DYNAMIC PRESSURE (q)—The pressure a mov- ing fluid would have if it were stopped. Reference  14 CFR 61.51(h). CTAF—See COMMON TRAFFIC ADVISORY  FREQUENCY. DATUM—An imaginary vertical plane or line from  which all measurements of moment arm are taken.  The datum is established by the manufacturer. EIS—See ENGINE INFORMATION SYSTEM. EMERGENCY FREQUENCY—Frequency that  is used by aircraft in distress to gain ATC assis- tance. 121.5 MHz is an international emergency  frequency guarded by Flight Service Stations and  some military and civil aircraft. Reference AIM  paragraph 6-3-1. E-LSA (EXPERIMENTAL LIGHT-SPORT AIR- CRAFT)—An aircraft issued an experimental  certificate under Title 14 of the Code of Federal  Regulations (14 CFR) part 21. DECIDE MODEL—Model developed to help pilots  remember the six-step decision-making process:  Detect, Estimate, Choose, Identify, Do, Evaluate. DECK ANGLE—The angle of the cart’s lower  frame (from the front wheel to the rear wheels), to  the landing surface. DENSITY ALTITUDE—Pressure altitude corrected  for variations from standard temperature. When  conditions are standard, pressure altitude and  density altitude are the same. If the temperature is  above standard, the density altitude is higher than  pressure altitude. If the temperature is below stan- dard, the density altitude is lower than pressure  altitude. This is an important altitude because it is  directly related to the PPC’s performance. ERROR CHAIN—A series of mistakes that may  lead to an accident or incident. Two basic prin- ciples generally associated with the creation of an  error chain are: (1) one bad decision often leads to  another; and (2) as a string of bad decisions grows,  it reduces the number of subsequent alternatives  for continued safe flight. Aeronautical decision  making is intended to break the error chain before  it can cause an accident or incident. FAA—See FEDERAL AVIATION ADMINISTRA- TION. DEPARTURE LEG—The leg of the rectangular  traffic pattern that is a straight course aligned with,  and leading from, the takeoff runway. DESIGNATED PILOT EXAMINER (DPE)—An  individual designated by the FAA to administer  practical tests to pilot applicants. FAA INSPECTOR—FAA personnel who can  administer practical and proficiency tests and can  issue pilot certificates. DIRECTIONAL STABILITY—Stability about the  vertical axis of an aircraft, whereby an aircraft  tends to return, on its own, to flight aligned with  the relative wind when disturbed from that equi- librium state. The pendulum design is the primary  contributor to directional stability, causing a PPC  in flight to align with the relative wind. FAA KNOWLEDGE EXAM—Written exam ad- ministered by the FAA as a prerequisite for pilot  certification. Passing the knowledge and practical  exams are required for pilot applicants to be issued  FAA certificates or ratings. FAR—See FEDERAL AVIATION REGULATIONS. FDC NOTICE TO AIRMAN (NOTAM)—Notice to  Airman that is regulatory in nature. DOWNWIND LEG—Leg of the traffic pattern flown  parallel to the landing runway, but in a direction  opposite to the intended landing direction. FEDERAL AVIATION ADMINISTRATION  (FAA)—The federal agency responsible to pro- mote aviation safety through regulation and educa- tion. DRAG—An aerodynamic force on a body acting  parallel and opposite to the relative wind. The  resistance of the atmosphere to the relative motion  of an aircraft. Drag opposes thrust and limits the  speed of the aircraft. DPE—See DESIGNATED PILOT EXAMINER. DRAG COEFFICIENT (Cd)—A dimensionless  number used to define the amount of total drag  produced by an aircraft. FEDERAL AVIATION REGULATIONS (FARs)— The division within the Department of Transporta- tion of the United States government that has the  responsibility of promoting safety in the air, by  both regulation and education. FIELD ELEVATION—The highest point of an  airport’s usable runways measured in feet from  mean sea level. DRIFT CORRECTION—Correction that is applied  to counter the affects of wind on an aircraft’s flight  and ground track. DUAL FLIGHT—Flight time that is received and  logged as training time. Dual flight time must be  endorsed by a Certificated Flight Instructor. FINAL—Leg of the traffic pattern that is a descend- ing flightpath starting from the completion of the  base-to-final turn and extending to the point of  touchdown. G-4