Positive control.  According to Title 14 of the Code of Federal Regulations, control of all air traffic, within designated airspace, by air traffic control. 

Preflight.  All preparations, including gathering information, assembly, and inspection performed by the pilot before flight. 

Pressure gradient.  In weather, the difference between high and low pressure areas. Wind speed is directly proportional to the pressure gradient. 

Pressure relief valve.  A device in a propane tank designed to release excess pressure—which may be caused by overfilling, overheating, or excessive nitrogen pressurization—to prevent tank rupture. 

Preventive maintenance. Simple or minor preservation operations and the replacement of small standard parts not involving complex assembly operations. 

Prohibited area.  According to Title 14 of the Code of Federal Regulations, designated airspace within which the flight of aircraft is prohibited. 

Propane. A colorless and odorless gas. Ethyl mercaptan is added to propane to give it a detectable odor. Propane weighs 4.2 pounds per gallon at 60 °Fahrenheit. 

Practical Test Standard (PTS). Book containing areas of knowledge and skill that a person must demonstrate competency in for the issuance of pilot certificates or ratings. 

Pull test.  A strength test in which a section of envelope fabric is pulled to a definite pound measurement to determine if it meets the certification requirements for airworthiness. 

Pyrometer.  An instrument used to measure air temperature inside the top of a balloon envelope. 

Rapid descent.  A relatively fast loss of altitude. A subjective term, but usually meant to describe a descent of more than 500 fpm. 

Rating. According to Title 14 of the Code of Federal Regulations, a statement that, as part of a pilot certificate, sets forth special conditions, privileges, or limitations. 

Red line.  Refers to a line which activates the deflation panel of a balloon, or the maximum envelope temperature allowed, or the maximum on a gauge. 

Repair station. A facility where specified aircraft and their parts may be inspected, repaired, altered, modified, or maintained. FAA approval is issued to a facility upon qualifications specified by the local FSDO. 

Repairman certificate. An FAA certificate issued to a person who is employed by a repair station or air carrier as a specialist in some form of aircraft maintenance. A repairman certificate is also issued to an eligible person who is the primary builder of an experimental aircraft, to which the privileges of the certificate are applicable. 

Required equipment. Equipment that must be aboard an aircraft, as required either by the FAA or balloon manufacturer, to maintain airworthiness. 

Restricted area. Airspace of defined dimensions within which the flight of aircraft is restricted in accordance with certain conditions. 

Return to service.  A certificated mechanic or authorized inspector must approve an aircraft for return to service after it has been inspected, repaired, or altered. In addition, an aircraft that has been modified must be test flown by an appropriately certificated pilot before return to service. 

Ridge.  In weather, an elongated area of high pressure with no rotative motion. 

Rip panel.  A deflation panel, usually circular or triangular, at the top of a balloon envelope, which may be opened by pulling a line in the basket to allow hot air or gas to escape, and the envelope to deflate. 

Rotator vent.  See Turning Vent. 

Rotor. May be found embedded in mountain waves. Formation usually occurs where wind speeds change in a wave, or where friction slows the wind near the ground. See Figure 4-22 of this handbook for a graphical representation of rotors. 

Sectional chart.  Published on a routine basis, these charts are similar to automobile road maps, and provide useful information regarding airspace, reference points, tower frequencies, etc., to a balloon pilot. They are generally not very helpful for navigation, as the scale, 1:500,000, is too small to be of use to the balloon pilot. 

SIGMET.  Significant Meteorological Information. 

