can be employed: “FROM HOT TO COLD, LOOK OUT  BELOW.” When the air is warmer than standard, the aircraft  is higher than the altimeter indicates. Altitude corrections for  temperature can be computed on the navigation computer.  Extremely cold temperatures also affect altimeter indications.  Figure 8-4,  which was derived from ICAO formulas,  indicates how much error can exist when the temperature is  extremely cold.  Most altimeters are equipped with a barometric pressure  setting window (or Kollsman window) providing a means  to adjust the altimeter. A knob is located at the bottom of the  instrument for this adjustment.  To adjust the altimeter for variation in atmospheric pressure,  the pressure scale in the altimeter setting window, calibrated  in inches of mercury ("Hg) and/or millibars (mb), is adjusted  to match the given altimeter setting. Altimeter setting is  defined as station pressure reduced to sea level, but an  altimeter setting is accurate only in the vicinity of the  reporting station. Therefore, the altimeter must be adjusted as  the flight progresses from one station to the next. Air traffic  control (ATC) will advise when updated altimeter settings  are available. If a pilot is not utilizing ATC assistance,  local altimeter settings can be obtained by monitoring local  automated weather observing system/automated surface  observation system (AWOS/ASOS) or automatic terminal  information service (ATIS) broadcasts.  Many pilots confidently expect the current altimeter setting  will compensate for irregularities in atmospheric pressure at  all altitudes, but this is not always true. The altimeter setting  broadcast by ground stations is the station pressure corrected  to mean sea level. It does not account for the irregularities  When over Mineral Wells, assume the pilot receives a current  altimeter setting of 29.94 "Hg and sets this in the altimeter  window. Before entering the traffic pattern at Abilene  Municipal Airport, a new altimeter setting of 29.69 "Hg  is received from the Abilene Control Tower and set in  the altimeter setting window. If the pilot desires to fly the  traffic pattern at approximately 800 feet above the terrain,  and the field elevation of Abilene is 1,791 feet, an indicated  altitude of 2,600 feet should be maintained (1,791 feet +  800 feet = 2,591 feet, rounded to 2,600 feet).  The importance of properly setting the altimeter cannot  be overemphasized. Assume the pilot did not adjust the  altimeter at Abilene to the current setting and continued using  the Mineral Wells setting of 29.94 "Hg. When entering the  Abilene traffic pattern at an indicated altitude of 2,600 feet,  the aircraft would be approximately 250 feet below the proper  traffic pattern altitude. Upon landing, the altimeter would  indicate approximately 250 feet higher than the field elevation.  at higher levels, particularly the effect of nonstandard  temperature. If each pilot in a given area is using the same  altimeter setting, each altimeter should be equally affected  by temperature and pressure variation errors, making it  possible to maintain the desired vertical separation between  aircraft. This does not guarantee vertical separation though.  It is still imperative to maintain a regimented visual scan for  intruding air traffic.  When flying over high, mountainous terrain, certain  atmospheric conditions cause the altimeter to indicate an  altitude of 1,000 feet or more higher than the actual altitude.  For this reason, a generous margin of altitude should be  allowed—not only for possible altimeter error, but also for  possible downdrafts that might be associated with high winds.  To illustrate the use of the altimeter setting system, follow a  flight from Dallas Love Field, Texas, to Abilene Municipal  Airport, Texas, via Mineral Wells. Before taking off from  Love Field, the pilot receives a current altimeter setting of  29.85 "Hg from the control tower or ATIS and sets this value  in the altimeter setting window. The altimeter indication  should then be compared with the known airport elevation of  487 feet. Since most altimeters are not perfectly calibrated,  an error may exist.  (Since 1 inch of pressure is equal to approximately 1,000 feet  of altitude, 0.25  ×  1,000 feet = 250 feet.)  Setting the Altimeter  Figure 8-4.  Look at the chart using a temperature of –10 °C and  an aircraft altitude of 1,000 feet above the airport elevation. The  chart shows that the reported current altimeter setting may place  the aircraft as much as 100 feet below the altitude indicated by  the altimeter.  8-5  Mineral Wells altimeter setting  29.94  Abilene altimeter setting  29.69  Difference  0.25  Height Above Airport in Feet  +10  0  -10  -20  -30  -40  -50  10  20  20  30  40  50  60  10  20  30  50  60  80  90  10  30  40  60  80  100  120  10  30  50  70  100  120  150  20  40  60  90  120  150  180  20  40  70  100  140  170  210  20  50  80  120  150  190  240  20  50  90  130  170  220  270  20  60  100  140  190  240  300  30  90  150  210  280  360  450  40  120  200  280  380  480  590  60  170  290  420  570  720  890  80 230 390 570 760 970 1,190  90 280 490 710 950 1,210  1,500  Reported Temp 0 °C 200 300 400 500 600 700 800 900 1,000 1,500 2,000 3,000 4,000 5,000 