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AIM 

6/17/21 

f. 

Some canyons run into a dead end. Don’t fly so 

far up a canyon that you get trapped. ALWAYS BE 
ABLE TO MAKE A 180 DEGREE TURN! 

g. 

VFR flight operations may be conducted at 

night in mountainous terrain with the application of 
sound judgment and common sense. Proper pre-flight 
planning, giving ample consideration to winds and 
weather, knowledge of the terrain and pilot 
experience in mountain flying are prerequisites for 
safety of flight. Continuous visual contact with the 
surface and obstructions is a major concern and flight 
operations under an overcast or in the vicinity of 
clouds should be approached with extreme caution. 

h. 

When landing at a high altitude field, the same 

indicated airspeed should be used as at low elevation 
fields. 

Remember: 

that due to the less dense air at 

altitude, this same indicated airspeed actually results 
in higher true airspeed, a faster landing speed, and 
more important, a longer landing distance. During 
gusty wind conditions which often prevail at high 
altitude fields, a power approach and power landing 
is recommended. Additionally, due to the faster 
groundspeed, your takeoff distance will increase 
considerably over that required at low altitudes. 

i.  Effects of Density Altitude. 

Performance 

figures in the aircraft owner’s handbook for length of 
takeoff run, horsepower, rate of climb, etc., are 
generally based on standard atmosphere conditions 
(59 degrees Fahrenheit (15 degrees Celsius), pressure 
29.92 inches of mercury) at sea level. However, 
inexperienced pilots, as well as experienced pilots, 
may run into trouble when they encounter an 
altogether different set of conditions. This is 
particularly true in hot weather and at higher 
elevations. Aircraft operations at altitudes above sea 
level and at higher than standard temperatures are 
commonplace in mountainous areas. Such operations 
quite often result in a drastic reduction of aircraft 
performance capabilities because of the changing air 
density. Density altitude is a measure of air density. 
It is not to be confused with pressure altitude, true 
altitude, or absolute altitude. It is not to be used as a 
height reference, but as a determining criteria in the 
performance capability of an aircraft. Air density 

decreases with altitude. As air density decreases, 
density altitude increases. The further effects of high 
temperature and high humidity are cumulative, 
resulting in an increasing high density altitude 
condition. High density altitude reduces all aircraft 
performance parameters. To the pilot, this means that 
the normal horsepower output is reduced, propeller 
efficiency is reduced, and a higher true airspeed is 
required to sustain the aircraft throughout its 
operating parameters. It means an increase in runway 
length requirements for takeoff and landings, and 
decreased rate of climb. An average small airplane, 
for example, requiring 1,000 feet for takeoff at sea 
level under standard atmospheric conditions will 
require a takeoff run of approximately 2,000 feet at an 
operational altitude of 5,000 feet. 

NOTE

 

A turbo-charged aircraft engine provides a slight 
advantage in that it provides sea level horsepower up to a 
specified altitude above sea level. 

1.  Density Altitude Advisories. 

At airports 

with elevations of 2,000 feet and higher, control 
towers and FSSs will broadcast the advisory “Check 
Density Altitude” when the temperature reaches a 
predetermined level. These advisories will be 
broadcast on appropriate tower frequencies or, where 
available, ATIS. FSSs will broadcast these advisories 
as a part of Local Airport Advisory. 

2. 

These advisories are provided by air traffic 

facilities, as a reminder to pilots that high 
temperatures and high field elevations will cause 
significant changes in aircraft characteristics. The 
pilot retains the responsibility to compute density 
altitude, when appropriate, as a part of preflight 
duties. 

NOTE

 

All FSSs will compute the current density altitude upon 
request. 

j.  Mountain Wave. 

Many pilots go all their lives 

without understanding what a mountain wave is. 
Quite a few have lost their lives because of this lack 
of understanding. One need not be a licensed 
meteorologist to understand the mountain wave 
phenomenon. 

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Potential Flight Hazards