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6/17/21 

AIM 

are operated under instrument flight rules, are in 
communication with ATC, and are appropriately 
equipped). 

c. 

UAS operations may be approved at either 

controlled or uncontrolled airports and are typically 
disseminated by NOTAM. In all cases, approved 
UAS operations must comply with all applicable 
regulations and/or special provisions specified in the 
COA or in the operating limitations of the special 
airworthiness certificate. At uncontrolled airports, 
UAS operations are advised to operate well clear of 
all known manned aircraft operations. Pilots of 
manned aircraft are advised to follow normal 
operating procedures and are urged to monitor the 
CTAF for any potential UAS activity. At controlled 
airports, local ATC procedures may be in place to 
handle UAS operations and should not require any 
special procedures from manned aircraft entering or 
departing the traffic pattern or operating in the 
vicinity of the airport. 

d. 

In addition to approved UAS operations 

described above, a recently approved agreement 
between the FAA and the Department of Defense 
authorizes small UAS operations wholly contained 
within Class G airspace, and in no instance, greater 
than 1200 feet AGL over military owned or leased 
property. These operations do not require any special 
authorization as long as the UA remains within the 
lateral boundaries of the military installation as well 
as other provisions including the issuance of a 
NOTAM. Unlike special use airspace, these areas 
may not be depicted on an aeronautical chart. 

e. 

There are several factors a pilot should consider 

regarding UAS activity in an effort to reduce 
potential flight hazards. Pilots are urged to exercise 
increased vigilance when operating in the vicinity of 
restricted or other special use airspace, military 
operations areas, and any military installation. Areas 
with a preponderance of UAS activity are typically 
noted on sectional charts advising pilots of this 
activity. Since the size of a UA can be very small, they 
may be difficult to see and track. If a UA is 
encountered during flight, as with manned aircraft, 
never assume that the pilot or crew of the UAS can see 
you, maintain increased vigilance with the UA and 
always be prepared for evasive action if necessary. 
Always check NOTAMs for potential UAS activity 
along the intended route of flight and exercise 
increased vigilance in areas specified in the NOTAM. 

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6.  Mountain Flying 

a. 

Your first experience of flying over mountain-

ous terrain (particularly if most of your flight time has 
been over the flatlands of the midwest) could be a 

never-to-be-forgotten nightmare

 if proper planning is 

not done and if you are not aware of the potential 
hazards awaiting. Those familiar section lines are not 
present in the mountains; those flat, level fields for 
forced landings are practically nonexistent; abrupt 
changes in wind direction and velocity occur; severe 
updrafts and downdrafts are common, particularly 
near or above abrupt changes of terrain such as cliffs 
or rugged areas; even the clouds look different and 
can build up with startling rapidity. Mountain flying 
need not be hazardous if you follow the recommenda-
tions below. 

b.  File a Flight Plan. 

Plan your route to avoid 

topography which would prevent a safe forced 
landing. The route should be over populated areas and 
well known mountain passes. Sufficient altitude 
should be maintained to permit gliding to a safe 
landing in the event of engine failure. 

c. 

Don’t fly a light aircraft when the winds aloft, at 

your proposed altitude, exceed 35 miles per hour. 
Expect the winds to be of much greater velocity over 
mountain passes than reported a few miles from them. 
Approach mountain passes with as much altitude as 
possible. Downdrafts of from 1,500 to 2,000 feet per 
minute are not uncommon on the leeward side. 

d. 

Don’t fly near or above abrupt changes in 

terrain. Severe turbulence can be expected, especially 
in high wind conditions. 

e.  Understand Mountain Obscuration.

 The 

term Mountain Obscuration (MTOS) is used to 
describe a visibility condition that is distinguished 
from IFR because ceilings, by definition, are 
described as “above ground level” (AGL). In 
mountainous terrain clouds can form at altitudes 
significantly higher than the weather reporting 
station and at the same time nearby mountaintops 
may be obscured by low visibility. In these areas the 
ground level can also vary greatly over a small area. 
Beware if operating VFR

on

top. You could be 

operating closer to the terrain than you think because 
the tops of mountains are hidden in a cloud deck 
below. MTOS areas are identified daily on The 
Aviation Weather Center located at: 

http://www.aviationweather.gov

Potential Flight Hazards 

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