Last Friday I took a slightly nervous flyer for a flight around Cornwall. It was a classic winter’s day: bright and cold with a few clouds sailing along serenely at 3000 feet on the brisk northerly wind. The wind was a bit of a problem actually, because we don’t have a northerly runway at Perranporth! The available runways are 05/23 and 09/27, so pretty much all crosswind whichever one you use. The official limit for our aircraft is 17 knots although I suspect it is often exceeded. Dealing with crosswinds is a skill one rapidly acquires when operating from a 300-foot cliff overlooking the Atlantic. More on this later.
So: we took off. My customer was initially nervous, but relaxed perceptibly as we climbed away from the ground. With increasing enthusiasm she started taking photographs as we cruised south towards St. Ives and Penzance. I have noticed that asking passengers to make a photographic record is a great way to reassure nervous flyers. They rapidly become so busy that they forget to worry about the height, weather, or the fact that they are in a small aircraft. Throw in a request to look out for other traffic, spot landmarks, or monitor the radio, and passengers rapidly become participants in managing the trip. As soon as they feel a measure of control, or gain more understanding, a lot of the initial panic seems to disappear. And we got some nice pictures of the old tin-mines with the low winter sunshine casting long shadows from the engine-house chimneys.
Anyway: back to our round-Cornwall tour. We admired Penzance, and then St. Michaels Mount. The tide was in over the causeway linking the island to Marazion and little boats were busily ferrying visitors across to the castle. After Marazion we were soon searching for Pendennis Castle at Falmouth. There wasn’t a lot of traffic about, so the radio was quiet which was nice. The RNAS airfield at Culdrose was closed [naturally: it was a Friday afternoon!] so no problem crossing the MATZ[1]. If I were going to invade the UK I’d choose a time between Friday lunch and Sunday evening: most RAF and RN airbases seem to close down promptly at 1400 for the weekend.
We trundled peacefully towards St Austell and made a short diversion to look for the domes of the Eden Project. These are surprisingly hard to spot: for some reason they have built the big glass domes in a hole in the ground! There didn’t seem to be many visitors in the gardens but it was a cold day. 1 at 2000 feet, but of course feeling much colder in the wind chill.
After St. Austell our route took us across Cornwall to the north coast near Bude, where we played the game of spot-my-house. For those who’ve not tried this pastime it can be surprising how unfamiliar a well-known locality can look from the air. What seems like a steep hill on the ground looks almost flat from the air, and sharp bends in the road become no more than gentle changes of direction.
Our return journey took us down the north coast past Padstow – a pretty fishing town –
and the resort town of Newquay. We had to pass Newquay airport, which was busy with commercial traffic. The three choices for passing Newquay are to divert inland, or out to sea, or climb to pass high above the runways. I always ask Newquay’s air traffic controllers which they’d prefer, and on this occasion we were asked to transit at 4000 feet which took us up through and then above the clouds, with occasional glimpses of the ground half-a-mile below through holes in the overcast. My passenger really enjoyed this bit!
Once past Newquay we made a rapid, ear-popping descent back down to 1000 feet before joining the Perranporth circuit.
By this time the sun was very low on the horizon, and the downwind leg for runway 05 was directly into the glare which sparkled off the scratched Perspex. It was like flying into brightly-lit fog. Luckily the turn onto our final approach put the sun behind us – I would not have enjoyed an into-sun landing in those conditions.
By this time the tower was reporting a steady 23 knots of wind from the north … a serious crosswind. To add to the fun, Perranporth offers some from interesting wind-shear effects when the wind is either north or south, due to the airfield being on a piece of flat ground bounded by steep-sided gullies on both sides.
Windshear is a rapid variation in the direction and/or strength of the wind with height. It is most important when taking off and landing, because that is when the aircraft changes height most rapidly.
Sailors think they know all there is to know about wind: it has a strength, and a direction. It may be steady or gusty. Essentially though wind on the surface just boils down to how strong it is, and where is it coming from.
As soon as you venture aloft you realise there is a third component to wind. It doesn’t just blow along, but up and down as well! Look at blowing leaves in the autumn: some are tossed high into the air, while others are forced down into the gutters. Winds blow vertically as well as horizontally, and this affects pilots.
Picture the north wind as a fast-moving river of air roaring across the Atlantic. There’s nothing to stop it until it meets Cornwall, when suddenly it finds a cliff blocking its path. What is the wind to do?
It can’t go back: the on-rushing air behind won’t let that happen. It can’t move the cliff. So the wind does the only thing that is left: it executes a neat right-angled turn and blows upwards. Stand on the cliff edge on a windy day and you can see it happening as seabirds and bits of foam shoot up into the sky.
What goes up must come down, so the wind doesn’t go on rising for ever. A few hundred feet above the ground the wind curls over like a wave, and a “rotor” forms: a rotating tube of air like a never-ending invisible breaker along the cliffs. Close to the cliff edge the wind may be moving up. Further away a down-draft will form. Now imagine a plane trying to fly through this invisible air-rotor. In one place the pilot will find himself going up, and then a short distance later descending rapidly towards the sea … this is why wind matters, and is why pilots often obsess about it.
North winds flow across the Atlantic, hit the cliff, and are deflected upwards. Southerly winds stream across the airfield and cascade off the cliff-edge like an invisible waterfall of air. In either case there is windshear, and at Perranporth the effects of windshear are complicated by the steep-sided gullies running down to the sea. As you pass over the gullies there are strange and rather unpredictable updrafts and downdrafts. The pilot has to react to all of these phenomena during the final stages of the approach.
Suffice it to say that it wasn’t one of my better landings,
but we got down safely. Which is all that matters really!
[1] MATZ: Military Air Traffic Zone