Mini flight reports:
Headcorn in poor visibility

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To Headcorn and back - and a rant about poor visibility!

22nd February 2003

Non-flying folk just don't understand visibility, do they? It's a warm sunny day with not a cloud in the sky - and you meet up with your mates with a grumpy look on your face. "I thought you'd have gone flying on a lovely day like this, Dave!" they all say, and you complain bitterly at how you can't see your hand in front of your face because "the vis is cr@p".

Today was one of those days, and I'd planned to fly down to Goodwood and on down to the south coast. I knew the visibility was going to be below par (to a pilot that means less than about 10km) but today it was worse than forecast. Mid-morning, Gatwick was reporting visibility of about 2500 metres - which is below the legal minimum for me to fly. It was gradually improving, but very slowly. By about mid-day it had crept up to 6000 metres, which is still bad enough to make navigation really difficult. So I decided to scrap the idea of Goodwood and instead go to Headcorn.

Two parachutists landing at Headcorn

Getting to Headcorn from Redhill is easy-peasy - you can simply use the "British Rail" school of navigation. There's a railway line that runs in a straight line between Redhill and Ashford, with Headcorn right next to it. By choosing such an easy route, I used this as an opportunity to gently stretch my personal weather limits and fly in visibility that was worse than I would normally contemplate.

Headcorn's a good place to sit in the sun and watch the aviation world go by. It's a busy parachute-dropping site, and there's nearly always somebody doing some aerobatics in the vicinity. The picture of the parachutists landing (right) shows just how gloomy it was in the haze.

So why is visibility a problem for pilots? Allow me to try to explain...

Most people would probably say that 3km visibility is not bad, and 6km must be fantastic. In everyday life or when you're driving a car, you find your way around by visual reference to the things around you. You recognise buildings, trees, the shape of the road - and of course you can read road signs. But all these things are probably within a few hundred yards of you, so 3km visibility is vastly more than you need. You don't get lost walking to the bus stop even in fog, because you can still see your neighbours' houses even if you can't initially see the bus stop itself - and that's enough for you to find your way.

When flying an aircraft and navigating visually, you do much the same thing. You find your way around by visual reference to what's around you (cross-checked to a chart, of course). But from a few thousand feet, you have to use features that are much further away - like the shape of a whole town, or the relative position of a lake with a road running to the south and a railway line to the west (for example). All these things are literally miles away - yet they're the only things that can tell you where you are (unless you cheat and use GPS!). The nearest object is right below you - but even that is nearly half a mile away (downwards!), and the chances are it's "just another field" that simply isn't marked on your map.

G-BSEP parked at Headcorn

Knowing where you are is only half the problem. Seeing and avoiding other aircraft is difficult even in good conditions, but it becomes really hard in poor visibility. When you're driving a car, you rely on the fact that oncoming traffic will stay on the other side of the road. But in the air there are no "roads", and traffic can be going in any direction. So your attention has to be spread over the whole 360 degrees around you.

If you have two modest single-engine aircraft heading straight towards each other, their closing speed is over 200mph. If the visibility is 3km, you have about 30 seconds before impact - and that's assuming you spot each other immediately (which you won't when you consider all the other things that occupy your mind when you're flying - map reading, radio, engine and fuel management).

There! I've got it off my chest! That's why pilots need much better visibility than you'd expect. Coming home to Redhill the visibility was truly appalling against the sun - probably down to about 3km, or even less (ahem... and therefore possibly not legal). Deciding to stick to an area I knew intimately was a sensible choice in these conditions. When I got to Redhill I was asked to hold at Godstone near the edge of the ATZ, and still I couldn't actually see the airfield even though I knew exactly where it was. Definitely not a day to be navigating!