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Welcome to the CPL Performance question and answer forum. Please feel free to post your questions but more importantly also suggest answers for your forum colleagues. Bob himself or one of the other tutors will get to your question as soon as we can.
172_Freighter created the topic: Ambient Conditions
Ambient conditions are defined as:
"Atmospheric Temperature, Pressure and wind conditions prevailing at a particular aerodrome during the period of 15mins preceding the take-off of the aeroplane"
Is that to say that should we be required to complete a landing distance calculation we should enter the chart with 'nil' wind even if we have the ATIS obtained within 15mins?
While im here another situation that I thought of for ETP/PNR calculations, should there happen to be an INTER at the departure and TEMPO at the destination, do I plan for the worst case scenario (60) or do they accumulate i.e 60 + 30 = 90mins holding?
captainellzy replied the topic: Re: Ambient Conditions
More often than not you will be required (for training and flight test) to produce a landing distance figure from the charts. However if you find that you have the time, tools and a stable surface to complete a landing distance chart in the aircraft within 15 minutes of your destination I suppose you could do that. I'm not so sure that it's at all practical or safe to be doing that during a busy approach segment of flight though
As for your next question (Bob or Richard will be able to be a bit more in depth with this one), a ETP or PNR calculation considers the departure aerodrome as far as INTER/TEMPO goes, so if there is either at the departure aerodrome you need only take fuel/alternate. Plan for the worst case, these are NOT cumulative.
Ellzy has already answered your question but I just wanted to add one more thing about using nil wind: when determining if you have a weight-limited take-off (i.e. MTOW, ZFW or landing weight limited) you must assume nil wind at the destination.
However, as Ellzy said, if an instructor wants you to calculate a value, or you want to see how much runway you're going to use then you can only use the wind you have been provided or the wind information you have from the destination.
In the exam, if they ask you for a landing distance calculation they will provide the wind and expect you to use it. If they ask you for a MTOW (ie checking where you are take-off weight limited) you will not use the wind in your calculation.
Also as far as the INTER/TEMPO goes, it will also have to take into consideration any holding/alternate requirements at the origin as well as the destination as Ellzy described.
The regulations (CAOs) are not very specific about this. However the common sense approach would be based on the following.
For take-off, always use ambient conditions because if you are not present at the airfield then obviously you can't take off. You would never use forecast conditions for take-off because you can observe the ambient conditions. Therefore you can always use the wind because, if it is not what you planned on, you don't have to take off. (all take-offs are optional).
However, if you are going to do a landing chart to determine a possible limit for take-off (i.e. the flight may be landing weight limited), then use no wind to establish a maximum landing weight. If your landing requires a particular wind component to be present at the moment you cross the threshold then clearly it can not be considered safe.
If the question simply says "What is the maximum landing weight permitted under the following conditions" with no mention of take-off considerations, then use the wind for the sake of the exam question.
It really does make you wonder why they put a wind argument on the landing chart in the first place!
John.Heddles replied the topic: Ambient Conditions
An additional thought to Bob's comments ..
In days of old, there was a landing planning requirement that went along the lines of nil wind on the main runway unless the forecast wind would give you an excessive crosswind on that runway. If that were the case, you also had to check the RLW for a subsidiary runway for which the forecast wind would be acceptable, in which case you planned on the lesser of main runway nil wind and subsidiary runway forecast wind.
Make good sense when you have a think about it ? You might like to dig through the current regs etc to see if anything along those lines still exists.
Engineering specialist in aircraft performance and weight control.