Subject: Instruments ATPL - Compass acceleration and de-acceleration
 

Hey everyone

JUst wondered in the subject "Instruments", i'm just getting stuck on how the compass acceleration and deacceleration errors work. And also how to remeber the visual fields and if the compass under reads and over reads, as its different for the northern hemisphere and the southern hemisphere. Just hoping someone can shed some light on this subject for me.

Thanks

BRI :8

My Brain Hurts!!
 

Hi mate..not the easiest to visualise i know!!
But remember compass card reads right to left. numbers increase from right to left..opposite way to reading a sentence i thought of..
bearing that in mind..
ACCELERATION=TURN TOWARDS NEAREST POLE..
DECELERATION=TURN TOWARDS FARTHER POLE..
Example..A/C in Nth Hem Hdg 090 (east)
Draw a diagram..a circle with a line across the center..the equater.
Draw an arrow in the Nth Hem hdg east..bend the arrow as in CAPITALS above..
Hope that makes sense..
Do a few to practice an it will click!!

Athens 07!! are you a red?:ok:

Summary of compass errors
Acceleration error - Affect us on East/West headings

In the Northern hemisphere use the pneumonic

NADS


Meaning

Compass indicates turn to NORTH on ACCELERATION and a turn to SOUTH on DECELERATION

In the Southern hemisphere use the pneumonic

SAND


Meaning

Compass indicates turn to SOUTH on ACELERATION and a turn to NORTH on DECELERATION

NB No errors on N / S headings (both hemispheres)

No errors at the magnetic equator (pivot/CG in line)

Example Question


When on approach to RW 10R at London Heathrow the aircraft decelerates to lower gear and flap. What is the effect on the direct reading compass (DRC)?





a) A turn to the South

b) A turn to the North

c) No apparent turn

d) The magnetic element rocks

Solution

London Heathrow in Northern hemisphere so use NADS


We are decelerating so compass indicates turn to the South answer a

Not sure if its what your looking for but I use UNO'S, easy to remember for me because of my Fiat Uno from uni, Undershoot north, Overshoot South, reverse for Southern Hemisphere :)

The unos thing is for turning errors, not accelaration/deceleration...still handy to remember tho..

Somthing I didn't really understand...?
 

Thanks for all the replies everyone.

Just one question for DFSpilot, how do you know that london heathrow is in the northern hemisphere? how do you determine which one is northern and which one is in the southern hemisphere?...
I got the whole thing till the end... sorry, do you determine it by the equator?, as if its about the equator then it is in the northern hemisphere then when it is below then it would be in the southern hemisphere? or is it something else?.
Thanks
Brian304 :ok:

yes ,you use the equator . anything north of it is in the northern hemisphere. how i remembered NADS and SAND was that i knew sand was southern hemisphere by just thinking of the SAND ON BONDI BEACH. worked for me every time.

For me it's easier to understand the reason for acc/deacc error(weight added due to dip, "needle" follows the magnetic flux, newtons laws, etc.) and then derive the correct answer from there.