ATPL Flight Planning

27 Jul 2022

One of the most common questions I get from people studying ATPL Flight Planning is… “What is the tolerance for the exam?”

While it may sound like a straightforward question, the answer is not quite so simple. 

You’ve probably heard once or twice someone claiming to know the tolerance; they say it is 1%, or 4% or 50kg or some other made-up figure… unfortunately, it doesn’t work like that. 

And it doesn’t really matter for the exam, for the majority of the questions you type in the answer and wont see any options. For the few questions where it is multiple choice- would knowing the tolerance persuade you to go for an option different than the closest? I hope not.

It does, however, help you learn the material and mark practice exams without being biased. 

So, let’s look at working out if you would be “within tolerance”. 

The main thing that will determine whether an answer you got will be close enough to the correct answer is WHY you got a different answer. If you’ve already started studying flight planning you’d realise how many times there are opportunities to make a decision that will affect your answer. These include but are in no way limited to:

• Altitude selection
• ISA deviation
• TAS
• Track
• Wind Component 
• Ground speed
• RSWT
• Distances
• EMZW

And heaps, heaps more… BUT- in theory, the only thing that we are allowed to get different that will differ my flight plan, your flight plan, and CASA’s flight plan is the wind component. If the wind component is different, so is the ground speed, ETI, zone fuel and end zone weights. (Plus a few other things…maybe).

You may have already noticed through the years, but every whiz wheel is printed slightly different, they are getting better and better but I still often see some slight differences. The other thing is point out is our interpretation of the whiz wheel, time and time again I’ll look at one and see a 34kt headwind for example, I show a few people and we all get a headwind between 32 and 36- and that’s using the same whiz wheel!!

Now if we have slightly different wind components over a short sector (400ish NM) it won’t make much of a difference at all in fuel used. If we have that same discrepancy over a long sector (1500+ NM) we could have a difference of a few hundred kilos!

So when you’re doing practice exams and studying the material and you get a different answer, investigate why you did. If you got it wrong because you used the wrong flight level or wrong Mach number for your fuel figures I can’t give you an excuse sorry 🙃… but if your wind component is SLIGHTLY (+/- 5kts) different from mine or the worked answers, you would most likely be within tolerance. If I used 40kts and you used 60kts, that indicates an error in procedure, if I used 40kts and you used 42kts, it indicated a different interpretation of the whiz wheel. This is fine!

If you want to check if your process is correct and that it's just the wind that is throwing you off- do a flight plan but use the wind components from my worked answer. If we use the same wind component then in theory we should get the EXACT same answer. If we don't, then you can explore what you did differently. That might help you discover a procedure you are doing wrong without just putting the error down to the wind.

If you don’t have my textbook, I have listed a ‘Basic Flight Plan’ below. A basic flight plan is one where you don’t have to refer to the RSWT or the map. It’s used to practice the procedure before adding the complexities of the weather and map interpretation. Because I have listed the wind components here, we should get the exact same answer assuming you follow all the correct procedures and the correct rounding rules. Try it yourself and see if we get the same- if we don’t, look into where you’re making mistakes and tidy them up!