1:60 rule confusion of methods

[Sul]

Hi,

I'm just a little confused about the rough methods given to me that can be used to approximately calculate heading corrections in the air using the 1:60 rule as a basis.

1. One method (in the PPL ground studies book) says that you estimate the track error and multiply that by either 1.5, 2 or 3 depending on whether you're a 1/4, 1/2 or 3/4 away from the last position fix.

2. Another - shown to me by my instructor, is basically estimating the track error and multiplying that by the reciprocal of the fraction of the way you're along your route since the last position fix.

The confusion is in the fact that when working out the heading correction, using each of these methods, for the same given situation, gives two very different answers.

e.g. If I was a quarter along my route and I was 4 degrees off-track (my track error), then using method one, it would give a heading correction of 6 degrees, but using method two it would give a heading correction of 16 degrees.

I'm a bit confused here.. would appreciate any help. :)

[BEagle]

Those methods are throwbacks to the dark ages. Instead, learn about the Standard Closing Angle technique from a FI intelligent enough to understand and teach it - if you can find one!

[Sul]

Thanks for the reply - I did check your other post where you described this method. I'll try it out. However, at the same time I'd like someone to help me with these two other methods - just to remove this cloud of confusion at least!

Also, with diverts, are there any good techniques you know of to help calculate the wind correction and ETA?

So far I've learnt the method that involves max drift for heading correction and the one with "one second per one knot head/tailwind per minute" for time correction.

[BEagle]

1. ALWAYS calculate max drift and ALWAYS draw a wind arrow on your chart. Then apply the relevant fraction of max drift (use the 'clock' method - 15 off is 1/4, 30 iff is 1/2, 45 3/4 and 60 or more 100%) to the track to obtain heading.

2. Apply the complementary fraction to the actual wind to establish head/tail component along track. I.e., if the wind is 60 deg off the nose, then the factor is '90-60=30' or half. So if the wind speed is 20 kts, the headwind factor will be 1/2 x 20 = 10 kts. Then consider it as an approx percentage (TAS 90 KTAS, headwind 10 kts - that's roughly 10%, so add 10% to the still-air estimate).

[Tallbloke]

You still need to know the 1 in 60 rule because ATPL exam questions specify "using the 1 in 60 rule....." Arcane, whatever. You need to know it.

[High Wing Drifter]

Sul,

Check with your FTO, I was taught that the Standard Closing Angle is fine for PPL but not for CPL. CPL requires the quickest, shortest route from where you currently are. The SCA method, as good as it is, produces and indirect heading adjustment designed to get you back on track. Saying that, the SCA is an excellent way to establish the correct position from which to assume your heading after departure. Bascially, I have been taught that The preferred method for the CPL is to correct your heading to arrive at your destination (unless you need to avoid enroute obstacles).

The 1 in 60 closing angle method is fine enough, but these are just as good in my experience:

Simplicity personified is simply drawing 10 deg drift lines outbound and inbound either side of your track. To avoid cluttering the chart, just draw stubs and extend with your pencil in flight to determine angles. You just add the outbound and inbound drift to get your closing angle.

To be frank, for CPL nav distances, simply quantifying your off trackness in simple terms such as small, medium and large is sufficient if you assign heading corrections of 5deg, 10deg and 15deg for each. I don't think flying should be an exercise in calculus, near enough is surely good enough.

With regard to diverts, BEagle's method can't be argued with. To get really quick at doing this stuff in your head, prepare your training PLOGs mentally using those techniques without using the whizz wheel. You will be at most 1 maybe 2 deg/kts out which is of no real consequence in the flight.

Furthermore, when you get your diversion just hand draw the line, I don't think there is any need to mess about with straight edges - it doesn't matter if it is a bit wobbly. Then align your pencil along the line and transpose the pencil to the nearest VOR rose to get your track. Do the above mental sums using your predetermined max drift and wind to calculate your heading and ETA. Then as you progress along the diversion and make your fixes mark the chart with a cross and the time of the fix. Then you can easily update your ETA or heading enroute if needed.

[BEagle]

I designed my Club's checklist to be printed with a laminated rear cover which is blank (to write things on with chinagraph pencil) except for a 1:500 000 ruler along the edge.

Put checklist on map, draw line from start of div point to diversion with chinagraph pencil.
LOOKOUT
Measure distance, write down distance on checklist.
LOOKOUT
Using checklist as a 'parallel ruler', transpose the track angle to a convenient VOR rose, then draw a chinagraph line through the rose.
LOOKOUT
Read off the angle, write it down on the checklist.
LOOKOUT
Work out the drift value ('clock fraction' of max drift) and apply to track to obtain heading.
LOOKOUT
Work out the still air estimate using (at 90 KTAS) 1 1/2 miles per minute. I.e., double distance and divide by 3 (in your head if poss). Write it down.
LOOKOUT
Work out head/tailwind component first as an absolute value, then as a percentage of your TAS. Extend/reduce the still air estimate by the same percentage; write it down.
LOOKOUT
Write heading and time on map, put checklist away.
LOOKOUT
NB if there are any good visual fixes on the route.

Fly a/c to start-of-div point.
Do pre-HAAT check, set off, note the actual time.
Add leg time to start-of-div time to obtain ETA.
Do post-HAAT check, fly as accurately as you can, using primarily heading and time backed up with some ground-to-map confirmation.

Normally on a PPL Skill Test diversion, the Examiner will allow you time to sort yourself out - and the diversion destination should be something you can recognise easily.

SCA is fine for ALL flying. The CPL-factories are talking rubbish when they say that you will always be permitted to track direct to the turning point if off-track. That might well cause you to infringe airspace later on. It is better to regain track as soon as practical by a simple, reliable method if you are off track; you will then be more likely to observe your pre-planned visual fixes.

The real reason that many CPL FTOs don't teach SCA is that they don't understand the theory and it isn't in their text books. Anyone ex-military has probably used it anywhere from 90-420 KTAS - and it works just fine.

In CAS, if ATC vector you off-track you might subsequenly be recleared DCT turning point - but you might also be told to regain the airway centreline.

[GuinnessQueen]

The real reason that many CPL FTOs don't teach SCA is that they don't understand the theory and it isn't in their text books. Anyone ex-military has probably used it anywhere from 90-420 KTAS - and it works just fine.

So come on then Beag's ...can you enlighten us?

I have several methods, taught by different schools and I know which one suits which situations.....I don't know which name refers to which method.

[Sul]

Thanks BEagle, you've been really helpful. :D

He has detailed the SCA method here GuinnessQueen: http://www.pprune.org/forums/showthread.php?s=&threadid=154455

Also, for convenience, I'll quote:

I use a version of the 1 in 60 termed the Standard Closing Angle method:

If you realise that you are a miles off track and wish to fly b miles back on to track, then you need to turn through an angle ö whose sine is equal to a/b. Now the 1 in 60 rule tells us that ö is more or less equal to (a/b)x60 and if you fly your distance b at v miles per minute for t minutes, then ö = (60/v)x(a/t). If a and t are made numerically the same, that is you fly for the same number of minutes as your number of miles off track, then a = t and a Standard Closing Angle ö of (60/v) can be used where v is expressed in miles per minute. Hence the SCA at 360 kts is 10°, at 120 kts it is 30° and at 90 kts the SCA is 40°.

With a SCA of 40 deg, along track velocity v cos ö is 0.766 v or roughly 3/4 of the original velocity; hence what would have taken 3 minutes now takes 4. The ETA should therefore be delayed by 1/3 of the time spent flying at the SCA.

It's so easy that many dyed-in-the-wool FIs won't trust it!

How far off track? 3 miles
Turn towards by 40 deg.
Fly for 3 minutes towards track and note that ETA at the end of the leg will be + 1 minute
Return to original heading, re-check DI synchronisation and slip ball.

What does HAAT stand for? Searched the forum/google.. doesn't come up. :confused:

[BEagle]

Not in this context it doesn't!

Heading
Airspeed
Altitude
Time(r)

pre-HAAT:

Read the Heading off the log and set it on the Hdg bug if you have one. Check DI and compass are synchronised.

Confirm the Airspeed is correct and the a/c is in trim.

Confirm the Altitude is correct and steady.

Check that whatever you're going to use to measure Time is ready to be started ('hacked') at the start point.

Overfly the start point on track, start the timer, note the time.

Then, as soon as possible:

Read the Heading off the DI, check it aaginst the compass, then cross-check it against the log (e.g. is it 123deg or 132 deg?)

Recheck that Airspeed and Altitude are steady and correct.

Check that the Timer is actually running.

Add the leg time to the start time and note down the ETA.

Put map down, LOOKOUT and fly accurately.

1-2 min before the pre-planned visual fix ( a rough fraction of the track length e.g. about 1/3 or 1/4 - or 1/2 if it's a short leg), note the actual elapsed time against the planned elapsed time then, if you've been flying accurately, adjust ETA by adding the appropriate multiple of the difference to the planned ETA. Otherwise, just carry the difference and apply to the ETA.

Do FREDA checks at low activity points, never at turning points. The ancient 'HATFIRE' check was rightly binned many years ago!

Don't get distracted by RT - only use the minimum service you actually need. Remember that VFR means SEE AND AVOID!!