Flight Training - August 2012 - 45

ORDINARY AIRPLANE ALTIMETERS are called “pressure altimeters” because they use air pressure to measure height above sea level. This gives accurate altitudes—as long as needed adjustments are used— because atmospheric pressure decreases with height, but not at a steady rate. The abbreviated Standard Atmosphere chart shows how. Nevertheless, when you’re near the ground, the rule of thumb that says atmospheric pressure decreases by one inch of mercury for each 1,000 feet in altitude gained works pretty well. In fact, you should use this figure for altimeter questions on FAA knowledge exams. An altimeter is a barometer that’s calibrated to read in feet above sea level instead of inches or mercury or millibars as barometers do. Altimeters have traditionally been sensitive aneroid barometers. An aneroid is a flexible metal bellows from which some air was removed before it was sealed. Pressures lower than the inside pressure allow the bellows to expand; higher pressures squeeze it, making it shorter. A lever attached to one end of the bellows moves as the pressure changes to point to a number on a dial indicating the surrounding air pressure. Altimeters are available that replace mechanical aneroids with pressure transducers, which converts pressures into

5,000 feet

25.74 inches of mercury

4,000 feet

5,000 feet indi

cated altitude

25.74 inches of mercury

Airport A 30.74 altimeter setting

Sea level

Airport B 29.74 altimeter setting

IF YOU FLY MORE THAN a few miles from your takeoff point, you need to set your altimeter to the nearest airport both en route and at your destination.

STANDARD ATMOSPHERE
Altitude (feet) Surface 1,000 2,000 3,000 4,000 5,000 6,000 7,000 8,000 9,000 10,000 Pressure (in. Hg) 29.92 28.86 27.82 26.82 25.84 24.89 23.98 23.09 22.22 21.38 20.57 Temperature (F) 59.0 55.4 51.9 48.3 44.7 41.2 37.6 34.0 30.5 26.9 23.3

Source: Aerodynamics for Naval Aviators

electrical signals that can be used to give altitude in digital form instead of with the traditional pointers. Atmospheric pressures lower than the surrounding pressure are associated with foul weather. The centers of storms are areas of low atmospheric pressure, while areas of high pressure are associated with clear, calm weather. For an altimeter to give accurate indications, adjustments must be made for these pressure changes. To do this you need a figure that all weather stations report called the altimeter setting. Before taking off for a flight your checklist should include altimeter setting, which you can obtain via radio if the airport has automated weather reporting or a tower with automated terminal information service—ATIS. An altimeter setting from a nearby airport would work fine. Except in the centers of strong storms, atmospheric pressures don’t change much over a few miles. When you have the setting you turn the knob to the setting number next to the pointer in the Kollsman window. When you set your altimeter to the correct setting it should read the elevation of where you’re sitting. If it doesn’t, your altimeter might need calibration. If a nearby altimeter setting isn’t available, set your altimeter to show the airport elevation when you are still on the ground. The figure above shows what happens when you don’t set your altimeter when

flying into an area of low atmospheric pressure. At Airport A, you set your altimeter to 30.74 and since you’re at sea level, it reads O altitude. As you climb, the altimeter senses lower and lower pressure until the pressure is 25.74 inches of mercury. The altimeter reads 5,000, and you level off and head for Airport B. Since the surface pressure is lower at B than at A, all of the levels aloft at a particular pressure slope down from A to B following the line labeled “Indicated 5,000 feet.” You’re so busy holding an indicated altitude of exactly 5,000 feet and enjoying the view that you neglect to obtain the altimeter setting for Airport B and do not reset your altimeter. As you arrive over B, your altimeter still reads 5,000 feet. But, how high are you actually above the sea level airport? When you reset your altimeter to Airport B’s 29.74 reading, you see that you are actually 4,000 feet above the ground. You can remember this example with the saying, “high to low, look out below.” If you fly toward an area of lower pressure you need to look out below because things such as mountaintops and television towers could be closer than you think. If in this example you landed, and then reset your altimeter to the airport’s setting of 29.74 and flew back to Airport A without setting your altimeter at an indicated altitude of 4,000 feet, you would again follow the orange line to be higher than indicted at A. You could

AUGUST 2012 FLIGHT TRAINING

/ 45



Flight Training - August 2012

Table of Contents for the Digital Edition of Flight Training - August 2012

Flight Training - August 2012
Contents
President’s Perspective
Right Seat
Letters
Something to See
How It Works
After the Checkride
Tech Tip
News
Final Exam
AOPA Action News
Since You Asked
Success Story News
Member Products
Training Products
ASI News
Flying Carpet
FOLLOW THE MAGENTA LINE
TIME TO CHILL
GETTING WET
TECHNIQUE
Weather
Accident Report
Flight Lesson
Perfect Storm for Pilot Shortage
Career Advisor
Tech Talk
Flight Instructors in the Hot Seat
Good Times for CFIs
Crossed Up
Advertiser Index
Debrief
Flight Training - August 2012 - Flight Training - August 2012
Flight Training - August 2012 - Cover2
Flight Training - August 2012 - Contents
Flight Training - August 2012 - 2
Flight Training - August 2012 - 3
Flight Training - August 2012 - President’s Perspective
Flight Training - August 2012 - 5
Flight Training - August 2012 - Right Seat
Flight Training - August 2012 - 7
Flight Training - August 2012 - Letters
Flight Training - August 2012 - 9
Flight Training - August 2012 - Something to See
Flight Training - August 2012 - 11
Flight Training - August 2012 - How It Works
Flight Training - August 2012 - After the Checkride
Flight Training - August 2012 - Tech Tip
Flight Training - August 2012 - News
Flight Training - August 2012 - Final Exam
Flight Training - August 2012 - AOPA Action News
Flight Training - August 2012 - Since You Asked
Flight Training - August 2012 - 19
Flight Training - August 2012 - Success Story News
Flight Training - August 2012 - Member Products
Flight Training - August 2012 - Training Products
Flight Training - August 2012 - ASI News
Flight Training - August 2012 - Flying Carpet
Flight Training - August 2012 - 25
Flight Training - August 2012 - 26
Flight Training - August 2012 - 27
Flight Training - August 2012 - FOLLOW THE MAGENTA LINE
Flight Training - August 2012 - 29
Flight Training - August 2012 - 30
Flight Training - August 2012 - 31
Flight Training - August 2012 - 32
Flight Training - August 2012 - 33
Flight Training - August 2012 - TIME TO CHILL
Flight Training - August 2012 - 35
Flight Training - August 2012 - 36
Flight Training - August 2012 - 37
Flight Training - August 2012 - GETTING WET
Flight Training - August 2012 - 39
Flight Training - August 2012 - 40
Flight Training - August 2012 - 41
Flight Training - August 2012 - TECHNIQUE
Flight Training - August 2012 - 43
Flight Training - August 2012 - Weather
Flight Training - August 2012 - 45
Flight Training - August 2012 - 46
Flight Training - August 2012 - Accident Report
Flight Training - August 2012 - Flight Lesson
Flight Training - August 2012 - Perfect Storm for Pilot Shortage
Flight Training - August 2012 - Career Advisor
Flight Training - August 2012 - 51
Flight Training - August 2012 - Tech Talk
Flight Training - August 2012 - Flight Instructors in the Hot Seat
Flight Training - August 2012 - Good Times for CFIs
Flight Training - August 2012 - Crossed Up
Flight Training - August 2012 - 56
Flight Training - August 2012 - Advertiser Index
Flight Training - August 2012 - 58
Flight Training - August 2012 - 59
Flight Training - August 2012 - 60
Flight Training - August 2012 - 61
Flight Training - August 2012 - 62
Flight Training - August 2012 - 63
Flight Training - August 2012 - 64
Flight Training - August 2012 - 65
Flight Training - August 2012 - 66
Flight Training - August 2012 - 67
Flight Training - August 2012 - 68
Flight Training - August 2012 - 69
Flight Training - August 2012 - 70
Flight Training - August 2012 - 71
Flight Training - August 2012 - Debrief
Flight Training - August 2012 - Cover3
Flight Training - August 2012 - Cover4
https://www.nxtbook.com/nxtbooks/aopa/ft_202107
https://www.nxtbook.com/nxtbooks/aopa/ft_202106
https://www.nxtbook.com/nxtbooks/aopa/ft_202104
https://www.nxtbook.com/nxtbooks/aopa/ft_202105
https://www.nxtbook.com/nxtbooks/aopa/ft_202103
https://www.nxtbook.com/nxtbooks/aopa/ft_202101
https://www.nxtbook.com/nxtbooks/aopa/ft_202011
https://www.nxtbook.com/nxtbooks/aopa/ft_202009
https://www.nxtbook.com/nxtbooks/aopa/ft_202008
https://www.nxtbook.com/nxtbooks/aopa/ft_202007
https://www.nxtbook.com/nxtbooks/aopa/ft_202006
https://www.nxtbook.com/nxtbooks/aopa/ft_202005
https://www.nxtbook.com/nxtbooks/aopa/ft_202004
https://www.nxtbook.com/nxtbooks/aopa/ft_202003
https://www.nxtbook.com/nxtbooks/aopa/ft_202001
https://www.nxtbook.com/nxtbooks/aopa/ft_201912
https://www.nxtbook.com/nxtbooks/aopa/ft_201911
https://www.nxtbook.com/nxtbooks/aopa/ft_201910
https://www.nxtbook.com/nxtbooks/aopa/ft_201909
https://www.nxtbook.com/nxtbooks/aopa/ft_201908
https://www.nxtbook.com/nxtbooks/aopa/ft_201907
https://www.nxtbook.com/nxtbooks/aopa/ft_201906
https://www.nxtbook.com/nxtbooks/aopa/ft_201905
https://www.nxtbook.com/nxtbooks/aopa/ft_201904
https://www.nxtbook.com/nxtbooks/aopa/ft_201903
https://www.nxtbook.com/nxtbooks/aopa/ft_201902
https://www.nxtbook.com/nxtbooks/aopa/ft_201901
https://www.nxtbook.com/nxtbooks/aopa/ft_201812
https://www.nxtbook.com/nxtbooks/aopa/ft_201811
https://www.nxtbook.com/nxtbooks/aopa/ft_201810
https://www.nxtbook.com/nxtbooks/aopa/ft_201809
https://www.nxtbook.com/nxtbooks/aopa/ft_201808
https://www.nxtbook.com/nxtbooks/aopa/ft_201807
https://www.nxtbook.com/nxtbooks/aopa/ft_201806
https://www.nxtbook.com/nxtbooks/aopa/ft_201805
https://www.nxtbook.com/nxtbooks/aopa/ft_201804
https://www.nxtbook.com/nxtbooks/aopa/ft_201803
https://www.nxtbook.com/nxtbooks/aopa/ft_201802
https://www.nxtbook.com/nxtbooks/aopa/ft_201801
https://www.nxtbook.com/nxtbooks/aopa/ft_201712
https://www.nxtbook.com/nxtbooks/aopa/ft_201711
https://www.nxtbook.com/nxtbooks/aopa/ft_201710
https://www.nxtbook.com/nxtbooks/aopa/ft_201709
https://www.nxtbook.com/nxtbooks/aopa/ft_201708
https://www.nxtbook.com/nxtbooks/aopa/ft_201707
https://www.nxtbook.com/nxtbooks/aopa/ft_201706
https://www.nxtbook.com/nxtbooks/aopa/ft_201705
https://www.nxtbook.com/nxtbooks/aopa/ft_201704
https://www.nxtbook.com/nxtbooks/aopa/ft_201703
https://www.nxtbook.com/nxtbooks/aopa/ft_201702
https://www.nxtbook.com/nxtbooks/aopa/ft_201701
https://www.nxtbook.com/nxtbooks/aopa/ft_201612
https://www.nxtbook.com/nxtbooks/aopa/ft_201611
https://www.nxtbook.com/nxtbooks/aopa/ft_201610
https://www.nxtbook.com/nxtbooks/aopa/ft_201609
https://www.nxtbook.com/nxtbooks/aopa/ft_201608
https://www.nxtbook.com/nxtbooks/aopa/ft_201607
https://www.nxtbook.com/nxtbooks/aopa/ft_201606
https://www.nxtbook.com/nxtbooks/aopa/ft_201605
https://www.nxtbook.com/nxtbooks/aopa/ft_201604
https://www.nxtbook.com/nxtbooks/aopa/ft_201603
https://www.nxtbook.com/nxtbooks/aopa/ft_201602
https://www.nxtbook.com/nxtbooks/aopa/ft_201601
https://www.nxtbook.com/nxtbooks/aopa/ft_201512
https://www.nxtbook.com/nxtbooks/aopa/ft_201511
https://www.nxtbook.com/nxtbooks/aopa/ft_201510
https://www.nxtbook.com/nxtbooks/aopa/ft_201509
https://www.nxtbook.com/nxtbooks/aopa/ft_201508
https://www.nxtbook.com/nxtbooks/aopa/ft_201507
https://www.nxtbook.com/nxtbooks/aopa/ft_201506
https://www.nxtbook.com/nxtbooks/aopa/ft_201505
https://www.nxtbook.com/nxtbooks/aopa/ft_201504
https://www.nxtbook.com/nxtbooks/aopa/ft_201503
https://www.nxtbook.com/nxtbooks/aopa/ft_201502
https://www.nxtbook.com/nxtbooks/aopa/ft_201501
https://www.nxtbook.com/nxtbooks/aopa/ft_201412
https://www.nxtbook.com/nxtbooks/aopa/ft_201411
https://www.nxtbook.com/nxtbooks/aopa/ft_201410
https://www.nxtbook.com/nxtbooks/aopa/ft_201409
https://www.nxtbook.com/nxtbooks/aopa/ft_201408
https://www.nxtbook.com/nxtbooks/aopa/ft_201407
https://www.nxtbook.com/nxtbooks/aopa/ft_201406
https://www.nxtbook.com/nxtbooks/aopa/ft_201405
https://www.nxtbook.com/nxtbooks/aopa/ft_201404
https://www.nxtbook.com/nxtbooks/aopa/ft_201403
https://www.nxtbook.com/nxtbooks/aopa/ft_201402
https://www.nxtbook.com/nxtbooks/aopa/ft_201401
https://www.nxtbook.com/nxtbooks/aopa/ft_201312
https://www.nxtbook.com/nxtbooks/aopa/ft_201311
https://www.nxtbook.com/nxtbooks/aopa/ft_201310
https://www.nxtbook.com/nxtbooks/aopa/ft_201309
https://www.nxtbook.com/nxtbooks/aopa/ft_201308
https://www.nxtbook.com/nxtbooks/aopa/ft_201307
https://www.nxtbook.com/nxtbooks/aopa/ft_201306
https://www.nxtbook.com/nxtbooks/aopa/ft_201305
https://www.nxtbook.com/nxtbooks/aopa/ft_201304
https://www.nxtbook.com/nxtbooks/aopa/ft_201303
https://www.nxtbook.com/nxtbooks/aopa/ft_201302
https://www.nxtbook.com/nxtbooks/aopa/ft_201301
https://www.nxtbook.com/nxtbooks/aopa/ft_201212
https://www.nxtbook.com/nxtbooks/aopa/ft_201211
https://www.nxtbook.com/nxtbooks/aopa/ft_201210
https://www.nxtbook.com/nxtbooks/aopa/ft_201209
https://www.nxtbook.com/nxtbooks/aopa/ft_201208
https://www.nxtbook.com/nxtbooks/aopa/ft_201207
https://www.nxtbook.com/nxtbooks/aopa/ft_201206
https://www.nxtbook.com/nxtbooks/aopa/ft_201205
https://www.nxtbook.com/nxtbooks/aopa/ft_201204
https://www.nxtbook.com/nxtbooks/aopa/ft_201203
https://www.nxtbook.com/nxtbooks/aopa/ft_201202
https://www.nxtbook.com/nxtbooks/aopa/ft_201201
https://www.nxtbook.com/nxtbooks/aopa/ft_201112
https://www.nxtbook.com/nxtbooks/aopa/ft_201111
https://www.nxtbook.com/nxtbooks/aopa/ft_201110
https://www.nxtbook.com/nxtbooks/aopa/ft_201109
https://www.nxtbook.com/nxtbooks/aopa/ft_201108
https://www.nxtbook.com/nxtbooks/aopa/ft_201107
https://www.nxtbook.com/nxtbooks/aopa/ft_201106
https://www.nxtbook.com/nxtbooks/aopa/ft_201105
https://www.nxtbook.com/nxtbooks/aopa/ft_201104
https://www.nxtbook.com/nxtbooks/aopa/ft_201103
https://www.nxtbookmedia.com