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AC 150/5300-4B CHG 3 12/5/78 Appendix 8 * (7) (8) Align the aircraft with the north magnetic heading and make the indicated reading correspond to the actual magnetic reading by use of the compensating magnets. Repeat for the east magnetic heading. Then place on south and west magnetic headings and remove half of indicated error by adjusting compensators. Engine(s) should be running. Turn the aircraft on successive 30-degree headings through 360 degrees. Placards should be marked to indicate correction at each 30-degree heading showing "radio on" and "radio off" corrections. b. Calibration and adjustment of remote indicating gyro compasses, polar path compasses, and other systems of this type should be accomplished by a qualified instrument technician. 4. DESIGN OF COMPASS CALIBRATION PAD. The design details shown in this appendix should be considered as guidance only and variations of these designs are acceptable provided the general requirements are met. a. The compass calibration pad provides a series of 12 radials, either painted on with nonmetallic paint or inlaid in the surface of the calibration pad, extending toward predetermined magnetic directions every 30 degrees beginning with magnetic north. Each radial should be marked with three separate magnetic headings; one at the end of the radial indicating the direction along which each line lies; and one on each side of the line which indicates the magnetic heading of the aircraft when it is oriented at 90 degrees to the radial. Markings facing the pilot must correspond to the airplane's heading when traveling in that direction. The markings must be large enough to be easily read from the aircraft cockpit as the radial is being approached. The last zero may be dropped from the heading designation. .A. layout of markings to be used is shown in Figure 1. b. Suggested types of calibration pads are depicted in Figures 2 and 3. Type I, as shown in Figure 2, can be constructed using either rigid or flexible pavement. Type II, as shown in Figure 3, is applicable only to rigid pavements. The pavement thickness of either type shall be as required to support the user aircraft in a critical area in accordance with AC 150/5320-6. With concrete pavements the joint type and spacing shall conform to standard practices, except that no magnetic materials are to be used and, therefore, dowels (where required) shall be of aluminum, brass, or bronze, rather than steel. c. Make the size of the calibration pad compatible with the require- ments of the user aircraft. For small airplanes make the radius of the pad 50 feet (15 m); for basic transports make the radius Page 2 Par 3