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Asked by: wes eads
How come one had to use the formula MH+RB=MB to dtermine the magnetic bearing? Why can’t i just fly to the RB of the ADF to get to the station?
Boiler on Feb 02, 2013
That equation is for a fixed card ADF. A fixed card ADF always shows North at the top and cannot be rotated. Therefore you need to use MH+RB=MB because you most likely aren’t heading North everytime you use your ADF.
With a rotatable card ADF you can turn it to your airplane’s heading which eliminates the need for the math. In that case, you can just fly the RB to the station (plus or minus wind correction).
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Wes Beard on Feb 02, 2013
You can. If you place the needle of the ADF directly on top of the ADF you will track towards the station but not directly to it.
Confused yet? In a no-wind situation, you will track directly to the station but with any wind you will make an arced path towards the station. Think about it. You set the ADF needle on top. The wind is blowing you off course so you correct by putting the needle back on top. The wind blows you off your new course and the process starts all over again. The instrument flying handbook has a good picture of this arc.
The reason why we want to know the magnetic bearing is so we can track directly to the station with or without winds. In this scenario, we determine if we are still on the MB to the station and if not, we correct by changing our heading and then letting the ADF needle fall back towards the MB we want.
The first method may make you fly into the side of a mountain. The second method will ensure you stay with the protected airspace for the airway or approach.
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wes eads on Feb 02, 2013
Thanks guys both answers helped very much!!!
Lucas on Feb 10, 2013
Here is a youtube video that shows how easy an ADF really is (it also helps you answer all the questions on the Knowledge exams:
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