aviation Aviation includes the activities surrounding mechanical flight and the aircraft industry. ''Aircraft'' include fixed-wing and rotary-wing types, morphable wings, wing-less lifting bodies, as well as lighter-than-air aircraft such as h ...

, vertical navigation (VNAV, usually pronounced ''vee-nav'') is

glidepath In aviation, instrument landing system glide path, commonly referred to as a glide path (G/P) or glide slope (G/S), is "a system of vertical guidance embodied in the instrument landing system which indicates the vertical deviation of the ai ...

information provided during an

instrument approach In aviation, an instrument approach or instrument approach procedure (IAP) is a series of predetermined maneuvers for the orderly transfer of an aircraft operating under instrument flight rules from the beginning of the initial approach to a lan ...

, independently of ground-based

navigation aid A navigational aid (NAVAID), also known as aid to navigation (ATON), is any sort of signal, markers or guidance equipment which aids the traveler in navigation, usually nautical or aviation travel. Common types of such aids include lighthouses, ...

s in the context of an approach and a form of vertical guidance in the context of climb/descent. An onboard navigation system displays a constant rate descent path to minimums. The VNAV path is computed using aircraft performance, approach constraints, weather data, and aircraft weight. The approach path is computed from the top of descent point to the end of descent waypoint, which is typically the runway or

missed approach point Missed approach point (MAP or MAPt) is the point prescribed in each instrument approach at which a missed approach procedure shall be executed if the required visual reference does not exist. It defines the point for both precision and non-precis ...

Overview

flight management system A flight management system (FMS) is a fundamental component of a modern airliner's avionics. An FMS is a specialized computer system that automates a wide variety of in-flight tasks, reducing the workload on the flight crew to the point that mod ...

(FMS) uses either a performance-based or a geometric VNAV system. A performance-based VNAV system computes a descent path from the top of the descent to the first constrained

waypoint A waypoint is a point or place on a route or line of travel, a stopping point, an intermediate point, or point at which course is changed, the first use of the term tracing to 1880. In modern terms, it most often refers to coordinates which spe ...

using idle or near idle power. This is referred to as an idle descent path at ECON (most economic, or most fuel-efficient) speed. This is very fuel efficient and therefore saves money and is great for budget-constrained airlines. Therefore, most large airliners feature a performance-based VNAV system, often connected to an

autothrottle An autothrottle (automatic throttle; also known as autothrust, A/T, or A/THR) is a system that allows a pilot to control the power setting of an aircraft's engines by specifying a desired flight characteristic, rather than manually controlling t ...

to automatically select idle thrust or increase thrust to maintain a set speed when an idle descent is not possible. This form of VNAV connected to an autothrottle is referred to as coupled VNAV. A geometric VNAV system, rather than calculating a path based on efficiency, calculates a path between waypoints either by selecting points to start descent to the next waypoint based on a predefined angle or descent rate - often 3 degrees or 1000 feet per minute - or by calculating the required angle between altitude or speed-constrained waypoinnts to keep a continuous descent. Geometric VNAV systems are most often found on general and business aircraft equipped with a flight management system and therefore, as most of these aircraft do not have an autothrottle, are not coupled. A special example of a VNAV system is that found on the Bombardier CRJ family, which calculates a geometric VNAV path but does not have an autopilot mode for following it (except CRJ1000 and select CRJ700/CRJ900 aircraft), nor a vertical path indicator on the PFD or ND. Instead, it uses an "advisory VNAV" system where the VNAV path is flown in V/S mode by selecting an amount of vertical speed that the aircraft indicates on the vertical speed indicator. Speed constraints must be manually taken into account as the aircraft does not have an autothrottle.

RNAV Area navigation (RNAV, usually pronounced as ) is a method of instrument flight rules (IFR) navigation that allows aircraft to fly along a desired flight path, rather than being restricted to routes defined by ground-based navigation beacons. ...

approaches combine VNAV navigation equipment with

LNAV In aviation, lateral navigation (LNAV, usually pronounced ''el-nav'') is azimuth navigation, without vertical navigation (VNAV). Area navigation (RNAV) approach plates include LNAV as a non-precision instrument approach (NPA). When combined with ...

navigation equipment to provide both lateral and vertical approach guidance. Vertical guidance comes from

WAAS The Wide Area Augmentation System (WAAS) is an air navigation aid developed by the Federal Aviation Administration to augment the Global Positioning System (GPS), with the goal of improving its accuracy, integrity, and availability. Essenti ...

GPS or a barometric VNAV (Baro-VNAV) system. The FMS provides flight control steering and thrust guidance along the VNAV path. VNAV information on an

approach plate Approach may refer to: Aviation *Visual approach *Instrument approach *Final approach (aeronautics), Final approach Music * Approach (album), ''Approach'' (album), by Von Hertzen Brothers * ''The Approach'', an album by I:Scintilla Other uses *A ...

includes the Final Approach Fix (FAF), the FAF crossing altitude, a Vertical Descent Angle (VDA), the landing runway threshold as a second fix, the Threshold Crossing Height (TCH), and perhaps a Visual Descent Point (VDP). A pilot uses the VDA, and

ground speed Ground speed is the horizontal component of the velocity of an aircraft relative to the Earth’s surface, also referred to as "speed over the ground". It is vital for accurate navigation that the pilot has an estimate of the ground speed that wil ...

, to compute a

rate of descent In aeronautics, the rate of climb (RoC) is an aircraft's vertical speed, that is the positive or negative rate of altitude change with respect to time. In most ICAO member countries, even in otherwise metric countries, this is usually expressed ...

(from a table found in the U.S. Terminal Procedures Publication), which is flown using the Vertical velocity indicator. Aircraft approved for LNAV/VNAV minimums include the

Boeing 737NG The Boeing 737 Next Generation, commonly abbreviated as 737NG, or 737 Next Gen, is a twin-engine narrow-body aircraft produced by Boeing Commercial Airplanes. Launched in 1993 as the third-generation derivative of the Boeing 737, it has been ...

, 767, 777, the

Airbus A300 The Airbus A300 is Airbus' first production aircraft and the world's first Twinjet, twin-engine, double-aisle Wide-body aircraft, (wide-body) airliner. It was developed by ''Airbus Industrie GIE'', now merged into Airbus SE, and manufactured f ...

and some

ATR ATR may refer to: Medicine * Acute transfusion reaction * Ataxia telangiectasia and Rad3 related, a protein involved in DNA damage repair Science and mathematics * Advanced Test Reactor, nuclear research reactor at the Idaho National Laboratory, ...

Autopilot

VNAV is also the name of

autopilot An autopilot is a system used to control the path of a vehicle without requiring constant manual control by a human operator. Autopilots do not replace human operators. Instead, the autopilot assists the operator's control of the vehicle, allow ...

vertical modes in several aircraft. Some aircraft have two VNAV modes, VNAV Speed and VNAV Path (or Open Climb/Descent and Managed Climb/Descent in Airbus aircraft, respectively). In VNAV Speed mode, the autopilot adjusts the aircraft's pitch to achieve and maintain a selected speed (similar to flight level change/speed mode). In coupled VNAV systems, the autothrottle will automatically select climb power for climb and flight idle for descent. In VNAV Path mode, the aircraft adjusts the pitch to achieve and maintain the desired vertical profile. In coupled VNAV systems, the autothrottle will select flight idle for descent but can add thrust if the aircraft is dropping below the selected speed. In many aircraft equipped with spoilers, the FMS may also display a "drag required" or "more drag" message to indicate to the pilots that the aircraft is unable to stay on the VNAV path and maintain the selected speed, telling the pilots they need to use the spoilers to add drag and decelerate the aircraft. In modern aircraft, the aircraft will often stay in VNAV mode for almost the entire flight. The aircraft will typically climb in VNAV Speed and descend in VNAV Path. In some Boeing aircraft, there is a single VNAV selector button, and the autopilot will switch between VNAV Speed and VNAV Path automatically. This is known as common VNAV.

References

External links

*{{cite web, url=http://www.ae.gatech.edu/people/jpclarke/cda/workshop2/presentations/Miller.pdf, title=Flight Management Computer System Vertical Navigation aka VNAV, author= Sam Miller, date= April 2006, access-date=2015-10-18, archive-url=https://web.archive.org/web/20110718205016/http://www.ae.gatech.edu/people/jpclarke/cda/workshop2/presentations/Miller.pdf, archive-date=2011-07-18 Air navigation

Overview

Autopilot

See also

References

External links