AIM

8/15/19

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14

Potential Flight Hazards

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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

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23, PIREPS

Relating to Turbulence).

FIG 7

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Plumes