ATPL theory questions
Joined: Jan 2011
Posts: 660
Likes: 20
From: England
The short answer to this question is that when we fly along with a constant Gyro Heading set, but no Astronomic Precession, the rate at which the Transport Wander changes the direction of flight, is exactly the same as the rate at which a great Circle track would change. So we are flying along a Great circle track.
The rather longer explanation is provided below.
A google search for “Astronomic Precession” reveals an explanation which concerns how the axis of rotation of the Earth describes a circular motion over a period of approximately 26000 years. This is obviously not the interpretation intended by the author of the question.
In this question Astronomic Precession is intended to mean Earth Rate Gyro Wander. It is caused by the facts that the Earth rotates about its spin axis and the Meridians converge towards the Poles. The equation for Earth Rate Wander (ERW) is:
ERW = 15 x Sin Latitude in degrees x time in hours
The number 15 is in this equation because the Earth rotates through 15 degrees of longitude during each hour. So for any given time period the equation can be restated as:
ERW = Change in longitude x Sin Latitude.
The condition of “with no astronomic precession” can be achieved for the purposes of this question by assuming that the Earth has stopped rotating. Or perhaps more realistically by designing a Latitude Nut system which automatically adjusted itself for changes in latitude. Either of these solutions would eliminate Astronomical Precession (ER) but would leave Transport Wander (TW) unchanged. The equation for TW is:
TW = East-West ground speed x time of flight x Sin Latitude.
East-West ground speed x time of flight = Change of longitude, so the equation can be rewritten as:
TW = Change in longitude x Sin Latitude…………………..Equation 1.
Great Circles have the following properties:
1. All Great Circle form straight lines on the surface of the Earth and have their
centres at the centre of the Earth.
2. All Great Circles which run in a true North-South direction cross the Parallels of
Latitude at a constant angle of 90 degrees.
3. The Equator is the only Great Circle which runs in a true East-West direction, and
this crosses all of the Meridians at a constant angle of 90 degrees.
4. All other Great Circles cross the Meridians at angles which gradually change as we
move around the circle.
So why is that Great Circles running other than north-south or east-west do not cross the Meridians at a constant angle? The reason of course is that the Meridians are parallel to each other only at the Equator, then converge as latitudes increase towards the Poles. So any straight line (Great Circle) running in a direction other than due north-south or due east-west, must cross successive Meridians at different angles. We can see this if we look at the equations for convergence of the Meridians and the Conversion Angle which defines the direction of the Great Circles.
Convergency = Change in longitude x Sin Latitude
And
Conversion angle = ½ Convergency = ½ Change in longitude x Sin Latitude
The change in direction of a Great Circle track between two points is twice the conversion angle, so:
Great Circle direction change = Change in longitude x Sin Latitude……Equation 2
So we now have:
Equation 1…….Transport Wander = Change in Longitude x Sin Latitude.
Equation 2…….Change in great circle track = Change in Longitude x Sin Latitude
This means that the rate of change of the Great Circle Track between two points is equal to the rate of Transport Wander. So as we fly along with a constant Gyro Heading set, the rate at which the Transport Wander changes the direction of flight, is exactly the same at which a great Circle track would change. So we are flying along a Great circle track.
The rather longer explanation is provided below.
A google search for “Astronomic Precession” reveals an explanation which concerns how the axis of rotation of the Earth describes a circular motion over a period of approximately 26000 years. This is obviously not the interpretation intended by the author of the question.
In this question Astronomic Precession is intended to mean Earth Rate Gyro Wander. It is caused by the facts that the Earth rotates about its spin axis and the Meridians converge towards the Poles. The equation for Earth Rate Wander (ERW) is:
ERW = 15 x Sin Latitude in degrees x time in hours
The number 15 is in this equation because the Earth rotates through 15 degrees of longitude during each hour. So for any given time period the equation can be restated as:
ERW = Change in longitude x Sin Latitude.
The condition of “with no astronomic precession” can be achieved for the purposes of this question by assuming that the Earth has stopped rotating. Or perhaps more realistically by designing a Latitude Nut system which automatically adjusted itself for changes in latitude. Either of these solutions would eliminate Astronomical Precession (ER) but would leave Transport Wander (TW) unchanged. The equation for TW is:
TW = East-West ground speed x time of flight x Sin Latitude.
East-West ground speed x time of flight = Change of longitude, so the equation can be rewritten as:
TW = Change in longitude x Sin Latitude…………………..Equation 1.
Great Circles have the following properties:
1. All Great Circle form straight lines on the surface of the Earth and have their
centres at the centre of the Earth.
2. All Great Circles which run in a true North-South direction cross the Parallels of
Latitude at a constant angle of 90 degrees.
3. The Equator is the only Great Circle which runs in a true East-West direction, and
this crosses all of the Meridians at a constant angle of 90 degrees.
4. All other Great Circles cross the Meridians at angles which gradually change as we
move around the circle.
So why is that Great Circles running other than north-south or east-west do not cross the Meridians at a constant angle? The reason of course is that the Meridians are parallel to each other only at the Equator, then converge as latitudes increase towards the Poles. So any straight line (Great Circle) running in a direction other than due north-south or due east-west, must cross successive Meridians at different angles. We can see this if we look at the equations for convergence of the Meridians and the Conversion Angle which defines the direction of the Great Circles.
Convergency = Change in longitude x Sin Latitude
And
Conversion angle = ½ Convergency = ½ Change in longitude x Sin Latitude
The change in direction of a Great Circle track between two points is twice the conversion angle, so:
Great Circle direction change = Change in longitude x Sin Latitude……Equation 2
So we now have:
Equation 1…….Transport Wander = Change in Longitude x Sin Latitude.
Equation 2…….Change in great circle track = Change in Longitude x Sin Latitude
This means that the rate of change of the Great Circle Track between two points is equal to the rate of Transport Wander. So as we fly along with a constant Gyro Heading set, the rate at which the Transport Wander changes the direction of flight, is exactly the same at which a great Circle track would change. So we are flying along a Great circle track.
Joined: Dec 2015
Posts: 507
Likes: 1
From: France
Could someone tell me the truth about NAT time periods ?
I know the numbers : daytime is Europe to America and is from 1130 to 1900 UTC, crossing 30W
From Paris to 30W there is about 2300km which would be about a three hour flight.
So takeoff from Paris would be between 0830 and 1600 UTC, that is between 930 and 1700 local time.
Maybe a tad earlier when accounting for the winds
So why the f would my book say that westbound flights take off early in the morning ??
When in facts they seem to be taking off all day !
And regarding the eastbound flights, validity is given between 1 and 8 UTC at 30W.
So 3 hours later you're between 4 and 11 UTC in Paris. Which is 5 to 12 local time.
There is no police working at such an early time is paris !
Thanks !
I know the numbers : daytime is Europe to America and is from 1130 to 1900 UTC, crossing 30W
From Paris to 30W there is about 2300km which would be about a three hour flight.
So takeoff from Paris would be between 0830 and 1600 UTC, that is between 930 and 1700 local time.
Maybe a tad earlier when accounting for the winds
So why the f would my book say that westbound flights take off early in the morning ??
When in facts they seem to be taking off all day !
And regarding the eastbound flights, validity is given between 1 and 8 UTC at 30W.
So 3 hours later you're between 4 and 11 UTC in Paris. Which is 5 to 12 local time.
There is no police working at such an early time is paris !
Thanks !
Last edited by KayPam; 12th February 2017 at 21:19.
Joined: Jun 2012
Posts: 1,175
Likes: 0
From: -
Indicated airspeed (as read on the on the airspeed indicator) will:
A - increase in tailwind
B - increase in headwind [I answered this]
C - decrease in tailwind
D - remain unchanged in headwind and tailwind [this is correct]
Who the hell writes this question? Is EASA trolling us really hard?!
/rant
A - increase in tailwind
B - increase in headwind [I answered this]
C - decrease in tailwind
D - remain unchanged in headwind and tailwind [this is correct]
Who the hell writes this question? Is EASA trolling us really hard?!
/rant
Last edited by RedBullGaveMeWings; 15th February 2017 at 11:44.
Joined: Jan 2011
Posts: 660
Likes: 20
From: England
RedBullGaveMeWings.
I suspect that you are reading the question as meaning something like " a sudden increase or decrease in headwind or tailwind" or "The sudden onset of headwind or tailwind". But the question does none of these things.
It simply asks how being in a headwind or tailwind will affect your IAS. What they want you to know is that an aircraft in flight has no way of knowing what the wind is unless of course the wind suddenly changes. In a steady headwind or tail wind, the IAS will be unaffected.
It would of course hav e helped if they had said that the wind was steady.
I suspect that you are reading the question as meaning something like " a sudden increase or decrease in headwind or tailwind" or "The sudden onset of headwind or tailwind". But the question does none of these things.
It simply asks how being in a headwind or tailwind will affect your IAS. What they want you to know is that an aircraft in flight has no way of knowing what the wind is unless of course the wind suddenly changes. In a steady headwind or tail wind, the IAS will be unaffected.
It would of course hav e helped if they had said that the wind was steady.
Joined: May 1999
Posts: 1,846
Likes: 4
From: Bristol, England
It's not you RedBull, the question is completely unclear. Answer (b) is correct for microburst type scenarios and (d) for steady or slow-changing conditions. In correct English you would also use the indefinite article, for instance "increase in a tailwind". This question was probably written by someone who also does not have English as a first language.
Joined: Dec 2015
Posts: 507
Likes: 1
From: France
So, I am taking my first exams in Toulouse the day after tomorrow.
Air Law, ops proc, communications, and I am consistently scoring 90-100% on aviation exam.
Could I encounter many new questions or not ?
Thanks
Air Law, ops proc, communications, and I am consistently scoring 90-100% on aviation exam.
Could I encounter many new questions or not ?
Thanks
Joined: Dec 2015
Posts: 507
Likes: 1
From: France
There were indeed questions that I suspect were new.
Nothing terrible.. I was uncertain about some answers but got my 75% in all exams.
Real score might be lost in the French DGAC system forever (in which case the exam lady told me that airlines could do with my school's final tests results, which would be VERY favourable
)
Nothing terrible.. I was uncertain about some answers but got my 75% in all exams.
Real score might be lost in the French DGAC system forever (in which case the exam lady told me that airlines could do with my school's final tests results, which would be VERY favourable
)
Joined: Jun 2012
Posts: 1,175
Likes: 0
From: -
I am going through Instruments questions and there's one I really don't understand EASA's reasoning. And I think the difference between inner and outer loop are fairly clear.
4 is pretty clear, but I don't understand what 2 and 3 have to do with the flight path. Altitude is a barometric setting which changes with meteorological conditions from place to place, and we can maintain a speed also during a climb or descend anyway. For example, if a plane slows down on an ILS, RoD decreases and vice-versa to stay on the path to the runway.
In an autopilot system, the flight path modes are:
1) Pitch attitude hold.
2) IAS and Mach speed hold.
3) Altitude hold.
4) Glide intercept and track.
The combination regrouping all the correct statements is:
A) 4 [my answer]
B) 2, 3, 4 [corect answer]
C) 3
D) 1, 2, 3, 4
1) Pitch attitude hold.
2) IAS and Mach speed hold.
3) Altitude hold.
4) Glide intercept and track.
The combination regrouping all the correct statements is:
A) 4 [my answer]
B) 2, 3, 4 [corect answer]
C) 3
D) 1, 2, 3, 4
Joined: Apr 2016
Posts: 162
Likes: 0
From: EU
Have you had a look at www.TheAirlinePilots.com :: View topic - Questions on Autopilot ? That website if great for quickly skimming common questions and topics.
In my opinion, IAS and altitude hold are very clearly properties of the flight path - You're trying to maintain a certain 3dimensional profile.
Holding the pitch attitude says nothing about the 3D flight path, just something about how the aircraft is oriented.
In my opinion, IAS and altitude hold are very clearly properties of the flight path - You're trying to maintain a certain 3dimensional profile.
Holding the pitch attitude says nothing about the 3D flight path, just something about how the aircraft is oriented.
Joined: Jun 2012
Posts: 1,175
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From: -
Ok I understood why Altitude Hold controls path according to the question, to a certain extent. Moving the subscale moves only the pointers on the altimeter but the aircraft keeps flying at that same pressure outside. At least with the autopilot taken in consideration in the exam. However, I still disagree with it. Pressure levels change, a flight path would not.
Joined: Dec 2015
Posts: 507
Likes: 1
From: France
RedBullGaveMeWings
It seems like you could just translate flight path mode into outer loop and then you would be completely all right
The ATPL exams are not included in the French education system
They really do not give a toss ? I heard flybe wanted 90% minimum.
It seems like you could just translate flight path mode into outer loop and then you would be completely all right
They really do not give a toss ? I heard flybe wanted 90% minimum.
Joined: Apr 2016
Posts: 162
Likes: 0
From: EU
They don't care about your ATPL scores, because they know everybody with half a brain should be able to get 90%+ with the way the current exams are set up.
It's not that 95% average makes you look clever/good, it's that having 80% and a resit makes you look silly. If you know what I'm trying to say with that?
It's not that 95% average makes you look clever/good, it's that having 80% and a resit makes you look silly. If you know what I'm trying to say with that?
Joined: Dec 2015
Posts: 507
Likes: 1
From: France
Hello
I just started performance
Could someone please confirm that the entire CAP698 document will be available during the exam ?
My book says things like : "this is included in CAP698 so it does not need to be learnt"
Thanks
I just started performance
Could someone please confirm that the entire CAP698 document will be available during the exam ?
My book says things like : "this is included in CAP698 so it does not need to be learnt"
Thanks
