ATPL Question
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ATPL Question
Hi everyone,
I sat ATPL Performance and Loading yesterday and sadly 68% was the best I could do.
In my KDRs was one of those minor questions that could make or break you.
I can't seem to find the correct answer in my study material.
I went for ( B ) and got it wrong.
Question, Holding Altitude for lowest SFC
A) as low as possible
B) as high as possible
C) Lower rather than higher
D) Higher rather than lower
I sat ATPL Performance and Loading yesterday and sadly 68% was the best I could do.
In my KDRs was one of those minor questions that could make or break you.
I can't seem to find the correct answer in my study material.
I went for ( B ) and got it wrong.
Question, Holding Altitude for lowest SFC
A) as low as possible
B) as high as possible
C) Lower rather than higher
D) Higher rather than lower
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Join Date: Aug 2009
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Hi JB235,
What notes are you using for study?
Let's look at what effects SFC:
RPM:
SFC reduces in the design RPM for a specific engine, Higgins puts it in the 92-98% range. An aircraft at a higher altitude will be holding at an engine RPM closer to the design RPM therefore a better SFC.
Temperature:
Not much of a change for a similar TAS; however
Altitude:
You'll get a better SFC with altitude up to the tropopause where the SFC will begin to become less-favourable again. This is where I think you've got the question wrong.
I'd be inclined to choose D in this case.
What notes are you using for study?
Let's look at what effects SFC:
RPM:
SFC reduces in the design RPM for a specific engine, Higgins puts it in the 92-98% range. An aircraft at a higher altitude will be holding at an engine RPM closer to the design RPM therefore a better SFC.
Temperature:
Not much of a change for a similar TAS; however
Altitude:
You'll get a better SFC with altitude up to the tropopause where the SFC will begin to become less-favourable again. This is where I think you've got the question wrong.
I'd be inclined to choose D in this case.
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Gday ConfigFull,
I am using AFT notes.
Yep I think your right.It was one of those curly ones.
I mean who is going to be holding above the tropopause
Thats why I went for as high as possible![Sad](https://www.pprune.org/images/smilies/puppy_dog_eyes.gif)
Cheers
I am using AFT notes.
Yep I think your right.It was one of those curly ones.
I mean who is going to be holding above the tropopause
Thats why I went for as high as possible
![Sad](https://www.pprune.org/images/smilies/puppy_dog_eyes.gif)
Cheers
I wouldn't have answered 'as high as possible'. That implies the aircraft's absolute ceiling is a possibility, which does not equate with the most efficient use of fuel. 'Higher rather than lower' however doesn't include a particular altitude that is inefficient, leaving the exact altitude open to suit the circumstances.
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Altitude:
You'll get a better SFC with altitude up to the tropopause where the SFC will begin to become less-favourable again. This is where I think you've got the question wrong.
You'll get a better SFC with altitude up to the tropopause where the SFC will begin to become less-favourable again. This is where I think you've got the question wrong.
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I would have thought that SFC was more applicable for the cruise rather than in a holding pattern. More thrust for less fuel flow per hour.
In a holding pattern your best altitude will depend on your aircraft weight as you will want to fly at min F/F.
B777-300ER:
340T - min F/F at 10 000FT
180T - min F/F at 30 000FT
Mind you it has been a few decades since I did ATPL performance and yet again I didn't RTFQ!
Oz
In a holding pattern your best altitude will depend on your aircraft weight as you will want to fly at min F/F.
B777-300ER:
340T - min F/F at 10 000FT
180T - min F/F at 30 000FT
Mind you it has been a few decades since I did ATPL performance and yet again I didn't RTFQ!
Oz