LNAV
Encyclopedia
Lateral navigation refers to navigating over a ground track with guidance from an electronic device which gives the pilot (or autopilot
) error indications in the lateral direction only and not in the vertical direction. In aviation lateral navigation is of two guidance types: linear guidance and angular guidance. Linear means that the left and right deviations of the aircraft are available as a distance of the aircraft from the desired ground track to its actual position on either side of the desired track. In angular guidance, the error indication is given in degrees of angle from the desired line relative to a ground-based navigation device. To provide an illustration, as the aircraft approaches the ground device with a constant angular error, its distance to the desired ground line decreases. In the context of aviation instrument approaches, an LNAV approach (one that uses lateral navigation) is implied to be a GPS-based approach and to have linear lateral guidance. A VOR
based approach will have angular lateral guidance.
approaches and RNAV approaches that incorporate vertical guidance. Aircraft executing an LNAV instrument approach must descend incrementally rather than follow a fixed glide slope. This is called a 'non-precision' approach to distinguish it from a precision approach in which there is electronic vertical (slope) guidance down to a decision altitude (DA). In the case of the non-precision approach, the aircraft can descend only to what is referred to as a minimum descent altitude or MDA
. An MDA segment is flown until the airport is in sight and the pilot can land. If the airport is not in sight by the time the pilot reaches a missed approach point
(MAP
) on the MDA, the aircraft must execute a missed approach
.
The GPS implementation of the non-precision LNAV approach can only be flown if satellite configuration at the time of the approach will accurately support a full scale course deviation indication of 0.3 nautical miles (about 1800 feet to the left and right or 3600 feet total) starting at the final approach fix and extending all the way to the missed approach point
. If this sensitivity does not occur, the pilot will be notified by the on-board receiver (via RAIM checking) and must not make the descent onto the final leg.
Autopilot
An autopilot is a mechanical, electrical, or hydraulic system used to guide a vehicle without assistance from a human being. An autopilot can refer specifically to aircraft, self-steering gear for boats, or auto guidance of space craft and missiles...
) error indications in the lateral direction only and not in the vertical direction. In aviation lateral navigation is of two guidance types: linear guidance and angular guidance. Linear means that the left and right deviations of the aircraft are available as a distance of the aircraft from the desired ground track to its actual position on either side of the desired track. In angular guidance, the error indication is given in degrees of angle from the desired line relative to a ground-based navigation device. To provide an illustration, as the aircraft approaches the ground device with a constant angular error, its distance to the desired ground line decreases. In the context of aviation instrument approaches, an LNAV approach (one that uses lateral navigation) is implied to be a GPS-based approach and to have linear lateral guidance. A VOR
VHF omnidirectional range
VOR, short for VHF omnidirectional radio range, is a type of radio navigation system for aircraft. A VOR ground station broadcasts a VHF radio composite signal including the station's identifier, voice , and navigation signal. The identifier is typically a two- or three-letter string in Morse code...
based approach will have angular lateral guidance.
Using LNAV on Instrument Approaches: The Non-precision approach
The approach minimums for LNAV approaches are higher than that of ILSInstrument Landing System
An instrument landing system is a ground-based instrument approach system that provides precision guidance to an aircraft approaching and landing on a runway, using a combination of radio signals and, in many cases, high-intensity lighting arrays to enable a safe landing during instrument...
approaches and RNAV approaches that incorporate vertical guidance. Aircraft executing an LNAV instrument approach must descend incrementally rather than follow a fixed glide slope. This is called a 'non-precision' approach to distinguish it from a precision approach in which there is electronic vertical (slope) guidance down to a decision altitude (DA). In the case of the non-precision approach, the aircraft can descend only to what is referred to as a minimum descent altitude or MDA
MDA
-Companies, organizations and government bodies:* Maritime Domain Awareness, part of a U.S. Government interagency and international maritime security effort* MDA , formerly the Museum Documentation Association...
. An MDA segment is flown until the airport is in sight and the pilot can land. If the airport is not in sight by the time the pilot reaches a missed approach point
Missed approach point
Missed approach point 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 precision and non-precision approaches when the missed approach segment of a flight begins...
(MAP
Map
A map is a visual representation of an area—a symbolic depiction highlighting relationships between elements of that space such as objects, regions, and themes....
) on the MDA, the aircraft must execute a missed approach
Missed approach
Missed approach is an instrument flight rules procedure which is a standard component segment of an instrument approach. Generally, if the pilot flying or the pilot in command determines by the time the aircraft is at the decision height or missed approach point , that the runway or its...
.
The GPS implementation of the non-precision LNAV approach can only be flown if satellite configuration at the time of the approach will accurately support a full scale course deviation indication of 0.3 nautical miles (about 1800 feet to the left and right or 3600 feet total) starting at the final approach fix and extending all the way to the missed approach point
Missed approach point
Missed approach point 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 precision and non-precision approaches when the missed approach segment of a flight begins...
. If this sensitivity does not occur, the pilot will be notified by the on-board receiver (via RAIM checking) and must not make the descent onto the final leg.
See also
- RNAV
- VNAVVNAVIn aviation, Vertical NAVigation is an autopilot function which directs the vertical movement of an aircraft while cruising and/or on approach to landing....
- LPVLocalizer Performance with Vertical guidanceLocalizer performance with vertical guidance are the highest precision GPS aviation instrument approach procedures currently available without specialized aircrew training requirements, such as required navigation performance...
- NavigationNavigationNavigation is the process of monitoring and controlling the movement of a craft or vehicle from one place to another. It is also the term of art used for the specialized knowledge used by navigators to perform navigation tasks...
External links
- FAA: LNAV (Lateral Navigation) (archived version)