NZ Week 23: VOR Orientation, Tracking, Holding & Cross Country

With airlines wanting to reduce their fuel bills it makes sense pilots fly the most commercially expeditious routes into and out of airports. But wait.. what about clouds.. how can pilots possibly know their position when they can't see the ground? Well.. this is where instrument flight rules really come into play. As trainees we are taught how to pinpoint our position without reference to ground features as well as how to navigate in the same sense by following published procedures (rules). To help pilots do this our aircraft are equipped with an array of navigation aids capable of communicating with stations on the ground as well as those in space in the case of GPS and in today's lesson we covered the basics of tracking and orientating ourselves with a VOR. 

What is a VOR?

VOR, short for VHF Omnidirectional Range, is a type of ground based navigation aid widely employed at airfields and en-route locations. When you look at the picture above you'll notice a ground station with an outer band of white transmitters and one central white transmitter. Those in the outer band transmit a unique reference signal while that in the centre transmits a variable signal around a 360° rotating axis. These transmissions in themselves are useless until receivers onboard the aircraft calculate the difference between them and output a position on your instruments. More on that in a second.

It's worth noting, however, that a single VOR is not accurate enough to provide a precise fix and pilots therefore require additional VORs or distance information to do so. In this case we'll use the latter and employ something called DME (Distance Measuring Equipment) installed on the same site as our VOR. In essence DME transmits a message from the aircraft to the ground and waits to receive that same message back again. The time between sending and receiving is used in a speed, distance, time calculation and the resultant distance is then displayed in nautical miles. One nautical mile is typically referred to as 1 DME, five nautical miles as 5 DME and so on. 

How is this information shown to pilots?

In most modern setups we're fortunate to have an instrument called the HSI (Horizontal Situation Indicator). This represents a compass rose, as above. This compass rose has been annotated to help you picture exactly what it is we're being taught in these lessons.

So, firsts things first... where's the VOR relative to us? Well, on the compass rose you'll notice a cyan arrow and by design the VOR will always sit slap bang in the middle of that (I've marked it with a hexagon - not shown on the actual instrument). The head of that cyan arrow points to a degree value we would need to turn to in order to track directly to the VOR and the tail of the arrow is our aircrafts current location (i've marked that with a red plane - not shown on the actual instrument). At the top of the HSI you'll notice the number "001°" and this is the current compass heading we are flying (i've marked on our direction of travel passed the beacon with a green dashed line - not shown on the actual instrument). The final bit of information is our distance. This is listed in the first of the two yellow boxes and in our cases we are 15 nautical miles away from the VOR, or 15 DME.

What is the above picture telling you?

Whenever we use VORs we're taught to take the information in front of us and visualise ourselves as that little red plane. So, with that information I can transpose the little red plane, the cyan bearing pointer and our current trajectory onto the Google maps image above to help you visualise it. By knowing the local area I can tell you our aircraft is abeam the ranges to the West of Rotorua and that we would be tracking Northwards parallel to the towns of Kinleith and Tokoroa. Rotorua VOR is at our two o'clock around 15 miles away and should we turn to intercept, we'd fly overhead the VOR after 6 and a half minutes at our Twinstar cruising speed of 140 knots. 

What do we use this information for?

We use VORs for a whole host of things and in my example it happened to be I knew the area well enough to place myself somewhere over the ground. That's not always the case with flying though as VORs can be employed for a whole host of things whether we know the area or not. What's more, we might also be in cloud and that VOR may well be our only reference to our position. Granted, most aircraft now have GPS too but it's still a useful aid.

In most situations we'd employ a VOR to depart from or arrive at an airfield and follow published procedures to that effect. These procedures are called SIDs or STARS respectively and tell pilots which degree on the compass (called a bearing or radial) they're to fly to/from the VOR and what to do at each point in respect of altitude and speed. However, if you're not actually arriving/departing then you can also use VORs as waypoints on your route by simply overflying them. Another implementation can be terrain clearance where pilots are told to fly inbound towards a VOR at 210° before then turning overhead and flying outbound at 080°. The latter technique is employed at perhaps one of the most beautiful approaches in the world, Queenstown Airport in the South Island of New Zealand. While i've not flown this first hand, the below Youtube video speaks for itself. As passengers gaze out the window at the beauty of the mountains (i know I would be) the pilots are focussing on ensuring that either they are flying, or their autopilot is flying, the correct headings at the correct speeds and altitudes in order to not collide with terrain. 

All of the above examples can be useful for navigation and as such it was great to be able to learn how to track and orientate with the VOR. We also use VORs to construct holding patterns in the sky and you've no doubt been held in one of these at some point whilst a passenger. Usually these are employed on arrival to busier airfields, such as Heathrow and Gatwick before clearance in for land can be given. VOR holds will be the subject of my next lesson.

With one course due to fly home on Thursday and a couple of them still yet to sit their CPLs they took priority today and as such I was booked in for a bad weather standby. I didn't mind too much as I'd only have been in the simulator while the weather outside was beautiful so a couple of us head to Taupo for a spot of lunch and exploring. I visited Taupo a few months ago but the clouds were incredibly overcast and it started raining so we weren't treated with quite as nice a view. You can just about make out the snowy peaks of the Mount Ngauruhoe and Ruapehu in the distance which add to the spectacular views. We were debating speed boat hire but in the end most of us decided we'd rather buy a weeks worth of food shopping, especially as money starts to run thin, but we did stop off at the Crater of the Moon thermal park on the way home as Jack had yet to go. All in all, it was a nice few hours in the sun and certainly good to get away from Clearways. 

AT LAST!! - It may have taken five attempts over the last month or so but I can finally tick off my cross country qualifier flight. For the most part it was excellent weather too! In previous attempts I tried flying to Napier and Gisborne to the South East of Hamilton but later turned back due to weather, so in not wanting this to happen again I planned a route North to Dargaville and KeriKeri. With a trusty steed ZK-ZAC booked in my name for most of the day I took off shortly after 9am. The route took me to the North West over the Port of Waikato before tracking the coastline, stopping at two airfields and returning in time for sunset (ECT). You'll notice the first leg from Hamilton was a little off track meaning I must have calculated my heading incorrectly while on the ground but I soon corrected for it and things then continued on without a hitch.

The views up the coast were truly stunning. I'd flown around the Raglan area before during General Handling flights but its' seldom you get the opportunity to fly along it in a straight line mile after mile. Due to various airspace around Auckland International Airport I was flying around 1,500 ft or less for the most part and to cure boredom on the return leg I made sure to tune Auckland's tower on the secondary radio. It was pretty cool listening out for and watching various commercial flights depart over the Tasman sea and if one things' for sure it's that seeing A320s zoom above your little Cessna goes a long way to topping up the motivation / happiness tank. 

The first stop on my travels was a small strip at a town called Dargaville on the Auckland Peninsula. The arrival to this airfield was spectacular as it tracked from the mouth of Wairoa river back upstream over it's many meanders. Having circled above the field and established the wind direction I came in for an approach to land. Unfortunately I made my turn on to final way to early and I was too high and too fast as a result. In choosing to go around I ensured ample spacing between me and the runway this time affording enough time to configure, slow down and trim. Unlike Hamilton with its' predominantly tarmac runways, the surface here was like landing on a gravel driveway and you can certainly tell the difference as you bring the aircraft to a stop. It's a talking point among other trainees that's for sure! I stayed in Dargaville for roughly half an hour which was just enough time to refuel the plane, eat a light snack, go to the toilet and reassess the weather enroute. 

The second stop of the flight, KeriKeri, was further inland and to the north but with clouds over the terrain I was unsure if I'd even make it. Determined to not let some pesky clouds get in my way I checked my map and decided to follow the coastline further north and through the valleys before then joining for landing overhead the airfield. You'll notice from the map above I began to do this and got a fair few miles North before then turning back due to the the presence of the devil - the cumulonimbus cloud. I'd already planned for this eventuality and instead tracked back to Dargaville and then onwards to Whangarei. 

Once on the ground I gave the duty instructor at Hamilton a call and updated him on my change of plan. As the fleet have trackers on board he was already aware I'd deviated from my intended route and joined the dots up prior to my call. He commented that Whangarei was the best option in this circumstance and confirmed I'd still meet the distance requirements of the cross country thanks to already travelling North before turning back. After re-fuelling I parked up by the local aeroclub before popping inside for a cup of tea and a spot of lunch.

Forty-five minutes later I was back in the plane and on my way to Hamilton. Given the forecast I was expecting a lovely headwind all the way back but it ended up being 10 or so knots faster and what should have taken a little over an hour took more like 90 minutes. By the time I'd joined the circuit, landed, re-fuelled and tied down the aircraft I walked into the training centre around two hours later than scheduled. I felt bad about that as I thought I'd caused the flight after me to be cancelled but operations managed to fix that by shifting that lesson onto another aircraft. Phew. I'd have hated to cancel somebody else but if there's one thing I've learnt from all of the course completing their cross countries it's that they never run to schedule!

It feels great to have finally completed the cross country as it's yet another big milestone flight to tick off. It does bring sadness though as each lesson from now on will be conducted in a dual capacity. All in all the flying totalled 4 hours and 45 minutes in duration, over 410 nautical miles. It's a shame I won't be able to take a plane up on my own again until I can one day afford the single engine class rating and associated aircraft hire costs. One thing at a time though!

I've now got Wednesday and Thursday off to co-incide with my primary instructors days off before hopping back into the simulator over the weekend to learn yet more instrument flight procedures. Lie in tomorrow then!

With Wednesday and Thursday being my rostered days off, I couldn't have asked for better weather. Being used to the British winter where coats are pretty much essential, it was great to be out in a comfortable 16 - 20 °C which for us Brits may as well be our stereotypical sunbathing weather. A couple coursemates and I head to the lake on Wednesday afternoon so not to waste the day. Who'd have thought throwing a frisbee around could kill so much time!! Thursday wasn't as fun considering I spent most of the day cleaning, washing, ironing, preparing meals or reading up on the next lesson. Nevertheless it was great to relax the brain chill!

Having learnt how to track and orientate an aircraft relative to a VOR we moved our attention to using this new found knowledge within a hold environment. From the perspective of passengers down the back, and I myself have been included in this in the past, a hold is nothing more than inconvenience. Holding is a typical cause of flight delays but from the perspective of flight crew can also be a benefit as much a curse. I say this loosely though as I'm certain there are plenty of occasions where pilots want to be on the ground as much as you do! In fact, I'd go so far as to say that the latter would be true in the majority of cases especially where busier airfields almost always result in holds being employed.

What exactly is a hold?

A hold is a racetrack pattern flown over and over again until clearance to leave it is granted. The location, size and duration of a hold is published in what pilots call 'plates'. A snippet of the Hamilton plate is included above where you'll notice three race track patterns displayed. One to the north of the field at TAYLA, one to the south at BUDEN and another overhead the VOR itself which happens to be less than a mile South of the runway. In publishing hold information in this manner pilots who fly to the airfield will have an understanding of what to expect when given hold instructions.

Typically holds are used for traffic separation but can also be requested by pilots for reasons such as weather or changes in clearance they didn't expect. The majority of times though pilots would be asked to enter a hold as part of their initial clearance. Here's an example:

ZK-CTN
Bay Approach, Good Afternoon, Charlie-Tango-November on the RNAV STAR for Hamilton Runway 18 Left. 6,000 feet, India, 1009, P.o.B Three.

Bay Approach
Charlie-Tango-November, Bay Approach, radar contact established. Due delays at Hamilton you are re-cleared direct to TAYLA. Hold at 3,000ft. Expect the VOR/DME Runway 18 left approach at two-zero. Squawk 5352.

ZK-CTK
Re-cleared to the hold at TAYLA 3,000ft. Expect VOR/DME Runway 18 Left approach at two-zero. Squawk 5352. Charlie-Tango-November.

If we translate this then the pilot has been instructed by approach controllers to take up a hold at TAYLA to the north of the airfield at an altitude of 3,000 feet. You can find the TAYLA hold on the plate graphic above which is denoted as 12 miles away from the field. Clearance at "two-zero" simply means to expect further contact from the controller at twenty past the current hour and that the aircraft should expect to hold until that time.

What was taught in the lesson?

On the face of it holds appear rather straight forward as you simply fly straight over the VOR, turn 180° fly for a minute, turn another 180° and fly back over the VOR. This is then repeated over and over until you're told otherwise or you request to leave. However, there are three different procedures for joining holds depending the direction you're flying towards them, as depicted in the graphic above. I spent the majority of the lesson entering and flying round and round in the hold before then repositioning the aircraft and flying towards it from another direction. Wind is a factor I also had to consider as it'll blow you off course and/or make see you fly slower/faster over the ground both of which alter the way you fly the hold pattern. With each straight leg only being flown for one minute you don't have much time to think about things and need to remain on the ball and as most holds are conducted inside controlled airspace I was introduced to some new radio calls. By the end of the lesson I had flown each hold entry two to three times and completed several loops of the holding pattern both with and without wind. It was a lot to take in, but I think I got the hang of it in the end.

What's next?

Just like the lesson before it, VOR Holding has lay the foundations required to complete the VOR approaches lesson where we look at the transition from the hold down to the runway for landing. My coursemate Chris (in this blogs cover photo) has already had this lesson and said I could sit in on it. It certainly helped me know what to expect so fingers crossed the approaches lesson won't come as too much of a surprise. At the time of writing the weekends schedule had been released and I've got that lesson at the bright and early time of 5.55am. It looks like I then have two further sims on Sunday where I'll be moving on to look at a different type of navigation aid, GPS, and it's associated hold and approach procedures. Guess you could say I have a busy weekend ahead.