PPRuNe Forums help needed with nav exam

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 9th Aug 2009, 16:13 #1 (permalink) Join Date: Jan 2007 Location: stoke on trent england Age: 38 Posts: 135 help needed with nav exam hi everyone im currently studying for the nav exam can you tell me if this is the correct way to fill these parts of the flight log? first calculate MSA if highest ground is terrain round up to next hundred add 1300? or if its a strucure round up to nxt hundred add 1000? hdg= true track of 085 plus var ie 5w = 090 west is best prompt! if calculating hdg T do i take allowance for the W/V and Magnetic var or just the wind? all my calculations seem to be off by a few degrees!! also when working out the distance of a line ive drawn from airfield to airfield do i need to start from the edge of the circle or in the middle as even this measurement can be out by half a mile!! im pretty sure in the real exam this would be considered a fail am i right? could it be that the book im doing the exams from is quite old now (jeremy pratt questions and answers 2003 edition? the chart i use is a a 1.500000 current vfr
9th Aug 2009, 21:22   #2 (permalink)

Join Date: Feb 2007
Location: Amsterdam
Posts: 4,201
Quote:
 first calculate MSA if highest ground is terrain round up to next hundred add 1300? or if its a strucure round up to nxt hundred add 1000?
Sounds correct. Remember that structures < 300' AGL are generally not shown on the map. That's where the difference between 1000' and 1300' comes from. (The exception is normally clearly identifyable structures that may help in navigation.)

Another method is to simply look at the sector highest obstacle elevation or sector MSA that's printed on the chart for every 1/2 degree of latitude/longitude. But manufacturers are not consistent in this respect: The ICAO chart for the UK uses the highest obstacle elevation, so you need to add 1000' to get the sector MSA, but the Jeppesen VFR charts use MSA.
Quote:
 hdg= true track of 085 plus var ie 5w = 090 west is best prompt! if calculating hdg T do i take allowance for the W/V and Magnetic var or just the wind? all my calculations seem to be off by a few degrees!!
Whatever you do, the end result should be that there's a number on your plog that you steer in the aircraft. So once in the air you try to limit the number of calculations to the minimum. No problem if you use true heading, or magnetic track as an intermediate point in your calculation, but eventually you should get magnetic heading.

Give us a full example, with wind and everything, and we'll be able to tell you where you're going wrong.

Quote:
 also when working out the distance of a line ive drawn from airfield to airfield do i need to start from the edge of the circle or in the middle as even this measurement can be out by half a mile!!
The center of the circle is where the airfield (or actually the "Airfield Reference Point" - marked as ARP on the approach plates) is. So what do you think?

In any case, 1/2 nm is only about 15 seconds of flight. Not enough to care.

 10th Aug 2009, 19:10 #3 (permalink) Join Date: Jan 2007 Location: stoke on trent england Age: 38 Posts: 135 nav questions I understand MSA . Below is a typical exam question i attempted a few days ago taken from the Jeremy Pratt questions and answers 2003 edition if that helps!! It is intended to fly a VFR cross country route from Hucknall airfield(N5300.85 W00113.10) to Manchester airport (N5321.22 W00216.50) via a turning point at Hawarden airfield (N5310.68 W00258.67), complete the attached flight log. Hucknall to Hawarden W/V is stated as 260/15 Tas 85kts Var 5W I dont really understand where they get 5W from but thats what it says in the book. My answers are as follows, MSA 3000 TRK 285 DRIFT 4 HDG T 281 HDG 290 GS 69KTS DIST NM 64.5 TIME 45.5MINS Hawarden to Manchester Stated W/V 280/20 Tas 90kts my answers MSA 2000 TRK T 067 DRIFT 7 HDG T 060 HDG M 072 GS 106KTS DIST NM 27.5 TIME 18.5 One of the errors i made was to base the time on airspeed not groundspeed so this i why the times dont add up i hope! also do i need to apply magnetic variation to hdg true? to make that correct. sorry if this seems tiresome but i cant rest until ive got it into my head!!.
 10th Aug 2009, 19:26 #4 (permalink) Join Date: May 1999 Location: Quite near 'An aerodrome somewhere in England' Posts: 20,178 MEFs as printed on CAA 1/2 mill charts are based on information available concerning the highest known feature in the associated area, including terrain and obstacles and allowing for unknown features. There is no need to add the mythical 300 ft as that is allowed for - if there are higher obstacles already known about, then they will have been included in the MEF. If not, then the 300 ft will already have been added. Regarding your question about deg T or deg M, the simplest option is to use deg T for everything, then finally apply variation (and deviation, if necessary) in order to obtain the value you will use on your aeroplane's magnetic compass and DI.
10th Aug 2009, 19:54   #5 (permalink)

Join Date: Feb 2007
Location: Amsterdam
Posts: 4,201
Quote:
 Hucknall to Hawarden W/V is stated as 260/15 Tas 85kts Var 5W I dont really understand where they get 5W from but thats what it says in the book.
Actually the real variation over there is more like 3 to 3.5 degrees west. You can find this on the map. On the ICAO one that I have the isogonal lines (the lines that connect points which have equal variation) run roughly NNE-SSW and are dashed blue. If you don't know where to find this information in your map, first look in the legend for the words "isogonal", find the corresponding symbol and then look for them in the map.

But we'll assume the given 5 degrees west for the rest of the calculation.

Quote:
 My answers are as follows, MSA 3000
Highest spot elevation (not obstacle) I found was 1657 near D304, so 3000 seems to be correct.

Quote:
 TRK 285
279 if I measure it. That, of course, skews the whole rest of the calculation.

Quote:
 DRIFT 4 HDG T 281 HDG 290 GS 69KTS DIST NM 64.5 TIME 45.5MINS
If you assume that 285 is correct (for the sake of argument), you should be getting:

DRIFT 4 west (from the flight computer)
TRUE HEADING 281 (=285 - 4)
MAG HEADING 286 (=281 + 5)
GS 72 KTS (from the flight computer)
DIST 64.5
TIME 53.7 minutes

If you assume that 279 is correct, the numbers are very slightly different:

DRIFT 3 west
TH 276
MH 281
GS 71 KTS
DIST 64.5
TIME 54.5 minutes

Quote:
 Hawarden to Manchester Stated W/V 280/20 Tas 90kts my answers MSA 2000
633 spot elevation near Macclesfield. So correct unless we both missed something.

Quote:
 TRK T 067 DRIFT 7 HDG T 060
So far so good. But how do you get from TH 060 to MH 072? The difference between the true and the magnetic heading is the variation. So even if you forgot which way the 5 degree variation went, the MH should be either 055 or 065. In this case, the variation is 5 west, so the MH is 065.

Quote:
 HDG M 072 GS 106KTS
More like GS 101 on my flight computer.

Quote:
 DIST NM 27.5 TIME 18.5
If you assume GS 101, then 27.5 nm takes 16.5 minutes. If you assume GS 106 then 27.5 nm takes 15.5 minutes.

So... Looks like you need to re-read the unit once more, particularly how magnetic variation influences your true heading. You did that wrong twice. And you need to re-read the notes that came with your flight computer, because you are making some basic calculation errors in your GS/DIST/TIME calculations.

Last edited by BackPacker; 10th Aug 2009 at 20:14.

10th Aug 2009, 19:58   #6 (permalink)

Join Date: Feb 2007
Location: Amsterdam
Posts: 4,201
Quote:
 MEFs as printed on CAA 1/2 mill charts are based on information available concerning the highest known feature in the associated area, including terrain and obstacles and allowing for unknown features. There is no need to add the mythical 300 ft as that is allowed for - if there are higher obstacles already known about, then they will have been included in the MEF. If not, then the 300 ft will already have been added.
Beagle, he's not using the MEF figures but calculating the MSA from either the highest marked obstacle (plus 1000' & rounded up) or the highest marked elevation (plus 1300' & rounded up) either side of the track. Can't blame the guy for that, as that's what he's been told to do.

Nevertheless, I agree with you. It's much easier to use the sector MEF figures and add 1000' to get the MSA if you're using the 1/2 mill CAA charts. And if you use the Jeppesen ones, the sector MSA is actually already printed on the map.

 10th Aug 2009, 20:34 #7 (permalink) Join Date: Jan 2007 Location: stoke on trent england Age: 38 Posts: 135 nav exam thanks for your help guys really appriecate that i will use the MEF figures from the map from now on seems way more simpler! ive booked an hours groundschool at my local field this week so hopefully any furthewr problems or errors can be put right!!! once again thanks
10th Aug 2009, 21:37   #8 (permalink)

I'd rather be floating

Join Date: Nov 2000
Location: Cambridge, England
Posts: 2,538
Quote:
 Nevertheless, I agree with you. It's much easier to use the sector MEF figures and add 1000' to get the MSA if you're using the 1/2 mill CAA charts.
Yes, and only if you don't like the answer do you bother with the more detailed examination of the map. Which you might do if, for example, the MEF is obviously due to a tall mast in the far corner of the square, nowhere near where you're going, and the MSA calculated on the MEF is higher than the base of CAS along your track.

But of course such real life discussions have only a little to do with guessing which is the right answer in a multiple choice exam ...

 12th Aug 2009, 18:45 #9 (permalink) Join Date: Jan 2009 Location: Cheshire Posts: 5 Nav Exam As a matter of interest does anyone know if you are given a complete map for the Nav Ground Exam or just a relevant a portion of it with the symbols & legend cut off? It would save a lot of memorising if complete, as you always get one you are not sure of.
 12th Aug 2009, 19:30 #10 (permalink) Moderator   Join Date: Mar 2003 Location: Orlando, Florida Age: 58 Posts: 2,598 The last I saw for the UK was a "portion" for the nav and a full southern England chart for the IMC. =^..^=

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