one of the most basic but often overlooked pieces of equipment we have in the airplane is the traditional magnetic compass with all of our modern avionics sometimes it's easy to forget just how important it really is if our a Harz or magnetometer won't ever fail you would have to rely on the magnetic compass for heading information which can present some interesting challenges of its own as we remember from our private pilot training the magnetic compass is subject to a couple of errors those being deviation and variation with that said there are a couple additional errors that we need to become familiar with these are referred to as turning errors and acceleration errors these turning errors and acceleration errors are results of magnetic dip magnetic dip is the result of a magnet trying to align itself with the Earth's magnetic field the Earth's magnetic field lines are not always parallel to the surface in fact near the north and south magnetic poles the magnetic field lines dip towards the center of the earth this dip combined with the way the magnet is balanced inside the compass causes turning errors and acceleration errors when you roll into a bank the magnet dips as it attempts to point to the magnetic pole and therefore shows an inaccurate heading until you roll out of the turn close to the equator this error is barely noticeable but in the higher latitudes when you're closer to the magnetic poles this error is much more pronounced to complicate matters this error changes based on whether you're turning to the north or to the south and if you're in the northern hemisphere or southern hemisphere don't worry though this is aviation and we have an acronym for everything let's start with turning errors when flying in the northern hemisphere we use the acronym you know soar undershoot North overshoot South what this means is that when turning towards the north the magnetic compass moves slower than you so you need to understand when you go wings level the compass will continue to rotate until it is caught up if you calculated your roll out heading correctly you should be on your desired heading conversely when you are making a turn to the south you will want to overshoot or fly past the desired heading once you roll out you'll notice that the compass will momentarily reverse course until it stabilizes on the correct heading now if or when you find yourself flying in the southern hemisphere the Aires will be the exact opposite the number of degrees you need to understand is based on your latitude and can be estimated with this rule of thumb take half your latitude that you are flying and add 15 degrees to it this means when you're at somewhere like Miami which is around 26 degrees of latitude you would want to overshoot or undershoot your desired heading by 28 degrees 1/2 of 26 is 13 add 15 to that and you end up with 28 degrees in New York you would need to understood your desired heading by 35 degrees since the city sits at just over 40 degrees of latitude half of 40 is 20 add 15 to that and we get 35 if we take the NewYork example and we're making a left turn from a heading of 0 9 0 2 3 6 0 then we would want to under shoot the roll up by 35 degrees or on a heading of 0 3 5 if you were instead making a right turn from a heading of 0 9 0 to 1 8 0 we'd want to overshoot the roll out by 35 or on a heading of 2 1 5 when you roll out on 2 1 5 in this case you'll see the compass backtrack to then show your desired heading of 1 8 0 let's now talk about the errors resulting from acceleration again due to how the compass is balanced inertia can cause the compass to display in accurate heading until you return to unaccelerated flight this error only occurs when the airplane is flying on a heading of east or west when flying north or south these acceleration errors are minimized for this error we like to use the acronym and/or accelerate north decelerate south what this means is that whenever you are on an easterly or westerly heading and you accelerate the compass will show a pull towards the north conversely when out an easterly or westerly heading and you slow down the magnetic compass will pull towards the south in those rare instances where you must rely on your magnetic compass for heading information keep these errors in mind and use the techniques we just discussed to make sure you always want to end up on the headings you want to be on when it comes to turning to a new heading often we just glance down at our HSI and begin to roll out when we get close to our desired heading but with a failed a cars or magnetometer it's not easy with just a magnetic compass especially when we think about the turning errors we just covered there's a rather simple solution to this predicament though and we call them time turns the goal of a time turn is to arrive at a desired heading using a clock or timer to do this simply figure out how many degrees of heading change you want and then divide by 3 why three because during a standard great turn we cover three degrees of heading change per second this equation leaves us with the number of seconds we should be turning to reach our desired heading now let's try putting this to use remember how we said making a turn to the north would cause the magnetic compass to lag slightly behind then catch-up once you've rolled out say we're on a heading of 270 row and want to make a turn to three six zero instead of calculating our lead or lag heading to roll out like we do for magnetic compass turns let's try using this trick instead turning from two seven zero to three six zero means we want to change ninety degrees of heading now we divide 90 by our three degrees per second turn to get 30 seconds with that in mind start a timer once you begin the turn to keep the duration accurate and with no luck required you'll roll wings level on your new heading remember that you must maintain a standard great turn during the whole duration of your turn turning faster or slower than standard rate will make it difficult to turn accurately at a hundred to 120 knots of true airspeed 15 to 18 degrees of Bank should help keep you in the airplane in a standard rate turn for smaller turns though like vectors from ATC when they ask for something small like a 10 degree heading change you may just want to forego the timer and just count to 3 seconds in your head this trick makes turns easy predictable and virtually eliminates any of the confusion from turning errors those are the basics behind magnetic compass turns and time turns primarily pilots rely on their working flight instruments and you won't need to use these methods often however in emergency situations with equipment failures these types of turns become critical to the safety of flight and help reduce pilot workload