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 . ight viewing screen that allows the pilot to watch the . ight instruments and other data while looking through the windshield of the aircraft for other traf.c, 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 (.rst 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 speci.ed 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 .x. 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 . ight 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.