Fly In The Yellow Arc?

Editorial Staff

Wednesday, April 20, 2022 at 07:04 PM ET

Verified

Les Abend, Contributing Editor

Key Takeaways:

Piston aircraft airspeed indicators feature color-coded arcs (white, green, yellow, red line) that denote various operating ranges and speed limits, with the yellow arc being a key distinction from turbine aircraft due to certification.
The yellow arc (a cautionary range between V_NO and V_NE) should only be entered in absolutely smooth air, as it significantly reduces safety margins to the never-exceed speed (V_NE) and increases the risk of structural stress from turbulence or sudden control inputs.
To decelerate from the yellow arc, retractable landing gear can act as speed brakes, or be deployed in emergencies (accepting potential damage); however, pilots are strongly warned **not to extend flaps** due to the high risk of structural failure and loss of control.
Being in the yellow arc often indicates a loss of control or a rapid descent, underscoring the need for smooth control inputs and, ideally, upset recovery training.

See a mistake? Contact us.

One instrument almost all aircraft have is an airspeed indicator. Of course, it’s important to know how fast we’re going, if for no other reason than bragging rights, and that’s true for airplanes, rotorcraft, gliders and even dirigibles (hot air balloons need not apply). Piston-powered personal airplanes, meanwhile, often have a bunch of color-coded markings on their airspeed indicator (ASI), denoting things like best single-engine rate of climb (V_YSE) or minimum-control airspeed (V_MC), when considering twins, and flap operating range (V_FO) and normal operating range (V_NO) for everything else, including the twins. There also are white, green and yellow arcs, plus another red line at the high end of the ASI when flying a twin. Single-engine airplanes just have the single red line at the top end, the never-exceed speed (V_NE).

One thing piston-powered airplanes have that turbine-powered airplanes don’t? A yellow arc, which is the airspeed range between V_NO and V_NE. That’s for certification reasons: if you replace a piston engine and bolt on a turboprop, your new red line is at the top of the green arc, and the yellow arc is eliminated. For that matter, the green arc may be eliminated, also, leaving only the white one.