Ab Initio 29: Chasing radiowaves

In which I spend a pleasant afternoon chasing radio beacons around the sky.

Coming back into Wales once from Cheltenham at the gee-gees, and once from Heathrow at the Flyer training show in the past two days had made me wish there was some instrument rating equivalent for the ground–the fog was atrocious. I was whiteknuckled in the back seat coming over the Seven Bridge on Friday evening!

It had cleared to a mucky haze by the Sunday afternoon of my lesson but showed no signs of further improvement so it was somewhat pessimistically I set out. I was therefore caught on the hop and distinctly underwhelmed when I arrived to find the vis was tolerable but the pigging ruddy wind was gusting 30 just off the shortest bounciest runway of the lot.

Circuits were out of the question but Laurie had just taken off with another student in the same position to do some radio navigation stuff. I was up for some of that, so Keith gave me a quick briefing on the various nav aids and kit in the aeroplane while he refuelled with a coffee and bacon sarnie.

It sounded simple enough on the ground, all drawn on the back of stray weather charts… I suspected it might not seem so obvious once you added the other things to be thought about at the same time up in the air!

I was rather pleased to be heading out to HotelUniform– my favourite of the school aeroplanes, I find it slightly lighter on the controls than SierraBravo and it’s well kitted out with all the flashy beeping boxes for the day’s excursion.

I ran through the checks as Keith climbed in and left the door open for now, as in spite of the wind the sunshine made the cockpit rather greenhouse-like otherwise. We went over the various nav instruments again.

I tried to keep all this in mind while I taxyed out to the end of 10–an adventure in itself as it’s got quite a steep slope falling away as you reach the threshold, and the intersection with the main runway is not exactly smooth by any definition. Taking off, the aeroplane hit it with a decided bump which nearly launched us into the air at nothing like flying speed. Nevertheless we got away without incident and it was a pleasant relief to climb away out of the low level turbulence and over the top of the murky inversion causing all that haze.

Once up at about 3000′ and with sky as smooth as anything in spite of an almighty wind, we started having an explore of the instruments. We had, as discussed on the ground:

An ADF, a wheely spinning arrow thing, and an associated box to enter a frequency. The idea being that the needle points to the beacon (NDB) you’ve tuned to. Fine, nice and simple in principle. This particular one was of the type that has a twirlable compass card that you can turn to match your heading so you can read off the magnetic bearing to the NDB straight away. If you remember to set it that is–I didn’t at least once! A bit of common sense needs to be applied so you don’t make utterly daft mistakes.

A DME which was just a digital readout and another box to enter a frequency. This will give you your distance from whichever station you tune in, and if you are tracking directly towards or away from it, will also give you groundspeed and time to reach it. Quite interesting that groundspeed readout with the strong wind we had, it varied from fifty knots to well over a hundred depending whether we were heading east or west.

Finally, and rather more complicated-looking we had the OBI for VOR tracking. This consisted of firstly the box to tune in a frequency and listen to the Morse ident (assuming we ever got high enough to pick it up–Brecon is a little on the hilly side and these gadgets work on line of sight of course). Secondly the readout itself which was a dial marked as a compass card which you could twist to select the radial you wanted (a specific bearing to or from whichever station you had tuned in) and a needle which showed you how far off that line you were. (It makes more sense with a picture or the thing in front of you–honest!). This was a bit of a tricky thing to fly with. It seemed you turned it for ages and ages with nothing happening then all of a sudden it’d jump right across to the other side of the display and overshoot. Trying to look out the window and fly and set it all at the same time proved something of a challenge!

We spent a while shuttling back and forth between the Brecon and Strumble VORs and practised intercepting radials to take up a course. The strong wind allowed plenty of opportunity to practise guessing at the right wind correction angle. We then spent some time on how to use the various nav aids for fixing position. This was where I can see it being easy to come unglued. Flying, and keeping a lookout and setting the instruments and fiddling around drawing lines on the chart is going to take some practise! Nevertheless the principles were clear enough and it’s very satisfying when it actually works!

We headed back to Swansea tracking towards the NDB. For practise we called them for a QDM. In theory this is a magnetic bearing to the field, and should tally with the bearing shown on the ADF.

It didn’t.

Hmm. A look out of the window at Three Cliffs bay sliding by underneath us, suggested that the instrument was correct and a moment later we got given a second, unasked for, QDM which did match, so presumably whatever had hiccupped had been spotted!

The hazy weather demonstrated rather well why such gadgetry was useful as even from a few miles out the field was tricky to spot in the haze, and if you didn’t know the local landmarks nearby it would have been extremely difficult.

We heard the air ambulance preparing to leave and looking for us as we rejoined so gave an extra call to let them know where we were. Aside from that, the circuit was comfortingly empty, the odds of spotting traffic in the murk would not have been encouraging.

The wind had dropped a little and the approach was relatively smooth given the turbulence but the landing itself was not altogether graceful. Or indeed, altogether on the centreline. I hit the ridge at the intersection again and spent another few seconds unintentionally airborne as a result before arriving with a marginally lighter thud than usual.

Pleasant afternoon though, a nice change of pace from circuits and all interesting stuff.


Leave a Reply

Fill in your details below or click an icon to log in:

WordPress.com Logo

You are commenting using your WordPress.com account. Log Out / Change )

Twitter picture

You are commenting using your Twitter account. Log Out / Change )

Facebook photo

You are commenting using your Facebook account. Log Out / Change )

Google+ photo

You are commenting using your Google+ account. Log Out / Change )

Connecting to %s