Hi all,
I have a question regarding how to apply wind data in the CASA CPL Flight Planning (CFPA) exam, specifically in relation to takeoff and landing performance charts. This format hasn’t been covered in any of the practice exams or theory resources I’ve used, so I’d like to confirm a few things before my attempt.
[u]1. Wind source for charts:[/u]
If actual wind / ambient wind / given W/V is provided, should we use that for both takeoff and landing charts?
If the wind is from a forecast source (TAF, ATIS, AWIS, etc.), do we use nil wind for the takeoff and landing charts?
[u]2. Gust factor:[/u]
If using wind, and a gust factor is included:
For headwind, do not apply the gust factor?
For tailwind or crosswind, do apply the gust factor?
[u]3. Wind limitations:[/u]
There is no specific tailwind limitation mentioned in the performance limitation box of the P-charts. Should we assume the default max tailwind limit is 5 kt?
For headwind, am I correct in assuming there is no upper limitation unless stated?
Would appreciate clarification from anyone who's sat the CFPA recently or has insight into CASA’s marking expectations. Thanks!
And a good question, it is.
[color=blue]If actual wind / ambient wind / given W/V is provided, should we use that for both takeoff and landing charts?[/color]
You need to process the data in a conservative manner. That is to say, do not be non-conservative.
Gusts, by their nature, are unpredictable. If the mean wind is a headwind, ignore the gust factor for calculations. If gusts don't appear for your operation, you will be conservative. If they do appear, then you will derive a modest advantage for the numbers. If the mean wind is a tailwind, do apply the gust using a similar reasoning but in reverse.
If the wind is current (takeoff or in the near circuit area for landing), use the wind advised. Otherwise, use nil wind on the main runway but, if the forecast wind is a potential crosswind problem, also check the weights on a subsidiary runway, acceptable for the crosswind. The lesser of the two weights so obtained becomes your limiting weight for the operation.
[color=blue]Gust factor:[/color]
As above. For considering crosswind limitations, it is appropriate to consider the gust as, by its unpredictable nature, you can't predict if it is likely to bite you or not. Be conservative.
[color=blue]There is no specific tailwind limitation mentioned in the performance limitation box of the P-charts. Should we assume the default max tailwind limit is 5 kt?[/color]
You don't need anything in the box. The chart grid for wind (for the exams) doesn't go more than 5 kts T/W so that is your limit. You have no knowledge necessary to do the extrapolation calculations so don't. You don't extrapolate any chart data.
[color=blue]For headwind, am I correct in assuming there is no upper limitation unless stated?[/color]
That's a reasonable approach. Generally, if the wind is very strong, turbulence and gust considerations will frighten you sufficiently to stay in the clubhouse before it gets to the point of being really dangerous.
The comments are with a certification/performance engineering hat on. I can't guarantee the examiner's view but I would be surprised if it were to be much different.
Engineering specialist in aircraft performance and weight control.
Hi John,
Just an additional question regarding P Charts:
If a P chart question provides only density height (e.g. DH = 4000 ft) with no temperature, Bob Tait suggests using ISA temperature for that altitude. However, in one answer key I’ve seen, it uses 15°C (which is ISA for sea level) instead of the expected 7°C (ISA for 4000 ft).
So, just to confirm, should we:
Enter PH as 4000 ft
And use ISA temp at 4000 ft, i.e. 7°C, rather than defaulting to 15°C?
Or is this one of those legacy quirks in CASA exams where they expect sea level ISA unless otherwise stated?
[color=blue]If a P chart question provides only density height (e.g. DH = 4000 ft) with no temperature, Bob Tait suggests using ISA temperature for that altitude. [/color]
Doesn't matter all that much. For pistons, the performance chart is plotted against density height. So, the charts you are using will have a scale of density height there for you. However, sometimes we don't label them so that makes it a little bit difficult. If you know what you are looking for, that's fine. However, for most folks, the easiest way, if you have a DH rather than PH/OAT entry arguments, is to use the same PH (as the quoted DH) and the standard OAT for that PH as Bob suggests. That minimises any errors associated with pilot calculation approximations.
[color=blue]Enter PH as 4000 ft. And use ISA temp at 4000 ft, i.e. 7°C,[/color]
Sounds good to me.
[color=blue]However, in one answer key I’ve seen, it uses 15°C (which is ISA for sea level) instead of the expected 7°C (ISA for 4000 ft)[/color]
Doesn't make any sense to me.
Engineering specialist in aircraft performance and weight control.
AV8,
In Bob's Performance text book, page 192 definitions, Ambient Conditions are defined as those provided within 15 minutes preceding take off. So using an old meter is not acceptable.
If you look in the AIP ENR 1.1 - 77 para10.7.2.1, which describes alternate weather requirements. The NOTE states that gusts must be considered for Tail and Cross wind limits. So the same thinking would apply to Take Off and Landing calculations.
Once again from the text book, the dashed line of 5 kts tailwind is a limit, whereas there is no limit for head wind, except that we don't interpellate outside of the last solid headwind line.
I hope that add more information for you.
