high unmetered fuel pressure. The pressure in a Teledyne-Continental fuel injector pump that is adjusted by the variable orifice.
high vacuum. An absolute pressure of between 1 x 10-3 and 1 x 10-6 millimeters of mercury.
hinge. A form of fastener that allows one connected piece to rotate with respect to the other. Hinges are used to connect a door to the edge of an opening in a compartment or bulkhead. The hinges allow the door to swing, or rotate, open or closed. Ailerons are attached to a wing trailing edge with hinges so they can rotate with respect to the wing surface.
Hipernik. The registered trade name for a magnetic alloy made of 50% iron and 50% nickel.
Hi-Shear rivet. A patented, high-strength, pin-type fastener used in aircraft construction. Hi-Shear rivets are often used in place of bolts in strong, lightweight structure.
The pin of a Hi-Shear rivet has a thin, flat head on one end and a groove around its shank at the other end. The pin is pressed through a tight-fitting hole in the pieces of metal to be joined, and a soft steel or aluminum alloy collar is slipped over its grooved end. A swaging tool forces the collar into the groove and pulls the head of the rivet tight against the metal through which it is installed.
HIWAS (hazardous in-flight weather advisory service) (air traffic control). Continuously recorded hazardous in-flight weather forecasts broadcast to airborne pilots over selected VOR outlets defined as HIWAS broadcast areas.
Hobbs meter. The registered trade name of an operating-time indicator used with reciprocating engines to show the number of hours the engine has operated. The Hobbs meter consists of a clock that is actuated by an engine oil pressure switch. When the engine is producing oil pressure, the clock runs, but when oil pressure is lost at engine shutdown, the clock stops.
hold, or holding, procedure (air traffic control). A predetermined maneuver which keeps aircraft within
a specified airspace while awaiting further clearance from air traffic control.
“Hold for release” (air traffic control). A phrase used by ATC to delay an aircraft for traffic management reasons; i.e., weather, traffic volume, etc. Hold for release instructions (including departure delay information) are used to inform a pilot or a controller (either directly or through an authorized relay) that an IFR departure clearance is not valid until a release time or additional instructions have been received.
holding coil (electrical relay). An auxiliary coil in an electrical relay. Current flowing through the holding coil keeps the relay energized after the control current that caused the relay to close has stopped flowing through the main coil.
holding fix (navigation). A specified fix identifiable to a pilot by navaids or visual reference to the ground, used as a reference point in establishing and maintaining the position of an aircraft while holding.
holding point (ICAO). A specified location, identified by visual or other means, in the vicinity of which the position of an aircraft in flight is maintained in accordance with air traffic control clearances.
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