Pressure and Density Altitude

Pressure and Density Altitude Reference Sources Pilot s Handbook of Aeronautical Knowledge o Pages 9-1 to 9-4, Aircraft Performance o Pages 9-20 to 9-21, Density Altitude Charts Study Questions 1. Where can the data pertaining to takeoff, climb, range, endurance, descent, and landing for a specific helicopter be found? a) The Pilot s Handbook of Aeronautical Knowledge, Chapter 9. b) www.faa.gov. c) Pilot s Operating Handbook (POH). 2. What is true of the performance information published by various manufacturers? a) Performance charts are standardized from one helicopter to another so that pilot s can interpret the information easily. b) Operational data is not essential to making practical use of the helicopter s capabilities. c) Tables, graphs, and other performance data furnished in the POH are not standardized across aircraft manufacturers. 3. Why does it matter how much air is around the helicopter at any time? a) The amount of oxygen molecules determines how much fuel can be burned and turned into power. b) Thrust is generated by the propeller spinning through air molecules and forcing them backwards. c) Lift is generated by smoothly turning a flow of air molecules downward by the wings. d) All of the above. 4. When the air is less dense, what is the resulting impact on the following aircraft performance factors? engine power propeller thrust wing (airfoil) lift 11A- Pressure and Density Altitude 1

5. Complete the following formula: = Mass (amount of air) Volume (space the air takes up) 6. At sea level on a standard day what are the air temperature and pressure? and 7. In standard conditions, how much does the air temperature and pressure drop with 1,000 feet of altitude? and 8. Which of the following are methods for determining Pressure Altitude? (Check two.) Subtracting the sea level temperature from Density Altitude. Setting the altimeter to 29.92 and reading the indicated altitude. Start with field elevation and use an altitude correction tied to the actual sea level pressure setting. 9. Density Altitude is Pressure Altitude corrected for. 10. Identify whether the conditions listed below are usually associated with high or low Density Altitude. Low Density Altitude High Density Altitude Poorer engine performance Very dense air Good propeller thrust Difficulty breathing Low density Lots of lift from the wings Hot, summer days Aspen, Colorado 11. An increase in air density means a higher / lower density altitude. 11A- Pressure and Density Altitude 2

12. Complete the following formula. Density Altitude = & Adjustment for nonstandard temperature 13. Using Figure 9-3, determine the Pressure Altitude at the following airports with conditions as indicated. Airport elevation = 2,200 feet MSL Altimeter setting = 30.50 Airport elevation = 300 feet MSL Altimeter setting = 29.80 Pressure Altitude Pressure Altitude Airport elevation = 800 feet MSL Altimeter setting = 30.00 Airport elevation = 6,000 feet MSL Altimeter setting = 29.55 Pressure Altitude Pressure Altitude Airport elevation = Sea level Altimeter setting = 29.85 Airport elevation = 1,000 feet MSL Altimeter setting = 30.35 Pressure Altitude Pressure Altitude 14. To calculate Density Altitude using a Density Altitude Chart like in Figure 9-4, start first at the correct Outside Air Temperature on the bottom axis, and a) Move straight up until you intersect the correct Pressure Altitude, then read the answer. b) Move diagonally until you hit the right border, then add 2,000. c) Divide by the correct Pressure Altitude. 11A- Pressure and Density Altitude 3

15. Use Figure 9-4 to determine the Density Altitude for each of the following conditions. Air Temperature = 35 C Pressure Altitude = 1,000 feet Air Temperature = 5 C Pressure Altitude = 3,000 feet Air Temperature = 70 F Pressure Altitude = 1,000 feet Air Temperature = 20 C Pressure Altitude = 2,000 feet Air Temperature = Standard Pressure Altitude = 3,000 feet Air Temperature = 40 F Pressure Altitude = 5,500 feet Density Altitude Air Temperature = 20 C Pressure Altitude = 3,000 feet Air Temperature = 26 c Pressure Altitude = 4,500 feet 16. Because of the way the Pressure Altitude lines are angled in Figure 9-4, which would be true about an increase in outside air temperature? a) An increase in air temperature has no impact on Density Altitude. b) For the same Pressure Altitude, an increase in air temperature results in a lower Density Altitude. c) For the same Pressure Altitude, an increase in air temperature results in a higher Density Altitude. 17. Why does the red dashed Standard Temperature line in Figure 9-4 angle upward and to the left? a) Air temperature increases with altitude, and the line reflects these values. b) As altitude increases, outside air temperature decreases. c) The line is actually vertical, but appears angled only by optical illusion. 8A- Pressure and Density Altitude 4

18. As altitude increases, air pressure, and based on the impact of the pressure change alone we would expect the air density to. a) Increases; increase b) Decreases; increase c) Decreases; decrease 19. As altitude increases, air temperature, and based on the impact of the temperature change alone we would expect the air density to. a) Increases; increase b) Decreases; increase c) Decreases; decrease 20. Given these two conflicting phenomenon, which will dominate and have a greater impact on air density? a) The decrease in air pressure dominates, resulting in an overall decrease in air density with altitude. b) The decrease in air temperature dominates, resulting in an increase in air density with altitude. c) The two effects cancel each other out, and the density of the air does not change with altitude. 21. Moisture has the effect of decreasing the air density. This is because a) Water vapor is lighter than air. b) Extra water in the air pulls the air more strongly downward to the center of the earth. c) Water molecules repel oxygen molecules. 22. Which can hold more water vapor, warm air or cold air? 23. Do performance charts typically show how to calculate the influence of the moisture content of the atmosphere on helicopter performance? a) Yes. b) No. c) Approximately half of them do. 8A- Pressure and Density Altitude 5

24. Select the answers below that make the statement true. There are / are no rules-of-thumb to compute the effects of humidity on Density Altitude, so pilots should know to expect an increase / a decrease in aircraft performance when flying in high humidity. FAA Questions 1. [3259, 3-10] What is pressure altitude? a) The indicated altitude corrected for position and installation error. b) The altitude indicated when the barometric pressure scale is set to 29.92. c) The indicated altitude corrected for nonstandard temperature and pressure. 2. [3388, 3-11] Under which condition will pressure altitude be equal to true altitude? a) When the atmospheric pressure is 29.92" Hg. b) When standard atmospheric conditions exist. c) When indicated altitude is equal to the pressure altitude. 3. [3293, 8-24] (Refer to Figure 8.) Determine the pressure altitude with an indicated altitude of 1,380 feet MSL with an altimeter setting of 28.22 at standard temperature. a) 2,991 feet MSL. b) 2,913 feet MSL. c) 3,010 feet MSL. 4. [3295, 8-22] (Refer to Figure 8.) Determine the pressure altitude at an airport that is 3,563 feet MSL with an altimeter setting of 29.96. a) 3,527 feet MSL. b) 3,556 feet MSL. c) 3,639 feet MSL. 5. [3297, 8-25] (Refer to Figure 8.) Determine the pressure altitude at an airport that is 1,386 feet MSL with an altimeter setting of 29.97. a) 1,341 feet MSL. b) 1,451 feet MSL. c) 1,562 feet MSL. 8A- Pressure and Density Altitude 6

6. [3258, 3-10] What is density altitude? a) The height above the standard datum plane. b) The pressure altitude corrected for nonstandard temperature. c) The altitude read directly from the altimeter. 7. [3289, 8-22] If the outside air temperature (OAT) at a given altitude is warmer than standard, the density altitude is a) Equal to pressure altitude. b) Lower than pressure altitude. c) Higher than pressure altitude. 8. [3389, 3-11] Under what condition is pressure altitude and density altitude the same value? a) At sea level, when the temperature is 0 F. b) When the altimeter has no installation error. c) At standard temperature. 9. [3394, 8-23] Which factor would tend to increase the density altitude at a given airport? a) An increase in barometric pressure. b) An increase in ambient temperature. c) A decrease in relative humidity. 10. [3292, 8-24] (Refer to Figure 8.) What is the effect of a temperature increase from 25 to 50 F on the density altitude if the pressure altitude remains at 5,000 feet? a) 1,200-foot increase. b) 1,400-foot increase. c) 1,650-foot increase. 11. [3294, 8-22] (Refer to Figure 8.) Determine the density altitude for these conditions: Altimeter setting 29.25 Runway temperature +81 F Airport elevation 5,250 ft MSL a) 4,600 feet MSL. b) 5,877 feet MSL. c) 8,500 feet MSL. 8A- Pressure and Density Altitude 7

12. [3296, 8-24] (Refer to Figure 8.) What is the effect of a temperature increase from 30 to 50 F on the density altitude if the pressure altitude remains at 3,000 feet MSL? a) 900-foot increase. b) 1,100-foot increase. c) 1,300-foot increase. 13. [3298, 8-22] (Refer to Figure 8.) Determine the density altitude for these conditions: Altimeter setting 30.35 Runway temperature +25 F Airport elevation 3,894 ft MSL a) 2,000 feet MSL. b) 2,900 feet MSL. c) 3,500 feet MSL. 14. [3299, 8-23] (Refer to Figure 8.) What is the effect of a temperature decrease and a pressure altitude increase on the density altitude from 90 F and 1,250 feet pressure altitude to 55 F and 1,750 feet pressure altitude? a) 1,700-foot increase. b) 1,300-foot decrease. c) 1,700-foot decrease. 15. [3246, 8-25] What effect does high density altitude, as compared to low density altitude, have on propeller efficiency and why? a) Efficiency is increased due to less friction on the propeller blades. b) Efficiency is reduced because the propeller exerts less force at high density altitudes than at low density altitudes. c) Efficiency is reduced due to the increased force of the propeller in the thinner air. 16. [3290, 8-23] Which combination of atmospheric conditions will reduce aircraft takeoff and climb performance? a) Low temperature, low relative humidity, and low density altitude. b) High temperature, low relative humidity, and low density altitude. c) High temperature, high relative humidity, and high density altitude. 17. [3291, 8-24] What effect does high density altitude have on aircraft performance? a) It increases engine performance. b) It reduces climb performance. c) It increases takeoff performance. 8A- Pressure and Density Altitude 8

18. [3300, 8-25] What effect, if any, does high humidity have on aircraft performance? a) It increases performance. b) It decreases performance. c) It has no effect on performance. 8A- Pressure and Density Altitude 9

Assignment Answers Answers 1. c 2. c 3. d 4. When the air is less dense engine power decreases propeller thrust decreases wing (airfoil) lift decreases 5. Air Density = Mass Volume 6. 15 C; 29.92 inches of mercury 7. 2 C; 1 inch of mercury 8. Subtracting the sea level temperature from Density Altitude. Setting the altimeter to 29.92 and reading the indicated altitude. Start with field elevation and use an altitude correction tied to the actual sea level pressure setting. 9. Nonstandard temperature 8A- Pressure and Density Altitude 10

10. Low High Density Density Altitude Altitude Poorer engine performance Very dense air Good propeller thrust Difficulty breathing Low density Lots of lift from the wings Hot, summer days Aspen, Colorado 11. Lower 12. Density Altitude = Pressure Altitude & Adjustment for nonstandard temperature 13. Pressure altitude = 1,670 feet Pressure altitude = 410 feet Pressure altitude = 725 feet Pressure altitude = 65 feet Pressure altitude = 6,345 feet Pressure altitude = 605 feet 14. a 15. Density altitude = 3,500 feet Density altitude = 3,000 feet Density altitude = 2,500 feet Density altitude = 2,000 feet Density altitude = 4,250 feet Density altitude = 3,000 feet Density altitude = 5,500 feet Density altitude = 6,600 feet 16. c 17. b 18. c 19. b 20. a 21. a 22. Warm air 8A- Pressure and Density Altitude 11

23. b 24. are no; a decrease FAA Questions 1. b 2. b 3. a 4. a 5. a 6. b 7. c 8. c 9. b 10. c 11. c 12. c 13. a 14. c 15. b 16. c 17. b 18. b 8A- Pressure and Density Altitude 12