In-flight diversion planning - help!

[sywell-flyer]

Hi,

I have my skills test tomorrow and am struggling to remember how to calculate groundspeed and wind correction angle mentally for the diversion on the Nav part of the test.

My instructor mentioned the method using the face of a watch but I seem to have forgotten the rest!

Is anyone able to tell me this method or any other good, reliable methods for doing this?

I don't have my books handy today so I haven't been able to try and look this up...

Cheers,

SF

[Darth_Bovine]

Hi,

Normally for inflight diversions they're looking to see you make a quick guestimate of things so you can start the diversion, then you can get more accurate once you are under way.

Typically, this means you need a bearing to fly before you can set course. I was always taught to eyeball this on the chart. Make sure you know where you are currently, figure out where you want to fly to and estimate the True Heading. Then add on your mag variance. You can also get the Magnetic heading from a handy VOR rose that may be on the chart by visualising the course on the rose and reading off the bearing. A pencil or pen sometime helps do this. Then you can add a drift due to wind to this. Again, unless you have a GPS system that tells you the real wind at your height then this will be another guess (it's effectively a guess at the planning stage anyways).


The examiner will be looking to see that you can make a good 'guess' at the heading to fly. After you've woked out the heading you can work out an estimate for GS and ETE (leg time). These can be done once you have taken up the bearing.

If you notice yourself offtrack, then make suitable adjustments as you would during normal navigation.

It will help if you do a few practice diversions in the comfort of your living room. Try and 'guess' everything, and then try it in full Nav planning mode. After a few attempts you'll find your guess is very close to the real calculated plan.

Have fun, and good luck in the skills test.:ok:

Cheers,
DB.

[Kaptain Kremen]

Hi,
Phone call to the school may be a good idea, but heres my thoughts:-

Allowing that for a cross wind component, 60 to 90 degrees is classed as max drift, you can see where the watch face comes in using 0 to 60 as a representative of 0 to 60 degrees.

Firstly, you need to know what the max drift would be at 90 degrees using your CRP1, and then mark this on the chart next to a wind arrow giving your direction. So now, on the chart, you have a max drift possible if the wind was blowing between 60 and 90 degrees off your diversion track.

You can then factor it down depending on your estimate of the angle between track and wind direction. I would only use the nearest to 20, 30, 40 or 60 degrees. The watch face can help with this as fractions of an hour used. For an angle of 20 difference between track and wind, use 20/60 (1/3rd) of the max drift. For 30 degrees off, use half, for 40 degrees use 2/3rds. For 60 degrees plus use max drift.
e.g
You have a max drift today of 15 degrees as calculated by the Crp 1 from a direction of 270
your diversion track is 300 degrees magnetic . so that is 30 degrees off the wind direction so apply half of the max drift as between 7 and 8 degrees. personlly i would fly to the nearest 5 degrees. say 295.
In the same example wind, for a diversion track of say 230, that is 40 degrees difference between wind and track, 40 is 2/3rds of an hour (60 mins) so apply 2/3rds of the max drift. This is 2/3rds of 15 = 10 degrees. New heading is 240.
The wind arrow on the chart ensures that you will turn the right direction into wind.
Hope this helps, but it easier face to face! :bored:
KK

[modelman]

I have my skills test on Friday ( although long range wx not looking too good...).
Before you set off,mark the forecast w/v on the the chart, let's say 300/20.If you are flying at 90kts then use 2/3 windspeed as WCA i.e.2/3 of 20=14 deg. ( if 60kts use all,if 120kts use 1/2 etc.)Mark this on your chart.
Similarly,if the wind is 90 deg to fuselage axis then there is no effect on g/s.For each 10 deg use 1/6 of the wind to get head/tailwind component.When you get to 60deg ( i.e. within 30 deg of fuse axis then use all the wind.)
To calculate ETA remember 60kt=1nm/min,90kts=1.5nm/min etc.
You can interpolate for in between speeds ( for 75kts,work time for 90 and 60 and take the mean)
Try a few practice diversion from the comfort of you armchair and check your results with the CRP.
All sounds so simple but I bet I couldn't explain it and fly at the same time.
Good luck with your test.
Modelman

[sywell-flyer]

Excellent replies so far! A combination of the above seems to be working for me...I'll work through a few more examples and get back to you!

Good luck on Friday MM

Cheers,

SF

[Boing_737]

Another thing you could do is create a "Wind Star". For your given wind on the day, create a compass rose with all the cardinal points on it, and then, using your whizzwheel find the drift and airspeed for each of these points. This should then give you a quick and easy reference for your diversion without the need for mental acrobatics just at the point when you don't need it.

[A V 8]

Yet such genious! I wish I'd thought of that! :ok:

[pipertommy]

Also another way to work out max drift is w/v x 60 dived by tas=max drift.This is 2/3 of windspeed ie 18kt wil give 12 degrees

[Martin @ EGLK]

With you on that one Boing 737. I always do that when I go x-country out of my local knowledge area.

Another cheat is to have a spreadsheet on a PDA with the maths programmed in. Just enter in the direction & distance & let Bill Gates earn his money.

[Boing_737]

Another thing you could do is create a "Wind Star". For your given wind on the day, create a compass rose with all the cardinal points on it, and then, using your whizzwheel find the drift and airspeed for each of these points. This should then give you a quick and easy reference for your diversion without the need for mental acrobatics just at the point when you don't need it.

'course, by airspeed, I meant groundspeed:ugh:

[IO540]

There is a much easier way but if I mention it (3 letters starting with a "G") the mods will split the thread, and the CAA will send somebody to loosen the nuts in my landing gear :)

[RatherBeFlying]

Mark where you are on the chart (or point you will be departing from) and where you're diverting to
draw line between points A and B
Lay pencil from A to B
Move pencil over map keeping parallel to course line until pencil over VOR rose
Read off magnetic heading
Move pencil to longitude line (the ones that run North-South) -- read off nautical miles.
Many trainers produce a groundspeed of 90 kt. -- so multiply by 2 and divide by three to get elapsed time estimate.
Add or subtract a couple minutes for winds if strong
Mark halfway point -- highly unlikely your examiner will divert you to anything more than 20 nm away.
Record time departing point A or start stopwatch
Work out heading to take out drift following new course, i.e. stay on top of or just to right of course line
at halfway point, update estimate.

Find a plastic folder to hold map and use erasable marker to practise diversions in armchair or a/c. Mark heading, distance, times directly on plastic.

[turniphead]

As this is skills test and good VFR..
Why does nobody suggest looking out of the window?
Draw line from where you are to where you are being diverted to.
Turn onto approx heading.
Look at chart and at ground. Fly eg left of that town there ,right of that motorway there, and careful to avoid that ATZ there, airspace there, pass the lake on your left etc etc?
Previous posts imply that in the diversion you will not face any air nav restrictions. Not usually true in the real world.
Usual methods already explained for estimating EET g/s etc

[SD.]

Mark where you are on the chart (or point you will be departing from) and where you're diverting to
draw line between points A and B
Lay pencil from A to B
Move pencil over map keeping parallel to course line until pencil over VOR rose
Read off magnetic heading
Move pencil to longitude line (the ones that run North-South) -- read off nautical miles.
Many trainers produce a groundspeed of 90 kt. -- so multiply by 2 and divide by three to get elapsed time estimate.
Add or subtract a couple minutes for winds if strong
Mark halfway point -- highly unlikely your examiner will divert you to anything more than 20 nm away.
Record time departing point A or start stopwatch
Work out heading to take out drift following new course, i.e. stay on top of or just to right of course line
at halfway point, update estimate.Find a plastic folder to hold map and use erasable marker to practise diversions in armchair or a/c. Mark heading, distance, times directly on plastic.

I teach what this man has said. Personally I wouldn't bother working out g/s and the amount of drift. Keep it simple and relax :ok:

[Gertrude the Wombat]

Here's a vastly simpler approach to most of those given.


Guess
Point the aeroplane in that direction
Fly for a bit
Check on the map
Nudge it left-a-bit or right-a-bit as required

[Stik]

I haven't done my skills test yet, but it's not far away. I asked the question about looking out of the window , and perversley ( or not ? ) feature crawling is frowned upon . . . we are expected to demonstrate navigation by ded. reckoning . . . .

[On-MarkBob]

It is important that you believe in the system and the basics of navigation. Time and heading are all important and must be kept together at all costs. Never change heading without noting the time! You shouldn't have to panic about making a diversion, presumably you had one in mind before you started the flight and you have sufficient fuel for it and a suitable reserve on top?
Start your diversion from a known point, over a town or something else depicted on your chart. Draw your line to your diversion from that point and use your protractor to get yourself a heading, (converted to magnetic if protracted in true). By the time you make your decision to divert, you should already have a good idea about what your drift angle is likely to be, double check the drift angle you want to apply and make sure it makes sense!! Finally, fly back to your diversion point and overfly the town, or whatever, on the heading you calculated.

That is how you have to do it for your CPL GFT. A diversion is not necessarily an emergency, take some time and calculate it properly, just blatting off in some general direction will increase your chances of getting lost!

One last tip, assuming your aircraft is properly trimmed (particularly Rudder, ie ball in the middle). Once you are established on your heading, concentrate to hold the wings level. If the wings are level the aircraft will not turn and holding the heading will be easier!

[sywell-flyer]

My test was cancelled in the end (due to weather) so I didn't get to try out some of the suggestions in anger.

Gotta wait until next week now!

Fingers crossed...

[BEagle]

Unplanned diversions are introduced in the latter stages of navigation training. By then you should have been introduced to MDR (Mental Dead Reckoning), including the calculation and application of Max Drift. We advocate:
Maintain VMC!
Know who to call for assistance if you doubt your ability to cope.
Choose somewhere visually significant to divert from as well as a suitable diversion.
Fly to the ‘divert point’.
The back of the checklist (ours are laminated and have a blank back with a 50 mile ½ mill scale on one edge!), a chinagraph and the CAA 1:500 000 chart are the only planning tools needed:
Use the edge of the checklist as a ruler between divert point and diversion and draw the track line on the chart. Then lookout.
Measure the length of the line, write it on the checklist – then lookout again
Make sure the divert point is still in sight!
Find a suitable VOR rose on the chart, use the checklist edge as a parallel rule and draw a line through the VOR rose parallel to the diversion track. Then lookout.
Read off the track angle – which, of course, is conveniently in degrees magnetic – write it on the checklist. Lookout again.
The 2 most important values, track and distance, are now known. Apply MDR to track (the pre-calculated max drift value is on the chart, of course!) and estimate the heading.
Note the head or tailwind component and work out groundspeed to the nearest ¼ mile per minute. Then use it as a fraction (e.g. 5/4 miles per min rather than 75 knots) – the error over the short distance involved is unlikely to be significant.
The hardest sum next! Time = Distance / Speed! Either mentally or on the back of the checklist. Write it down, then lookout.
Pre-HAAT check, overfly the divert point, post-HAAT check.
Fly heading and time diligently. Lookout and look down for visually significant points to confirm track maintenance.

[d192049d]

My two penneth....

For Time

If IAS = 100 knots your ground speed will be 10 nautical miles every 6 minutes [the length between tip of thumb & 1st knuckle]. It works for all IAS excluding wind, so if your IAS is 90 Knots you will travel 9 nautical miles in 6 minutes excepting wind. If in a PA 28 or C152 and your track is three thumbs long [30 nm] the time will be 18 to 20 minutes.

For direction

On the map Up is 360 right is 090 down is 180 and left is 270...just make a guess by quartering halfing angles angles. Perhaps a VOR is located near your intented track, which can help here.

Max drift - Rule of thumb

= 0.75 times the forcast wind which is half of the wind + half of the half....in words if the wind is 20 knots max drift will be 10 + 5 = 15 so you apply + / - 15 degrees to your heading depending on where it is coming from. This is there or there abouts for government work

Tolerance

I cannot remember but think it might be + / - 2 mins on time and getting in the general area enough to be able to positivley identify your diversion point...but maybe wrong here...

Hope this helps & good luck....!!!!:)

M

[pipertommy]

Instead of doing calculations in your head you can by a small ruler with distance on the edge and times for that distance and different speeds ie 50kts through to 140kts called a CPM1.Got it from AFE brilliant bit of kit:ok: