| | Title | Definition |
|
| Undetected | Failure is not detected by the function or system or no timely mitigating action is possible, and the failure is not annunciated [AMC to CS25.1309]. |
|
| Unnanunciated | No warning or indication is given to to the flight crew, or warning/indication gives insufficient time fo the flight crew to react to the failure [AMC to CS25.1309]. |
|
| V (code) | Schedule of indicated airspeeds stipulated for different phases of flight (see following). |
|
| V1 | Decision speed during takeoff. Aircraft is committed to fly when this speed is passed. |
|
| V2 | Takeoff safety speed. Minimum control speed plus safety margin to allow for engine failure and other contingencies. |
|
| VASIS | Visual approach slope indicator. System of lights located on ground on either side of runway to indicate correct angle of descent to approaching aircraft. |
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| VFR (Visual Flight Rules) | Stipulated flight procedure for navigating aircraft visually, clear of cloud, in Visual Meteorological Conditions. |
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| VHF (Very High (radio) Frequency) | In general use for inflight radio communications on air routes. Its frequency band from 30 to 300 MHZ is largely free from interference and static, but range is limited to "line of sight". |
|
| VMC (Visual Meteorological Conditions) | Weather providing specified range of visibility, making it possible for pilots to use visual means to avoid obstructing terrain and other aircraft. |
|
| Vne | Never exceed speed. |
|
| VOR | Very High Frequency Omnidirectional Radio Range. |
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| Vr | Rotation speed. Speed at which aircraft is "rotated" into liftoff attitude by raising the nosewheel off the runway. |
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| Vref | Flap reference speed. Landing speed for stipulated number of degrees of flap extension. |
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| VSI (Vertical Speed Indicator) | Instrument displaying rate of climb or descent in feet per minute. |
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| Waiver | A written authorisation by the engineering authority to accept an item (or limited quantity of), which during manufacture, or after submission for inspection or acceptance, is found to depart from specified requirements, but nevertheless is considered suitable for use "as is" or after repair by an approved method. Also known as a Concession. |