Having completed the first part of the course, and having gained some proficiency in basic instrument flying, it was time to put these skills to use in 'applied instrument flying' which required learning about radio navigation in all its various forms. I started with the VOR which will be familiar to most readers I am sure. As previously stated, this series is not meant to be instructional - there are many excellent 'how to' guides out there. Having said that, the VOR (very high frequency omni-directional radio range) is a radio beacon which emits radials outwards from its center in all 360 degrees. You can track along a radial, to the beacon or away from it, use it to position fix, define an airway, use as a holding fix, or have as the primary navigation aid used in an approach.

During PPL training this is the most commonly taught radio navigation aid, and as a student pilot I was instructed in its use in a fairly basic sense (and in visual conditions). All my comments here relate to traditional type instruments - I have no experience in glass panel aircraft.

SID (select identify and display) is the acronym used here, and although basic, my instructor reminds me of the necessary steps to use the VOR. First you select the relevant frequency, then you listen to the morse identifier to confirm that you are tuned into the desired beacon, and finally you check the display to see that there are no warning flags. Once these steps are completed you can then use the beacon. The VOR cockpit instrument is called the 'omni bearing indicator' (OBI). The 'omni bearing selector' (OBS) is the knob used to turn the course card to the correct reading, and the needle which centers when you are on the desired radial is called the 'course deviation indicator' (CDI).

Finally there is a to/from arrow which as you might guess indicates whether you are tracking to or from! People can get confused with the difference between heading, track and radial, but provided you get the basics correct in your head, the VOR is a straightforward and very useful navigation aid. During PPL training students are taught to fix their position using one or two VORs. The two VOR method involves drawing a line out from two different stations and seeing where they intersect to confirm your position. The single VOR method can only be used with a VOR which also has DME (distance measuring equipment.) In either case, this is really difficult to do, due to having to also fly the aircraft at the same time, while drawing neat lines on a chart using a pen and ruler! The VOR in instrument flight is more often used as a waypoint along a route, or a particular radial can define an airway. My initial VOR work revolves around tracking to and from them, and intercepting various radials. I spent plenty of time refining my technique. Here is where I am faced with one of THE secrets to good instrument flying - wind correction!

To tell the truth, it is one of THE secrets to any navigation! Before any flight I am taught to estimate a maximum drift angle, which allows me to estimate wind corrections when in the air. Flying is full of 'rules of thumb' and a good one for max drift calculation is: wind speed divided by true airspeed multiplied by 60.

So for example, if we are flying at 3000 feet, with the forecast wind at 25 kts, and my TAS is 100 kts then the max drift would be 15 degrees. This is a starting point for corrections and of course represents the maximum correction required if the wind is coming at you from right angles to your desired track. Keeping in mind the actual wind direction, you can then estimate a corrected heading and see if this keeps you on the selected radial, adjusting as required. The horizontal markings which the CDI swings across are each worth two degrees, so the object is to keep the CDI centered in order to keep to the correct track/radial.

The VOR becomes more sensitive the closer you get to it, so at distance it is fairly easy to track accurately. Once closer in, it becomes more difficult, and finally you enter the 'cone of confusion', ultimately losing the signal briefly as you pass over the beacon, (confirmed by the to/from indicator flicking off then changing) as you continue on and get further away, things become more stable. Every VOR has a DOC (designated operational coverage) in other words a maximum range it can be received at. There is a formula to calculate this, taking into account your altitude. Also the signal is 'line of sight' so high terrain can block reception.

Having achieved an acceptable standard in the basics of VOR work, I then go on to put it to a practical use by doing standard instrument departures (SIDs) out of Glasgow, which use VOR tracking. These involve following a VOR radial for a defined distance, while climbing to set altitudes, before turning to intercept other radials, all of which serve to take you safely via a defined route out of the airport area, prior to transitioning to the enroute phase of your flight.

Things are going well, and I have now logged about 10 hours on the IMC course over a period of five months. My instructor is now happy for me to fly in real clouds when the opportunity arises.

I have to say that flying in actual cloud is really quite different from using vision limiting devices. The white cloud completely envelops you, and there is no peripheral vision which you can get from hoods/foggles so it's a far more disorientating experience. As long as you stick to the techniques taught it's all good, but for sure it is a different ball game compared to simulated bad weather.

I get the chance to have a 'back seat flight' with a pilot who is being prepared for his instrument rating renewal test. We are given radar vectors for an ILS approach into Glasgow. We are in real IMC and are given a heading to take us north (towards a lot of high ground) before being turned east to intercept the localiser. It is in this flight that it comes home to me how dangerous and demanding real IMC flying actually is, as we are in the clouds, heading towards high ground, and the ATC seem to take forever to give us the turn to take us back towards lower terrain. It's one thing flying in visual conditions with your IMC hood on and an instructor sitting beside you keeping a look out, and it's another thing altogether to be in actual cloud, with only your instrument skills to keep you alive - a sobering experience and a good one for me.

I never seem to have much luck when it comes to flight training (see Going Solo!) and now I hit a major problem. For reasons which are outside the scope of this article, we have to move our training base out of Glasgow and relocate to Prestwick International Airport. Getting this set up takes some time, and I don't get back into the air for a frustrating five months. Currency is vital to keep skills up to standard, and once back in the air, I have to do some revision before continuing to work through the course. Added to my lack of currency, I have to switch from Cessna 172s to PA28s. I do have some time logged in the PA28 previously, but it's another adjustment I have to make, which doesn't help matters!

As it happens, Prestwick is in some ways a better place to train compared to Glasgow. Glasgow is pretty busy, and there are frequently delays departing due to commercial arrivals and departures, and when returning from a lesson, I often have to hold for 5/10 mins (burning fuel and money) before being cleared to land. Prestwick is a large airport, but has become very quiet due to major operators moving to other locations over the years. It used to be a major destination for transatlantic flights, but less so in recent years. There is a lot of freight traffic, and also USAF operations, which makes it interesting for plane spotters! Running at a loss, and in danger of closing, the Scottish Government bought the airport a few years back for a nominal £1, and has subsidised it ever since, all the while looking for a commercial buyer - but so far without success.

The good things from my point of view is that it has two runways (four possible landing directions), an NDB beacon on the field, an ILS system, and a VOR to the southwest (the Turnberry VOR - also location of a golf resort owned by a certain famous American...)

I continue getting back into currency for instrument flying, and do SID practice (using the Turnberry VOR) before being introduced to the next radio navigation aid, the ILS.

I have to say that this is one part of the course that I have been really looking forward to, and indeed assume that it will be fairly straightforward. ILS of course stands for 'Instrument Landing System'. I have done many ILS approaches on flight sim over the years, but being self taught, this has led me into some bad habits. I will stand up and argue with anyone who says that flight simulators are no good for learning about real world flying, as I have used my sim setup regularly over the years to enhance and maintain my skills.

In my experience, most of these criticisms are generally related to student pilots (who have a simming background) keeping their heads too much inside the cockpit when being taught visual flying. Head tracking software readily addresses this issue! Instrument work can be easily practised on a simulator, provided that you use the correct techniques of course. The cockpit instrument for the ILS system is somewhat similar to the VOR with the obvious difference that as well as the vertical needle (now used to track the localiser which is aligned to the extended center line of the runway) there is a horizontal needle which represents the glideslope. The ILS system is exceptionally sensitive, and becomes more so as you come closer to the runway threshold.

As a warm up for ILS work my instructor helpfully decides to give me a demonstration of the sensitivity of the localiser needle by having me line up on the runway, put on my IMC hood, and do the take off using only the localiser needle for left/right guidance. I have to say it is one of the most uncomfortable/terrifying things I have done so far in aviation, however I do manage (just!) to perform a take off while 'blind' without crashing!. The markings on the ILS gauge have much lower values than the VOR. As previously stated, the VOR 'dots' are worth 2 degrees each, whereas the ILS localiser dots are each worth 0.5 degrees, and the glideslope markings are worth 0.14 degrees each!

Suffice to say that the sensitivity is considerable. My self taught methods are my undoing, and as I begin to practise ILS approaches, my attempts to 'chase the needle' result in a series of ever increasing 'S' turns and corrections! As I said previously - wind correction is key - so I am taught to initially estimate a good heading to use, then back it up with reference to the localiser needle adjusting as required. The glideslope is more straightforward. All I generally need to do is reduce power to the correct setting, and a suitable descent will generally follow. The problem however is that wind naturally eases and changes direction as you descend, so the nice heading you estimated 10 miles out just doesn't work closer in, add to that the needles getting more sensitive, and it's a constantly increasing work load all the way down to decision height!

I start to learn how to use and read approach plates, and work my way through lots of ILS approaches. Using your feet (rudder pedals) is vital, and any heading changes to the localiser course with the last 2/3 miles should be no greater than five degrees. Fly the heading and wait to see how the instruments react is the advice I am constantly given. Before commencing the approach, you need to be sure of all the necessary information, such as the decision height and the missed approach procedure. As explained in my last article, the IMC course has certain limitations applied to it compared to the full IR, one of these being a higher decision altitude. Having said that - this is advisory, and although my DA for a precision approach should be 500 feet above ground level, my instructor often makes me go down to the full DA of 200 feet. It's amazing how much harder that final 300 feet is!

ILS systems generally use a three degree glideslope, and a good 'rule of thumb' to calculate the desired rate of descent is to take the airspeed and multiply it by five. For example 100 kts times five is 500 - so 500 feet per minute. 80 kts - 400 fpm etc.

My ILS approaches are improving, and I now move onto the next item on the syllabus - the NDB!

That however will need to wait until the next time!

One final note before signing off for this instalment. One consequence of my aviation adventures is getting to know various commercial pilots. The chances of coming across them when they are at work however is slim, so you can imagine my surprise when I get on a British Airways flight from Glasgow to London City, and hearing the usual cockpit announcement 'welcome from the flight deck this is Captain XXX and assisting me today is first officer XXX' to realise that I know BOTH pilots! I know them as instructors, and at the conclusion of the flight, I get to tour the cockpit of the Embraer Jet - how cool is that!

Happy simming!

Chris Liddell
christopherliddell@yahoo.co.uk