U.S. Military Aircraft Gauge Markings

Beginning in about 1943-1944 or thereabouts; US Military aircraft began to carry color gauge markings as standard; making pilot's lives much much much easier; as you no longer had to remember exact bands of “go/no-go” limits; and you just had to “follow the markings”.

Piston-Engined Aircraft


MANIFOLD PRESSURE GAGE


TACHOMETER

Blue Arc

Indicates the range within which operation is permitted in auto-lean. The bottom of this arc indicates the minimum manifold pressure desirable in flight determined by engine characteristics. The top of this arc indicates the manifold pressure at which mixture control must be moved into auto-rich.

Blue Arc

Indicates rpm range within which auto-lean, operation is permitted. The bottom of this arc indicates the minimum rpm desirable in flight because of engine limitations, generator cut-out, etc. The top of this arc indicates the rpm at which the mixture control must be moved to auto-rich.

Green Line or Arc

Describes the range within which operation must be in auto-rich. The radial or top of this arc indicates maximum continuous power. All operation above this manifold pressure is limited in time (usually 5 or 15 minutes).

Green Line or Arc

Indicates rpm range within which auto-rich operation is required. The radial or top of this arc indicates maximum continuous power. All operation above this rpm is limited in time (usually 5 or 15 minutes).

Short
Red Line

Indicates manifold pressure for takeoff.

Red Line

Indicates maximum rpm.

Long
Red Line

Indicates maximum dry war emergency manifold pressure.

Red Arc

May be used to show region of prohibited operation because of dangerous vibration or similar reasons.

Long
Red Line

Indicates maximum war emergency manifold pressure with water injection.




CYLINDER HEAD
TEMPERATURE GAGE


CARBURETOR
AIR TEMPERATURE GAGE.

Blue Arc

Indicates the range within which operation is permitted in auto-lean. The bottom of this arc indicates the minimum temperature desirable for flight (minimum engine warmth required for good fuel vaporization and efficient engine operation). The top of this arc indicates the temperature at which the mixture control must be moved to auto-rich.

Yellow Arc

Indicates the temperature range within which undesirable conditions may exist such as danger of icing or poor fuel vaporization.

Green Arc

Describes the range within which operation must be in auto-rich. The top of this arc indicates maximum continuous power; all operation above this temperature is limited in time (usually 5 or 15 minutes).

Green Arc

Indicates the temperature range of best operation and assures good vaporization.

Red Line

Indicates maximum permissible temperature.

Red Line

Indicates maximum permissible temperature, usually because of detonation danger.


COOLANT TEMPERATURE GAGE

TORQUEMETER

Green Arc

Describes the range within which the temperature must remain during continuous operation. The bottom of this arc indicates minimum desirable temperature for flight. The top of this arc indicates maximum continuous power. All operation above this temperature is limited in time (usually 5 or 15 minutes).

Blue Arc

Indicates the range within which operation is permitted in auto-lean. The bottom of this arc indicates the minimum torque pressure desirable in flight determined by engine characteristics. The top of this arc indicates the torque pressure at which mixture control must be moved into auto-rich.

Red Line

Indicates maximum permissible temperature.

Green Arc or Line

Describes the range within which operation must be in auto-rich. The radial or top of this arc indicates maximum continuous power. All operation above this torque pressure is limited in time (usually 5 or 15 minutes).

Red Line

Indicates war emergency maximum temperature.

Short
Red Line

Indicates maximum dry torque pressure.

Long
Red Line

Indicates maximum wet torque pressure.

Turbine-Engined Aircraft

TACHOMETER

EXHAUST TEMPERATURE GAGE

Green Arc

Describes the range within which the rpm must fall during continuous flight operation. The bottom of this arc describes the minimum rpm for best cruising. Considerable range will be lost when operating below this rpm. The top of this arc indicates maximum continuous rpm; operation above which is limited to a specified length of time.

Red Line

Indicates minimum permissible temperature during flight.

Red Line

Indicates maximum rpm.

Green Arc

Indicates desirable temperature during continuous operation.

Red Arc

May be used to show region of prohibited operation because of dangerous vibration or similar reasons.

Red Line

Indicates maximum permissible temperature for flight.

Red Line

Indicates maximum permissible temperature during starting or acceleration.

Helicopters

DUAL TACHOMETER

ROTOR

Green Arc

Indicates rotor rpm range during powered flight. The bottom of this arc describes minimum rotor rpm for continuous flight. The top of this arc indicates maximum rotor rpm with power.

Red Line

Indicates maximum permissible autorotative rpm.

Red Arc or Line

May be used to show regions of prohibited operation because of dangerous vibration or similar reasons.

ENGINE

Red Line

Indicates maximum rpm.

NOTE: To locate a particular rotor speed on a universal type dual tachometer on which the rotor scale is not calibrated, use the following procedure.

(1) Find the speed on the engine scale corresponding to the desired rotor speed point by multiplying the desired rotor speed by the engine rotor gear ratio of the particular aircraft.

(2) Draw a line from the engine speed point on the engine scale, as determined above, to the center of the dial. The point where this line crosses the rotor scale is the desired rpm point on that scale.

(3) The above procedure can be used to locate any point on the rotor scale. The reverse of this procedure can be used to determine the rpm value of any point marked on the rotor scale.

All Types of Aircraft


OIL PRESSURE GAGE


OIL TEMPERATURE GAUGE

Lower Red Line

Indicate, minimum oil pressure permissible in flight.

Lower Red Line

Indicates minimum permissible temperature during flight.

Green Arc

Indicates desirable oil pressure range during continuous operation.

Green Arc

Indicates desirable temperature during continuous operation.

Upper Red Line

Indicates maximum permissible oil pressure.

Upper Red Line

Indicates maximum permissible temperature.



AIRSPEED INDICATOR

HYDRAULIC PRESSURE GAGE

Yellow Line

Indicates maximum permissible airspeed with either full flaps or landing gear extended. When the maximum permissible speed with flaps down differs from that with gear down, the lower speed and condition will be given. A notation in parenthesis will also be included to show the higher limiting speed and condition.

Yellow Line

Indicates pressure required for one brake application.

Red Line

Indicates maximum permissible diving speed at design gross weight.

Green Arc

Indicates normal operating pressure. The lower end of this arc indicates hydraulic pump cut-in pressure and the upper end indicates cutout pressure.

Yellow Arc

Defines the range of maximum permissible diving speeds from maximum to design gross weight.

Red Line

Indicates maximum permissible pressure.



SUCTION GAGE

DEICER GAUGE

Red Line

Indicates minimum desirable suction.

Green Arc

Indicates desirable pressure range.

Green Arc

Indicates desirable suction range.

Red Line

Indicates maximum permissible pressure.

Red Arc

Indicates maximum desirable suction.



FUEL PRESSURE GAGE

Lower Red Line

Indicate, minimum fuel pressure permissible in flight.

Green Arc

Indicates desirable fuel pressure range during continuous operation.

Upper Red Line

Indicates maximum permissible fuel pressure.

Resources:
TM 55-1500-345-23 – Painting and Marking of Army Aircraft (12 June 1986)
Pilot Training Manual for the A-26 Invader (WW2 Era)