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or moon at its center. Coloration of a halo changes from red inside to blue outside, which is opposite to the
coloration of a corona. See corona.
A halo is fixed in size and has an angular diameter of 22° (common) or 46° (rare). Halos are
characteristic of clouds composed of ice crystals and are useful in telling the difference between cirriform
(ice) clouds and lower clouds, which are composed of liquid water.
halo (cathode-ray oscilloscope). A bright ring around the spot produced by a beam of electrons striking
the fluorescent coating in a cathode-ray tube. The halo is caused by light reflecting from the back side of
the phosphorescent screen.
halogen. Any of the five chemical elements in Group VII of the periodic table of chemical elements.
Fluorine, chlorine, bromine, iodine, and astatine are the halogens.
halogenated hydrocarbon. A hydrocarbon compound in which one or more of the hydrogen atoms have
been replaced with an atom of one of the halogen elements, such as fluorine, chlorine, or bromine.
Halon 1211. A halogenated hydrocarbon fire-extinguishing agent that is used in many of the HRD
(high-rate discharge) fire-extinguishing systems for powerplant protection. The technical name for Halon
1211 is bromochlorodifluoromethane.
Printed from Summit Aviation's Computerized Aviation Reference Library, 2/7/2007
Page 289
Halon 1301. A halogenated hydrocarbon fire-extinguishing agent that is one of the best for extinguishing
cabin and powerplant fires. It is highly effective and is the least toxic of the extinguishing agents available.
The technical name for Halon 1301 is bromotrifluoromethane.
hammer. A hand-held tool used for pounding. A hammer has a heavy, hard steel head mounted across the
end of its handle. There are a number of types of hammer heads. Claw hammers have claws on one side of
the head for removing nails. Ball peen hammers have a ball on one side of the head for forming heads on
rivets. Cross peen and straight peen hammers have a wedge on one side of their head for shaping sheet
metal.
hammer welding. A form of forge welding in which the edges of two pieces of metal are heated red-hot
and then pounded together with a hammer.
handbook. A manual that describes an operation or a system of operations. A handbook normally contains
specific rather than general information, and is usually prepared in a format that allows it to be kept at the
point it is to be used. For example, a handbook on the operation of a piece of machinery should be kept
with the machinery, rather than in a library or office.
hand-cranked inertia starter (reciprocating engine starter). A starter for a large aircraft reciprocating
engine that uses a hand crank to store energy in a spinning flywheel. The crank drives the flywheel through
a high-ratio gear system to spin it at a high speed and store a great deal of kinetic energy. When the
flywheel is spinning, the hand crank is removed and the flywheel is coupled, through a slip clutch, to the
engine crankshaft. There is enough energy in the spinning flywheel to turn the engine fast enough for it to
start.
Many electric-inertia starters have provisions for spinning the flywheel with a hand crank when
there is no electrical power available for starting.
hand drill. A hand-operated tool used to turn a twist drill. The twist drill is mounted in a drill chuck which
is turned with a set of bevel gears driven by a hand crank.
hand forming (sheet metal forming). A method of forming sheet metal parts by using a soft-faced
hammer to shrink or stretch the metal. The metal may be formed over forming blocks or dies, or it may be
shaped by hammering it into a sandbag.
hand-off (air traffic control). An action taken to transfer the radar identification of an aircraft from one
controller to another if the aircraft will enter the receiving controller’s airspace and radio communications
with the aircraft will be transferred.
hand-operated bending tool (tubing bending tool). A tool used to bend thin-wall tubing without it
collapsing.
Printed from Summit Aviation's Computerized Aviation Reference Library, 2/7/2007
Page 290
The tubing is bent around a deep-grooved radius block, using a sliding bar with a matching
groove.
hand pump (hydraulic system component). A device used in a hydraulic system to move fluid.
Most hand pumps are of the piston type, in which movement of the pump lever, or handle, moves
a piston inside the pump.
Some hand pumps are single-acting, which means that they move fluid only during one stroke of
the handle. No fluid is moved during the return stroke. Other hand pumps are double-acting, which means
that they move fluid during both strokes of the handle.
Most aircraft hydraulic systems that use an engine-driven or electric motor-driven hydraulic pump
　
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