Metering valve.  A valve on a balloon heater that can be set  to allow propane to pass through at a specific rate. O-Ring.  A doughnut-shaped packing, usually rubber, used  between two moving parts to act as a seal. Balloon heater  and tank valves usually have O-rings between the valve stem  and valve bonnet. Orographic.  A term pertaining to mountains or anything  caused by mountains, as in orographic wind (wind formed by  mountains) and orographic cloud (a cloud whose existence is  caused by disturbed flow of air over and around a mountain  barrier). Methanol.  A type of alcohol, usually fermented from wood,  required by most balloon manufacturers to be introduced into  propane tanks annually to adsorb, and thus eliminate, small  quantities of water from the fuel. Mildew.  A gray or white parasite fungus which, under warm,  moist conditions, can live on organic dirt found on balloon  envelopes. The fungus waste materials attack the coating  on the fabric. Mooring. Operation of an unmanned balloon secured to  the ground by lines or controlled by anything touching the  ground. See Title 14 of the Code of Federal Regulations,  part 101. Overtemp ( or over temperature).  The act of heating the air  inside a hot air balloon envelope beyond the manufacturer’s  maximum temperature. Oxygen starvation.  The condition inside a balloon envelope  where all available oxygen has been consumed by the heater  flame and additional burning is impossible since propane  must have oxygen to burn. In extreme cases, the blast flame  and pilot light flame will extinguish after a long burn or  series of burns and may not relight until the envelope has  “breathed” additional air. Mouth.  The bottom, open end of a hot air balloon envelope.  Also called the “throat.” MSL.  Mean sea level. Neutral buoyancy. A condition wherein a balloon is  weightless and is neither ascending nor descending. Nitrogen charging.  A technique of adding nitrogen gas to  propane tanks to increase fuel pressure. Used in place of  temperature to control propane pressure in hot air balloons  during cold weather. Parachute top. A deflation system wherein the deflation  port is sealed with a disc of balloon fabric shaped like a  parachute. Lines attached to the edge of the parachute disc  gather into a single line that may be pulled down by the pilot  in the basket. Pibal.  Pilot balloon; a small helium-filled balloon sent aloft  to help determine wind direction, velocity, and stability. Pilot in Command (PIC). The pilot responsible for the  operation and safety of an aircraft during flight. Piezo. (Pronounced pee-ate' zo). A piezoelectric spark  generator that is built into many modern balloon heaters to  ignite the pilot light. Pilot light. A small, continuously burning flame used to  ignite the main “blast” flame of a balloon heater. Pilotage.  Navigation by visual reference to landmarks. Pinhole.  Any small hole in a balloon envelope smaller than  the maximum dimensions allowed for airworthiness. Porosity.  A condition of the envelope fabric that allows hot  air to escape. Excessive porosity requires increased fuel use  and results in higher envelope temperatures. OODA Loop. An aeronautical decision-making model  particularly suited to ballooning. Originally devised by Col.  John Boyd for use by Air Force combat pilots, it has come  to be widely utilized in the business community. See the  discussion in chapter 1 of this handbook.  Nylon.  The registered name for a polymeric fabric. Most  balloon envelopes are made of nylon. Notice to Airmen (NOTAM). A notice containing  information concerning facilities, services, or procedures,  the timely knowledge of which is essential to personnel  concerned with flight operations. Nonporous.  The state of having no pores or openings which  will not allow gas to pass through. New hot air balloon fabric  is nearly nonporous. Nomogram. Technically, a calculating chart with scales  that contain values of three or more mathematical variables,  widely used in engineering. In ballooning, a balloon’s  performance chart is a nomogram.  G-6