range marking

The colored marks on aircraft instruments that indicate the ranges of operation of that system as specified in manufacturers’ manuals. The ranges and colors most often used are

i. A red radial line, which means, “Do not exceed the parameter beyond this.”

ii. A green arc, indicating the normal operating range.

iii. A yellow arc, which indicates the caution zone.

iv. A blue radial line, which is used only in an ASI (air-speed indicator), shows the best single-engine-rate-of-climb speed.

v. A white arc, which also is used only in an ASI, shows the flap-operating speed.

Range marking on an air speed indicator.