Hi Bob,

Thanks for the Performance course in January. I sat my exam the other week, and was pleased to get 92%. I managed to get 4 x 1 mark questions wrong; they were silly mistakes but I ran out time in the end and wasn't thinking clearly.

The following question still has me stumped: "If the TORA is 1350m, the threshold is displaced 50m, the ASDA is 1450m, and 'no other clearway available', the TODA is:

• 1350m
• 1300m
• 1450m
• 1400m"

I selected 1350m as I thought a displaced threshold only applied to the LDA, and the extra 100m would be a stopway, not a clearway.

Also, if the weight of an aircraft is increased, is Va (manoeuvring speed) lowered? I initially selected lower but for some reason changed the answer to it would "remain the same". The other answers were "depends on the aircraft" and "higher".

Thanks again,

Craig.

Hi Kenny - great to hear you got through the performance exam! Well done

A stopway can function as a clearway as well. The displaced threshold does indeed only affect the LDA so the TORA will still be 1350m. Add the 100m of the stopway and you end up with a TODA of 1450m.

Here's a handy image to clarify (example (e) is the closest.):



V_a increases with weight. A lighter aircraft will have a lower V_a than a heavier aircraft. One way to picture this is to imagine the following situation. Think of an aircraft whose wing stalls at 18 degrees angle of attack. now, generally (depending on the aerofoil), if you double the angle of attack, you roughly double the lift and therefore double the wing loading. If you triple the angle of attack you roughly triple the lift and so on.

Consider two aircraft, one heavy and the other light. If both are cruising at 95kt, the heavier aircraft will have a higher angle of attack (say, 9^o) but the lighter aircraft will have a lower angle of attack (say 4^o). If the structural limit on an aircraft is +3.8G and it stalls at 18 degrees angle of attack, lets look at what happens when the pilots pull hard back on the control column of their respective aircraft.

HEAVY: doubling the angle of attack up to 18^o doubles the lift and thereby doubles the load factor up to 2. Any further increase in angle of attack now though will actually stall the wing and cause a reduction in wing loading. The maximum lift spike was only 2G so the pilot can't damage the airframe of the heavier aircraft with savage control inputs at this speed because the wing will stall first.

LIGHT: doubling the angle of attack up to 8^o doubles the lift and thereby doubles the load factor up to 2. But the wing hasn't stalled so double it again. Now the angle of attack is 16 degrees, the lift has increased by a factor of 4 and the load factor is now 4 and the airframe is subjected to 4G. The wing hasn't stalled yet but the airframe has already exceeded the 3.8G limit.

V_a for the lighter aircraft must be somewhere below 95kt whereas that for the heavier aircraft lies somewhere above 95kt. Remember, it's the change in the angle of attack that causes the spike in wing loading.

Cheers,

Rich

Thanks for your reply Richard, very informative.

I understand your statement regarding the first 50m of a stopway doubling as a clearway also, however figure C on the diagram was what I was envisaging in the exam. In that figure no portion of the stopway has been included in the TODA, so that figure still confuses me unfortunately. I see figure E includes the stopway as part of the TODA, however the clearway is longer than the stopway anyway. Is there any reference to say the first 50m of a stopway can double as a clearway?

At least the ERSA RDS makes it clear what is available for a particular runway.

The explanation of changes in Va with changes in weight was great, I understand now.

Thanks,

Craig

I'd like to know about this question too.
If ASDA = TORA + SWY
and TODA = TORA + CWY
The question states "no other clearway available"
You said that the first 50m of the stopway can double as a clearway. Is this published information? and why only 50m?

Thanks for all the help!

Any extra info?

First off, I had a mistyping in my first post - I meant 60m for the clearway not 50m, which was the displaced threshold distance in the question. After digging a little deeper I have also edited the answer in that first post.

A clearway according to the Manual of Standards 139 - Aerodromes 6.2.30 says that a clearway can't be more than half the length of the TORA and needs to be available for an aircraft to make its initial climb to 35ft (10.7m) above the ground at the end of the clearway.

If you look at the ERSA RDS, all clearways if present are 60m i.e. the TODA is 60m longer than the TORA. This 60m may stem from the requirements of CAO 20.7.2 which specifies in the definitions that for aircraft not above 5700kg on RPT ops, the TODA is TORA plus a maximum of 60m of clearway. That is why I suspect the ERSA gives the clearway lengths as 60m to satisfy the requirements of that CAO.

However, if you look at CAO 20.7.4 (Private, aerial work and charter) it just says TODA is the effective operational length (EOL) for take-off at Government or licensed aerodromes or the distance available for take-off on an ALA. The EOL is the lesser of TODA and ASDA.

Since the CPL exam focuses on Charter and Aerial work ops rather than RPT, we can work on the assumption CAO 20.7.4 applies and we are not restricted to considering 60m of any available clearway. Apart from that none of the answers given allow for a 60m clearway. They are all multiples of 50m

So, that means the TODA will be the full TORA + the full length of the stopway because:

1. The displaced threshold doesn't affect our take-off unless the surface is unserviceable
2. The stopway doubles as clearway since if it can be used as stopway it has to be suitable as a clearway too.

So, I'd go for (c) 1450m.

Cheers,

Rich

P.S. here are some references:

• CAO 20.7.2: Aeroplane weight & performance limitations - Aeroplanes not above 5 700 kg - Regular public transport operations
• CAO 20.7.4: Aeroplane weight & performance limitations - Aeroplanes not above 5 700kg - Private, aerial work (excluding agricultural) & charter operations
• Manual of Standards 139 – Aerodromes ( www.comlaw.gov.au/Details/F2012C00095 )

Thanks for clarifying and supplying the references Rich, much appreciated.