Premium on Safety - Issue 33, 2019 - 3

QUIZ

Hot, Heavy, Humid, High
Do You Know Your Density Altitude Risks?
BY AMY LABODA, MANAGING EDITOR, USAIG PREMIUM ON SAFETY

Density altitude is pressure altitude corrected for
nonstandard temperature. As temperature and
altitude increase, air density decreases. In a sense,
it's the altitude at which the airplane "feels" its
flying. As the density of the air increases, engine
power output, rotor efficiency, wing efficiency, and
aerodynamic lift all decrease. On a hot and humid
day, the aircraft will accelerate more slowly down
the runway, will need to move faster to attain the
same lift, and will climb more slowly. The less dense
the air, the less lift, the more lackluster the climb,
and the longer the distance an aircraft needs for
takeoff and landing.
Here are a few questions to test your knowledge on
air density and quality and aircraft performance.

1

Why does oxygen decrease with altitude?
A) The atmosphere is just thinner up there
because there is less gravity.
B) Oxygen is a heavier element so it sinks to the surface
of the earth. Most of the earth's oxygen is below
35,000 feet. Other elements are lighter so they are
higher in the atmosphere.
C) The air is hotter higher up because it is closer
to the sun.

2

Why do we need a standard atmospheric
day determination?
A) Without standards aviation can't function.
B) The standard atmospheric temperature (15 C, 59 F) and
pressure (1013mb, 29.92 in) is a baseline for calculating
aircraft performance throughout a range of atmospheric
conditions.
C) Most days are standard, so that is why they picked it.

3

Prior to departing an airport with a calculated high
density altitude in a normally-aspirated piston aircraft,
you should run up the engine to full power and lean the
fuel mixture to achieve best power for takeoff.

4

High humidity can negatively effect aircraft
performance, even in jets and helicopters.
A) True
B) False

5

What are some reasons your aircraft performance may not
match the POH performance charts?
A) Temperatures at the surface are hotter than reported
B) The engines don't develop the same power as when new
C) You (probably) are not a test pilot
D) Your tires are under-inflated
E) You've underestimated your takeoff weight
F) All of the above
Answers on page 7

A) True
B) False

USAIG's Director of Aviation Safety Paul Ratte is a member of the NBAA
Safety Committee and recently participated in a Podcast on the genesis
of the NBAA's Top Safety Focus Areas for 2019. Listen here.

3
Premium on Safety - Issue 33, 2019

Table of Contents for the Digital Edition of Premium on Safety - Issue 33, 2019
