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How to get accurate hud altitude reading above 300


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I was doing the 2nd training mission for navigation, and i'm stuck. I can't figure out why I can't get an accurate reading past 300. The mission made it seem like I would just hit the switch by altitude hold and change it to BR from RD, but I get the same altitude reading with both of these.

 

Here is a video of what I am getting.

 

 

Thanks so much for any input

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The radar altimeter can only read up to 300 meters. The "p" after the number means it's a radar height. Once you go above 300 meters above the ground, the reading automatically switches from radar height to barometric height. Changing the altitude hold switch on the autopilot panel just changes whether your autopilot will hold a radar height or a barometric height. As such, you should probably stay below 300m above the ground to reliably use the radar altitude hold setting, although it may work above 300m, I have not tested it. But at any rate, the display will switch to barometric altitude any time your radar altitude goes over 300m.

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YOu should not fly above 30m anyway :doh:

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Training mission has given you the wrong idea. BR/RD switch does absolutely nothing about how the altitude is displayed on your instruments. The only thing it does is choose which sensor source is used for altitude hold function.

 

Outside of radio altimeter distance of 300m from ground the HUD switches automatically (no pilot control) to barometric altimeter source. Calibration of the barometric altimeter source is done by the black knob in the lower left corner of the barometric altimeter.

 

It's perfectly normal for a calibrated (QNH) altimeter and radio height meter to have a discontinuity when changing. In fact that jump should be equal to the elevation of the terrain below. E.g. you are flying 300m above 144m elevation terrain. Your radio height is 300m but your altitude is 444m; HUD reads "300p". When you fly 1 meter higher you are at 445m altitude and your HUD shows "+445".

 

In the particular case of a QFE calibrated altimeter and you're flying over terrain with elevation equal to the airbase elevation then the values should match during changeover.

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Other than what has already been said, keep in mind you can get the same reading of radar altitude on its relative analouge instrument. It is located on the frontal panel about full left/centre and has a scale up to 300m.

 

On that instrument, you can set the radar altimeter warning. Switch the knob to the desired altitude, if you go below that, a warning tone will be heard.

 

Also if you are totally new about radar/baromethric altitude, nothign explains better the difference than flying within 300m from a hill's edge. When you do that, read the radar altitude instrument and baromethric instrument

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