Laserfiche WebLink
12/5/78 AC 150/5300-4B CHG 3 <br />Appendix 8 <br />APPENDIX 8. COMPASS CALIBRATION PAD <br />*1. PURPOSE. This appendix provides guidelines for the design, location <br />on the airport, and construction of a compass calibration pad and basic <br />information concerning its use in determining the deviation error in <br />an aircraft magnetic compass. <br />2. BACKGROUND. <br />a. An aircraft magnetic compass is a navigation instrument with <br />certain inherent errors resulting from the nature of its construction. <br />All types of magnetic compasses are designed to indicate direction <br />with respect to the earthts magnetic field. This is true even for <br />the gyro -stabilized and/or fluxgate compasses. Aircraft navigation <br />is based on applying the appropriate angular corrections to the <br />magnetic reading in order to obtain the true heading. <br />b. The aircraft magnetic compass should be checked following pertinent <br />aircraft modifications and on a frequent, routine schedule. One <br />method of.oalibrating the compass is to use a compass calibration <br />pad to align the aircraft on known magnetic headings and make <br />adjustments to the compass and/or placard markings to indicate the <br />required corrections. There are other methods available for <br />calibrating a magnetic compass, but for small aircraft the method <br />outlined herein is normally used. <br />3. APPLICATION. <br />a. The process of aligning an aircraft on known magnetic headings for <br />the purpose of determining the degree of error in the magnetic <br />compass is commonly referred to as "swinging the compass." The <br />technique which should be used is as follows: <br />(1) Place the aircraft on a compass calibration pad. <br />(2) Place the aircraft in level flying position. <br />(3) Remove compensating magnets from chambers or reset the <br />fixed compensating magnets.to neutral position, whichever is <br />applicable, before swinging. <br />(4) Check indicator for fluid level and cleanliness. If fluid <br />is required, the compass is defective. <br />(5) Check the pivot friction of the indicator by deflecting the <br />card with a small magnet. The card should rotate freely in <br />a horizontal plane. <br />(6) If radio is used in the aircraft,there should be corrections <br />noted for "radio on" and "radio off" conditions. <br />* <br />Par 1 Page 1 <br />