. Aerographer's Mate 3 & 2. United States. Navy; Meteorology; Oceanography. Chapter 2 —PRESSURE. NEW ORLEANS 1009 MB MIAMI 1019 MB Figure 2-9.—Altimeter errors due to change in surface pressure. cause the aircraft to gradually lose altitude; and although the altimeter indicates 500 feet, the aircraft would be actually flying at approx- imately 200 feet over New Orleans. The correct altitude can be determined by obtaining the correct altimeter setting from New Orleans, resetting the altimeter to agree with the destination adjustment. NOTE: The following relationships generally hold true up
. Aerographer's Mate 3 & 2. United States. Navy; Meteorology; Oceanography. Chapter 2 —PRESSURE. NEW ORLEANS 1009 MB MIAMI 1019 MB Figure 2-9.—Altimeter errors due to change in surface pressure. cause the aircraft to gradually lose altitude; and although the altimeter indicates 500 feet, the aircraft would be actually flying at approx- imately 200 feet over New Orleans. The correct altitude can be determined by obtaining the correct altimeter setting from New Orleans, resetting the altimeter to agree with the destination adjustment. NOTE: The following relationships generally hold true up to approximately 15,000 feet: 34 millibars = 1 inch (Hg) = 1,000 feet elevation. Since 1 millibar is equal to about 30 feet below 10,000 feet altitude, a change of 10 millibars would result in an approximate error of 300 feet. Altimeter Errors Due to Variation From Standard Temperature Another type of altimeter error is due to nonstandard temperatures. Even though the alti- meter is properly set for surface conditions, it will often be incorrect at higher levels. If the air is warmer than the standard for the flight altitude, the aircraft will be higher than the altimeter indicates; if the air is colder than standard for flight altitude, the aircraft will be lower than the altimeter indicates. (See fig. 2-10.) RADIO ALTIMETERS This type of altimeter transmits a signal that varies in frequency at an extremely rapid and constant rate. The receiver picks up the reflected signal in a frequency measuring device, which measures the difference in frequency between the transmitted and reflected signal at any instant. This difference generates a voltage which is linked to an indicator calibrated in feet. Radio altimeters work better over water than land because the water reflects the radio signals better. Radio altimeters are very helpful in deter- mining clearance from the surface. As such, they are extremely helpful in avoiding collision with the terrain. They are also useful unde
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