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HeliTorque Forum Index » Ground School

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More tricky questions
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paddywak
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PostPosted: Mon Aug 01, 2011 7:33 pm    Post subject: More tricky questions Reply with quote

Ive been doing a bit of revision in preparation for my Canadian CPL
and came across this question:

When taking off out of a confined area surrounded by high trees, the PIC must:
a. Precede each takeoff with an IGE power check

b. Takeoff into the direction of the lowest obstacle

c. always takeoff into wind

d. Takeoff downwind

Which you going for? like most of you I always do a power check to enable me to gauge how much I have in hand and which takeoff I can use. I chose (a)

Then this one :

What happens to the indicated airspeed if the pitot tube becomes blocked?

a. it will under read in a climb

b. it will over read in a descent

c. it will act like an altimeter

d. it will read zero

my understanding is that the dynamic pressure can no longer enter the pitot tube and the remaining pressure will leak out of the drain until the pressure inside will equalize with the static pressure and there will be no difference in the pressures so it must read zero. No not according the answers.
Im beginning to think I may have wasted 35 on a book which is leading me to doubt the basics which I was taught.

Evil or Very Mad
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flip2
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PostPosted: Mon Aug 01, 2011 9:30 pm    Post subject: Reply with quote

Hi paddywak,

For your first question, I'm thinking the book may be looking for B - takeoff in the direction of the lowest obstacle.

Taking off into wind is not always the best option, ruling out (C).

Taking off downwind needs good reason, ruling out (D).

Regarding (A) - precede each takeoff with an IGE power check. OGE performance is of most relevance here but sometimes an approximation from an IGE power check is your only option (and indeed if a power assurance hasn't been done it is a way of confirming that the engine(s) are meeting specification). However, would you perform that power check before every take-off? You may be doing 2 minute ferry sectors meaning you need to do that take-off every few minutes all morning long on a revenue flight.

For your second question, I think your book may be looking for C: It will act like an altimeter.

When these questions talk about pitot tube blockages they are normally based on the entire pitot system becoming a sealed unit - no air in or out.
This will mean that the IAS remains the same in level flight (provided that the ambient air pressure doesn't change) irrespective of speed changes.
In a climb, the static pressure decreases which means that the IAS will increase, and the opposite is true in a descent. So in that regard it operates like an altimeter:
You go up, the needle goes up
You go down, the needle goes down
You change speed, nothing happens

HTH
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paddywak
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PostPosted: Sat Aug 06, 2011 4:59 pm    Post subject: Reply with quote

Well done that chap, you are 100% right, those are the answers in the book.

I still do a power check in my WORMT check when leaving a confined area and also a power check in flight before my approach. But I suppose that is because I only operate on a PPL level and I am not subject to commercial operations and I have never flown 2 minute ferry flights. This is a type of operation I had not previously thought about.

Perhaps I need to start thinking like a CPL in order to pass these questions.

I do understand that the ASI acts like an altimeter if completely blocked but as the question states "when the pitot becomes blocked" I took it as the pitot drain was not.

Must do better, stand in corner with hands on head and all that Laughing
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flip2
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PostPosted: Sat Aug 06, 2011 6:10 pm    Post subject: Reply with quote

Quote:
Must do better, stand in corner with hands on head and all that

I wouldn't say that!

You are correct that there is a slight change in thought processes required when you move from PPL to CPL level (and indeed when you move between roles post-CPL). In the UK most pilots are trained to PPL level, but in many other countries the balance swings the other way i.e. most pilots know they want to "go commercial" from day one and the PPL student is the novelty. I have not operated in Canada but I get the impression that flight training is very much orientated towards future utility / bush work (which would be a novelty rather than the norm for a UK pilot).

For the second question you gave a correct and reasoned answer for how you had interpreted the question.

Smile
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