2.
Service Level C is a service in which the human observer, usually an air traf.c controller, augments or adds information to the automated observation. Service Level C also includes backup of ASOS/AWSS elements in the event of an ASOS/AWSS mal-

function or an unrepresentative ASOS/AWSS report. In backup, the human observer inserts the correct or missing value for the automated ASOS/AWSS elements. This service is provided by air traf.c controllers under the Limited Aviation Weather Reporting Station (LAWRS) process, FSS and NWS observers, and, at selected sites, Non-Federal Observation Program observers.
Two categories of airports require detail beyond Service Level C in order to enhance air traf.c control ef.ciency and increase sys-tem capacity. Services at these airports are typically provided by contract weather observers, NWS observers, and, at some loca-tions, FSS observers.
3. Service Level B is a service in which weather observa-tions consist of all elements provided under Service Level C, plus augmentation of additional data beyond the capability of the ASOS/AWSS. This category of airports includes smaller hubs or special airports in other ways that have worse than average bad weather operations for thunderstorms and/or freezing/frozen pre-cipitation, and/or that are remote airports.
4. Service Level A * * *
Table 7–1–3 * * * * * SERVICE LEVEL D This level of service consists of an ASOS or AWSS continually
measuring the atmosphere at a point near the runway. The ASOS or AWSS senses and measures the weather parameters listed to the right.Wind Visibility Precipitation/Obstruction to vision Cloud height Sky cover Temperature Dew point Altimeter
7–1–17 Reporting Prevailing Visibility
a. Surface (horizontal) visibility is reported in METAR reports in terms of statute miles and increments thereof; e.g., 1/16, 1/8, 3/16, 1/4, 5/16, 3/8, 1/2, 5/8, 3/4, 7/8, 1, 1 1/8, etc. (Visibility reported by an unaugmented automated site is reported differ-ently than in a manual report, i.e., ASOS/AWSS: 0, 1/16, 1/8, 1/4, 1/2, 3/4, 1, 1 1/4, 1 1/2, 1 3/4, 2, 2 1/2, 3, 4, 5, etc., AWOS: M1/4, 1/4, 1/2, 3/4, 1, 1 1/4, 1 1/2, 1 3/4, 2, 2 1/2, 3, 4, 5, etc.) Visibility is determined through the ability to see and identify preselected and prominent objects at a known distance from the usual point of observation. Visibilities which are determined to be less than 7 miles, identify the obscuring atmospheric condition; e.g., fog, haze, smoke, etc., or combinations thereof.
* * * * *
7–1–31 International Civil Aviation Organization (ICAO) Weather Formats
* * * * *
b. * * * * * * * *
6. * * *
(a) * * *
(b) Automated visibility. ASOS/AWSS visibility stations will show visibility 10 or greater than 10 miles as “10SM.” AWOS visi-bility stations will show visibility less than 1/4 statute mile as “M1/4SM” and visibility 10 or greater than 10 miles as “10SM.”
* * * * *
7–5–12 Light Ampli.cation by Stimulated Emission of Radiation (Laser) Operations and Reporting Illumination of Aircraft
* * * * *
f. Pilots are also encouraged to complete the Laser Beam Exposure Questionnaire (See Appendix 3), and fax or email it, per the directions on the questionnaire, as soon as possible after landing.
* * * * *
7–5–15 Avoid Flight in the Vicinity of Thermal Plumes (Smoke Stacks and Cooling Towers)
a.
Flight Hazards Exist Around Thermal Plumes. Thermal plumes are de.ned as visible or invisible emissions from power plants, industrial production facilities, or other industrial systems that release large amounts of vertically directed unstable gases. High temperature exhaust plumes may cause signi.cant air distur-bances such as turbulence and vertical shear. Other identi.ed potential hazards include, but are not necessarily limited to, reduced visibility, oxygen depletion, engine particulate contamina-tion, exposure to gaseous oxides, and/or icing. Results of encoun-tering a plume may include airframe damage, aircraft upset, and/or engine damage/failure. These hazards are most critical during low altitude .ight, especially during takeoff and landing.

b.
When able, a pilot should .y upwind of possible thermal plumes. When a plume is visible via smoke or a condensation cloud, remain clear and realize a plume may have both visible and invisible characteristics. Exhaust stacks without visible plumes may still be in full operation, and airspace in the vicinity should be treated with caution. As with mountain wave turbulence or clear air turbulence, an invisible plume may be encountered unexpect-edly. Cooling towers, power plant stacks, exhaust fans, and other similar structures are depicted in Figure 7-5-2. Whether plumes are visible or invisible, the total extent of their unstable air is dif.-cult to ascertain. FAA studies are underway to further characterize the effects of thermal plumes as exhaust ef.uents. Until the results of these studies are known and possible changes to rules and policy are identi.ed and/or published, pilots are encouraged to exercise caution when .ying in the vicinity of thermal plumes. Pilots are encouraged to reference the Airport/Facility Directory where amplifying notes may caution pilots and identify the loca-tion of structure(s) emitting thermal plumes.
　
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