Compass Errors
Reference Source

Pilot’s Handbook of Aeronautical Knowledge (PHAK), Chapter 6-15 to 6-17, Compass
Errors
Study Questions
Module Objectives
1. The floating magnetic compass has long been a navigational aid to pilots, however
a) The technology is outdated and no longer useful.
b) Changes in the aircraft attitude, heading, and airspeed can cause erroneous readings.
c) If your helicopter has a gyroscopic heading indicator the compass is no longer needed.
PHAK – Chapter 6
2. Select the answers below that make the statements true.
One of the seemingly bizarre errors associated with the magnetic compass is that it will
indicate a turn to the north / south when the helicopter is accelerated, and a turn to the
north / south when the helicopter is decelerated (speed is reduced). The errors are
most pronounced when the helicopter is flying on a heading of east or west / northwest,
and are a result of one end of the compass needle wanting to dip toward / point away
from the earth.
3. Student pilots can remember how the compass reacts to acceleration with the acronym
ANDS.
A
N
D
S
When ________________________ (on a easterly or westerly heading),
the compass will show a turn to the ________________________.
When ________________________ (on a easterly or westerly heading),
the compass will show a turn to the ________________________.
4. Compass turning errors are most apparent when turning to or from a heading of
_________________________________________________________
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5. When flying south and turning to the right or left, the direction indicated on the compass
will turn faster than the actual turn the helicopter is making.
a) True.
b) False.
6. When flying on an eastbound heading, the helicopter is most susceptible to
________________ errors, and least susceptible to ________________ errors.
7. Create your own memory aid to help you remember how the compass reacts when turning
to or from a north/south heading.
___
N
___
S
The compass will ______________________________________________,
when turning to or from a heading of North.
The compass will ______________________________________________,
when turning to or from a heading of South.
N
W
A
C
E
S
E
F
B
D
G
8. In the diagram above, which of the helicopters should expect the largest compass errors
while accelerating or decelerating?
a) Helicopters A, D, and F.
b) Helicopters D and E.
c) Helicopters B, C, and G.
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9. How will the magnetic compass indicate during Helicopter E’s turn?
_________________________________________________________
10. How will the magnetic compass indicate during Helicopter D’s turn?
_________________________________________________________
11. If Helicopter A accelerates, what indicates should be expected on the compass?
_________________________________________________________
12. As Helicopter G rolls into a right 30° turn, what will the magnetic compass indicate?
a) A 30° turn to the left.
b) A turn to the right, but at a faster rate of turn.
c) The compass will indicate normally.
FAA Questions
1. [3280, 3-16] In the Northern Hemisphere, a magnetic compass will normally indicate initially
a turn toward the west if
a) A left turn is entered from a north heading.
b) A right turn is entered from a north heading.
c) An aircraft is accelerated while on a north heading.
2. [3281, 3-16] In the Northern Hemisphere, a magnetic compass will normally indicate initially
a turn toward the east if
a) An aircraft is decelerated while on a south heading.
b) An aircraft is accelerated while on a north heading.
c) A left turn is entered from a north heading.
3. [3282, 3-15] In the Northern Hemisphere, a magnetic compass will normally indicate a turn
toward the north if
a) An aircraft is decelerated while on an east or west heading.
b) A left turn is entered from a west heading.
c) An aircraft is accelerated while on an east or west heading.
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4. [3283, 3-15] In the Northern Hemisphere, the magnetic compass will normally indicate a
turn toward the south when
a) A left turn is entered from an east heading.
b) A right turn is entered from a west heading.
c) The aircraft is decelerated while on a west heading.
5. [3283-1, 3-15] What should be the indication on the magnetic compass as you roll into a
standard rate turn to the right from a south heading in the Northern Hemisphere?
a) The compass will initially indicate a turn to the left.
b) The compass will indicate a turn to the right, but at a faster rate than is actually
occurring.
c) The compass will remain on south for a short time, then gradually catch up to the
magnetic heading of the helicopter.
6. [3284, 3-16] In the Northern Hemisphere, if an aircraft is accelerated or decelerated, the
magnetic compass will normally indicate
a) A turn momentarily.
b) Correctly when on a north or south heading.
c) A turn toward the south.
7. [3286, 3-16] During flight, when are the indications of a magnetic compass accurate?
a) Only in straight-and-level unaccelerated flight.
b) As long as the airspeed is constant.
c) During turns if the bank does not exceed 18°.
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Assignment Answers
Answers
1. b
2. North; south; west; dip toward
3. A
N
D
S
When accelerating (on an easterly or westerly heading),
the compass will show a turn to the north.
When decelerating (on an easterly or westerly heading),
the compass will show a turn to the south.
4. North or south.
5. a
6. Acceleration; turning
7. Make up your own. But UNOS is a common one.
U
N
O
S
The compass will undershoot (or lag behind),
when turning to or from a heading of North.
The compass will overshoot (or jump ahead),
when turning to or from a heading of South.
8. c
9. Undershoot (or lag behind) the turn and then eventually read correctly in level flight.
10. overshoot (or jump ahead) the turn, indicating that the helicopter has turned farther than it
actually has, and then eventually read correctly in level flight.
11. Should not affect the magnetic compass.
12. c
FAA Answers
1. b
4. c
6. b
2. c
5. b
7. a
3. c
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