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Advice on using the E6B to calculate a diversion

Asked by: 5121 views
General Aviation

Hi guys!  I am hoping someone can provide me with some advice.

I have used the wind side of my E6B to calculate my heading and my groundspeed.  No problem there.

Now if I want to divert to another location during flight, could I keep the E6B set to the current heading and groundspeed and simply rotate the dial to my new diverted course heading? 

Or, do I have to start from scratch again on the wind side of the E6B by inputting the winds and then rotating to the new course heading (followed by TAS, etc.)?

Why or why not?

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1 Answers

  1. Steve Pomroy on Feb 11, 2011

    Hi Wright Brothers.
    It’s been eons since I’ve used an E6B (I use the CR3 and the wind side is very different), but I’ll take a stab at this one anyway.
    If I recall correctly, the dot you place on the E6B represents your wind vector.  So, assuming you’re diverting with winds that are the same ones you based your initial flight planning on, it seems to me that you could just turn the dial to your new course and work from there.
    The problem, of course is in the assumption.  Are your winds the same?  Why are you diverting?  Are the winds not as planned, so you need to make an unplanned fuel stop?  Have you changed altitude because of cloud cover, turbulence, icing, etc.?  These changes might mean you can’t use your original winds.
    Of course, if you’re just diverting because you changed your mind about where you want to go (or had you mind changes for you by a passenger!), using your original winds may work just fine.  But think before you act.
    With regard to using a flight computer for a diversion, I must admit that I find that a bit odd.  Up here North of the border, diversions are taught and conducted with rules of thumb and mental math.  In fact, on ride day, the Flight Test Guide specifically forbids the use of flight computers, rulers, etc. for the diversion.  I don’t see anything at all wrong with using your E6B.  It’s just a bit different from what I’m used to.  For the sake of training, you might find that doing a few diversions with just rules of thumb and mental math will build your navigation skills and comfort/confidence level.
    Some rules of thumb you might find useful (where “groundspeed” means the typical approximate groundspeed of the aircraft you fly, or the approximate groundsped you anticipate if you know you have a strong headwind or tailwind):
        groundspeed = 60 kts:  Time to dest (minutes) = distance
        groundspeed = 90 kts:  Time to dest (minutes) = distance * 2/3
        groundspeed = 120 kts:  Time to dest (minutes) = distance / 2
        For distance measurement:  1′ Lat = 1 NM, VOR compass rose = 25 NM
        For direction:  follow a major landmark (road, river, power line, etc.), or
        For direction:  measure against a VOR compass rose (already corrected for variation)
        ETE/ETA corrections:  rather than measuring out precise checkpoints, eyeball the halfway point (or for longer diversions, the 1/3 point or 1/4 point).  Time to get halfway = time to get the rest of the way.  Time to get 1/4 of the way * 3 = time to get the rest of the way.

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