30. What colors and color schemes should powerplant instruments use? Powerplant instrument range markings are intended to provide status information to the operator about the powerplant. Powerplant instruments (displays) should show whether the current operations are normal, acceptable for a limited time, or unauthorized. These markings are based on the installed engine operating limits, which may not exceed (but are not necessarily equal to) those limits provided by the engine manufacturer. A powerplant instrument general color marking scheme consists of three colors: red, green, and yellow, in addition to white, which is generally used for numerals and graduation marks. Many powerplant instruments are electromechanical round-dial type with a graduated scale and a rotating needle indicator. Electronic displays may adopt similar presentations as their analog equivalents, use linear scales, or another means. The paragraphs below describe markings more closely related to round-dial instruments; however, when appropriate, electronic displays may incorporate the same guidelines. All markings whether a round-dial instrument or electronic display, should be explained in the AOI/POH.
a. When marking the instruments, the colored markings should be placed directly over the instrument graduations in a manner that does not obscure the graduations themselves. When in this position, if the markings interfere with the instrument's readability from the operator’s position, adjustment of the colored markings above or below the graduations should be considered. The colored markings may be placed on the cover glass of the instrument provided the readability of the instrument is not compromised and there is a means to maintain the correct alignment of the cover glass with the dial face.
b. The color red indicates an operating condition beyond authorized limits and/or requires a specific action on the part of the operator. The specific action to be taken should be described in detail in the AOI/POH. Red radial lines should be used to identify only the established maximum and minimum safe operating limits (when applicable). Where appropriate, the maximum should be the limit for takeoff operation. Red radials should be located so the edge nearest the normal operating range is placed on the limit value. In use, when the needle point touches the edge of the red radial nearest the green arc, the limit is met. To minimize confusion the use of multiple red radials should be avoided, except for certain conditional limits. Multiple red radials can be displayed on electronic displays with switching accomplished automatically. If possible, multiple read radials should have distinguishing features, such as one solid line and one dashed line, or lines of different lengths.
c. A red arc requirement(s) may be satisfied by marking the applicable instruments for all speed ranges which are restricted because of the excessive vibration and other stresses induced by reciprocating masses such as the engine or propeller. This requirement applies to tachometers; however, the red arc may also be used on other powerplant instruments. The dial should not be marked to indicate restricted operating range when the restriction applies only under certain conditions (for example, a propeller vibratory stress restriction that applies only when the aircraft is in a specific configuration). Instead of a red arc, it may be satisfactory to provide an adjacent placard covering such restricted ranges.
d. The color green is used to indicate a normal condition for operation, both ground and flight. Where applicable, the high-value end of the green arc should indicate the maximum limit for normal operation, and the low-value end of the green arc should indicate the minimum limit for normal operation. Where appropriate, there may be blank gaps, or other colors, inserted into the green arc. Either the upper or lower end of the green arc may extend to the red radial or stop short of it as appropriate to the measurement being marked.
e. The color yellow is used to indicate either a takeoff or cautionary range where limited operation is permissible as directed by the applicable AOI/POH. An example of compliance with the precautionary range requirement is the yellow arc marking on the carburetor air temperature gauge to indicate the range of temperature where carburetor icing may occur.
f. Other informational markings (such as warranty ratings), may be included on the instrument face provided they are not red, yellow, or green marks and they would not be confused with other powerplant instrument markings. These types of marks should be explained satisfactorily in the AOI/POH.
g. Some displays may utilize a servo-driven indicator or electronic display with vertical or horizontal scale. The same basic color markings as a dial/rotating needle type should be used.
h. On a vertical or horizontal scale instrument, a red line or stripe applied across the scale to mark the maximum (and minimum, when applicable) authorized operating limit is comparable to the red radial line applied to round-dial instruments. Green, yellow, or red lines or stripes parallel to the scale with the ends of the lines at the specified range limit graduations are practical methods of conveying the same type of information as provided by the colored arcs on round-dial instruments. On a moving tape instrument, the operating range markings should be either placed on the face of the tape or affixed adjacent to the tape.
31. How should powerplant instruments be marked? Common powerplant instruments should display the general marking scheme as previously discussed. Common powerplant instruments such as the carburetor air temperature indicator, cylinder head temperature indicator, manifold pressure indicator, fuel pressure indicator, oil pressure and temperature indicator, tachometer, and torque indicator may be marked with color ranges and/or colored marks. Any additional markings to these instruments may be added as desired, provided the marking does not conflict with general marking scheme. All powerplant instrument markings should be detailed and explained in the AOI/POH. Other powerplant instruments not discussed may also need to be marked and should follow the general instrument marking schemes. Instruments using electronic displays should present information similarly to their corresponding analog equivalents. Arcs used in analog instruments to describe a range may be represented in electronic displays by using a linear tape scale or some other means.
a. Carburetor air temperature indicator.
(1) Red radial. At maximum permissible carburetor inlet air temperature as referenced in the AOI/POH.
(2) Green arc. Normal operating range for trouble-free operation with the upper limit at maximum permissible carburetor inlet air temperature and the lower limit at the point where icing may be anticipated. Additional green arc may be required in the temperature range below the icing range.
(3) Yellow arc. Range indicating where icing is most likely to be encountered.
b. Cylinder head temperature indicator.
(1) Red radial. At maximum permissible cylinder head temperature.
(2) Green arc. From maximum permissible temperature for continuous operation to minimum recommended for continuous operation, as referenced in the AOI/POH.
(3) Yellow arc. From maximum temperature for continuous operation to maximum permissible temperature.
c. Manifold pressure indicator.
(1) Red radial. At maximum permissible manifold absolute pressure for dry or wet operation, whichever is greater.
(2) Green arc. From maximum permissible manifold pressure for continuous operation to the minimum manifold pressure selected by the aircraft manufacturer for cruise power.
(3) Yellow arc. From maximum manifold pressure for continuous operation to maximum permissible manifold pressure.
(4) Red wedge shape. At normal takeoff rating, if less than maximum limit.
(5) Striped green arc. From the normal takeoff rating (red wedge shape) to the maximum limit (red radial).
d. Fuel pressure indicator.
(1) Red radial. At maximum and/or minimum permissible pressure as established in the engine operating limitations. For engines with variable minimum permissible pressure limits, the lower red radial should be placed at the highest minimum absolute pressure allowed.
(2) Green arc. Normal operating range.
(3) Yellow arc. Cautionary ranges indicating any potential hazard in the fuel system such as malfunction or icing.
e. Oil pressure indicator.
(1) Red radial. At maximum and/or minimum permissible pressure as established in the engine operating limitations.
(2) Green arc. Normal operating range.
(3) Yellow arc. Cautionary ranges indicating any potential hazard due to factors such as overpressure during cold start or low pressure during idle.
f. Oil temperature indicator.
(1) Red radial. At maximum and/or minimum permissible temperatures established as engine operating limitations.
(2) Green arc. Normal operating range.
(3) Yellow arc. Cautionary ranges indicating any potential hazard due to factors such as overheating or high viscosity at low temperature.
g. Tachometer.
(1) Red radial. At maximum permissible rotational speed (rpm).
(2) Green arc. From maximum rotational speed for continuous operation to minimum recommended for continuous operation (except in the restricted range, if any).
(3) Yellow arc. From maximum rotational speed for continuous operation to maximum permissible rotational speed.
(4) Red arc. Range(s) in which operation is restricted, except to pass through, for all operating conditions due to factors such as excessive stresses.
h. Torque indicator.
(1) Dashed red radial. At maximum permissible torque limit for conditional operation (if applicable).
(2) Red radial. At the normal maximum permissible torque limit.
(3) Green arc. From maximum torque limit for continuous operation to the minimum recommended torque value.
(4) Yellow arc. From maximum rotational speed for continuous operation to maximum permissible rotational speed.
32. Do the markings outlined in this AC for powerplant instruments apply to electric motors? No, the guidance in this AC applies to aircraft with reciprocating engines only.
Refer to 14 CFR § 1.1, General definitions.
33. Where can I find this AC? You can find this AC at http://www.faa.gov/regulations_policies/advisory_circulars.
James D. Seipel Manager Production and Airworthiness Division
Appendix A A-1 Appendix A. Related 14 CFR Parts
1. 14 CFR part 1, Definitions. Part 1 provides definitions for terms used in the regulations.
2. 14 CFR part 21, Certification Procedures for Products, Articles, and Parts. Part 21 sets forth rules for the issuance of and change to type certificates, and issuance of production certificates, airworthiness certificates, and export airworthiness approvals. It also sets forth the rules governing the holders of these certificates and the approval of certain articles.
3. 14 CFR part 45, Identification and Registration Marking. Part 45 sets forth rules for display of nationality and registration marks, display of special airworthiness classification marks, identification plates for products, and identification of certain replacement and critical aircraft articles.
4. 14 CFR part 47, Aircraft Registration. Part 47 sets forth rules for registering an aircraft.
5. 14 CFR part 91, General Operating and Flight Rules. Part 91 sets forth rules governing the operation of most aircraft within the United States.
Appendix B B-1 Appendix B. Related Publications FAA Order 8130.2, Airworthiness Certification of Aircraft and Related Products AC 20-88A, Guidelines on the Marking and Aircraft Powerplant Instruments (Displays) AC 45-2D, Identification and Registration Marking FAA-H-8083-25, Pilot’s Handbook of Aeronautical Knowledge FAA-H-8083-1A, FAA Aircraft Weight and Balance Handbook