Goniometer. As used in radio frequency (RF) antenna systems, a direction-sensing device consisting of two fixed loops of wire oriented 90° from each other, which separately sense received signal strength and send those signals to two rotors (also oriented 90°) in the sealed direction-indicating instrument. The rotors are attached to the direction-indicating needle of the instrument and rotated by a small motor until minimum magnetic field is sensed near the rotors. 

GPS.  See global positioning system. 

GPS Approach Overlay Program. An authorization for pilots to use GPS avionics under IFR for flying designated existing nonprecision instrument approach procedures, with the exception of LOC, LDA, and SDF procedures. 

Graveyard spiral.  The illusion of the cessation of a turn while still in a prolonged, coordinated, constant rate turn, which can lead a disoriented pilot to a loss of control of the aircraft. 

Great circle route.  The shortest distance across the surface of a sphere (the Earth) between two points on the surface. 

Ground proximity warning system (GPWS). A system designed to determine an aircraft’s clearance above the Earth and provides limited predictability about aircraft position relative to rising terrain. 

Groundspeed.  Speed over the ground, either closing speed to the station or waypoint, or speed over the ground in whatever direction the aircraft is going at the moment, depending upon the navigation system used. 

GS.  See glide slope. 

GWPS. See ground proximity warning system. 

HAA.  See height above airport. 

HAL.  See height above landing. 

HAT.  See height above touchdown elevation. 

Hazardous attitudes. Five aeronautical decision-making attitudes that may contribute to poor pilot judgment: antiauthority, impulsivity, invulnerability, machismo, and resignation. 

Hazardous Inflight Weather Advisory Service (HIWAS). Service providing recorded weather forecasts broadcast to airborne pilots over selected VORs. 

Head-up display (HUD).  A special type of flight viewing screen that allows the pilot to watch the flight instruments and other data while looking through the windshield of the aircraft for other traffic, the approach lights, or the runway. 

Height above airport (HAA).  The height of the MDA above the published airport elevation. 

Height above landing (HAL).  The height above a designated helicopter landing area used for helicopter instrument approach procedures. 

Height above touchdown elevation (HAT).  The DA/DH or MDA above the highest runway elevation in the touchdown zone (first 3,000 feet of the runway). 

HF.  High frequency. 

Hg. Abbreviation for mercury, from the Latin hydrargyrum. 

HIWAS. See Hazardous Inflight Weather Advisory Service. 

Holding. A predetermined maneuver that keeps aircraft within a specified airspace while awaiting further clearance from ATC. 

Holding pattern.  A racetrack pattern, involving two turns and two legs, used to keep an aircraft within a prescribed airspace with respect to a geographic fix. A standard pattern uses right turns; nonstandard patterns use left turns. 

Homing.  Flying the aircraft on any heading required to keep the needle pointing to the 0° relative bearing position. 

Horizontal situation indicator (HSI).  A flight navigation instrument that combines the heading indicator with a CDI, in order to provide the pilot with better situational awareness of location with respect to the courseline. 

HSI.  See horizontal situation indicator. 

HUD.  See head-up display. 

Human factors.  A multidisciplinary field encompassing the behavioral and social sciences, engineering, and physiology, to consider the variables that influence individual and crew performance for the purpose of optimizing human performance and reducing errors. 

