Navbox Just the Thing for Cross Country Pilots

To tell the reasoning behind the birth of Avec’s child, christened simply and descriptively the Navbox, doesn’t take long and is worth reading before you leap out and buy one.

The Navbox was invented- or at least the concept devised – by a pilot, for pilots. The reason for it was to get to the now of what your flight planning was all about – calculated position, updated and displayed in real-time on your WAC or whatever you use, as easily as zeroing a VOR needle.

The secret of Navbox’s success is its simplicity. It does one important thing – makes flight planning a necessity because you have first to make up your own strip map before fitting It into the Navbox.

The makers don’t make hairy claims for their product; it’s simply a device that makes D/R navigation an orderly business. It takes WACs, sectionals, locals and even nautical charts, with an aviation speed range from 90 knots to 540 on WACs, and 45- 270 kts on sectionals. The range on the WAC selection goes from 430 nm to 3333 nm, in case anyone thinks the Navbox is a toy.

Powered by a single Duracell 9 v battery, the little computerised navaid does its job with an almost awesome ease as we found out after reading the Manual and doing a dummy run.

The model we evaluated was apparently a Mk II in the series. The original Navbox had a Distance spindle instead of a rubber-padded knob, and a plastic outer cover which, according to the makers, tended to have an insignificant but unacceptable breakage component built into it- so an alloy cover ·has been substituted.

Despite its metallic content, you can stow your Navbox as close as about 6 in from the magnetic compass.

Avec takes great pains to advertise the fact that their little wonder isn’t the answer to everything one has to do in preflight and actual route-flying. And they sensibly add that the user must take adequate measures in advance to ensure safety in the event of a Navbox failure. Sensible advice, which is why we wouldn’t recommend it to students- although we know some pilots who jeopardise their safety by taking only one pencil into the air, without a pencil sharpener!

Now what’s all this Navbox business? When Australian Aviation first heard that Skygear International of Sydney was importing a test batch of Navboxes we made sure we were first in the queue for their first copy.

Unpacking the device disclosed a little thing looking rather about the size of an old Dalton knee-mounted CSC- or a small book, if you haven’t seen a Dalton.

We read the Manual carefully before trying the thing on for size- and that was one of the hardest things about the whole evaluation. However, some serious study (about half an hour) pays off before you take off the lid.

One of the ‘sensible’ bits in the Manual is the part where it emphasises that the Navbox enforces flight planning. And that enforcement comes in making up your own strip map.

We urge all Navbox users to use new or near-new WACs. We cut up an old East Coast WAC for our first attempt and the creases and tiny tears in it soon made it apparent we weren’t going to get anywhere.

A simple and sensible method of turning corners on your strip map is explained in the Manual, and one can make up to 20 ft of strip map. Try stuffing that lot into a knee pocket or somewhere out of the way in your cockpit!

Navbox comes with enough space inside it to stow the cutter, a Mylar template about 4¼ in wide, spare spools and perhaps a few Minties plus a spare transistor battery.

We eventually chose a WAC with a sentimental tinge about it – at one stage we used to help out flying newspapers up the North-West coast of Western Australia, and we had a spare WAC of that sector.

Cutting the strip map made it apparent there was enough space on it to plot a diversion 25 miles on each side of the track if necessary- and we fed in one or two during our ‘flight’ test.

Then, with the strip flight-planned (and we used the old ten mile tick markings on our track line to check out the accuracy of the Navbox’s speed meter) and installed in the Navbox with about as much ease as putting a film into a camera, we looked over the device in detail.

The Navbox we evaluated had a ‘windowless’ cover over the stirp map- we applauded that, and also the fact that the device was not fitted with knee straps. The logic behind the maker’s decision was that the Navbox, if strapped to a pilot’s knee, could impede wheel movement at a crucial moment.

Along one side of the Navbox are a set of controls – two knurled knobs permitting movement either way of the strip map; a distance knob which interconnects with a speed meter which itself has a needle indicating a 100-degree sweep/10 mins.

At this stage of development, the Navbox is still a manually moved map display. Automatically moving map displays get very pricey indeed these days, although development and technology could eventually solve that problem.

The only control having to be moved, apart from the strip-map display knobs, is the speed knob. It confirms ground speed when one re-sets at each subsequent checkpoint en route.

When you get used to operating your Navbox you can make your own chinagraph marks on the uncalibrated speed scale. We did this after the first two checkpoints and found it accurate to within a knot each side.

How does Navbox work?

In layman’s terms, you start the device when setting course over the top or on departure. You can expect a speed reading inaccuracy for the first period up to the first checkpoint.

While you’re doing that, a little distance wheel is being energised underneath your strip map, reading off how far you have flown – but it doesn’t really operate until you reach your first checkpoint.

OK, you arrive. Turn the strip map until that checkpoint appears against your reference point. Then zero the speed needle to give you an accurate indication of your ground speed from then on. The speed needle won’t give you a ‘figure’ reading of your ground speed- its speed range is too great for that as it has to cope with everything from slow nautical charts to WACs and sectionals.

You want to know when you’ll arrive at the next checkpoint? In our case, we set ten-minute intervals on our strip map, and scrolled the strip to our next checkpoint when we arrived over our current one. This sets the speed needle back below zero. At the end of ten minutes, the speed needle crept back to zero – in your actual aircraft, you merely look for your checkpoint when the speed needle zeroes in and it’s a pound to a pinch of snuff you’re right over it.

That’s what dead reckoning is all about. . .

Using Navbox makes all the difference between a sometimes awkwardly folded WAC and using a neat, centralised device that takes up about the same space as half of one of the new style VFGs- the ones in the new Dayglo folder.

Once again we urge Navbox buyers to really put some guts into studying the Manual first- tell the truth, we’ve been guilty ourselves of skimming through Manuals, thinking we’ve got the principle of the thing and then spending precious time having to read the Manual properly after a frustrating period of fiddling around with no real result.

It is not Australian Aviation’s intention to reprint the entire Manual, but come with us on a dummy run – that newspaper delivery route we mentioned earlier in this evaluation article.

We flight-planned from Learmonth to Port Hedland, using a handy ground speed of 120 knots after applying corrections for theoretical wind and temperatures:

We disregarded the hint that pilots might use the actual Mylar strip for plotting, after having traced the route on the Mylar fabric itself. We have had too many experiences of things being mysteriously rubbed out or vital figures disappearing off kneepads . . . !

We set the course over Learmonth at 0252, after setting what we thought might be a good speed mark on the speed wheel. What one actually does is to set a speed, any speed, and correct it by moving the pointer back to zero on reaching the first checkpoint or around the first 15 nm mark.

Oh, and we checked that our Sifeba plotter and doughty Douglas fitted and operated across the top of Navbox’s windowless window. They did.

At Time 02 we DR’d that we should be about halfway across Exmouth Gulf, with Simpson Island about six miles to starboard. On that DR mark, we adjusted our speed needle back to zero after finding it had slipped a little below the zero point when we wound on the ten-mile mark to the reference point- in our case the bottom frame of the window. (Avec say most pilots prefer to use the top frame, but we like to see a lot of where we’re going rather than a lot of where we’ve been. )

Time 12, and we DR’d that we were over the low-lying country and about abeam Troubridge Point after intersecting Tent Point. We adjusted the speed needle again- it was still running a whisker astern of station – and made a mark on the Navbox’s side to indicate that was the 120 knots ground speed mark. It stayed accurate to within a knot for the rest of our ground-bound evaluation.

At Time 22 we’d just overflown Five Mile Pool with Onslow about eight miles ahead, ground speed was spot on the mark at 120 knots.

Ten minutes later we were traversing Mangrove Passage, and just for kicks fed in a track drift of five miles to starboard. We used the Sifeba to work out a correction of 20 degrees to port, flew that for five minutes then resumed heading.

Amending our ten-mile ticks, we made the initial correction to recapture heading over the intersection of the Cane River and the telegraph line. At the point of resuming the original heading, we were abeam Middle Island in Mangrove Passage, with ground speed still spot on.

We had enough confidence in Navbox by this time to switch off, back-plot to Learmonth work out a new wind within a minute, and switch back on again.

We kept up our ten-mile checks on ground speed, stretched them out to 20 miles to give Navbox a better chance to settle down, and at Time 0302 decided to introduce a quick diversion around an imaginary Charlie Bravo about 20 minutes from Karratha, inbound. We swung 70 degrees off course, flying about 10 nm to hit Cape Preston after five minutes, then came back on our original heading plus 17 degrees (courtesy of Sifeba) to make Karratha with more amendments to our ten-mile check ticks en route.

(Don’t forget one has to attend to the engine, comm and other chores while playing with Navbox, but what an easy way to lighten the load rather than have charts parked every which way, and other paperwork stuck in every place from the coaming to one’s shirt pockets. )

At Time 32 we were seven miles from Roebourne, speed needle settled right down to hair’s breadth accuracy, with the same spot-on readings at Times 42, 52 and 0402.

If we’d needed Navbox any more after that we should have had our optics tested. Most pilots know the main road into Port Hedland like the backs of their hands, especially where it swings left to cross the Turner River just before Boodarie Post Office.

It takes time to appreciate this mini-computer, but by golly, when you’ve made its acquaintance- and have your own set of strip maps prepared if you’re a regular route pilot flying anything from a light single to a corporate twin, charter aircraft or third level type, you’ll really appreciate what Avec’s Navbox can and will do for you in terms of lightening workload.

All we used in our ‘flight’ was a flight planning sheet, the Navbox, a pencil, Sifeba and Douglas. No whacking great chart, no folding and unfolding. ·

There could be problems if one is called upon to divert more than 25 nm on either side of the track- and Avec also points out that their Navbox needs the usual care and attention most precision instruments desire.

They don’t like being left in the sun on a coaming for hours on end. They won’t run without a good battery; and like all electronic devices, it could one day fail – so any pilot using a Navbox must be prepared to do his own navigation at any stage.

We like the Navbox as a professional instrument worthy of special mention. It’s sensible, logical, accurate and well worth considering by pilots who believe there’s more to flying from A to B than just impressing the girlfriend or giving DoT Flight Service Units a lot of trouble by asking where the hell they are, or not bothering to lodge or make a flight plan.