The chart data is there to provide usable information to the pilot.

Whence would you obtain TAS as an instrument reading in the cockpit of a small GA training aircraft ? Perhaps better (and easier) to use what you do have, viz., IAS from the ASI

On modern, large aircraft, the pilot usually has a TAS readout as direct information but one would never use it for a takeoff or landing speed reference. Note, though, we do routinely keep an eye on G/S readouts to provide some level of guard against windshear, especially on approach and landing.

There would be no particular reason why chart data could not be presented as TAS if you wanted that, but it would be done through IAS in any case so all it would achieve is saving your having to run a calculation on the whizz wheel.

Given that TAS is of little interest for takeoff and landing, why would you bother too much about it for light aircraft operation ?

I understand that. But in the charts I had interpolated between two tas figures for 5000ft at a weight of 2700kg. The answer comes to 94 knots.
109+99=208÷2=104 knots. Then I subtracted the 10knots headwind to find the Groundspeed. Which came up to 94knots. Using the formulae in the book I used 94 knots × 6% gradient to find my ROC of 564fpm. But in the answer book it tells me to convert my Groundspeed of 94 knots back to tas at 5000ft because it's considered as a IAS which gives a tas of 101 knots then you minus headwind and it gives you 91 knots ground speed and a roc of 546fpm. Which totally different toy answer.

Unfortunately, I don't have any of the paperwork to which you are referring so I'm a little bit wading about in the swamp, here. I had presumed that you had obtained the initial data from a takeoff chart, or similar ?

Perhaps you can either post some scans or, if the material be copyright sensitive, email some scans, and we can continue the discussion ?

Attached is the question. Question no.8 with the chart I used.

Ah hah ! Now I am in the picture.

Afraid you are using the wrong chart. Q8 relates only to the takeoff chart and has naught to do with the climb chart data. It is useful that you have raised the question as there is a general lack of understanding regarding the 6% climb figure.

I'm a bit tied up just at the moment to run up a detailed answer but will do so for you and any others who might be following the thread, hopefully tomorrow.

Thank you sir. much appreciated

It is how the question is worded.... Its asking the climb rate if the TOSS (indicated airspeed) is used for the initial climb out... If you find the TOSS from the ECHO take off chart attached and then convert it to TAS using your wizz wheel and 5000ft density altitude, you should get 101kts. Then minus the headwind.

Hope this helps.

Thank you I finally found where the 94knots came from. The wording of the question got me confused.

The question is referring to Take-Off Safety Speed from the take-off chart. That is always given as IAS.
[attachment=1343]Screen Shot 2018-06-18 at 4.11.20 pm.png[/attachment]

Following on from my earlier comments.

You now have the answer as to how to approach the question.

However, it is worth including a comment as to the question's interest in a 6% climb gradient.

You will be aware that CAO 20.7.4.7 restates the now defunct CAO 101.22 certification requirement that a light aircraft has to be able to achieve a takeoff WAT limit climb not less than 6%. This is to prevent takeoffs at excessive weights where the climb gradient capability is a bit too low for comfort.

What this meant under 101.22 was, and for 20.7.4, is, that, if an aircraft at higher weights (and, typically, higher altitudes and OAT) could not make 6% at the take off safety speed, then the takeoff chart had to have some subsidiary data to restrict the takeoff weight so that the 6% could be achieved. Many light aircraft are never WAT-limited.

If you refer to the exam booklet at the Fig 3 takeoff chart (in the old DCA P-chart format) you will see that there is a climb weight limit shown in the density height grid in the lower left hand corner. The take off chart at Fig 5 shows an alternative presentation with a climb limit.

If you have a look at the Echo takeoff chart, you will see that there is NO climb limit included. What this means is that the Echo, for any takeoff within the conditions of the takeoff chart, will ALWAYS see MORE THAN 6% at the takeoff safety speed.

You will see questions, such as the one you have cited in this thread, where the thrust of the question is to find a ROC to achieve 6% for the Echo at the takeoff safety speed and takeoff power. Now, if you are always going to see MORE than 6% under those conditions then, unless the question says something like "minimum ROC" it is a bit meaningless. To achieve 6% for the Echo on takeoff, you would have to reduce the power setting.

Such questions are a bit silly but you will need to answer them in the manner sought by the the examiner. Just keep in mind that, should you be in a non-WAT limited aircraft, and you see a ROC relevant to 6%, then something is not quite right for the takeoff.