AIRCRAFT MAINTENANCE TIPS By: Rick Farmer iPads and Compass Deviation Magnetic compass deviation is a phenomenon that occurs when the electrical field created by the electronic equipment in the aircraft disturbs the magnetic compass, causing it to deviate away from magnetic north. To correct this magnetic influence, two adjustable compensating magnets are mounted on the compass and are set to minimize this deviation by a mechanic. A compass card is then installed so the pilot can determine how many degrees of deviation to expect during flight. This deviation card will only tell you how many degrees of deviation to expect with the equipment that was installed in the aircraft during this initial compass calibration. This is the reason why deviation cards state whether or not the radios were on or off during the compass swing. Therefore, this deviation card does not take into account any accessories you bring with you in the airplane such as Hand held GPS's, iPads, Smart Phones, etc. All of these devices can cause additional deviation with surprising results. We performed a “not so scientific” test of this phenomenon by placing an iPad on the glare shield of a Cessna 172 and found that it caused approximately 60 degrees of deviation when placed within two inches of the compass. While modern electronics have proven to help organize and simplify cockpit management, these devices can also cause potentially serious problems if you are not careful when using them. Without Ipad With Ipad