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I was wrong the other day... it seems I do need to cover the NZ low flying and terrain avoidance syllabus before they'll let me convert my license. In fact there are some manoeuvres in that course that are covered in the BFR, so yesterday I spent a good hour or so in our local low flying areas.
Wow.
Here the normal minimum height for flight is 500' above ground level - similar to the law in the UK - but that's relaxed in the LFAs. I wouldn't normally dream of flying so low, but knowing what to do is one of those skills that could save your life if you're boxed in by terrain and/or weather.
We fly at slow speed at low level. One of the net effects of this is to allow us to turn more tightly, but it comes at a price: we're also closer to the edges of the flight envelope. When making a turn, we bank the aircraft so that its lift vector - that generated by the wings - is no longer parallel to the gravity vector; the realigned lift vector "pulls" us round the turn, at the cost of sacrificing some of that force against gravity. At cruise speed this is fine; we are trained to apply a slight pitch up input to maintain height at the cost of airspeed. However at slow flying speeds you don't have that margin of airspeed, so instead you have to add power while you turn. (This is the same principle which says you have to increase power when carrying out a steep turn.) You have to be sharp with the controls: if you add power too soon or take it off again too late you'll speed up very quickly, widening your turn radius something rotten, but if you're too slow in putting it on or too quick to take it off again your airspeed can fall dangerously quickly.
So what did we do? First of all we went around the edge of the first local LFA to identify it for me. The edge of a forest, a hedge line, another hedge zig-zagging towards a triangular paddock, and back to the forest corner.
There's another wrinkle: the wind. As well as with airspeed, one's turning radius varies with the wind - for a given angle of bank, the radius will be tighter when turning the aircraft nose through the wind, and wider when turning the tail through the wind. This leads nicely onto one of the manoeuvres, the constant radius turn. That's just what it says on the tin; pick a ground reference point and adjust the angle of bank (and hence power too) to fly a circle around it.
We also covered the reversal turn. This is when you're following a line feature in less than ideal visibility, and something appears in front of you (bad weather, say) that causes you to decide to turn around. For the purposes of the exercise you imagine the visibility is poor in all directions and you need to keep the feature in sight in order to find your way home. It's a 180 degree turn, but The Rules of the Air dictate that, whenever possible, one should follow a line feature by keeping it on one's left: so the turn has to be planned so that you come out with the line on your left. In order to take account of the wind, you may need to first turn up to 45 degrees away from the line feature to put some space between you and it before carrying out the reversal.
There's also a variant on that theme called the coastal reversal. This is similar, but you imagine you're following a rugged coast, flying below ground level (as found, for example, in Fiordland). Obviously you can't keep the line feature on your left in one direction, but it's critical that you not overcook the turn - so you plan an escape route whereby you abort the turn if it looks like you're not going to clear the scenery.
Then we went off to the adjacent part of low flying area which runs up the Waimak river. It's a braided river, like so many on this island; the instructor had me pick a braid and follow it as closely as possible for a while, occasionally climbing because while I was holding station at a given altitude, the ground was rising to meet me as I flew upstream...
I have to do another two hours of that, then book one of the senior instructors to go and feel what the air is like in the mountains. Then, finally, I should be able to book my BFR.
Wow.
Here the normal minimum height for flight is 500' above ground level - similar to the law in the UK - but that's relaxed in the LFAs. I wouldn't normally dream of flying so low, but knowing what to do is one of those skills that could save your life if you're boxed in by terrain and/or weather.
We fly at slow speed at low level. One of the net effects of this is to allow us to turn more tightly, but it comes at a price: we're also closer to the edges of the flight envelope. When making a turn, we bank the aircraft so that its lift vector - that generated by the wings - is no longer parallel to the gravity vector; the realigned lift vector "pulls" us round the turn, at the cost of sacrificing some of that force against gravity. At cruise speed this is fine; we are trained to apply a slight pitch up input to maintain height at the cost of airspeed. However at slow flying speeds you don't have that margin of airspeed, so instead you have to add power while you turn. (This is the same principle which says you have to increase power when carrying out a steep turn.) You have to be sharp with the controls: if you add power too soon or take it off again too late you'll speed up very quickly, widening your turn radius something rotten, but if you're too slow in putting it on or too quick to take it off again your airspeed can fall dangerously quickly.
So what did we do? First of all we went around the edge of the first local LFA to identify it for me. The edge of a forest, a hedge line, another hedge zig-zagging towards a triangular paddock, and back to the forest corner.
There's another wrinkle: the wind. As well as with airspeed, one's turning radius varies with the wind - for a given angle of bank, the radius will be tighter when turning the aircraft nose through the wind, and wider when turning the tail through the wind. This leads nicely onto one of the manoeuvres, the constant radius turn. That's just what it says on the tin; pick a ground reference point and adjust the angle of bank (and hence power too) to fly a circle around it.
We also covered the reversal turn. This is when you're following a line feature in less than ideal visibility, and something appears in front of you (bad weather, say) that causes you to decide to turn around. For the purposes of the exercise you imagine the visibility is poor in all directions and you need to keep the feature in sight in order to find your way home. It's a 180 degree turn, but The Rules of the Air dictate that, whenever possible, one should follow a line feature by keeping it on one's left: so the turn has to be planned so that you come out with the line on your left. In order to take account of the wind, you may need to first turn up to 45 degrees away from the line feature to put some space between you and it before carrying out the reversal.
There's also a variant on that theme called the coastal reversal. This is similar, but you imagine you're following a rugged coast, flying below ground level (as found, for example, in Fiordland). Obviously you can't keep the line feature on your left in one direction, but it's critical that you not overcook the turn - so you plan an escape route whereby you abort the turn if it looks like you're not going to clear the scenery.
Then we went off to the adjacent part of low flying area which runs up the Waimak river. It's a braided river, like so many on this island; the instructor had me pick a braid and follow it as closely as possible for a while, occasionally climbing because while I was holding station at a given altitude, the ground was rising to meet me as I flew upstream...
I have to do another two hours of that, then book one of the senior instructors to go and feel what the air is like in the mountains. Then, finally, I should be able to book my BFR.
exhilarated