navigation ... the big picture

Irv Lee offers confidence for those who find navigation an uncertain business.
reproduced from GASCO

Irv Lee works mostly out of Popham, which is an unlicensed airfield that is the base for some 110 aeroplanes and microlights and has a club with around 500 members. You will find it by road or by air half a thumb south west of Basingstoke, ' just off the A303. Why do I speak , in thumbs? Read on.

Irv is an experienced instructor who gave up a successful career in IT to offer instruction and advice to pilots who already have a PPL, but want to extend their experience and skills. You may have encountered him as part of the Flying Doctor series in Flyer magazine and full details of what he offers can be found on .

This article sprang from a chance conversation between Irv and myself on the thorny issue of navigation. I asked Irv whether the introduction by the CAA of a navigation leg in the requirements for a revalidation or renewal test was causing any problems for PPLs. I asked the question because on the website there is frequent discussion on how it is that PPLs keep busting control areas with such sad regularity and why poor standards of navigation are so common. I seemed to touch a sensitive spot here, and Irv reported that he does encounter PPLs whose aircraft handling skills are fine, but whose navigation is substandard. Can I use GPS?, was the question most frequently put when a pilot discovered the new requirement for the navigation leg.

In parenthesis, I should explain at this point that if you are one of the many who revalidate their PPL by flying at least 12 hours in two years and take a flight with an instructor (a revalidation flight) during that time, then that instructor may not seek to explore your navigational ability. But if you are one of those' who, for all sorts of reasons, needs a revalidation or renewal test, then you will have to undertake the navigation leg and a fail in that will mean an outright fail.

Whatever the regulations may require, it does seem to Irv, and to me a sad state of affairs if there are many pilots amongst us whose handling skills are good but whose navigation is too uncertain for them to contemplate leaving their local area without the help of GPS. The pages of this magazine are often filled with the forthright comments of both the supporters and the decriers of GPS. Irv Lee is one of the supporters but neither Irv nor any other supporter claims that pilots should put all their trust in GPS and make no check of their navigational progress by other means. For the VFR pilot 'other means' must almost always mean visual navigation, that is to say, the techniques that we were all taught in order to get our licences in the first place.

A lot of the problem, as Irv sees it, is that the standard VFR navigation techniques - the whizzy wheel, the stop watch, the compass and the map with its track and 5 degree and 10 degree off track lines - leave many PPLs feeling defeated and confused. You study the Met, you draw all those lines, you whiz the wheel and you end up with a heading of 248 degrees and a time to the first checkpoint of 13 minutes. You fly, as best as you can, 248 degrees for 13 minutes and there you are, uncertain of your position again. You fly on for a further 5 minutes and things get no better, so once again you sadly lament your failure as a navigator and your utter reliance on your GPS set, whether it is right or wrong.

Irv acknowledges that the classic VFR navigational techniques, with all their absorbing detail, are meat and drink for some PPLs. Their plots before the flight are masterpieces of intricacy and their flight logs after the flight are miniature copy books, straight out of a manual of navigation. For others, however, the flight log ceases somewhere about the first checkpoint as the pilot searches in vain for the cross between a river and a railway line that should have appeared. Four minutes after the ETA has passed that pilot eventually comes across a river and railway line cross, seizes on this without further checking and steams off on the next section into the even more unknown. At that point, as confusion and tension heighten, any further attempt to maintain a log is abandoned.

If your own navigation sounds more like the second version above, take heart. It may be that the classic technique is not really for you and you need to try something along the lines of Irv Lee's Big Picture navigation. If this sounds like an easy cop out for simpletons, take heart. A millennium or so ago, I was taught something very similar in the RAF. They called it Pilot Nav, and they argued that someone hurtling around the sky in a single seater would have neither the time nor the inclination to dwell upon the minutiae of navigation and so they made us simplify the whole procedure and, in effect, to think mostly about what Irv now calls the Big Picture.

A more defining title for this method might be termed, When Airborne, Approximate and Simplify. So you do all the pre flight planning and preparation as you have always done, but in the air you concentrate on the Big Picture and avoid too much confusing detail. For example, your whizzy wheel commanded a heading for the first leg of 248 degrees, but consider in practice, what this will mean. If you set out on a heading of 248 degrees, how closely will you actually fly to this figure, assuming that you will also be dealing adequately with all the other tasks of the flight? You will do well to end up averaging a heading of anything between 245 and 250 degrees.

And how did you arrive at this magical figure of 248 degrees in the first place? Well you fed into the whizzy wheel a True Air Speed (TAS) figure whose accuracy much nearer than, say, two or three KTS either way must be questionable. Worse, you fed in a forecast wind, but how confident are you that the actual wind has turned out the same as was forecast?

"Life's too short", says Reggie Bender, "to phone 0500 354802 before take off "

So, after allowing for vagaries in your heading keeping ability, the variations from your plot figures of TAS and wind speed and your invariable failure to apply the compass deviation shown on the card near your aircraft's compass (does anyone?), you cannot regard that 248 degrees as anything more than an approximation anyway, no matter how much care you may have put into its original calculation. So the Big Picture is that you are setting out on your first leg on a roughly WSWIy heading which should take you roughly in the direction of the first check point but do not imagine that the features that lie along your carefully drawn track line are going to pop up, one by one, as the flight proceeds. Look upwards, Big Picture pilot, if not to the skies, then at least towards the horizon and navigate as much by what you see there as by what lies directly beneath.

The smart new Pilots' Briefing Room at Popham.

There's a range of hills coming up on your right in the middle distance and that must be the Quantocks, there's a whole lot of flat countryside beneath with no particular features but on this heading you will meet the M5 before long and will then be able to identify Bridgwater or Taunton. So meanwhile, although you cannot tell precisely where you are, you know where you are going, so you will stick to your heading, keep scanning the horizon for more clues (the Bristol Channel coastline?, the Blackdown hills?) and expect to cross the M5 in six minutes time. If you cannot see it in three minutes, something will be amiss and you will have to take action (e.g. climb in a circle while looking for more clues, seek help from Yeovilton LARS, or call Distress and Diversion on 121.5 - they genuinely welcome a little challenge). Meanwhile, you should just check that six minutes to the MS estimate. Refer back to the last definitely known position (that's 'definitely', not `probably') and apply Irv Lee's Rule of Thumb.

Your typical six minute thumb aeroplane. (W J Bushell)

Irv Lee's Rule of Thumb is both simple and effective. It says, quite simply, that, with neither headwind nor tailwind, you fly across the map at the rate of 6 minutes per thumb. How does he know that? Because as well as having a degree in Aeronautical Engineering, he can do simple arithmetic. Your average light aeroplane cruises between 90 and 110 KTS and your average thumb's knuckle to tip measures about 10 n.m. on a half mill map. 10 n.m. is about one tenth of the amount the average light aeroplane does in an hour and one tenth of one hour is six minutes. Irv's case rests: in no wind one thumb equals six minutes.

Sticklers for accuracy can make their own adjustments to this Rule to match their own particular thumb/aeroplane combination and we must all have our own still air thumb time to start from. A large thumbed goalkeeping giant flying a flexwing might have an 12 minute thumb, while a small thumbed petite lady flying a Columbia 400 might have a three minute thumb but for most of us it is going to be pretty close to six minutes.

That's all very well for the no headwind or tailwind situation but for most of the time we have that factor to take into consideration. Here's how a Big Picture navigator works out the effect of a headwind or tailwind once airborne. You start with the forecast wind: let's say it is 280 deg/ 20 KTS. If your heading is 248 deg, the wind is about 30 deg off the nose. Common sense tells you that if the wind is in exactly the same or in exactly the opposite direction as your heading, you must apply all of the wind as your headwind or tailwind component. As for other wind directions, you must either commit the next bit to memory or write it down on your knee pad:

If the wind is 45 deg off your heading, allow three quarters of the wind for your headwind/tailwind component and if it is 60 deg off, allow half. Interpolate (i.e. make a rough guess) for anything else.

These fractions are not absolutely accurate (but then, nor is the forecast wind) but they are near enough for Big Picture nav. So in the case in point, we are looking at nearly 20 KTS of headwind, in which case our ground speed is going to be around 80 KTS and one thumb will then represent 10/80 ths (one eighth) of an hour, or 60/8 minutes, or 7Yz minutes. If you want to devise a table of thumb distances for different ground speeds, you can, but you might well do better to keep things simple and to just reckon that if you have a substantial headwind on a leg, your minutes per thumb are going to be a fair bit more than the standard six: say, seven or eight minutes in this case.

A thumb will be worth more than six minutes in this one. (W J Bushell)

Are you getting the idea? When airborne you deal all the time in approximations and in that way you keep yourself in touch with what is really going on in practice, and you don't bother much about the theory. Always consider what the wind is doing to you and what the appropriate number of minutes per thumb should be on each leg.

Drift is the other issue to consider. A 100 KTS aeroplane suffers 3 deg maximum drift for every 5 KTS of crosswind. So a 10 KTS crosswind will give 6 deg maximum drift and 20 KTS will give 12 deg. That works just fine for a crosswind blowing at 90 deg to our heading, but what about crosswinds from other directions? In our example, the wind is 20 KTS, so that could cause drift up to a maximum of 12 deg, depending on the wind's direction in relation to our heading.

This is the Rule:

Allow half of the maximum crosswind at 30 deg off and all at 60 deg off or more. Interpolate in between.

Again, these are only approximate figures but they are good enough for the Big Picture.

The maximum drift from our 20 KTS wind is 12 deg and our  280/20 wind is blowing at 30 deg to our 248 deg heading. We must allow half of the maximum for a 30 deg crosswind so we must allow 6 deg. So lets try that again with a wind this time of 145/25 on our 248 deg heading.

The wind direction is 100 deg less than our heading, so that means that there is virtually no tailwind component and our thumb will represent six minutes on this leg. At 3 deg max drift per 5 KTS of crosswind the 25 KTS crosswind will create 15 deg max drift. The crosswind is well over 60 deg off - nearly 90 deg in fact - so we take the maximum of 15 deg and we steer, say, 235 deg (once airborne, life's too short to worry about intervals of less than five degrees).

So that is all that you need to know about time and drift. Of the two, time is probably the more important. Unconfident pilots usually manage to fly within a reasonable corridor along the planned track, even if they fail to identify any part of the terrain beneath at times. (They would be wise, in any case, to look out for any features within, say, 10 n.m. of the track line and thus allow for a bit of wandering from track.) However, they can easily become fixated on just sticking to their heading, sometimes well after the ETA for the next waypoint, in the forlorn hope that the waypoint is going to appear magically at last. So be disciplined about your ETA and if the waypoint fails to appear on time, do something positive.

Always consider what the wind is doing to you and what the
appropriate number of minutes per thumb should be on each leg.

Irv Lee's Higher Plane seminar takes a whole day and navigation is only a part of it. This is not the time to stray into other issues, but here are two that have an important bearing on navigation and should therefore be mentioned.

The first is the forecast wind. Most pilots use Metform 214 as their source of information here and tend to regard its word as gospel. Excellent as our Met Office is, their Metform 214 needs the application of some caution before using any wind forecast. Looking at the spot wind forecast at 0845Z today for the winds between 0600 and 1200, I see that the nearest box is forecasting a 2,000 ft wind of 270/10. So if I am going to make my flight later this morning, that is the wind I should use. Or is it? Consider some other factors: the next nearest box, not much further away than the nearest, shows VRB/10. The forecast is dated 0312Z so by 1200Z the forecast will be nine hours old, and an awful lot can happen to our British weather in nine hours, some of it sometimes unforetold.

Still a six minute thumb for this one - but all three thumb sections in this case. (via W J Bushell)

Irv Lee therefore counsels a reality check before take off. Find out what is the surface wind at your departure airfield. Do you recall that during the day the 2,000 ft wind is usually about 30 deg more and is double the strength of the surface wind, less 10 per cent? Apply those figures to the current surface wind and compare the result with your forecast wind. If they differ significantly, then ignore the forecast wind and use your new calculated actual wind; it will be far more accurate.

As you fly your route, do not imagine that the 2,000 ft wind will necessarily remain constant but put your faith in observation of the wind effect on the first thumbful of each leg. That is the most accurate forecast wind that you will ever get, and you don't have to make all those theoretical calculations, you just observe that this leg is giving you a five and a half minute thumb and a bit of drift to the right.

Find out what is the surface wind at your departure airfield.

The final issue is NOTAMs. Getting hold of NOTAMs can be difficult and deriving useful, relevant and practical information from them can be even more so. Consequently an awful lot of pilots do not even try. The result of busting a Temporary Restricted Airspace (a TRA is usually a Royal Flight) could be bad enough but what might happen if you were to find yourself in the middle of a Red Arrows display scarcely bears thinking about. Nonetheless 14 hapless pilots have bust Red Arrows displays in the past three years. Fortunately there have been no mid airs so far, although several PPLs have been severely punished. Irv's point is simple: while there may be some rather unconvincing excuses for not getting and understanding NOTAMs there can be absolutely no excuse for not, at least, phoning 0500 354802 for information on TRAs and Red Arrows displays on that day. It's free, it takes only about a minute, and pilots who cannot be bothered at least to make this simple check before take off will have few friends if their idleness leads to a Red Arrows bust.