Area Navigation (RNAV) - A method of navigation, which permits the operation of an aircraft on any desired flight path; it allows its position to be continuously determined wherever it is rather than only along tracks between individual ground navigation aids.  RNAV includes Performance Based Navigation (PBN) as well as other RNAV operations that are not within the definition of PBN.

Bypass Ratio - The bypass ratio of a turbofan engine refers to the ratio of air that bypasses the core as compared to the air that flows into the engine core and is used for combustion.  The ratio is expressed in the following manner 10:1, with the first number representing the bypass airflow and the second number representing the core airflow.  In the example above a 10:1 bypass ratio means that for every 10 kg of air that bypasses the core, 1 kg. enters the core.

Calm Winds - The FAA defines calm wind conditions as a situation in which the wind velocity is less than 3 knots.  During calm winds, the runway selection is up to the FAA but usually reverts to the established preferred runway direction which in the case of San Jose is north flow with arrivals and departures using Runways 30L and 30R.

Estimate of Position Uncertainty (EPU) - A measure based on a defined scale in nautical miles (NM), which conveys the current position estimation performance, also known as Actual Navigation Performance (ANP) and Estimate of Position Error (EPE) in certain aircraft.  The EPU is not an estimate of the actual error, but a defined statistical indication.

Federal Aviation Administration (FAA) - The agency of the Department of Transportation responsible for the regulation and oversight of civil aviation within the U.S., as well as operation and development of the National Airspace System.  Its primary purpose is to ensure the safety of the flight.  The FAA controls and oversees all aspects of civil aviation including certification of aircraft, pilots, and airlines, as well as managing all aircraft operating within the airspace of the United States.

Flight Management System (FMS) - 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 modern civilian aircraft no longer carry flight engineers or navigators. A primary function is in-flight management of the flight plan. Using various sensors (such as GPS and INS often backed up by radio navigation) to determine the aircraft's position, the FMS can guide the aircraft along the flight plan. From the flight deck, the FMS is normally controlled through a Control Display United (CDU) which incorporates a small screen and keyboard or touchscreen.  The modern FMS was introduced on the Boeing 767 in 1981.  All FMSs contain a global navigation database that contains the elements (waypoints, navaids, arrival, departure, and approach procedures and airport information) from which the flight plan is constructed.  The navigation database is normally updated every 28 days.

Glide Slope (G/S) - A system of vertical guidance built into the instrument landing system (ILS) which indicates the vertical deviation of the aircraft from its optimum path of descent to the landing runway.  The glide slope station uses an antenna array positioned to one side of the runway touchdown zone.  The G/S signal is transmitted on a carrier signal using a technique similar to that for the localizer.  The center of the glide slope is arranged to define a glide path of approximately 3 degrees above horizontal (ground level).  The vertical beam is 1.4 degrees in-depth (0.7 degrees below the glide-path center and 0.7 degrees above).

Global Navigation Satellite System (GNSS) - A generic term for a worldwide position, velocity, and time determination system, which includes one or more satellite constellations, aircraft receivers, and system integrity monitoring.  GNSS includes GPS; Satellite-based Augmentation Systems (SBAS) such as the Wide Area Augmentation System (WAAS); Ground-Based Augmentation Systems (GBAS) such as the Local Area Augmentation System (LAAS); Global Orbiting Navigation Satellite System (GLONASS); Galileo; and any other satellite navigation system approved for civil use.  GNSS can be augmented as necessary to support the RNP for the actual phase of operation.

Global Positioning System (GPS) - GPS is a U.S. satellite-based radio navigation system that provides a positioning service anywhere in the world.  The definition of the service provided by GPS for civil use is in the GPS Standard Positioning System (SPS) Signal Specification.  GPS is the U.S. core Global Navigation Satellite System (GNSS) satellite constellation providing space-based positioning, velocity, and time.  GPS is composed of space, control, and user elements.

Inertial Navigation System (INS) - A navigation device that uses a computer, motion sensors (accelerometers) and rotation sensors (gyroscopes) to continually calculate by dead reckoning the position, the orientation, and the velocity (direction and speed of movement) of a moving object without the need for external references.  Often the inertial sensors are supplemented by a barometric altimeter and occasionally by magnetic sensors (magnetometers) and/or speed measuring devices.  The Boeing 747-100 which entered airline service in January of 1970 with Pan American World Airways was the first new commercial aircraft to be fitted with INS.  The airplane contained three Delco Carousel INS computers that were synched for redundancy.

Instrument Landing System (ILS) - A system that works by sending radio waves downrange from the runway end, with aircraft that intercept it using the radio waves to guide them onto the runway.  The system provides aircraft with both horizontal and vertical guidance during the approach and, at certain fixed points, indicates the distance to the reference point on the runway.

Localizer (LOC) - A system of horizontal guidance built into the instrument landing system (ILS) which is used to guide aircraft along the axis of the runway and keep them laterally lined up with the runway centerline.

Localizer Performance with Vertical Guidance (LPV) -An approach with vertical guidance that uses GPS instead of a ground-based instrument landing system (ILS) to deliver vertical and lateral guidance signals for landing aircraft.  LPV approaches are much more cost-effective because they eliminate the need for expensive ILS equipment that only serves a single runway.  LPV is a cost-effective way for the FAA to add precision instrument approaches at lower volume general aviation-focused airports.

Performance-Based Navigation (PBN) - An advanced, satellite-enabled form of air navigation that creates precise 3-D flight paths.  PBN is an umbrella term that includes both RNAV and RNP and requires various avionics capabilities depending on the level of navigation precision involved.

Precision Approach - An instrument approach and landing using precision lateral and vertical guidance with landing minima as determined by the category of operation.  By contrast, a non-precision standard instrument approach procedure only provides horizontal guidance.  In a precision approach, landing minima are spelled out in two ways, decision height (DH) and decision altitude (DA).  They are the specified lowest height or altitude in the approach descent at which, if the required visual reference to continue the approach (such as the runway markings or lights are not visible to the pilot, the pilot must initiate a missed approach.  Decision height is measured in feet above ground level (AGL) while a decision altitude is measured in feet above mean sea level (MSL).  The specified values for DH and/or DA at a given airport are established with the intention to allow a pilot sufficient time to safely re-configure an aircraft to climb and execute the missed approach procedures while avoiding terrain and obstacles.

Radius to Fix (RF) Leg - An RF leg on an RNP approach is defined as a constant radius circular path, around a defined turn center, that starts and terminates at a fix.

Required Navigation Performance (RNP) - A family of navigation specifications under Performance-Based Navigation (PBN) which permits the operation of aircraft along a precise flight path with a high level of accuracy and the ability to determine aircraft position with both accuracy and integrity.  RNP is a statement of the 95 percent navigation accuracy performance that meets a specified value for a particular phase of flight or flight segment and incorporates associated onboard performance-monitoring and alerting features to notify the pilot when the RNP for a particular phase or segment of a flight is not being met.  RNP offers safety benefits by means of its precision and accuracy and it reduces the cost of operational inefficiencies such as multiple step-down non-precision and circling approaches.

Required Navigation Performance (RNP) Approach - A precision approach built to a certain RNP performance value that can be used by aircraft equipped with GPS or GPS enhanced by WAAS.  RNP approaches permit aircraft with the required navigation performance to operate on any desired course within the coverage of the navigation signals in use.  Tens of thousands of general aviation aircraft equipped with WAAS use more than 3,800 localizer performance with vertical guidance (LPV) approach procedures at more than 1,880 airports.

Required Navigation Performance Approach with Authorization Required (RNP AR) - A more precise level of RNP which enables qualified operators with equipped aircraft to fly with great precision on the same flight path every time near high terrain or in congested airspace.  To fly these procedures, aircrews must be trained and authorized by the FAA to fly RNP, and aircraft must be certified.  Some RNP AR approaches enable aircraft to fly a curved path to a runway even when other aircraft are approaching to land simultaneously on parallel runways.

Required Navigation Performance (RNP) Value - The RNP value designates the lateral performance requirement in nautical miles (NM) increments associated with a procedure.  Examples of RNP values for an approach are 0.15, 0.3, or 1.0.  An RNP value of 0.3 indicates that the aircraft navigation system must be able to maintain a track within .03 nautical miles (1,823 feet) left or right of the track centerline at least 95% of the time.

Vectoring - At certain times even when following an instrument flight plan, a pilot may be instructed by ATC to fly a certain vector.  This instruction requires the aircraft to capture and maintain a certain compass heading.  Aircraft can be assigned to fly a vector for numerous reasons but the primary ones are conflicting traffic, to maintain minimum aircraft spacing and weather.  ATC will usually indicate the reason why the aircraft was instructed to fly a certain vector and sometimes will communicate the expected duration.

Wide Area Augmentation System (WAAS) - An air navigation aid developed by the FAA to augment the Global Positioning System (GPS), with the goal of improving its accuracy, integrity, and availability.  Essentially, WAAS is intended to enable aircraft to rely on GPS for all phases of flight, including precision approaches to any airport within its coverage area.  It may be further enhanced with the Local Area Augmentation System (LAAS) also know by the preferred ICAO term Ground-Based Augmentation System (GBAS) in critical areas.  WAAS uses a network of ground-based reference stations, in North America and Hawaii, to measure small variations in the GPS satellites' signals in the western hemisphere.  Measurements from the reference stations are routed to master stations, which queue the received Deviation Correction (DC) and send correction messages to geostationary WAAS satellites (every 5 seconds or less).  Those satellites broadcast the correction message back to Earth, where WAAS-enabled GPS receivers use the corrections while computing their positions to improve accuracy.

Wind Velocity - Is a measure of both the wind speed and the direction the wind is blowing out of.  For instance, if air traffic control reports winds are 270 at 10 knots this means that the wind is blowing out of the west at 10 knots.  In aviation, both components are critical as the velocity determines which runway will be used to ensure that airplanes take off and land into the wind.  If winds are not steady ATC will also report the maximum gust value in knots.  For instance, if the controller reports wind 270 at 10 gusting to 18 knots.  This lets the pilot know the winds are variable and to expect fluctuations in the wind-speed by as much as 8 knots above the steady-state wind speed.