View Full Version : Examiners: items for in flight diversion

3rd Jul 2009, 18:56
Quick question: During PPL, CPL skills test when an examiner gives a diversion is there any rule which states one must use a flight computer to work out the necessary calculations (hdg m, dist, GS, time etc.) I always used the CRP-5 for my skills tests but recently noticed some items on Pooleys website which can give you some of the required information without the need for the CRP-5 although not all of the info required. I know the Faa allow pilots to use an electronic flight computer for skills tests but the Caa do not as far as I know - what is the reason for this ? Is a calculator and other various items acceptable for use ? Basically can someone name what is acceptable and what is not acceptable please.

3rd Jul 2009, 19:07
No-one seriously uses a CRP in flight for a diversion do they?

Draw line on map - LOOKOUT - estimate track - LOOKOUT - estimate effect of wind using MDR / pre calculated max drift - LOOKOUT - estimate heading - LOOKOUT - estimate distance - LOOKOUT - estimate time enroute - LOOKOUT - diversion planning done!

Worked fine on my CPL skills test and with all the PPLs I teach.

3rd Jul 2009, 19:34
So you are only required to give a rough estimate ?

Christ I actually did use the CRP-5 as I thought one had to be as accurate as possible. The examiner must have thought I was a nutcase ! Spinning the wizz wheel whilst trying to fly was always most akward I thought.

Cows getting bigger
3rd Jul 2009, 20:03
Hand drawn line on chart, max drift, clock code (quarter/half/three quarters/full) to calculate wind correction, 10nm thumb, halfway point on new leg (for drift and ETA calculation) and Robert is your mother's brother.

Oh, and LOOKOUT! ;)

3rd Jul 2009, 20:24
I am amazed this rough estimate is acceptable for a skills test. So basically what your saying is you draw a line then work this all out roughly in your head and just tell the examiner hdg, dist, time. How does the examiner know your not just guessing all this apart from the obvious of not arriving at the correct diversion and timing is out. Whats the bloody point in carrying the CRP-5 then ?

3rd Jul 2009, 20:35
You may call it a rough estimate but it can be remarkably accurate. Remember the wind speed and direction you use with the CRP is only a forecast (guess) so the calculated answer is based on an assumption anyway!

As the others say, draw a line, parallel to a nearby VOR to get Trk(m) and you could always notch your chinograph with a distance scale.

Aviation is full of rules of thumb

Arm out the window
4th Jul 2009, 07:36
As mentioned above, you can get surprisingly accurate track estimation by eyeballing it on a hastily-drawn map line (or even a fold in the map in case of a catastrophic pen failure), remembering variation of course.

Measure distances with whatever handy implement you have available (again the pen can work well) against the latitude scale.

Distance gives you time (based on estimated G/S in nm/min adjusted for known or forecast wind - use percentages if you like, eg. a 20 kt headwind would add a little bit less than 20% time to your leg if you cruise at 120 kt, for example).

Time gives you fuel - very important.

Here's the key point though - don't just blindly trust your estimates - sort out a pinpoint a third or halfway down the leg, and adjust heading by the 1 in 60 rule, timing proportionally (eg I was 1 minute later than expected halfway down, so I'll be 2 minutes late at the end ... amazing mental maths skills required).

Consider restricted areas, controlled airspace, diversion radio calls, tiger country you may be diverting over, last light etc.

Liberate yourself from old style nav computers and their digital offspring - nice to have but by no means necessary. Amaze your friends with your mental DR skills.

4th Jul 2009, 08:13
You really should not be using a Prayer Wheel (Nav Computer) in the Air! If I see one, I throw it in the back!

For a Diversion, a rule and pen is useful to draw a nice straight line, though not essential, and a Douglas Protractor to measure the track, thereafter everything else should be done by rule of thumb and estimation. From the end of your thumb to the knuckle is 10nm on a 1/2 mil chart.

A Douglas Protractor will fit into most kneeboards.

4th Jul 2009, 09:22
Redout, you have already (hopefully) already demonstrated your ability to plan a flight on the ground with all the normal planning facilities to hand. The diversion is to see how you can handle unplanned changes in the air - the last thing we want to see is people turning the aircraft into a planning room with CRPs and charts all over the place, accompanied by the inveitable spiral descent. You can use whatever you need, including radio navaids, but it is not a planning exercise. Probably the best way I have seen it done is just to have a straight edge marked with 5/10/15 etc nm (a ruler will do) and then once aligned with your planned track, draw it across to the nearest VOR rose - conveniently already aligned with magnetic North - and there is your track and distance. Add 5/10/15 etc. degrees into wind (can you fly to 1 or 2 degrees?) and there's your heading. Then GET GOING and work out your ETA once en route. By far the most common debrief point I have for people concerning diversions is the amount of f***ing about they do before actually setting off on the div. It's not a precision exercise, you just have to get there (without totally gashing it).

4th Jul 2009, 10:01

You have been given good advice. Two additional points that I would make is;

The distance calculation isn't really necessary. The only measurement of value once airbourne, is time. I would spend my efforts in estimating elapsed time for the diversion based on the previous known progress on the already flown legs. Together with track made good assesment, at a predetermined pinpoint along the way, the time will also be revised. The Examiner will not expect a final heading or eta to be given until you have been able to revise based on a fix (pinpoint) along the way.

Don't rush to divert, identify a point ahead of your track, say 5 minutes of flying time to allow unrushed inflight planning. You should then consider other factors such as a MATZ and notified airspace which must be avoided. Where you may need to transit a MATZ or controlled airspace diverting from a point somw minutes ahead on your track will allow you time to gain clearances etc.

4th Jul 2009, 20:40
I'm no examiner, but I'll add my tuppence;

The diversion does indeed need to accurate, but at destination.

This worked for me:

1) Draw line from current position to diversion. Mark half way point (this can be done at any point you get there)

2) Use a protractor thingy to get a rough mag track.

3) Add or subtract 0/5/10/15/20 degrees for drift accordingly. This is your heading. Tell the examiner.

4) Give them a time based on a rough calculation. This depends on what speed you cruise at, but find a rule of thumb that works.

5)Start clock and fly the heading untill the halfway point. Nice and relaxed.

6) At HWP, double your time and heading error (there will be one) and correct it all. Now you do have very accurate figures. Dead easy.

Example, you are 2 mins early at HWP. You will be 4 mins early at diversion.
You are 6 degrees left of track. Turn right 12 degrees.

Tell the examiner your new figures and they (should be) spot on.

So, from a rough bit of guestimation you later end up with some spot on figures. Bang on time. You will notice that the only thing you have to do accurately is work out the HWP. But you have ages in the cruise to do that before you get there.

And of course, between each of the points above, LOOKOUT!

Works for me. Open to much more experienced suggestions though.


4th Jul 2009, 22:11
Mark half way point (this can be done at any point you get there)
WHY?Start clock and fly the heading untill the halfway point. Nice and relaxed.
How will you recognise this halfway point? It is only a line on the map!

Don't you mean pick a feature at roughly half way?

I see students marking halfway points all the time, they are totally useless because they don't relate to anything!

4th Jul 2009, 22:24

The assumption is that there will be an identifyable feature there. If not, then use the nearest one.

In my expereince this has never been an issue.

Nit-picking rather than a vaild point methinks?

Cows getting bigger
5th Jul 2009, 06:34
Did anyone mention LOOKOUT? :)

PS. Fly the heading as well. Too much fannying about with charts makes for erratic headings (and probably altitudes).

5th Jul 2009, 06:50
Nit-picking rather than a valid point methinks? Far from it, it is singularly the worst and most consistent error I see on nav tests. Candidates relying on imaginary lines that mean nothing. Your watch tells you when you are half way! Navigation in general is poorly taught and this is one of the results. Heading and Time Heading and Time! How many actually start the clock and measure something useful?

5th Jul 2009, 08:58

Agree absolutely! Heading and time is the key for they are the only measures of value once airborne.

Choosing the simplist to identify and least ambigous feature at whatever point along the track is paramount. Doubling the track error dosn't have to lead directly to the turning point/destination. Doubling the error prior to halfway will also bring you back onto the planned track when a revised heading should be used to the next planned point. If the fix is more than half way then treble the error which will return you to track/destination in half the distance and time.

A halfway mark in ther middle of nowhere is pointless though continues to be taught in some places for some mystifying reason.

5th Jul 2009, 11:43
Fair enough guys. I'm currently doing an FIC so will bear it in mind when briefing.

Any more tips?


5th Jul 2009, 16:41
Unfortunately there is not enough time on an FIC course to spend much time on navigation yet it is by far the weakest skill on test. It seems instructors do not teach any method of navigation and the student believes that map reading is navigation. Mark a fix every 6 mins and put the elapsed time by it to the nearest 6 seconds, then use it to check track and ETA. Encourage students to put the map away between fixes and fly the aeroplane accurately.

5th Jul 2009, 17:34
I find it interesting that no one has mentioned the standard closing angle method of regaining track, but are still using 1/4, 1/2 and 3/4 waypoints.

I would be interested to know which technique people prefer and why?

Cows getting bigger
5th Jul 2009, 18:10
I prefer the one I was taught on my CPL. Two fan lines (one at either end of leg). Once you have ascertained your position, estimate how many degrees you are off track from your starting point, then estimate how many degrees you are off track from your next way point. Add the two numbers together and apply this correction. It gets you to your waypoint in the most direct route. It's so simple I don't know why others don't teach it. And before cries of "Off side referee", my CAA examiner seemed very pleased with this method and subsequent students have never been criticised by their PPL examiner.

Oh, and I'm with the chaps above - put the chart away and don't even think about looking at it until a couple of minutes before a waypoint or a 'checkpoint'.

5th Jul 2009, 22:22
My examiner said he wanted to see a line on the chart and I was to get us to the destination.

The idea of trying to use a whizz wheel in a 150 with 2 POB is a bit scary, add in a bumpy ride in summer weather and I think you'd have a problem.

Try 'diversion Planning' by Martyn Smith. It's not the only method, possibly not the best thereis, but it's a system and it works.

5th Jul 2009, 23:17
Using the whizz wheel in a 150 whilst doing an exam is most certainly doable although most awkward. Although if one was to draw a line, set a rough heading and trim correctly then I see no reason as to why a person could not use the CRP-5 to work out an accurate GS and use a plotter to get a more accurate heading and apply variation etc. should take no more than 45sec with the wheel.

6th Jul 2009, 06:08
I find it interesting that no one has mentioned the standard closing angle method of regaining track The thread is about diversion technique not navigation technique but as you ask! This is a military method that works well for fast aircraft that have a good reason for staying on track. It can be difficult for some PPL students who may finish up flying a saw tooth pattern because they fail to correct properly, or may result in them getting further off track because they fail to turn back on after a 30 degree correction. They also forget to correct the timing. I have seen more problems with this method than advantages.

There is no requirement in the PPL test to regain track, only to navigate to the turning point.

Keep it simple! Remember you have got to teach the student how to do it.

Using the whizz wheel in a 150 whilst doing an exam is most certainly doableAnd totally detrimental to LOOKOUT! As an Examiner that's not what I want to see!

6th Jul 2009, 17:49
Hi Whopity

I take it you are a PPL examiner. I am interested in your comments as I have heard several people say, including a senior examiner, that the standard closing angle method is now an expected method of VFR navigation as it gets the aircraft back on the planned track quickly rather than fly a 'new' track to the turning point.

I am not saying that I agree if it is better or not, but I am interested in current views re what method is expected, (if any)


Cows getting bigger
6th Jul 2009, 18:23
Bingo, I'm not so sure the CAA would be so prescriptive. They wouldn't endorse feature crawling but any of the other methods would probably meet with approval. For them to favour a particular technique may be seen as starting down the slippery sloe. What next - preference of wing-down to crabbing for crosswind landing? Or how about "point and power" over "power for flightpath, pitch for speed"?

See what I mean?

7th Jul 2009, 13:21
Yes, I agree. Teach a student whatever method works for that student. However, I think the SCA reared its head a few years ago when nav was a major feature in test failure and it was put forward as the 'cure all' by some.
I am aware it is a military method, from CFS and had to be adapted to work at typical GA aircraft speeds, which in itself made me wonder about its suitability.
Personally, I would like to think that an examiner has the ability to understand several techniques and can test a student on their chosen method. As long as it is a 'method' and not feature crawling I see no reason why it should not be acceptable.

7th Jul 2009, 14:37
As an examiner it is clear to me that you must test on the basis of the recognisable navigation technique to be used and stated by the candidate prior to flying.

However i'm sure that the CAA Chief Examiner, Pat Lander has said (I cannot find the reference) that the preferred techniques were those that regained track. That makes sense to me taking into account the increasing number of airspace infringements made worse by the increasing allocation of controlled airspace of course.

NATS are complaining bitterly with regard to Stanstead infringments which occur not only but extensively along the western side where aircraft are sqeezed between Stanstead and Luton airspace. SCA techniques will be more likely to cause an infringement where the intended track allows little variation for a track made good and a revised closing angle track could be insufficient to remain clear.

The planned track must always be the best one.

7th Jul 2009, 15:53
I am interested in your comments as I have heard several people say, including a senior examiner, that the standard closing angle method is now an expected method of VFR navigationExpected by who? It is certainly expected by those who teach it but it is not the CAAs job to prescribe methods. I have certainly taught at a school that prescribes SCA and so have seen many people use it. Its an excellent military technique but not suited to all so I prefer some of the simpler methods.

For the purpose of test, the candidate is required to demonstrate a method of navigation whereby the aircraft is flown using a series of headings deduced logically.

Cows getting bigger
7th Jul 2009, 17:02
Homeguard, I vaguely recollect something similar. For the life of me I can't find a source document (good bit of Trainingcom refresher reading though :) )