Using nature to navigate a small aircraft

Below is a transcript of an article written by Tristan Gooley and published by the Royal Institute of Navigation in Navigation News June 2004. To obtain a copy of the original article contact the RIN

In some ways my efforts to improve as a pilot had made me a worse one.

After a couple of years dominated by instrument flying and the luxury of a GPS back up, I noticed that my visual awareness of what was outside the cockpit and on the ground was suffering. In fact this reached such a low point during an instrument flight check that as we taxied out in a Seneca at Bristol, the examiner pointed out that it was difficult to see clearly out of the cockpit due to the melting ice in front of us. I had wrongly thought that because I felt I could see enough to get us airborne safely and would then transfer to instruments, the condition of the windscreen was not of great concern. The examiner put me straight pretty sharply, ‘You wouldn’t dream of driving looking through that, so why on earth would you consider flying?” He had a very good point and fortunately after clearing the ice things went more smoothly.

It was time to make amends, time to take a really good look outside the cockpit. What could I deduce without the GPS, the compass, the DI, the clock?

The inspiration for this trip came from the writings of the legendary navigator, Harold Gatty, which are a must-read for anyone who feels strongly that the GPS is not the be-all-and-end-all of navigation. I wanted to try to spot some of the clues that he would have noticed – this would be a flight with the spirit of Harold Gatty on the back seat. (Referring to the Pilots’ Operating Handbook for the Piper Cherokee PA28 180 and finding no mention of spirits, I decided that it would not be necessary to amend the weight and balance calculations.)

The planned flight was from White Waltham near Maidenhead to Perranporth on the north coast of Cornwall. For safety I would of course refer to the chart and all my instruments and plan for the flight using the standard methods, but I was curious to see what it would be possible to tell if they weren’t there. At two-hundred miles and crossing no oceans, it may not have been the sort of trip that would get Mr Gatty too excitable, but it would be a big enough helping of land, coast and sea to take in plenty of new sights.

After the walk round on a sunny Saturday spring morning, I climbed in to G-AVBG with Ross, who had volunteered to join me as photographer and second pair of eyes. Lining up alongside runway 25 at 08.55 was the first opportunity to take note. The windsock was limp which was to be expected as we were near the centre of a high pressure system and the accompanying light variable winds dominated. Glancing back to check we were ‘clear behind’ for the power checks, we squinted into the bright sun and confirmed nicely that we would indeed be taking off in a westerly direction. At 60 knots one of the bumps on the grass strip helped us on our way and our shadow raced off in front of us.

After departing the circuit to the west it was time to take the first good hard look at our surroundings. Despite a little haze, the visibility was good and this would be crucial for this exercise. Natural navigation usually relies on using the five senses and we would be hard pushed to make any use of four of them. Although the sound of the engine and the feel of the controls are used instinctively to monitor the aircraft’s performance this is not usually done for navigational purposes, they form part of the first and most important of the mantra: aviate, navigate, communicate. As for the other two senses, the not-recently-refurbished cockpit of a 1968 Piper is unlikely to treat the pilot to any enlightening tastes or smells.

The railway line that runs between Reading and Newbury is known to plenty of London commuters, it is also well known by the members of West London Aero Club as it skirts the northern perimeter of the White Waltham airfield. It could be clearly seen as a line etched in the ground and leading off to the south-west. Our first pass over the Thames came a couple of minutes later with Henley clearly visible over the starboard wing. Henley is easily identified by a pilot flying over it for the first time because of the way the built up area is positioned in relation to a sharp bend in the river, it also has well defined road junctions and a bridge over the river. It is a fantastic example however of a place that is identified in a totally different way by a pilot who knows it from the air, the unmistakeable Temple Island stands out like a beacon – a godsend in poor visibility. Something I noticed for the first time however was the direction of the stream and since the river is non-tidal here it could be relied upon as a signal – up or downstream, or in very broad terms – towards or away from London!

We crossed the Thames again less than ten minutes later and a visual fix was easy as the river was kind enough to line up with a road, a railway line and a village either side of it at this point. We felt very happy with our early progress, but whenever I spot a river I am reminded of one of my favourite Gatty tips for when you feel really lost, ‘in nine cases out of ten rivers will lead, if not home, at least to someone else’s home.’

This close to London there is a wealth of man-made features to chose from and at times there can be too much; the ground below you can seem cluttered as it takes time to filter out useful sights. Clearly identifiable landmarks are always welcome however and there was no shortage of these. The disused airfield at Welford passed under the starboard wing, followed shortly by junction 14 of the M4 and then if we had still been in any doubt as to our location the 500 foot high mast at Membury appeared in our 2 o’ clock. High masts are a good test of both your confidence in your position and the visibility. When you know where one should appear and it obliges in good time, it is a wonderful feeling. When you are less sure of your position and it is hard to see enough to get a good fix you would rather they just were not there.

Trying to remain in open airspace we worked our way into a funnel as we headed west. To the south and north we were squeezed by military zones with a sprinkling of danger areas for good measure. Just as we were enjoying the view of one of the white horses between Marlborough and Devizes, I thought it was time to take that step further and see what our chances would be without this wealth of man-made features.

The funnel we were passing down was also a physical one. The Vale of Pewsey with higher ground to the north and south was as clear as a signpost for the track we wanted to follow. It was no coincidence that the railway and a lot of water followed this path also.

The natural clues were not confined to the ground: the first clouds were now visible in a predicted layer between three and four thousand feet. It was still well before midday and the eastern edges of these ‘few’ cumulus clouds were well defined and were noticeably brighter than the western sides. The shadows of the clouds were also clearly visible on the ground to the west and slightly north of them. It may just have been possible to navigate roughly west using just these aerial signposts, but the shadows of tall features on the ground would have been a better guide.

Nature is sparing with straight lines and a straight river stands out like a Roman road. One of the canals between Taunton and Glastonbury bore the hallmarks of man’s intervention and our track took us perpendicularly over it, giving us an excellent check on our heading. We were getting well away from sprawling suburbs now and a technique that is useful to all pilots and invaluable during night-time flying becomes easier to use. Nearly all towns have a distinct shape, a kind of fingerprint, which can be used to both identify them and check your heading. A fat old finger of Taunton pointed us on our way.

Passing over the M5, the coast which had been clearly visible to the north, became briefly visible to the south also. Any navigator who could not have picked a westerly course with west-east coastlines visible on either side should not be allowed in the air and so on we trundled confidently towards Exmoor. Here the shape of land helped our cause again, as we dissected the horse-shoe of high ground that curves round from the Ilfracombe area to the east and then back round west to the Eaglescott airfield. When the ground started to look ominously featureless compared to the Thames valley, the prominent Wimbleball lake in the centre of this high ground confirmed we remained on track and its unusual mutated ‘L’ shape helped check the heading also.

One of the aspects of navigation that is the same whether you are in an aircraft, on a boat or on land is that it is often easy to find the coast, it is sometimes more difficult to work out exactly which bit you have found. The good visibility made this much more straightforward than it could have been. We planned to coast out briefly at Clovelly near Hartland Point, but as we approached it Bideford Bay and its estuaries opened up in front us magnificently. The shape of the estuaries was all the confirmation that was necessary, but a bridge appeared where it should have been at Westward Ho! just to add to the picture. Then Lundy Island appeared in the dark blue waters to our right and the incoming tide left a wake around it pointing out to sea. The architecture must have been changing gradually since we set off and a better-trained eye would have noticed more subtle differences, but no-one could mistake the metamorphosis as we passed the coastal holiday and retirement resorts, neat rows of light and bright low-rise buildings.

The final leg was a south-west run down the coast to Perranporth and could not have been simpler. This gave us more time to search for the small details. In one of the small bays between jutting rocky peninsulars there were some unusual patterns in the water, which no doubt local fishermen would have been able to deduce much from, but which remained a mystery to us. We also saw some interesting bird life, but struggled to identify it. I knew from reading Gatty’s books that we should be able to learn lots from these details, but my lack of knowledge in this area let me down.

Recovering from this setback I noticed a thick plume of smoke rising from a farm on the coast near Bude and it was not going straight up. After flying in a westerly direction for two hundred miles we had reached out from the centre of the high pressure and there was a clearly visible element of south-easterly in the slightly stronger winds.

The approach to Perranporth’s runway 09 in a light cross-wind was a good challenge because the finals take you from the sea over the cliffs. Just when it seemed that the senses could offer no more clues, our sense of touch offered us our final reminder, albeit through our backsides. As we passed over the cliffs some gentle turbulence confirmed that we were passing over the cliffs.

Shutting down and climbing out there is always that sense of a successful navigation exercise when, by using all the senses available, you take in your surroundings and agree that you have indeed arrived at the destination you wanted to be at.

Over a cup of tea on the ground I thought about the things that I had noticed, but not understood – the birds and the patterns in the sea. I wondered about all the things that I had seen but not taken proper note of, things that Harold Gatty undoubtedly would have done. Instead of being frustrated they were comforting to think about, if the mysteries of natural navigation could be mastered easily I would have one less excuse for going up again.

Gatty once wrote, ‘In our increasingly urban civilization the necessity of observing and interpreting nature’s signs is, I suppose, slowly disappearing.’ He wrote this long before the advent of GPS, which might have added to his concerns. I am not concerned, the enjoyment and better understanding I gained from reawakening my senses will be with me for a long time.

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For a complete guide to Natural Navigation read Tristan’s books.