Friday, 10 September 2010

Instrument flying, Navigation and Diversion (CPL)

The MEP being completed, we jumped straight on to the CPL course, and I must say, it all goes really fast all around.
We started with some navigations (planned legs), flying to small villages like Wedmore, Axminster, Sturminster, Kingsclere, Petersfield, etc ...
Then came the unplanned navigation, basically en-route diversion.
This is the kind of flying a PPL should be familiar with, however the way you fly it as a CPL student is all new, especially if you've been trained in a flying club.
The standard navigation technique we use is known as Dead Reckoning. We do not use radio-navigation for planned legs, and we do not randomly correct if it gets obvious we've been moved off track. Instead, we use one of three heading correction techniques, which aim at coming back exactly on track, or flying direct to the intended destination from the present off track position.

We can either double the track error (in degrees) for the same amount of time we've been flying from the previous turning point, and then continue on half that value for the remaining part of the leg.
If we opt for a quicker way to regaining track, the Standard Closing Angle works best. It is based on 60 / TAS(nm/min), about 25° at 140kt for a Be76 Duchess. For each nautical mile off track, we alter the heading in the opposite direction for 1 min (or 2 min for 2nm, 3 min for 3 nm and so on) by 25°. Then on, we turn back on the previous heading, correcting by the amount of track error (in degrees, this time).
If the mid-point has been passed, the best method becomes the Inverse Fraction. We estimate how many degrees off track we currently are, work out a fraction corresponding to our position along the leg (for example, at 15 nm for a 22 nm leg, we've been flying 2/3 of the whole leg).
The correction to be made is then 1/(2/3) x the track error (in degrees). Say it was 4°, we'd have to alter the heading by 1/(2/3) x 4 = 3/2 x 4 = 6°. That new heading bringing us directly towards the destination without having to regain the initially planned track.
As to make things easier, we draw 10° lines from the planned track on the chart, and from those lines we can get a rough idea of how many degrees we are from the intended track.

That's the navigation bit. Then comes the Matz (Military Air Traffic Zone), ATZ penetration and zone transits. Those are pretty straight forward, but as the frequencies tend to get busy at times (especially Farnborough), with very little time to change from one to another and pass on all our details (e.g. Boscombe to Farnborough, or Farnborough to Southampton), all this while trying to figure out where the destination is, the workload makes a big jump up and getting everything right isn't as straight forward as it seems in the first place.
That's when you get an engine failure (simulated), and have to rejoin a busy airfield with a lot going on. Get the radio out of the way, work out the joining procedure (deadside rejoin, base rejoin, ...), descent to circuit altitude while doing the pre-landing checks, position yourself on final, and at commital altitude (200 ft AGL), you get an asymmetric go-around ... followed by a lot of flapless and asymmetric circuits.
On the way back, you track NDB and VOR radials using your RMI and/or HSI, get a position fix (Tacan (DME) + VDF for example), and then do some instrument flying. The instructor puts on a set of screens that hide the outside view to simulate IMC (instruments conditions). But that'd be too easy, you also get your Artificial horizon hidden, and you also loose the HSI and RMI. You now have to rely on the turn coordinator to check your wings level and your altimeter to check your attitude. As for your heading, and turning through a new heading, you figure it out with the not-so good compass, and do some timed turns (turning at Rate 1 (3°/sec), turning from 010 onto 285 will be 85° left, roughly 28sec, that is if you stay right on a rate 1 turn, which isn't easy when the weather gets gusty).
Later on comes the unusual attitudes bit, where your flight instructor takes control and puts the plane on a very steep climb (or descent) while over-banking the aircraft on wide side, before handing the controls back to you. You're still flying instruments with no artificial horizon, no way to be sure of an even rough attitude, and you now have to bring back the plane to a safe a stable straight and level flight. You are to use the airspeed indicator (speed increasing -> descent attitude -> ease back on the yoke until the speed reverses, and then damp on the speed changes) and the turn coordinator (showing a turn to the left -> you roll the plane to the right until you've gone past the no-turn position by about half a deviation).

The CPL is well fun, but on a 28h course (of which 6h are MEP course), it is a lot to do.
So far, I've been flying 17h, the 5h simulator (FNPT1, cf photos) part is now completed, and the 'in-house' profile test is due for tomorrow if weather permits.


Sandra said...

good luck for today!!!!

Tony Harrison said...

Wow, that is a lot happening! Best of luck with the test (should already have taken place) and that'll line you up for more training?

Makes me glad for the open airspace of Oz, we have a few restricted areas, but not much - those legs of yours sound frenetic!

Thanks for the post, and looking forward to more...

Golfcharlie232 said...

Thanks for the comment.
Actually, we had to cancel the test due to some pretty nasty weather.
I got to do a radar vectored ILS instead and I must say, it was incredible. The sight of the runway appearing in front of you ... that's just thrilling!

The airspace in the UK is not that full of restricted and danger areas to be honest.
I mean, if I compare it to that of France, it is a lot easier to fly around in England.

Any chance you could post a link of a OZ VFR chart ?