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AIM 

6/17/21 

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15.  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

1

21, PIREPS 

Relating to Turbulence). 

FIG 7

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Plumes 

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Potential Flight Hazards