• IFR Training Part 3

    IFR Training Part 3

    By Chris Liddell

    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).

    IFR training - VOR / OBS
    VOR cockpit instrument

    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.

    IFR training
    Cloud surfing

    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.


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