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AIM 

4/20/23

 

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16

Potential Flight Hazards

5.

AC 120

60, Ground Deicing and Anti

icing Program.

6.

AC 135

16, Ground Deicing and Anti

icing Training and Checking. The FAA Approved Deicing

Program Updates is published annually as a Flight Standards Information Bulletin for Air Transportation and
contains detailed information on deicing and anti

icing procedures and holdover times. It may be accessed at

the following website by selecting the current year ’s information bulletins:
https://www.faa.gov/other_visit/aviation_industry/airline_operators/airline_safety/deicing/.

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16. Avoid Flight in the Vicinity of Exhaust Plumes (Smoke Stacks and Cooling Towers)

a. Flight Hazards Exist Around Exhaust Plumes.

Exhaust plumes are defined as visible or invisible

emissions from power plants, industrial production facilities, or other industrial systems that release large
amounts of vertically directed unstable gases (effluent). High temperature exhaust plumes can cause significant
air disturbances such as turbulence and vertical shear. Other identified potential hazards include, but are not
necessarily limited to: reduced visibility, oxygen depletion, engine particulate contamination, exposure to
gaseous oxides, and/or icing. Results of encountering a plume may include airframe damage, aircraft upset,
and/or engine damage/failure. These hazards are most critical during low altitude flight in calm and cold air,
especially in and around approach and departure corridors or airport traffic areas. 
 
Whether plumes are visible or invisible, the total extent of their turbulent affect is difficult to predict. Some
studies do predict that the significant turbulent effects of an exhaust plume can extend to heights of over 1,000
feet above the height of the top of the stack or cooling tower. Any effects will be more pronounced in calm stable
air where the plume is very hot and the surrounding area is still and cold. Fortunately, studies also predict that
any amount of crosswind will help to dissipate the effects. However, the size of the tower or stack is not a good
indicator of the predicted effect the plume may produce. The major effects are related to the heat or size of the
plume effluent, the ambient air temperature, and the wind speed affecting the plume. Smaller aircraft can expect
to feel an effect at a higher altitude than heavier aircraft.

b. When able, a pilot should steer clear of exhaust plumes by flying on the upwind side of smokestacks

or cooling towers. 

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 unexpectedly. Cooling towers, power plant stacks, exhaust
fans, and other similar structures are depicted in FIG 7

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2.

Pilots are encouraged to exercise caution when flying in the vicinity of exhaust plumes. Pilots are also
encouraged to reference the Chart Supplement U.S. where amplifying notes may caution pilots and identify the
location of structure(s) emitting exhaust plumes.

The best available information on this phenomenon must come from pilots via the PIREP reporting procedures.
All pilots encountering hazardous plume conditions are urgently requested to report time, location, and intensity
(light, moderate, severe, or extreme) of the element to the FAA facility with which they are maintaining radio
contact. If time and conditions permit, elements should be reported according to the standards for other PIREPs
and position reports (AIM paragraph 7

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21, PIREPS Relating to Turbulence).