Density Altitude

Question 1

Air density is affected by what 3 factors

Answer 1

1. Pressure
2. Temperature
3. Humidity

Question 2

The main 2 concerns affecting aircraft performance due to air density are;

Answer 2

1. Engine power output
2. Aerodynamic lift

Question 3

What are the pressures (hPa) for the following levels

Sea Level
5000
10,000
20,000
30,000
35,000

Answer 3

Sea Level - 1013
5000 - 840
10,000 - 700
20,000 - 466
30,000 - 300
35,000 - 240

Question 4

Marry up the following pressures (hPa) to the correct level

1013
840
700
466
300
240

Answer 4

Sea Level - 1013
5000 - 840
10,000 - 700
20,000 - 466
30,000 - 300
35,000 - 240

Question 5

Air density is DIRECTLY or INVERSELY proportional to atmospheric pressure

Answer 5

DIRECTLY

Less pressure = less dense air

Question 6

Air density is DIRECTLY or INVERSELY proportional to Altitude

Answer 6

INVERSELY

MORE altitude = LESS dense

Question 7

In the troposphere, what is the standard temperature lapse rate

Answer 7

(minus) -1.98 ℃
Per 1000 ft

Question 8

Air is MORE or LESS dense with increase in temperature

Answer 8

LESS

Question 9

Density altitude is impacted more by which affect;
1. Increase in altitude
2. Decrease in temperature

Answer 9

INCREASE IN ALTITUDE

Question 10

Air with the highest moisture content is typically found at what altitude and what temperature

Answer 10

1. LOW altitude
2. GREATER temperature

Question 11

A defined standard atmosphere is required for what 4 reasons

Answer 11

1. Performance calculations
2. Traffic Separation
3. Expected temperatures at altitude
4. Baseline (for forecasts)

Question 12

What is the pressure lapse rate, and up to what altitude

Answer 12

1. -1 hPa per 30 ft
2. 20,000 ft

Question 13

POH performance figures are based on what atmospheric conditions

Answer 13

ISA CONDITIONS

Question 14

Air Density affects

Why does air density have an affect on engine power

Answer 14

LESS oxygen in air to mix with fuel

Less dense air means less oxygen to mix with fuel, meaning less power to engine

Question 15

Air Density affects

Why does less dense air have an affect on aerodynamic lift

Answer 15

LESS dense air means LESS lift

Less dense air requires more physical speed from the aircraft to produce the same lift than in more dense air. Thus, at higher altitude, TAS is faster than at lower altitude, but IAS would be the same

Question 16

When calculating for density altitude;

What 2 correction steps need to be carried out

Answer 16

1. Differences in ISA atmopsheric pressure at altitude
2. Differences in ISA air temperature at altitude

Question 17

Define the difference between PRESSURE altitude and DENSITY altitude

Answer 17

1. PRESSURE altitude is the altitude we would be at under ISA conditions i.e. 1013 hPa
2. DENSITY altitude is the altitude level the aircraft will perform as based on temperature and pressure corrections, irrespective of actual altitude

Example, An aircraft in ISA conditions at 10,000 ft will have better performance than an aircraft at 10,000 ft but where the temperature is +10℃ warmer. This is because the air is warmer. Warmer air is less dense, less dense air means less oxygen to mix with the fuel so less performance

Question 18

Calculate the difference in pressure altitude

Flying at 4,300 ft with 1032 set on the subscale, what is the pressure altitude

Answer 18

Pressure Alt - ISA Alt
1032 - 1013 = 19 hPa
Lapse rate 1 hPa = 30 ft
19 x 30 = 570 ft
4300 - 570 = 3,730 ft

REMEMBER:
Wind off pressure, Wind off altitude
Wind on Pressure, Wind on Altitude