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Lecture 12

Lecture 12. Interpreting Weather Data Chapters 7, Jeppesen Sanderson Weight & Balance Chapters 8, Jeppesen Sanderson. Weather Data Reports. Printed weather reports Aviation Routine Weather Report Printed weather forecasts Terminal Aerodrome Forecast (TAF)

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Lecture 12

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  1. Lecture 12 Interpreting Weather Data Chapters 7, Jeppesen Sanderson Weight & Balance Chapters 8, Jeppesen Sanderson

  2. Weather Data Reports • Printed weather reports • Aviation Routine Weather Report • Printed weather forecasts • Terminal Aerodrome Forecast (TAF) • Severe weather report and forecasts • AIRMET • SIGMET

  3. Printed Weather Reports • Before flying a pilot has to know the current weather condition and the weather forecasts of the plane’s starting location, its route, and its destination. • Even some ground workers who are responsible for preparing for the flight have to know these information. • Thus printed weather reports are important information. • Printed weather report includes aviation routine weather report (METAR), radar weather reports, and weather forecasts.

  4. Aviation Routine Weather Report (1) • An aviation routine weather report (METAR) is an observation of surface weather reported in a standard format with codes. • The codes are adopted worldwide but each country is allowed to make modifications or exceptions, e.g., in order to accommodate local procedures or units of measurements used. • The system used here (following Jeppesen) is the U.S. system. Slight modifications used in Hong Kong will be discussed in the lecture.

  5. Aviation Routine Weather Report (2) • The codes in an aviation routine weather report (METAR) includes the following information: • Type of Report • Station Identifier • Time of Report • Wind Information • Visibility • Weather • Sky (Cloud) Condition • Temperature and Dewpoint • Altimeter • Remarks

  6. Aviation Routine Weather Report (3) • Example of METAR : METAR KTPA 122150Z 08020G38KT 1/2SM R36L/2400FT +TSRA SCT008 OVC012CB 20/18 A2995 RMK TSB24RAB24 SLP134 (Fig 7-3)

  7. Example of METAR (7-3)

  8. Type of Report & Station Identifier • Type META …. • There are two types – META which is routinely taken everyday, and SPECI (special aviation weather report) which is an unscheduled report when significant changes happens • Station Identifier …. KTPA…. • Each reporting station is listed by its 4-letter ICAO identifier. Here K is for the U.S. and TPA is the internal identifier inside the U.S. (for Tampa, Florida)

  9. Time of Report • Time of report ….122150Z…. • The date and time follows the station identifier. The time is Zulu time. Note that the month and Year are not given. • This might be followed by an optional modifier. For example, if the report is generated entirely automatically, the modifier AUTO is given.

  10. Wind Information • Wind Information …. 08020G38KT…. • The wind direction is reported in 3-digits, 080 for the direction of 80○ relative to true north. • If the direction varies more than 60○, then the extremes of the directions are reported after a V. (e.g., 080V150 for a variation of 70○) • The next 2-digits is the wind speed in knots. It the wind speed is over 99 knots, 3-digits will be reported. The example here indicates a wind speed of 20 knots (KT). • G38 is optional, reported only if there is gusty wind. Here, G38 means there is gusty wind up to 38 knots wind speed.

  11. Visibility • Visibility …. 1/2SM R36L/2400FT…. • Prevailing visibility is the greatest distance an observer can see and identify objects (e.g., a tower) through at least half of the horizon. If the visibility varies from one part of the sky to another, the visibility in the majority of the sky is the data reported. • In the U.S. system visibility is reported in units of statute miles (SM). (1/2 statute mile in the example.) • Prevailing visibility might optionally be followed by the Runway Visual Range (RVR)which is what a pilot can see looking down the runway. RVR starts with R, followed by the runway number (36L in the example), a slash (/), and the visual range in feet (FT)

  12. Weather (1) • Weather …. +TSRA…. • The weather codes are reported in the following order: intensity, descriptor, and precipitation (or weather phenomena) • Intensity can be heavy (+), light (-), or moderate (no sign). In our example, the precipitation [in this case, rain (RA)] is heavy. • Descriptor describes the precipitation. In our example, the descriptor is thunderstorm (TS), meaning that the precipitation (rain) is in the form of thunderstorms.

  13. Weather (2) • Weather (continued) …. +TSRA…. • Descriptors can be • TS – thunderstorm DR – low drifting • SH – shower(s) MI – shallow • FZ – freezing BC – patches • BL – blowing PR – partial • Weather phenomena covers 8 types of precipitation, 8 types of obscurations, and 5 types of uncommon weather events. (Figure) • Up to three types of precipitations can be reported in a group.

  14. Weather phenomena (p. 7-14)

  15. Sky Condition (1) • Sky condition …. SCT008 OVC012CB…. • Sky condition describes the amount of clouds, if any, their heights, and optionally their type. In addition, a vertical visibility may optionally be reported if the height of the clouds cannot be determined. • The amount of clouds covering the sky is reported in eighths (octas) of the sky covered. • Depending on how many eighths of the sky is covered, different 3-letter codes are used to code the conditions as follows.

  16. Sky Condition (2) • Sky condition (continued) …. SCT008 OVC012CB…. • The codes are: • CLR – (clear) no cloud • FEW – (few) less than 2/8 of the sky are covered • SCT – (scattered) 3/8 to 4/8 • BKN – (broken) 5/8 to 7/8 • OVC – (overcast) 8/8 are covered • Reports are given for sky conditions at different heights. However, at any height, the cloud layer at that height plus those at lower heights are included in the reporting code. (Fig 7-6)

  17. Codes for higher layers include lower layers (7-6)

  18. Sky Condition (3) • Sky condition (continued) …. SCT008 OVC012CB…. • The heights are reported in hundreds of feet above ground with 3-digits. Thus 008 means 800 feet, and 012 mean 1200 feet above ground. • In our example, at 800 feet, 3/8 to 4/8 of the sky is covered (thus SCT). At 1200 feet, all the sky is covered when we include the clouds at all layers up to 1200 feet. (Therefore coded as OVC) • CB is the type of cloud present. Cloud type can only be reported with manual reports, and even there, it is optional.

  19. Temperature and Dewpoint • Temperature and Dewpoint …. 20/18…. • The air temperature and dewpoint (in degrees Celsius) are reported immediately after the sky conditions. • In our example, the temperature and dewpoint are 20 degrees C and 18 degrees C, respectively. • Temperatures below 0 degree are prefixed with an M to indicate minus (e.g., M12).

  20. Altimeter • Altimeter …. A2995…. • The altimeter setting is reported in inches of mercury in a 4-digit group prefaced with A. A decimal place, although not reported, is implied after the first 2-digits. • In other words, since air pressure decreases with altitude, the altitude can be found from a chart when the pressure is known. • Our example thus reports an altimeter of 29.95 inches mercury.

  21. Remarks • Remarks …. RMK TSB24RAB24 SLP134…. • Remarks are reported after the code RMK. • Other useful weather information can also be reported as remarks. The types of information include wind data, variable visibility, pressure, the beginning and ending times of a particular weather phenomena, etc. • The beginning of an event is shown by a B followed by the time in minutes after the hour of the report. • In our example, a thunderstorm began at 24 minutes past the hour (TSB24). Rain also began at 24 minutes past the hour. Also the sea level pressure (SLP) was 1013.4 millibars, or hectoPascals (hPa). 1 millibar = 1 hPa = 0.001 of one atmosphere.

  22. Printed Weather Forcasts • Printed weather forecasts are similar to weather reports. The difference is that weather reports indicates the current situation while the forecast indicates the predicted situation. • One of the best forecast on the weather around the specific airport is the Terminal Aerodrome Forecast (TAF). • TAFs normally are valid for a 24-hour period and are scheduled for times a day at 0000Z, 0600Z, 1200Z, and 1800Z. • Each TAF includes: type, location, issuance date and time, valid date and time, and the forecast.

  23. Severe Weather Reports & Forecasts • While routine weather reports and forecasts are done every day, more and more attention is now also put to and reporting and forecasting special severe weather conditions like severe storms, hurricanes, and other severe conditions. • AIRMET (airman’s meteorological information) warns of weather conditions that are useful for all aircrafts but are especially important to small airplanes that are light weight and have less equipment and instrumentation, or pilot qualification.

  24. AIRMET • AIRMETs are issued for moderate icing, moderate turbulence, sustained winds of 30 knots or more, cloud ceilings less than 1,000 feet and/or visibility less than 3 miles affecting over 50 percent of an area.

  25. SIGMET • SIGMET(significant meteorological information) are issued for hazardous weather which is considered significant to aircrafts of all sizes. It reports severe icing, severe or extreme turbulence, dust storms, sandstorms, volcanic eruptions and volcanic ash lowering visibility to less than three miles.

  26. Weight & Balance • Importance of Weight and of Balance • Weight and Balance Terms • Principles of Weight and Balance • Arm and moment • Center of Gravity • Determining total weight and CG • Computation • Table • Graph • Weight shift formula • Effects of high weight

  27. Importance of Weight • The weight of the airplane and the balance of those weight is extremely important for the safe operations of the plane. • An overloaded plane has higher takeoff run, needs higher takeoff speed, reduced angle and rate of climb, reduced cruising speed, shorter range, higher stalling speed, and longer landing roll. It has larger risk of structural damage if you encounter turbulence or in a hard landing.

  28. Importance of Balance • Balancing the weight is just as important. Improper balance can lead to serious control problems. • You can check the balance condition of the plane by locating its center of gravity (CG). • For safe operation under a particular operation category the weight has to be under a certain limit and the CG has to be within a certain range, called the CG limits. (Fig 8-23)

  29. Center of gravity limits (8-23)

  30. Weight and Balance Terms (1) • These terms are specified in aviation context: • Reference datum– is an imaginary vertical plane from which all horizontal distances are measured for balance purposes. • Commonly used reference datum, depending on the manufacturer, are the plane’s nose, the engine firewall, or the leading edge of the wing. The datum location is specified in the POH. (Fig 8-24)

  31. Reference datum chosen in different planes (8-24)

  32. Weight and Balance Terms (2) • Basic empty weight– the weight of the standard airplane, optional equipment, unusable fuel, and full operation fluids including full engine oil. • Anything that significantly changes the weight or the CG should be documented in the plane’s weight and balance papers. • Ramp weight– is the weight of the airplane loaded for flight.

  33. Weight and Balance Terms (3) • Takeoff weight– the weight of the plane just before you release the brake for takeoff . It is the ramp weight minus the weight of the fuel used going from the ramp to the point when you release the brake on the runway to begin the takeoff roll. • Landing weight– the weight of the plane when you land. It is the takeoff weight minus the weight of fuel used enroute.

  34. Weight and Balance Terms (4) • Useful load– the ramp weight minus the basic empty weight. Useful load is thus the weight of the flight crew, usable fuel, any passengers, baggage, and cargo. • Payload– is the weight of only the passengers, baggage, and cargo. • The fuel available for your flight is called the usable fuel.

  35. Weight and Balance Terms (5) • Some POHs may use the general term total weightto refer to the airplane and everything carried in it. • Most airplanes cannot support a full payload and full tanks of fuel. Thus you have to make a choice between having a full payload but less than full fuel tanks, versus having full fuels tanks but less than maximum payload.

  36. Principles of Weight and Balance (1) • When children plays a seesaw, and move up and down, they are moving around the fulcrum(also called a pivot point). • In order to balance on the seesaw, the CG of the two children must be over the fulcrum. (Fig 8-26) • If one of them is lighter than the other child, the lighter child has to move farther away from the fulcrum to get the balance. They are actually moving the CG so it aligns with the fulcrum.

  37. To balance the seesaw, CG over fulcrum (8-26) Fig 8-26.To balance the seesaw the center of gravity must above the fulcrum.

  38. Principles of Weight and Balance (2) • To do a balance, we need to know the weights and also where the weights are. • The distance of a weight from any reference datum is called the arm of the weight. • The longer the arm is, the more tendency the weight is causing a rotation around the datum.

  39. Principles of Weight and Balance (3) • The product of the weight and the arm is called the momentof that weight. • Moment = (weight x arm) • Thus the unit of moment is pound-inches. • The larger the moment the larger the tendency of the weight to rotate around the datum. • If the arm on one side of the datum is defined as positive, the arm on the other side has to be defined as negative.

  40. Principles of Weight and Balance (4) • To find the location of the CG of a group of weights, we can first find the moments of all those weights from the datum (taking into consideration of both positive and negative arms). Add them together to get the total moment. Then divide this total moment by the total weight. The result will be the arm of the CG, i.e., the distance of the CG from the datum. (Example in Fig 8-28)

  41. Example in finding location of CG from datum (8-28) Fig 8-28. Using the left end of the seesaw as the datum, the position of the CG is calculated using the children’s weights and the weight of the seesaw itself.

  42. Principles of Weight and Balance (5) • Fig 8-30 shows how to find the CG of an empty plane with the pilot sitting in it, given the weight and the arm of the empty plane, and the weight and arm of the pilot. • The distance of the CG from the datum (sometimes called the CG arm) is calculated by adding the moment of the empty airplane to the moment of the pilot, divided by the total weight.

  43. Location of the CG of a plane plus pilot (8-30) Fig 8-30. Multiply the pilot’s weight by the distance from the datum to get her moment. The weight and moment of the airplane are found in its weight and balance documents.

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