10.airspeed-indicator-markings-vne-vno-va. Airspeed Indicator Markings (VNE, VNO, VA)
The airspeed indicator (ASI) is a sensitive, differential-pressure instrument that compares ram (pitot) pressure with static pressure to display the aircraft's speed through the air. To make this raw speed information immediately useful in the cockpit, the FAA requires the face of the ASI to be marked with a system of color-coded arcs and radial lines that summarize the airplane's certified operating envelope. A pilot who understands these markings can manage the aircraft within its structural and aerodynamic limits at a glance, without referring to the Pilot's Operating Handbook (POH) in flight.
The standard color-coded markings, derived from 14 CFR Part 23 certification, are as follows:
- White arc — Flap Operating Range. The lower limit is VS0, the stalling speed or minimum steady flight speed in the landing configuration (gear and flaps fully extended). The upper limit is VFE, the maximum speed with the flaps extended. Operating within the white arc indicates the airplane is in a speed regime where flap deployment is structurally safe.
- Green arc — Normal Operating Range. The lower limit is VS1, the stalling speed or minimum steady flight speed in a specified configuration (typically clean — gear and flaps retracted). The upper limit is VNO, the maximum structural cruising speed. Most flight operations occur within the green arc.
- Yellow arc — Caution Range. This range lies between VNO and VNE. The airplane may be operated in this band only in smooth air and with caution, because gust loads encountered in turbulence can produce structural stresses that exceed design limits.
- Red radial line — Never Exceed Speed (VNE). This is the absolute maximum speed at which the airplane may be operated in any condition. Exceeding VNE risks structural failure or destructive flutter.
Some airspeed indicators also display additional reference marks. Multi-engine airplanes are required to show a red radial line at VMC (minimum control speed with the critical engine inoperative) and a blue radial line at VYSE (best rate of climb speed, single engine). These help the pilot manage an engine failure with reference to the ASI alone.
Several important V-speeds are deliberately not marked on the face of the ASI because they vary with weight or configuration:
- VA — Design Maneuvering Speed. The maximum speed at which the flight controls can be fully and abruptly deflected, or at which the airplane can encounter a vertical gust at limit load factor, without exceeding the airplane's structural limits. Below VA, the wing will stall before the limit load factor (typically 3.8 g in the Normal category) is exceeded — the stall acts as an aerodynamic safety valve. Above VA, abrupt control inputs or sharp gusts can produce loads that bend or break the structure. Because the load factor at which the airplane stalls depends on weight, VA decreases as gross weight decreases. For example, a Cessna 172 might publish VA of 99 KIAS at 2,400 lb but only 92 KIAS at 2,000 lb. Pilots must look up VA in the POH for the current weight, particularly before flight in turbulence.
- VLE / VLO — Landing Gear Speeds. VLE is the maximum speed with the gear extended; VLO is the maximum speed at which the gear may be operated (raised or lowered). These appear in the POH but not on the ASI.
Practical Use of the Markings
- During the approach and landing, flaps should not be extended above the top of the white arc (VFE).
- In cruise, normal operations should remain within the green arc.
- The yellow arc is reserved for smooth air only. If turbulence is encountered or anticipated, reduce speed to VA or slower.
- The red line (VNE) is never to be exceeded, even momentarily. In descents or with a tailwind component, monitor airspeed carefully.
A Caution Regarding Indicated vs. True Airspeed
The colored arcs are referenced to indicated airspeed (IAS). Because true airspeed (TAS) increases with altitude for a given IAS, an airplane operating in the green arc at 12,000 ft is actually moving faster through the air than the same indication at sea level. For most light airplanes this is not limiting, but some high-performance and pressurized aircraft impose a Mach or TAS limit at altitude in addition to the IAS-based red line. Always consult the POH for altitude-dependent limitations.
Example Markings for a Typical Trainer (Cessna 172S):
- White arc: 40 – 85 KIAS (VS0 to VFE)
- Green arc: 48 – 129 KIAS (VS1 to VNO)
- Yellow arc: 129 – 163 KIAS (VNO to VNE)
- Red line: 163 KIAS (VNE)
Memorizing the meaning of each arc and line — and knowing which critical speeds (VA, VLE, VLO) are not marked — is fundamental airmanship and a routine area of questioning on the private pilot oral exam.