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    Re: Units in Navigation
    From: Gary LaPook
    Date: 2020 Sep 25, 11:44 -0700

    Yep, but "flight levels" in the U.S. and in Europe and (I believe) in the rest of the world, are still spaced one-thousand FEET apart to provide safe separation in altitude between aircraft flying in clouds or above the "transition altitude," which in the U.S. is 18,000 feet and at various altitudes in other parts of the world, and 5,000 FEET over the ocean. One hundred meters is too close and one thousand meters is too far appart which would limit flight capacity. Below the "transition level" you have concerns with bumping into mountains so the various countries set their "transition altitudes" to be high enough to clear all their terrain. When flying in the flight levels all aircraft set their altitimeters to "QNE", 29.92 INCHES of mercury or 1,013.2 millibars (depending on the setting scale in your altimeter,)  so that all aircraft are using the same setting to assure that 1,000 foot spacing in altitude. When descending through the "transition level," in the U.S., FL180, you must get a local altimeter setting so that you can set your altimeter to "QNH"  to assure that you know your altitude in relation to terrain and in relation to  the local airport elevation.  "QNE", "QNH" and "QFE" are "Q-signals" used in radio telegraphy. There are many "Q-signals" used in marine and flight navigation which are three letter code groups, all beginning with the rarely used letter "Q" so when an operator hears  "dah-dah-dit-dah"  the receiving operator knows that it is a code group coming in. "QNE" lets you know your altitude in relation to the standard level of 29.92. The "QNH" setting is the local  barometer corrected to sea level pressure in the local area so it causes your altimeter to show your height above sea level so you can know your height above airport runways and terrain since they are charted above mean sea level,  when you land your altimeter shows the elevation of the airport above sea level. "QFE" is the actual atmoshperic pressure at the destination airport so when you land your altimeter reads zero. 

    Since 1973, in the U.S., new aircraft have airspeed indicators  marked in knots when before they were marked in mph. Airplane salesmen like to use mph because it makes a bigger number. Would you rather buy a "Mooney 201" (cruises at 201 mph) or a 'Mooney 175?"


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