[Luke Hewgill]

Hi all,

I am new to the forum and quite new to flying, so apologies if this is a stupid question! I am trying to study from home, but i am now getting frustrated and cannot find the answer i need!

So, i have just started unplanned diversions, i am struggling massively whilst in flight to control the aircraft and sort my mapping out, but that’s a whole different subject....

The part i am really struggling with is the clock code for unplanned diversion. My School has given me a worksheet which states that if the wind is 15 degrees off the nose, use 1/4 of the max drift rule i.e. if max drift is 8 degrees, drift would be 2 degrees, 30 degrees off the nose, 2/4 etc. = 4 degrees and so on.

This is the part where i think i am being stupid, surely if the wind is 45 degrees off the nose using the clock code, this would be the same as 30 degrees but from the opposite side of the aircraft?

I think also the way i have been taught to calculate has confused me but if someone could enlighten me, that would be great.

Thanks in advanced for your help

[GolfHotel]

First. Don’t worry if some things seem a bit difficult, it happens to most of us.

You need to separate clock code and degrees. You can’t have “45 degrees of the nose using the clock code”.

45 degrees of the nose is half way between 1 and 2. In the same way 15 degrees is half way between 12 and 1. It will get confusing trying to change between them. You need to learn both. But don’t use them together.

If you have to convert each number on the clock code to the next is 30 degrees.

I think you may be mixing up minutes with the clock code.

12 o’clock is straight ahead
3 o’clock is to your right
6 o’clock is behind you
9 o’clock is to your left.

[c750X]

There are lots of methods and "quick calcs" for diversions, they don't suit everyone. For what it is worth this is the method that worked for me.......

Firstly, draw a massive arrow on your chart for the wind. At a glace you can see how it is going to work with your track and you'll know straightaway if you should be adding or subtracting for your heading so works nicely as a gross error check.

Secondly, the max drift rule is handy but at the same time I found it easier to get a more accurate heading by using a windstar sheet and/or a diversion plotter. At your preflight planning once you've got the wind up on your whizzwheel it's an extra minute to fill in all the details as +/- degrees and groundspeed in the boxes. You need a rule to draw a straight line anyway and a protractor to get the heading so why not use a tool that will do both, and also give you your timings. The more you use it, the more you understand what's going on and once you've worked through a few it's less concentration to do it meaning you can concentrate on keeping the examiner happy by holding your altitude and heading, and arriving on time.

This is the one I use, in fact it's the second as the first one wore out;


Used it on my GFT, had the diversion planned and managed in under a minute.

[Luke Hewgill]

Thanks guys, I am going to sit at home tonight and go through both of your examples and methods.

With regards to the diversion plotter, I do have one of these however my instructor has said he doesn’t want me to use it until I have mastered the art of diversions using the basics (spoil sport!!!!) haha.

[GrahamB]

It’s a method of approximation which is good enough. The simplest way to think of it is that a wind 60 degrees off the nose (or tail) will near enough result in max drift.

15 degrees off the nose will therefore result in a quarter of that drift, 20 degrees a third, 30 degrees half and so on.

The ‘clock’ bit is only a way of visualising that for example 15 degrees (minutes) equals a quarter of 60 (an hour) and has nothing to do with the direction the wind is coming from.

[leiafee]

So, i have just started unplanned diversions, i am struggling massively whilst in flight to control the aircraft and sort my mapping out, but that’s a whole different subject....

I'm not sure that is unrelated y'know

Are you freeing up as much brain capacity for the Maths In Public as possible, before worrying about the drift when flying?

i.e.

Have you practised estimating angles on the chart by eyeball so you can quickly get a rough non-drift heading?

Are you looking for large conspicuous landmarks along that to make sure you're heading in broadly the right direction?

Are you turning onto that rough first, and then fine tuning with your drift once you've got things stable and more or less heading in the right direction?

Whatever arithmetic method you end up finding easiest it'll all be harder in the air if you're multitasking to excess.

[johnm]

Flying is all about being systematic and having procedures to follow. So if you aren't being taught a diversion procedure you need to invent one as Leia suggests.


Something like:


Identify target on map relative to present position.

Estimate heading (could use the tool shown above ) and turn on to it.

Highlight a couple of way points to check against

Note expected wind direction relative to heading

Use clock type code to estimate drift
15 degrees 1/4 of max. 30 degrees, 1/2 max, 45 degrees 3/4 60 degrees up to 90 full max drift.


Stabilise heading and check for waypoints and adjust heading as necessary

[Charles Hunt]

I think you may be mixing up minutes with the clock code.

12 o’clock is straight ahead
3 o’clock is to your right
6 o’clock is behind you
9 o’clock is to your right.

Just to reduce confusion, 9 o'clock is to your left.

I have taken the admin liberty to edit the quoted post above to correct this!

[Charles Hunt]

This is the part where i think i am being stupid, surely if the wind is 45 degrees off the nose using the clock code, this would be the same as 30 degrees but from the opposite side of the aircraft?

No.

Simply saying 45 degree off the nose tells you nothing - you need to know is it from the left or right.

If from the right, converting to clock code it would be from 1:30, if from the left it would be from 10:30 (not that :30 divisions are used in practice.)

Try to get the big picture. I haven't got a chart to hand but try to get the big picture in your head first before worry about a few degrees of heading.

If flying from say Sandown to Fairoaks, magnetic track should be (guess) 060.

What happens if the wind is from the north?

The wind will be hitting the left hand side of the aircraft, pushing the a/c to the right and slowing you down a bit. You will need to point the a/c to the left to heading say 055 degrees.

Draw this out for each cardinal wind direction (N E S W), guess the answer, then try some calculations.

[Irv Lee]

Angle.... draw the diversion line.... you should already have a 'wind' line so you can now visualise the angle of the wind to your track. Remember the wind line is usually just someone's idea of the wind vector when he/she was sitting in an office in Exeter about half a day earlier, so don't get totally hung up about it.

[iaindings]

+1 for the plotter shown above. I was fairly comfortable with how my examiner taught me, which was

- Have wind drawn on map on a VOR rose
- Draw a quadrant split into thirds, showing max drift, 2/3rds and 1/2 for the 3 quadrants
- During flight, draw line (freehand), 10 degree drift line and mark half way point
- Hold pen to line then to VOR rose to get a magnetic heading - with a bit of practice you can be +-5 degrees. Add or subtract drift using the rough angle shown on the quadrant you drew during planning
- Use rule of thumb to calculate time - find out what duration a thumb length is and use that. Dont bother compensating for wind with ground speed, as you can use your midway point to revise the ETA by doubling the time it took you to get there

I don't buy into the complicated calculations for students, the exercise is all about taking an informed guess that's pretty rough but accurate enough to get you somewhere and revise it later. If you draw the wind on a VOR rose, the same one you use to measure the track - all you need to do is hold the pen to it and look at it. You can quite quickly see whether the wind is right on your side, in which case add most or all of max drift, or at your nose/tail - in which case add 1/2 or even less. You can see which way it is, just remember you have to steer into wind - I even got used to turning the pen towards the wind and seeing if it was a clockwise or anticlockwise rotation. You wont be accurate to the degree, but you'll be close enough to make a correction at a suitable point. It's pretty hard to fly much more accurately than +-5 degrees in a little Cessna with an old DI anyway, so worrying about 1 or 2 degrees either way is a bit pointless.

That always worked out in practice but it was the part of the test i was most concerned about - just because of the unknown. When it came to my test, my instructor had never actually let me control the plane while doing this which added to the nerves. So I bought the ruler above and did some practice at home with it I found it a bit fiddly, especially trying to read the heading but I figured out that marking the plastic with a pen then lifting it off the paper made it much easier to read. I went into the exam prepared for either method, still unsure of which I would use. So it comes to the skills test, I still dont know exactly how the examiner will handle the diversion but it went a bit like this

- Hit first waypoint without any issues. Small angle correction at 2/3rds of the way along but ETA worked well
- Turned onto new heading, knowing that the diversion would happen someway along that leg
- He asks to take control then hands me the map. He asks if I can pinpoint our location - we were over moorland over a big forest so that was easy to pick out. He asks if I could pick out the water feature (a lake next to the forest) and dips the wing so I can see it.
- He then asks me to plan a diversion, I get my pen and ruler out and draw the line between the points
- He hands back control to me, the plane was already setup in a gentle orbit around the wooded area
- Quickly draw drift line and mark halfway point, look up
- Measure track, look up
- Check drift and ground speed on wind rose, look up
- Measure time against the nearest speed on the ruler, look up
- Scribble the heading and duration on the chart, look up
- Point the plane in the right direction, start stopwatch on transponder and note current time
- Add duration to start time and give examiner the ETA
- Along the route, glance down to examine the chart for landmarks and features along the route

It was really a lot easier than I thought. You have all the time in the world to get it planned, if you get into a slow orbit around a prominent feature you wont lose track of your starting point. Just make sure you do each thing bit by bit and look up after each one - both to look outside and scan instruments to make sure you're not losing height or speed or anything. It would have worked out perfectly if ATC hadn't asked me to move over a bit to clear an approach path (the route took us overhead another airport). I dont think he minded me deviating for that

Really, I was stressing about nothing, it was really simple in the end

[Luke Hewgill]

Thanks guys, really appreciate all of your help! I am now going sit with my iPad and work through all of your comments and try and work out some examples!!!
Thank you!!!

[BehyBill]

On my PPL skill test exam I struggled a lot with those calculations (the examiner did not seem to care that much) to get a HDG and ETA to the new airfield, these were not far away from the simple no wind approximation

What was interesting is that we both struggled to find that "Laindon Airstrip" as we flew low over the area for a longtime before finding it (I suggest you look at all of possible diversions on google map and zoom in/out first )

As long as you know where you are and you next 6 min fixes, you look far away while keeping a constant heading then any +/-20 HDG should work (that amount to +/- 30kts crosswind), if you are happy with what you get and see don't improve your guesstimates unless you feel there is an operational need for it, of course you can "calculate" HDG to one arc second or ETA to millisecond

In the other hand, if you fly low navigation is difficult as hell, so if you can try to fly high if you can that helps a lot

If you plan to pass the CPL skill test that is a different story, if not you will have a VOR needle or you can simply join the "magenta line tribute"

[Genghis the Engineer]

Can I offer a somewhat different take on it.

You are flying along minding your own business when your instructor gives you a diversion. DO NOT TURN TOWARDS IT. DO NOT PLAN TO IT FROM WHERE YOU ARE NOW.

Carry on to your next waypoint, or a point en-route along that line, that's already planned and set up, so fly it. TAKE YOUR TIME, and plan from that waypoint, when you get there THEN turn. This will massively reduce cockpit stress.

Also you will make errors in your calculations in the air, so don't set yourself up to fly straight to your alternate with no easily followed features. The temptation is to try and turn immediately and fly exactly to it - which is just a recipe for unhappiness.

- Fly to a line feature that goes to the alternate, make sure you are definitely flying to one side of the alternate, then turn and follow the line feature there, or

- Fly to a really easy to identify place near the alternate - say a large distinctive town, and then do the last few miles accurately from there (which again, you've plenty of time to prepare for), or

- Fly to a distinctive point, then route to another distinctive point - the route to which takes you over or very close to your alternate - if you miss the alternate, you can turn around and try again.


What's really important to remember with diversions is that you are not trying to get there quickly or accurately. You are trying to get there safely and reliably: take your time to get it right, and it'll all come together fine.

In the real world, I'd do exactly the same if I didn't have GPS (and have done many times), with GPS, I'd cut the corner a bit, but still try to use broadly the same approach as even with GPS, you still need to visually identify where you are at the end.

G

[TopCat]

Can I offer a somewhat different take on it.

You are flying along minding your own business when your instructor gives you a diversion. DO NOT TURN TOWARDS IT. DO NOT PLAN TO IT FROM WHERE YOU ARE NOW.

Carry on to your next waypoint, or a point en-route along that line, that's already planned and set up, so fly it. TAKE YOUR TIME, and plan from that waypoint, when you get there THEN turn. This will massively reduce cockpit stress.

All very well for the artificial case of a skills test in good VMC.

In the real world, the diversion is likely to be because the weather in front of you is deteriorating, and you may not even get to your next waypoint.