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6 Answers

Flight planning in mph

Asked by: 6209 views Flight Instructor

In preperation for presenting a lesson on a VFR flight plan (CFI ride), everything on the arrow i fly is in MPH. So should i use statue miles instead of nautical miles? And should i convert MPH into knots for TAS on a flight plan, etc? Any suggestions would be nice. And also all i have is a Michigan Aeronautical chart, no sectional would that be sufficient enough (legal for navigation)

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6 Answers

  1. Brian on Aug 05, 2011

    Interesting question Luke. In my opinion as long as you’re consistent with whichever unit you choose all should be well. Typically, as you know, flight plans are in knots. However, since your aircraft presents in MPH I’d say you have strong arguments for using either unit. 
    As for the sectional, are you unable to aquire a legal sectional for your area? This one, at least with the upbringing I had in this industry, would be a big no no. You should not go on a cross country flight without an up to date sectional.

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  2. John D. Collins on Aug 05, 2011

    It is a personal preference to use statute miles or nautical miles.  I would personally prefer to use nautical miles as the charts, GPS, DME and other tools such as the various flight planners also use nautical miles (some may be configured to use either units), and position reports are expected to be based on nautical miles.  Converting the speeds from miles per hour to Knots, multiply by .87 or divide by 1.15.  So 150 miles per hour is 150 * .87 = 130.5 Kts or 150/1.15 = 130.4.  Either is good enough for government work.
    Regarding your plan to use the Michigan Aeronautical Chart, I would advise against it.  Although I don’t have any personal knowledge about the update cycle for the Michigan Aeronautical Chart, the state charts I am familiar with are updated annually, whereas the Sectionals are updated twice per year.  The current Michigan Sectional expires on Oct 20,2011, get one for the check ride and don’t take a chance on being busted for $8.

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  3. Bob Watson on Aug 05, 2011

    I’d go for the “path of least conversions” because each conversion is an opportunity for a miscalculation (the Mars lander mission comes to mind).
    Your plane’s speeds are in MPH so there’s probably three speeds you’ll need for your flight plan: Climb, Enroute Cruise, and Descent (and the last two are probably the same). OTOH, as John points out, all other speeds you’ll see are in Knots: Wind, position reporting, DME, GPS, etc. are in knots (and those numbers change all the time). So, you could convert 2 or 3 numbers once at home, or you could convert many numbers everywhere you go. IMO, that makes it a no-brainer: use knots.
    In the Arrow that I fly with MPH as the unit, the ASI has a scale for Knots on it so it’s easy to convert in-flight. IIRC, the ASI is the only thing in MPH. So, you fly the numbers from the AFM on the MPH scale and then read from the Knots scale to use for everything else (like flight planning & navigation).
    WRT which chart to use, if it were me, I’d spend the $8 and get a sectional chart. That’s a lot cheaper than paying another examiner fee or waiting to reschedule the check-ride. I suppose you could call the examiner and ask, but then if this is the CFI ride, that might be awkward (as in, shouldn’t you know?). If it says it’s suitable for navigation, is it the most current information that you could have so that you can satisfy FAR 91.103? If you think it is, then go with it. If there’s any doubt, get a current sectional.
    Good luck on your checkride!

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  4. Andy Neumann on Aug 05, 2011

    My addition to this conversation is related to the checkride itself and the attitude you should have going into it.  This is not like any other checkride you’ve had.  The examiner won’t just be looking to see that you have the right chart and that you can do a flight plan.  He/she will be checking that you can TEACH a student about charts and flight plans.  That means you want to come to the checkride prepared to teach ANYTHING in the CFI PTS.  How could you teach about sectional charts if you don’t bring one?  The fact that you got your commercial license means you know the material at a high level, but this is more than just checking boxes, this is about you being able to TEACH.  Good luck, be over-prepared, and let us know how it goes! 

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  5. James MacGregor CFI on Aug 05, 2011

    Convert it all to knots and nm.
    I would also mention this during the checkride, infact it could be a lesson (or mini lesson).

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  6. luke larson on Aug 06, 2011

    Thanks for the feedback guys. I dont know why i didnt just ask my instructor but its nice to get opinions from others. I’ll just go ahead and grab a current chicago sectional. As far as the checkride goes, I pretty much got out of flying for a couple years so im making sure i cover all my bases, which is good, and not good, because i tend to over think things, which im working on- just clear, simple answers. And after going through some of the gouges of local examiners i seem to be on the right path as far as over-preparing. Now i just have to remember how to fly the dang plane! So it will probaly be at least one more week before being signed off.

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