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AIM

10/12/17

7−5−14

Potential Flight Hazards

7−5−15. 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 7−5−2.
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 7−1−23, PIREPS

Relating to Turbulence).

FIG 7−5−2

Plumes

3/15/07

7110.65R CHG 2

AIM

3/29/18