Section One: 4. The Magnetic Compass and Direction Flashcards
045, 135,225 and 315 degrees are what kinds of directions?
Quadrantal points
Grid north is the same as
True North
What is ‘variation’?
Angular difference between North Geographic and Magnetic Poles
Why is magnetic variation not uniform across the Earth’s surface?
Due to the angular difference between the two kinds of Poles
What is an isogonal?
Line joining locations of equal magnetic variation
What kind of variation is experienced over the UK currently?
Western
What is an agonic line?
Indication of where magnetic variation is 0
Isogonals are shown for every what increment in mag variation?
0.5 degrees
If mag north is WEST of true north (westerly direction), the magnetic direction will have a
Higher angular value than true direction
If mag north is EAST of true noth (easterly direction), the magnetic direction will have a
Lower angular value than true direction
If magnetic direction has a higher angular value than true direction, what variation exists?
Westerly
If magnetic direction has a lower angular value than true direction, what variation exists?
Easterly
Rhyme to remember for mag/true variation
Variation west - Magnetic Best, Variation East - Magnetic Least
The metallic structure and equipment of an aircraft has what effect on navigational ability?
Compass deviation occurs
Rhyme to remember for compass deviation
Deviation west - compass best, deviation east - compass least
Why is magnetic compass reliability poor near the magnetic poles?
Magnetic dip is greater
Weaker horizontal component
At what approximate latitudes does do magnetic compasses become unreliable?
60 degrees North or South
The horizontal component of magnetic flow is greatest where?
Equator
How do magnetic compass cards minimise the effect of magnetic dip?
The float is displaced
What is the drawback to having the float displaced on magnetic compasses?
It causes turning and acceleration errors
Why do compasses give incorrect readings in turns?
The pivot and float’s C of G are not correctly aligned with magnetic north
When turning through the nearest magnetic pole, the compass will…
Underestimate the actual magnetic heading
When turning through the furthest magnetic pole, the compass will…
Overestimate the actual magnetic heading
Why does a compass turning error not occur during turns through 90 or 270 degrees?
The pivot and float’s C of G are aligned during the turn
Acceleration errors in compasses walkthrough
Aircraft accelerates
Float CoG’s inertia causes clockwise rotation
Compass heading underestimates
Decceleration errors in compasses walkthrough
Aircraft decelerates
Float’s CoG thrown forwards causing anti-clockwise rotation
Compass heading overestimates
Why do acceleration errors not occur on headings of 360 and 180?
Pivot and float’s CoG are aligned
A compass pivot and float’s CoG rotate clockwise in a change of speed. What is occuring?
Aircraft is accelerating and the compass will overestimate
A compass pivot and float’s CoG rotate anti-clockwise in a change of speed. What is occuring?
Aircraft is decelerating and the compass will underestimate
A compass will underestimate during what change of speed?
Acceleration
A compass will overestimate during what change of speed?
Deceleration
An aircraft accelerates on a heading of 360 degrees. What compass error will occur?
None, as the pivot and float CoG are aligned
An aircraft turns from 060 to 120. What compass error will occur?
None, as the pivot and float CoG are aligned
Northern Hemisphere compasses are compensated how?
Displaced towards the south pole to compensate for dip
The Earth rotates how many degrees an hour?
15 degrees
Directional indicator (gyro) drift occurs how?
Indicator axis is fixed in space by the gro and drifts in accordance with the Earth’s rotation
Why can the correct functioning of the HI only be checked when the engine is running?
The vaccum system needs to be operational
Acronym to remember for compass deviation in turns?
UNOS
Acronym UNOS is..
Undershoot North, Overshoot South
UNOS means when turning onto a northerly heading, you should
Roll out before compass indicates North
Acronym to remember for compass deviations when accelerating/decelerating?
ANDS
Acronym ANDS is.
Accelerate North, Decelerate South
Acronym for heading calculations involving drift, variation etc?
TVMDC
TVMDC acronym remembered by?
True Virgins Make Dull Companions
