Francis Meyrick

Moggy’s Tunaboat Helicopter Manual “GPS 4-3 “

Posted on April 13, 2010

Moggy’s Tunaboat Helicopter Manual

Section 4. GPS Systems and Offshore Navigation Issues

4-3 Digital Select Calling, the Ross DSC500, and other clever stuff

Okay, we’ve given you some anecdotes, to wet your appetite, now for some clever ‘technical schtuff’
To recap, these days just about everybody uses GPS systems. There are a few purists left, amateurs flying open cockpit biplanes perhaps, gaily flaunting silk scarves, determined to buck the trend. But the rest of us have succumbed. They are reliable, easy to buy, and make for much more relaxed flying. Maybe they are TOO damn reliable. When they fail, as any man made device surely will, one day, and if you are sixty miles from the ship when it happens… it can surprise you.

Coming out to the ‘tuna fields’ you absolutely must have a good understanding of Latitude, Longitude, meridians and parallels. You must be much more than just a ‘blind number plugger’ who only is capable of plugging in numbers into his GPS, and blindly following them, like a little puppy behind its master. Just typing in numbers, and then meekly following those numbers, makes you a SINR. (situationally ignorant number runner) It is going to bite you. Sooner or later. You will get away with it hundreds of times. To the point where you think you’re actually an ace. Then, one day…

Let me just mention that it’s all too easy to get into this habit, and forget even the basic stuff. On one of the ships I worked on, the captain told me he had to explain meridians and parallels to his pilot. He showed me -in some disgust- the drawings he used. Some real, real basic stuff. This pilot (he got fired) was a prime example of a SINR. Oh, and he got lost as well, and had to land on the water, on several occasions…

Technology marches on, and new stuff comes on the market all the time. I’ll describe to you the ‘Ross DSC 500’ set up, which I used 1996 to 2000, simply because it illustrates the principles. You may see one, or you may never see one. But if you get the general idea, it will help you master whatever clever gizmo system is fitted to your helicopter.

The Ross DSC 500

‘DSC’ stands for ‘Digital Select Calling’. There is no substitute for studying the manual, but just to give you a nibble at the pie, here are some bare basics. These ‘basics’ do not in anyway presume to supplant careful study of the manual….!
1) Bottom right hand corner, you will see a button labeled FNC. (Function)
Press it.
2) Middle bottom, you will see a button with above it the label DSC. (Digital Select calling)
Press it.
3) There’s a ‘left arrow’ and a ‘right arrow’. Press the ‘right arrow’ three times.
You will go to ‘request position’. (via ‘DSC calling’ and ‘send position’)
4) Press ENT (Enter)

What you are now doing is requesting the ship to pass you its position. Assuming they have the corresponding Ross Radio unit on the bridge switched on (one dozy old navigator I had repeatedly either forgot, or switched it off during the flight), you will, after a few seconds, hear an annoying ‘deedle-deedle-dee’, after which the ship’s latitude and longitude will flash up on the screen.
Poof! Magic! Just like that!
If your ship is out of range, or if your dopey navigator has accidentally switched the ‘twin’ Ross Radio unit on the bridge off, you will get a cryptic ‘no response’. If you want to, you can try again. This time though, you don’t have to go through all that palaver again. Just press ENT (Enter). Sometimes the buttons are a bit funny, and you have to press smoothly but firmly.

One other function useful to know: pressing EMERG (Emergency) for FIVE seconds, as I understand it, will broadcast a MAYDAY to any station fitted with a Ross. Even if they are not on Channel 16, their radios will automatically flip to ’16’ and display a message:


…with your position in latitude and longitude. Comforting, and nice to know, eh? There is also an earsplitting warbling screech that wakes everybody up!

So now…. we at least know where the ship is. This information is not worth a tinker’s curse (Irish panhandler/beggar/philosopher type) unless you know where the helicopter is. This is where your GPS comes in. I’m tempted to assume everybody knows the next bit, but just in case of a student who does not, bear with me while I spell it all out.

To set up the GPS you need to know whether or not your GPS has a clue which Ocean you are in. That may sound laconic, but you must know that the first time a GPS hand held unit has to figure out where it is, may take a long time. Technology advances in leaps and bounds, and millions and millions of calculations can now be done blazingly fast. In 1996, 1997, 1998, I was using units which took a long time to initialize. Up to thirty five minutes or so. After that, it’s quicker, maybe two minutes or so.
What I did then with my GPS (in those days, a ‘Trimble Transpak II’) is this:

1) after start, after the helicopter generator comes on line, and after that nasty initial current surge has settled back down, I switch the avionics on, and the GPS I select “STS “. (STATUS)
This step is not necessary. You can skip it. I do it, because it’s fun. I still do the equivalent today, April 2010, here in the Gulf of Mexico on my Bell 407 Garmin GPS.
2) We are interested to see if the beast has managed to ‘capture’ any ‘space vehicles’. Satellites to you and me.
Depending on what unit you are using, it may tell (or visually show) you something like this.

tracking 0 space vehs.

After a while,it will track 1, then 2, then 3. Ultimately, it may track 8 or so really strongly. On the Garmin, the vertical green pulsating bars give you acquisition strength information. My simple pilot mind finds it fascinating, even after all these years. Imagine, somewhere out there in cold space, these man made contraptions, that cost millions of dollars to build and get there, are at my beck and call. Little moi. They are bouncing signals back and forth to my little GPS. All for my personal convenience. It’s a magnificent trick, undreamed of only a few decades back. I watch the satellite acquisition process with a strange awe. It seems a shame many pilots so quickly get blase and bored with this.
It’s magic…
Once you’ve got three captured, you’re pretty well in business. This may take a few minutes. I don’t mind taking off with only 1 or 2 captured,because I know the rest will follow soon. I wouldn’t take off with ‘zero’ captured, because after several minutes that might mean something is wrong. Corrosion in that environment is an ongoing problem, and many a time we have traced GPS reception problems, not to the actual GPS unit itself, but to helicopter antenna mount corrosion, and poor ground connections due to corrosion.
Same here in the Gulf. A frequent giveaway is when you have intermittent GPS problems. It works fine, and then it messes up, and then (usually when a mechanic come out to look at it) the cursed contraption decides to behave impeccably.
fuk’n intermittent @!!# !! gremlins…

I have learned from long, bitter experience to start strongly suspecting antenna connection and grounding problems when I see this sort of intermittent ‘schtuff’ beginning to annoy the living heck out of me…
3) We know from the ‘Ross’ (or its equivalent today) what the position of the ship is. Sometimes the ‘Ross’ will kindly tell the GPS automatically for you. That’s nice. All we have to do now is select NAV (navigation) and it will tell us our magnetic heading to the ship, our range in nautical miles, groundspeed, and the time it will take us to get there. Yes, it’s that easy.
4) If the ‘Ross’ (or its equivalent) does not update the GPS, either because it’s improperly set up, or because something has gone and broke, it’s easy to perform this update manually. Go to WPT (Waypoint). You can call your ship any number you like. (or use letters). We want to update, say, number 27. Go to ‘Edit’. Using the ‘left-right’ toggle. Once the cursor is flashing over ‘Edit’, press the vertical toggle ‘up’. The cursor goes back to the position. Enter the lat and long. There are only two ‘toggles’ and if you experiment you’ll soon get the hang of it. And there’s always the M-A-N-U-A-L. Right?
It will ask if you want to ‘save’ it. Yes, we do, so ‘up toggle’, and now waypoint 27 (The ship’s position) is saved. Click back to NAV (Navigation) and make sure you are looking at the correct waypoint (top left hand corner). If that says ’25’ or ’99’ then you need to use the toggles to select ’27’. This is important, or things could become very embarrassing. If you have carefully entered the ship’s lat and long under ’27’ and then you click to ‘Nav’ and start following directions to waypoint ’25’ or ’99’…
Go back to the bottom of the class.
Should you want to know your position righ there and then, because you are over a foamer or a log for instance, then select POS (Position).

I’ll leave my super shortened explanation of Tuna Field GPS operation there for right now, and I apologize to all the outraged purists. (Oh, heck, why should I? Knickers, if you don’t like it.) Remember… there is NO substitute for reading the M-A-N-U-A-L. But at least this will maybe give you a rough idea.
Remember also this: The Ross DSC 500 (or its equivalent) tells you where the ship is. (and it tells the ship where you are). Your onboard GPS tells you where the helicopter is, and gives you magnetic heading TO the ship, range, groundspeed and time.

I try and check everything is working, whilst I am still running up on the helideck. You should get a reading off the GPS giving you a very short distance to the ship (you’re sitting on it!)

After take-off, as I climb out to 900 feet, I want to know toute-suite if the GPS is giving me a sensible heading and distance to the ship. If not, why not?

Periodically, during the flight, I will also check this. I want to keep a mental picture of where I am in relation to the ship. If the GPS fails suddenly, I want to know. Some pilots have a little cardboard compass rose with a pointer, which they manually set to point to the ship. That’s okay, as long as you remember to set it.
I keep the ‘picture’ in my head, and I will explain later on the various ways you can achieve just that.

More than anything else, avoid the Big Trap. Getting way, way too comfortable with your fancy-dancy onboard electronics, and starting to totally 100% RELY on it. You MUST be able to be NOT surprised when the electronic gremlins strike. If you have to fall back on dead reckoning (time-distance-heading), then so be it.
It will happen. Sooner or later. Imagine if you have a Hamlet Cigar moment like I had one day, forty odd miles away from the ship:

thick white smoke pouring out of the radio stack.
Strong, biting smell of electrical burning. Followed by…..
lights out.

I knew where I was, and we just turned around and went home. (Well, we cursed a bit, him in Canton Chinese, and me in Paddy Irish) The ship freaked out a bit as well, because the Ross didn’t give them a position for us anymore, but we were quite happy really.
In your heart and soul, if you are flying along, twisting and turning, popping down to look at this log and that foamer….and if you know damn well inside your own head, that you don’t have a CLUE where the ship is unless you look at the GPS… then you are setting yourself up for a fall one day. Don’t be a SINR.

More on this… later!

Francis Meyrick

Last edited by Francis Meyrick on April 13, 2010, 4:21 pm

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