of the calculations required and whichever comes out the lowest weight is limiting for the takeoff.

Second - the note at the bottom of the chart re A and B relates to the two variable limit sample calculations which have to be considered for this aircraft when doing a takeoff calculation -

(a) A is the runway-limited calculation - ie considers all those things which relate to the runway and the ambients on the day. For the old CASA P-chart presentation style (which is the chart you are playing with on this occasion), this is the final answer once you have done the "round the chart" thing with your sharp pencil. You will see that A lies at the end of the dotted line running through the various chart carpets.

(b) B is the quite separate climb-limited calculation. You will see that B lies at the end of the dotted line coming across from the left. This line comes from the climb limit data presented in the single straight line (running from lower left to upper right) in the DH carpet.

(c) whichever of A and B is the lower weight is the limiting of the two calculations and you can't go above that for takeoff.

Now, if you start in the DH carpet (lower left hand carpet in the P-chart) at the intersection of PH = 5000ft and OAT = 25C, then run vertically up to the climb limit line (quite a short distance on this occasion) and then across to the W/C carpet (in a manner similar to the sample calculation line) you will end up pretty close to 1000 kg. Now I did my calculation with a thumbnail dipped in tar on the screen so I am taking a bit of liberty with accuracy but 1000kg looks to me to be the required answer (as it is less than the runway-limited calculation which, for your results, gave something in the range 1025-1050kg).

Comment re climb limited weight

The P-chart format was in vogue prior to the changes in Regs from the old DCA rules to NAA accepted certification.

For the old rules, it is quite some years, now, since I have played with little aeroplane certification things but, unless the rules changed in the meantime prior to the move to NAA acceptance, this limit provides a minimum AEO climb capability of 6 percent (per the old CAO 101.22 rules) which is what you balance against the STODA numbers out of the ERSA RDS book for the usual TO calculations.

I am presuming that the exam chart is an old one which the examiners co-opted for exam purposes, in which case the 6 percent probably applies. For the later NAA accepted certifications, the overseas rules differ a bit .. but the philosophical intent (to keep you going up, rather than not) still apply even if the actual numbers are a bit different

Note this climb limit relates to AEO and is quite irrelevant if you lose one on takeoff in a light twin .. OEI becomes a whole different ball game.

John is correct. That particular question is describing a climb-weight limited situation. 1000 kg is the maximum weight that will allow the aircraft to climb at a gradient of 6% under the ambient conditions with engine/s operating at take-off power and the aircraft in the take-off configuration (gear down and take-off flap set). In that case, the runway length, surface slope and wind are irrelevant. It doesn't matter how long the runway is, if you can't climb at 6% you can't take off at that weight.

For a multi engine aircraft, that assumes BOTH engines are operating at take-off power. If one engine of a multi engine aircraft fails immediately after take-off, all bets are off. You would have to consult you multi engine aircraft's operating manual for details on engine-out climb performance.

The RDS supplement for ERSA gives supplementary take-off distances required to clear obstacles based on single-engine climb performance - but that's another story and doesn't apply for a single.

Hey Guys,

Thanks for your explanations of the P chart. John was right, i didn't fully understand the climb weight limitations and how they are displayed on the chart. Hopefully will now be an error of the past as i have a much clearer understanding of the mechanics behind it all. If i have a P chart issue in the future i know where to direct my query!

Thanks again,

Tom

Bob introduces an interesting concern for newchum consideration.

Where I was referring to 6% climb, I was talking about the old (local Australian) certification standards requirement of CAO 101.22 - now defunct, dead and buried. This basically stuck some extra, local, requirements onto foreign designed and certificated aircraft imported into Australia and was the bane of the aircraft importing and selling fraternity. One of the reasons for the old Civil Mk X local flight manuals was to facilitate the introduction into aircraft operational documentation of such differences between one country and the next. Quite commonly, we used to run local flight test programs for new Types and Models - I did more than a few of these - and produce data which ended up in the local AFM. (I acknowledge that the local AFMs, in general, were pretty dreadful documents and of little practical use to the pilot other than for takeoff and landing data and weight and balance things.)

Bob, I suspect, was referring to the operational requirements in CAO 20.7.4.7 - reproduced below for convenience -

7 Take-off climb performance

7.1 In the take-off configuration with landing gear extended, an aeroplane must have the ability to achieve a climb gradient of 6% at take-off safety speed, without ground effect, and with all engines operating at take-off power.

Although there was the odd glaring discrepancy betwixt the local certification requirements of old and operational requirements, in general, things worked more or less OK.

Post the Ron Yates' Report many years ago, now, Australia moved to automatic acceptance of foreign certification of aircraft .. ie, one could basically import the foreign aircraft, lock, stock and barrel without too much in the way of local interference. This was to assist the airline folk but, in its wake, caused some strife in respect of light aircraft requirements.

One consequence was that the local certification requirements progressively were binned along the way.

So now we moved to a situation where we had local operational requirements but no local, compatible certification requirements. The situation could arise where the imported aircraft, certificated to foreign requirements, might have some embedded things which did not meet the local Australian operational requirements.

Now, how do you, as the PIC, determine that the requirements of CAO 20.7.4.7, for instance, are met by your aircraft on the day ? Given that the foreign certification requirements are different how do you dot the i's and cross the t's to keep you sweet for a ramp audit in which the surveyor asks the question ? Never mind that this is unlikely to happen .. how would you satisfy the questioner were such a question to be posed ? Unless the foreign flight manual data has been modified to reflect the CAO - and that may have occurred in which case there should be some evidence of the change in the AFM - I suggest that you might just have a problem on your hands.

There is a variety of similar potential discrepancies floating around .. matters for thought in the world of increasing Regulatory strict liability, don't you think ?