Archive for the Navigation & Planning Category

Flight Performance & Planning Exam: Passed

Monday, November 11th, 2013 | Permalink

Principles of Flight / Flight Planning & Performance: PPL 4

Principles of Flight / Flight Planning & Performance: PPL 4

This blog is getting completely out of sync with the actual time scales of everything but “logically” it’s about right, but is now a few months out of sync with the actual dates things happened…….must try harder!

Challenging the Nav Exam for the most amount of math, Flight Performance and Planning had a lot of scope to go very wrong.

….and it very nearly did.

All the practice papers I’ve ever seen and everything in existing text books do not show any implication of requiring a map.

Clearly none was expected either as the required items on the morning of setting the paper were glanced through by the examiner and it didn’t jump out as required – but three quarters of the way through it:

Using a Chart of Southern England, plot the following route:  Cardiff to…..via….

Pardon me?   Plot a route, nobody said anything about plotting a route anywhere.   In my Navigation exam I’d attempted to bring my own map, but had been told there was a specific map provided for the test, this time I brought no such kit and was clearly in need of a map (and a pen and a ruler and a protractor and….).   The aero club lent me all of this and it came as a bit of a surprise to them as well I think.

I guess:  be warned.

Having had to scramble for a map/chart and try to remember how to use one 😉    I was really, really doubtful about getting through this.   Very pleased (and a little shocked), when the phone rang and verdict was:

Passed:  80%

I’ll take that, on to the next one.



Navigation Exam : Passed

Friday, August 2nd, 2013 | Permalink

Navigation  - PPL3

Navigation – PPL3

Having done my four dual navigation lessons, only 2 land away lessons remained before my first solo navigation.  The catch being, if you’ve not passed the Navigation exam, you can’t go on your first solo nav.  So time was becoming of the essence.

Put a date in the aero club diary ~2.5 weeks away – you can read the books, but you revise better once there’s a deadline.

Both practice papers I did came out as 84% and there was some very questionable flight computer results in the answers of the book (but that will always be the flaw of such mechanical machines).

Passed :  84%

Not my best score and I think the margins of error on mechanical things may have got me on one question for sure, but that doesn’t matter now.

Yay!!! We can go flying far away on our own now, very soon!

A huge relief because I really hadn’t planned in any contingency time had I needed to resit.


Flight Planning : Nav. #1

Thursday, February 28th, 2013 | Permalink

Briefing in preparation for a day when the weather turns good.  I was feeling about 90% myself, having just recovered from a cold, mentally all with it, but looking back it’s probably a good thing the cloud base was low.

One of those, write it down and maybe some of it will sink in (might even be right) posts and it may even be useful or interesting to someone else, you never know 🙂

Trip to East Bergholt

East Bergholt (Location)

East Bergholt (Location)

This is the standard “Dual Nav #1” destination and at this stage I’m happy to fly almost anywhere, so no I’ve never heard of the place either, but that doesn’t matter – it’s just somewhere to go (no doubt picked for a variety of good reasons – possibly because the locals haven’t got sick of Cessna’s doing 180’s over their village yet).

To plan the trip we’ll be needing the following toys (and a pen):

  • Flight Computer
  • Square Protractor
  • Ruler (scale markings in Nautical Miles, 1:500,000)
  • A current aeronautical map
  • Some paper (preferably with relevant columns and such like for flight planning).

If you need sticky back plastic, something has probably gone wrong…..

Magnetic Variation

Is the angle / difference, from magnetic north to true north, aviation maps are based on Truth North but once in the plane everything (Direction Indicator) is setup with reference to a compass which will measure magnetic north (ignoring some other errors which are calibrated out and we won’t go into).

If your variation is West, add it……if it’s East, subtract it.   Giving to the slightly politically incorrect phrase

West is Best……East is Least

It could be a big number, but for around these parts it’s variation comes out at roughly +1 to the true heading

So when we’ve compensated for wind etc. our final heading needs to be adjusted by +1.

A useful website if you want to know your magnetic variation.

Safety Altitude

Map Marked for East Bergholt

Map Marked for East Bergholt

This potentially will impact the wind velocities we need to input – we know where we’re going so we can figure out the safety altitude, then we can think about a flight altitude for the trip and finally that will let us think about the wind velocities.

There are generally two ways to determine a minimum safety altitude.

Option 1:  Plot the route as per something like the picture on the right, then taking 5 miles either side of the route, find the highest obstacle – but be weary some items do not need to appear on the map (e.g. a mast that is 299ft), which means a mast on top of a hill could catch you out.

Option 2: You’ll see on the map (chart), some elevation markings “09”, “08” etc. in purple, take the biggest number your route crosses and add 500ft.  This is the absolute minimum safety height.

Our route crosses 900ft, so our absolute minimum is 1,400ft.

Flight Altitude

Above 1,400ft but we can’t fly in cloud and we might also get restricted by airspace.

On this particular route, anything above 5500ft and we’ll be heading into Class A airspace, we can’t do that.   So something below 5,500 and above 1,400ft.

What about the clouds, well I’m rarely lucky enough to get a cloud base above 4,000ft, so something below that.   How about we aim for a nice round 2,000ft.

The Wind

Whatever it happens to be on the day – but we actually care about what the wind is doing at our intended flight altitude for the trip, not the surface wind.   You can find this quite easily thanks to the Met Office and Form 214 (UK Spot wind chart).  For the purpose of walking this through let’s say 330 degrees, 15 knots (330/15).


If there was no wind and no magnetic errors, this is the direction we’d want to fly – we’re never that lucky, but to work out the rest you need a reference.   So using our map and a square protractor we can figure out which way we’d point the plane in an ideal world – just to highlight the route, I’ve emphasized it in yellow.

Protractor Overlay

Protractor Overlay

The picture doesn’t do it justice, but trust me it’s about 115 degrees (True).


East Bergholt - Distance Measurement

East Bergholt – Distance Measurement

Hopefully you’ve noticed that we’ve marked up the route on the map (we know where we are, we know where we want to go and give or take, there’s nothing stopping us from going in a straight line to get there – the beauty of flight!)

What you might not have noticed is that the starting point is from a known reference point, a point by which we will hopefully have set our speed, be straight and level and not have much else to do but press “start” on the clock.  In this case, it’s 6 mile bottom and as luck would have it, is about 6 miles from the airport.

Using the most expensive piece of plastic you may have ever bought, measuring the distance in nautical miles is a 10 second affair, place ruler on line, read off the distance (just be sure you’re using the correct scale!)

Give or take a little, we can call that 29 nautical miles (flying in knots remember).

Now all we need to do is figure out which way we should actually point the plane in order to reach our destination (i.e. do our best to avoid going randomly off course due to wind and magnetic variation).


Keep it simple a nice round cruise speed of 100 knots today.

Flight Computer

Flight Computer (CRP-1)

The Flight Computer

You can do this next bit with graph paper and a calculator, but it’ll take you longer and would be using the universal language of mathematics……to hell with that, we’re paying £3/min to be in this party, time to crack out the toy that make this flying business look complicated to the outside world 🙂

Firstly we know that if there was no wind and we could fly a true heading, we’d want to fly 115 degrees (see track).   There is wind, 330/15, so we need to correct for this.

Using the “Wind Down” method on the flight computer:

  1. Flip it over to the “wind” side and set the little circular dot to the top of the ‘low speed wind’ chart.
  2. Turn the dial until “Index” is set against the wind direction (330)
  3. Now mark the wind speed, perpendicular to the circular dot (see picture), 15 knots today.
Wind Speed Marked

Wind Speed Marked

Heading & Groundsped on a Flight Computer

Heading Correction & Ground Speed

Now to find out what the heading correction needs to be:

  1. Slide the centre plastic part up until the circular dot is against our intended airspeed (100).
  2. Now turn the dial until it’s set to the Track (115)

As you can see and might expect, the mark we made for the wind speed, has now moved out to the right, give or take 1 degree (largely hinges on how good your marker pen skills are), if you look down from the mark to the line reading “10, 20, 30…”), you’ll see the difference between the centre and where the mark crosses this line is about 5 degrees.

So we’re going to be pushed at an angle of 5 degrees to the right, therefore we fly a heading (True) of 110 degrees.

However, the flight computer has one other trick up its sleeve – when walking through the briefing, when asked how could I work out the groundspeed, my first thought was “I know the wind, I can therefore work out the headwind/tailwind component”.   You could, but this involves a new set of tasks with the flight computer……..look again at the flight computer, you’ll notice that the marked cross is horizontally aligned with 112, that will be our ground speed if the wind stays constant.

So we now also know our ground speed will be 112 knots.

We know our ground speed (112 knots), we know our distance (29 nautical miles), thus we can work out how long the trip will take.   Just flip the flight computer over.

Setting Ground Speed on a CRP-1

Setting Ground Speed

The first thing to remember is that a flight computer is a circular slide rule.  Therefore it’s up to you to remember where you put the decimal place (e.g. 10 can be, 1, 10, 100, 1000….) and as long as you keep track of where the decimal point is today you’ll be good……..the task of doing so however introduces risk of human error.

The steps are as follows:

  1. Find the Index marker (Red Triangle marker in this case, marked “60”).
  2. Rotate the dial such that the point of this index is aligned against your previously calculated Ground Speed (112) on the outer maker.

Note what I said about a slide rule, in the photo on the right you might easily think I’ve just aligned it to “11.2”, but what is actually happening is I’m essentially shifting the decimal place out to the right by one place and thus it’s now “112”

All that’s left to do now is to find the distance we’re traveling and read off the time it’ll take to get there:

Time to Travel on a CRP-1

Time to Travel

  1. Find the distance to travel on the outer scale (29 nautical miles in our case) – note that the outer scale changes its precision at some points (e.g. some points like 11->12 have 10 increments and others, 21->22 have only 5 increments), thus the precision of the answer you get will vary.
  2. Now read off the number from the inner scale, you’ll see in our example it reads around 15 minutes 30 seconds – you can round up.   We’re going to break the flight up into shorter legs anyway, this just tells us within 30 seconds when we should be at our destination.

The process for measuring the distance on the map and then computing ETA’s can be repeated to break the trip up into shorter legs, thus ensuring that you don’t drift to far off track (at least that’s the general theory).

One final correction to Heading

It flowed better to go through the flight computer stuff in one hit, but waaaaay back at the top of this post I mentioned magnetic variance and about 6 paragraphs or so back I mentioned the flight computer had told us we wanted to fly 110 degrees True.

All good, but we need to compensate for that variance or we’ll have an error creeping in that will send us off track the further we fly.

The variance was 1 degree west, so we add this to the True heading (110) to get our final heading (magnetic) of 111 degrees.

And that is the theory……Verifying your Answer

Humans make random mistakes, the Flight Computer is very accurate, but lacks precision and prone to errors.   Digital Machines however are very repeatable things, so a well tested digital tool is a good way to verify your own multi-step, manage your own decimal place, try not to get distracted human process 🙂

Enter SkyDemon Lite set where you are, where you want to go.   Add your speed and the wind and you’re done!!!

SkyDemon PLOG

SkyDemon PLOG

Our mechanical numbers agree to within 1 degree, that’s about as good as it’s going to get (and good luck flying +/-1 degree anyway), so I’ll take that. The time looks about right to, remember I rounded up to 16 minutes.  Oh yeah and the level is wrong, just ran with their default, we were flying at 2,000 in my example but doesn’t matter for our example as we’ve set the wind the same.

Lesson 24: Circuits (Cancelled – High Wind)

Monday, June 25th, 2012 | Permalink

The day before the lesson, the wind was forecast to be 24 mph (20 knots) and gusting even higher.

So, I was well prepared when the phone rang for this lesson to be cancelled.

It wasn’t a total loss, I guess as my instructor was just going to be sitting around anyway she said to come in and we could get some other ground work bits and pieces signed off in my training record.

You don’t pay if the propeller ain’t spinning (money makes the propeller go round), so this was a bit of a freebie, we like free stuff 🙂


Metars are actual observations of the weather, they attempt to give you a picture of what it’s like right now.

TAF’s (Terminal Aerodrome Forecast) are, as the name suggests, forecasts of the weather and give you a ‘best guess’ at what it might be like in the near future and for how long it might be like that.

Both come in an encoded text format, standardised by the ICAO if you can read them in one location, you should be able to read them anywhere in the world.

Met Office : Aviation Services

If you want accurate and up to date METAR’s & TAF’s, one of/the best source at least in the UK is The Met Office and thankfully they offer an “Aviation” service, for free.  You just need to register (free) and then login and you can get at all the information.

In addition to METAR’s & TAF’s, The Met Office provides Form F214 & 215, which provide wind speeds and graphical displays of the weather updated regularly during the day.

Really good service, if you haven’t found it/aren’t fully using it to its full potential yet, check it out.   As with all big websites there’s a lot of information and it’s sometimes hard to find where the good stuff on there is, but just those handful of bits are useful.

Aerodrome Information

Having gone through that lot and decoded a few METAR’s & TAF’s (more stuff signed off in the training sheet), I was shown possibly the only book I’ve yet to buy, the UK VFR Guide.

Maybe I shouldn’t have jumped in with “Ahhh yes, I need one of those….”  Because the excitement was shot down pretty promptly by a reminder that actually, it can go out of date and the publisher is under no requirement to inform you.

The official source of information for aerodromes, should be the CAA’s AIP, specifically the Aerodrome section.   If something changes, they will re-issue the page(s) affected.   So another useful bookmark to have is where you can find all of this information.

In addition on there you can quickly search NOTAM’s (NOtice To Air Men) and find out things like why an area is currently marked as a danger area etc.

The Out of Date Chart

When you start to fly, there’s a lot of stuff you need and you’ll either buy it all in one big spending spree of ‘super preparation’ (there’s not masses of point to this), or you’ll add loads of it to wish-lists etc. and get friends & family to buy it you….. After years of “What do you want for….???”   I finally had a huuuge list I could point people at 🙂

So of course when asked “Do you have a chart?”

The answer was an excited “Yes”, finally the beginnings of using it in anger for something!

Nicely folded, we began to unfold it and discovered it was Issue 37……bought just around the new year marker (guess), we had sailed past April and well, now it was out of date!    Issue 38 is now out 🙁

If you ever wanted proof that buying stuff before you really need it  isn’t useful, this is it – but hey, I got to practice my map folding with it so it wasn’t a total loss.

Now for the bad news, I couldn’t get the box for “Current / Valid Chart” ticked off, I might have had a very recent chart, but it wasn’t the current one  🙁

A good hour on the ground

All in all, a very enjoyable hour on the ground learning some new things, getting better at others and being shown around a few sites I probably should have been playing with a long time ago but have been far to busy with flying 🙂



Lesson 20 & 21 : Circuits

Monday, June 18th, 2012 | Permalink

As it was my birthday I decided what better way to spend it then to go flying all day long, so I’d booked in for two lessons on the same day (each lesson is a two hour slot, so other than a spot of lunch in the middle for 4 hours of the day you’re either checking a plane, talking about planes or flying the plane 🙂  ).   There really are worse ways to spend a weekend….


We went through the calculation for working out the crosswind component.

There are many ways to do this, the technically most accurate is:

XWind = WindSpeed * sin(WindDiffAngle)

Where “WindDiffAngle” is the difference between the runway angle and the wind angle, assuming you want the crosswind component of flying into that runway.  Good luck trying to remember your sine tables while somewhere in the circuit or on approach to an airfield.

Lets say the runway is 23  (230 degrees), and there’s a crosswind from 270 at 14 kts.

Flight Computer computing Crosswind Component

Calculating Crosswind Component

Because a Flight Computer (the UK  mandates use of a mechanical version, which for me is stretching the bounds of what you should be allowed to call a “computer”), is essentially a circular slide rule, it can do this equation for you.   Well sort of, because it’s mechanical its solution is that you set the circular part to the wind direction, then mark with a pencil the wind speed.   Then as you rotate the circular part to the runway direction, your pencil mark will move, giving you the final crosswind component for that runway (I can’t wait to try and do all that faffing in the air!)

Mechanical flight computers lack precision and are exposed to the mercy of human error, most of the time you just want a ball park figure anyway – especially when you’re busy doing the top priority of ‘aviating’ in the circuit.

There are many schemes for getting in the ball park, arguably the simplest is the “Clock” rule of thumb.

Quite simply, draw a clock with 60 at the top, 30 at the bottom etc.   Now take difference between the runway and the wind direction (in the above example: 270-230 = 40).   40 is two thirds of 60, so the crosswind component is roughly two thirds of the wind speed – so in our example, 14kts * 0.666 = ~9.32 kts.

If we used the equation to compute this we’d get:   (14 * (sin(40)) = 8.99 kts

So the rule of thumb method has an error of 0.33 kts (for this scenario, the rule has a huge 13% error at 60 degrees), but it gets you in the ball park.   You don’t need to worry too much about that big error at 60 degrees difference between runway & wind direction, because the clock rule of thumb is pessimistic.   It will result in you multiplying the reported wind by 1, instead of 0.87, this will give you an answer with a higher crosswind component then there actually is.

Look closely at the image of the flight computer, the pencil mark is now showing maybe 8kts or maybe 9kts of crosswind.   As I said above, being mechanical, they lack precision and this lack of precision comes from:  How thick was the pencil?  and the tolerance spacing between markings of 2kts per box.   Still, it’ll do the computation.

Taxi to Delta… where?



Flying G-SHWK, if the weather hadn’t been so bad the month before I’d hoped to have made this set of lessons the one where I went solo.   However, it was unlikely now, especially as the last lesson had ended with a need to see a couple of lessons of good landings before sending me solo.   At times I’d take 1 good landing, forget a lesson full of them, that is where my head is at this point in the training.

An amazingly hot sunny day, we got clearance to taxi down to holding point ‘Delta’ (where the heck is that!).   I’ve flown here for like a year, we’ve never gone there, I didn’t even know it existed.   Shocking.

Starting to be grateful about not being let loose on my own, I clearly don’t even know my home airport.   Still, it’s easier when there’s someone in the right seat to give directions 🙂

Emergency Stops on the Runway

Once down at Delta, which is the worlds longest taxi.  We waited for a plane to come in, then my instructor asks permission to do an emergency stop on the runway – now rather then getting our clearance, we get told to hold…….forever, for the longest time we were sat there, feet on the toe brakes just waiting for this jet coming in on the ILS (Instrument Landing System).   Waiting and waiting, there was even time to discuss having an ice cream out on the wing!

Finally cleared to go we line up and stop, the instructor runs me through how to do the emergency stop.

Full power on, then a voice “STOP!”    It’s all go from that moment, I pull the throttle out, then probably in a moment of wrongness start applying the brakes, I stop doing that and the plane attempts to get airborne!

The nose wheel is off the ground, we do maybe 50 meters on the back wheels alone before getting the nose back down.   This must have looked properly bonkers to onlookers.   Still, it stops and we have well over half the runway remaining.

Note:  We were not cleared for a take-off, we had been cleared to do an emergency stop.   So we have to ask for clearance again to take off.


The rest of the day was spent flying (right hand) circuits:  Up, round, down, land – almost always not applying enough back pressure.   Up, round and down.

Because I’m not applying enough back pressure my instructor tells me to trim the plane on approach so its nose wants to come up on the approach and basically fly it down with a little forward pressure.   Now on hold off it will be naturally trimmed closer to want to lift the nose…….this makes it a bit easier, but in my head I know I’m now cutting a corner and I want to avoid this trick.

It was a really enjoyable day of flying in some great weather, but I didn’t leave either lesson feeling much closer to going solo.

The positives are that I’m not flying with a map over my instruments, my instructor isn’t having to constantly tell me to “Look up!”   and other than a bit of convergence in the downwind, my circuits are now pretty good.    I just need that last 50ft to be as if I’ve done it a million times before……..and at this rate, I will have done it a million times 🙂

Barometric Pressure: QNH / QFE

Sunday, July 31st, 2011 | Permalink

Cessna 172 AltimeterAltimeters give a measurement with respect to air pressure, they are therefore essentially a sensitive barometer.  It’s the age old way of measuring an aircraft’s altitude and as such the equipment is arguably more robust than ‘modern’ advances such as GPS.   Additionally not all light aircraft have GPS fitted, so it’s important to know how it works and what it is actually telling you (not necessarily your altitude!).

Altimeters can only tell you:  Vertical distance above the datum selected.

So if you leave the altimeter alone for long enough and just keep flying at a ‘constant’ indicated altitude, as pressure changes – so will your real world / true altitude.  This is because if the pressure goes down and you keep flying a ‘constant’ altitude on the altimeter, you’ll actually be descending.   Thus the saying “High to Low, down you go….”. The reverse is equally true, giving the saying “Low to High, up you fly.”

It’s what can cause pilots crash into hill sides.

To avoid this problem, the altimeter needs to be regularly calibrated against a known pressure (datum).   There are three types available:

  • QNH : Altimeter reads aircraft Altitude above mean sea level.
  • QFE : Altimeter reads aircraft Height above a set datum (e.g. height above the airfield).
  • Flight Level (FL): Altimeter reads flight level above 1013mb/hPa of mercury.

QFE is by its nature localised, but good for flying in airfield circuits (you’ll land with the altimeter reading 0ft which is reassuring).   For cross-country QNH is typically more commonly used.

QNH gives altitude relative to mean sea level, good because everything else that is high is measured with respect to sea level.   QNH once set is only valid for the Altimeter Setting Region (ASR) you’re in and then only valid for one hour.

Flight Level (FL), above the Transition Level you can fly at ‘Flight Levels’, you’ll see them abbreviated to FL35 for example (FL35 = approx. 3500ft).  Typically the transition level is 3000ft but….   Not all flight levels are available all of the time, for reasons that will remain for another post.   Above the Transition Level, the altimeter can be set to the International Standard Setting of 1013mb/hPa.    The theory behind flight levels is fairly straight forward, at this setting everyone is flying at a relative level, they’re all going up and down with respect to each other in the same area of pressure.   So even though their indicated altitudes may not perfectly match their true altitude, a pilot flying at FL35 and a pilot flying at FL40 in the same area are in no risk of crashing into each other (even if for this example they’re a bit close).

Don’t forget Temperature….

It was all going smoothly, yet it doesn’t stop there, the thing with pressure is it changes with temperature.  Consequently if you’re flying on a very hot day then the same pressure will now be at a higher altitude – the catch being altimeters are calibrated against the International Standard Atmosphere (Temperature at Sea Level is +15C with a lapse rate of 2C per 1000ft).   If the air your flying in is hotter than this, then the altimeter will be wrong and the aircraft will be higher than indicated.   Equally on a cold day, you will be lower than indicated.

All that being said, the error temperature plays on altimeters is small (but many small errors add up, so it’s worth remembering)

…… you know why the US Military thought GPS would be a pretty neat idea!