1:60 rule
You need at least 3 identifiable features. One at the start of the track deviation, one for the off track fix and the third at the track regain fix although you could DR the last one with some loss of certainty of position.
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At halfway your correction angle CA will be 2 X Track error (TE)
at 1/4 CA= 1.5 X TE
at 3/4 CA= 3 X TE
Basically, the rule is that for each 1 degree deviation from planned track the aircraft will be 1 nm off track after flying 60 miles.
So,
(distance off track ( in nm) /distance travelled(nm)) x 60 = TE in degrees.
and,
( distance off track ( nm) /distance to go(nm)) x 60= Closing angle in degrees
Correction angle = TE + Closing Angle.
At the halfway mark Distance travelled and distance to go is the same so TE and closing angle have equal values hence Correction angle = 2 xTE
If you like maths there is a much more detailed explanation - but you can work that out. Think about Sine rule.
at 1/4 CA= 1.5 X TE
at 3/4 CA= 3 X TE
Basically, the rule is that for each 1 degree deviation from planned track the aircraft will be 1 nm off track after flying 60 miles.
So,
(distance off track ( in nm) /distance travelled(nm)) x 60 = TE in degrees.
and,
( distance off track ( nm) /distance to go(nm)) x 60= Closing angle in degrees
Correction angle = TE + Closing Angle.
At the halfway mark Distance travelled and distance to go is the same so TE and closing angle have equal values hence Correction angle = 2 xTE
If you like maths there is a much more detailed explanation - but you can work that out. Think about Sine rule.
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Featureless terrain or water - now there's a challenge. Is this from point of origin to point of arrival or only over part of the route.
You will still be flying along your chinagraph pencil line but have no ground features to refer to. You will still be able to establish the expected position on the line form elapsed time. So you will then need to get a fix using VOR/ADF which will give you an approximate position which you can assess relative to you original track.
If you're making long flights over water or desert the a GPS would be advisable.
You will still be flying along your chinagraph pencil line but have no ground features to refer to. You will still be able to establish the expected position on the line form elapsed time. So you will then need to get a fix using VOR/ADF which will give you an approximate position which you can assess relative to you original track.
If you're making long flights over water or desert the a GPS would be advisable.
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try these "real numbers" :
I am on (already computed) heading 285
XTE
I am now aware of being 3nm to the right after 27 miles
I am doing 89 kts
FIRST CORRECTION
so I turn 50 deg to the left immediately ( I've memorised this number)
my aim is to get back on track in 3nm/min that's 3 min.
SECOND CORRECTION
now time to think is about 2.5 min...
recall 3 to Right having run 27 approximates 6 in 60 or 6 deg
I now turn an extra 6 deg to the left.(optional)
THIRD CORRECTION
3 mins up: original 285 less 6 say 280 should do it for amended heading. If that optional extra correction was made as above, the corrected heading will be 50 deg to the right, a reversal of the original sharp turn. Otherwise its 50-6=44 to turn to the new heading.
80kts turn 50(49)
90kts turn 45(42)
100kts turn 40(37)
110kts turn 35(33)
120kts turn 30(30)
figures in brackets are precise.
track error is always positive and never greater than 7%
now put in your own numbers
I think its quick and dirty!
I am on (already computed) heading 285
XTE
I am now aware of being 3nm to the right after 27 miles
I am doing 89 kts
FIRST CORRECTION
so I turn 50 deg to the left immediately ( I've memorised this number)
my aim is to get back on track in 3nm/min that's 3 min.
SECOND CORRECTION
now time to think is about 2.5 min...
recall 3 to Right having run 27 approximates 6 in 60 or 6 deg
I now turn an extra 6 deg to the left.(optional)
THIRD CORRECTION
3 mins up: original 285 less 6 say 280 should do it for amended heading. If that optional extra correction was made as above, the corrected heading will be 50 deg to the right, a reversal of the original sharp turn. Otherwise its 50-6=44 to turn to the new heading.
80kts turn 50(49)
90kts turn 45(42)
100kts turn 40(37)
110kts turn 35(33)
120kts turn 30(30)
figures in brackets are precise.
track error is always positive and never greater than 7%
now put in your own numbers
I think its quick and dirty!
Last edited by hhobbit; 6th Aug 2009 at 13:19.
Grandpa Aerotart
Ok crash one, and anyone else that is interested, an example of use of the 1/60 over ocean/featureless terrain.
Once upon a time, some years before GPS came on the market, I was tasked with flying from A to B, at night, over the Solomon Sea from PNG to Honiara in a Beech Queenair. I had to track via an NDB on a small Island called Gizo (due IFR enroute navaid requirements) and then down The Slot to Honiara.
As an aside it was a PNG Govt charter and they required 2 pilots so a newbie, who arrived in PNG that morning, was tasked to warm the right seat. The pax were duly loaded, along with some locked large tin boxes (which I was not allowed to know the contents of) and away we went.
Our point of departure had a VOR/DME but terrain would ensure that we lost reception of those not far past TOPC. My plan was to fix my position before we lost those navaids and then do a 'Running Fix' (something I learned navigating yachts on coastal races as a teen (LONG before even Satnav let alone GPS) as I passed abeam an Island with an NDB that would be barely in range - but better than nothing. A Running Fix is when you take a note of the time your relative bearing to a place is 45 degree off and 90 off - if you know your speed then it is easy to calculate how far abeam you were at the 90 off and, therefore, whether you're on track/how far off track and do a 1/60 to resolve any issue. All based on an Equilateral Triangle.
Just past TOPC I gave the DME dist from departure and the time to my 'copilot' and we preceded on our merry way as the sun set rapidly behind us. Some hours later I tried to record the 45/90 off but never received the aid - it only surprised me slightly - this being the SWP navaids were always failing and going unreported for days. I asked my erstwhile companion for the dist/time I had given him before - "Dunno, I didn't write them down".
As I sat there pondering this something that I couldn't put my finger on but that had been bugging me since before we departed suddenly made itself manifest. I handed over control to the newbie (no autopilot - well except for the voice activated one in the RHS) and pulled out the weather reports and perused the forecast winds aloft which I had dutifully applied to the track we were flying giving us a heading. Memory dims but they indicated NW at about 15kts (our track being ENE). It suddenly occurred to me that this was the wrong time of year for NW winds - it was the SE Trade wind season and they typically blow at 15-20kts. In my defense I was a bush pilot who spent his days in the mountains flying VERY short legs between mountain strips and NEVER applied wind to a flight plan in the normal course of a working week...or month...in fact not for a few years.
I turned to my copilot and informed him I believed we were left of track - a long way...which was why we never got the Misima NDB. He sorta looked wide eyed as I explained my logic. Fair enough it was his first day using his brand new CPL.
I sat there with my chart and a pencil and calculated where I believed we were based on the heading I'd been holding (very carefully) and what I believed the real upper winds were. I then worked a DR 1/60 to track direct to Gizo figuring we'd only have to be within +/- 30nm to actually pick up the NDB and make a final course correction.
From memory the heading change I came up with was 40 degrees.
I don't remember what my copilot actually said - but the look on his face was a mixture of horror and 'you gotta be ****ting me'. He'd only met me for the first time 6-7 hours before.
I retook control, altered heading (with my heart in my mouth) and we droned on into the night - me with a very real sense of how Earhart had felt in this same area 50 years before.
Maybe another hour passed and I was really expecting to be well within the range of the Gizo NDB soon if not already - only a DR GS to work off but how far out could I have been? The ADF just swung lazily around the dial - plenty of Equatorial Night TSs around and it was doing its poor mans weather radar imitation.
About 20nm ahead was a line of TS - I intently watched a spot that stayed dark just a fraction right of the nose - maybe a nm or two off my new track - and aimed us through it - no weather radar. 5 minutes or so later we bashed our way through the line of storms and...there was an Island!!
Quite possibly the most beautiful island I have ever seen, bathed in moonlight and ringed by villages...maybe 20nm away. And right then the ADF sprang to a relative bearing of damn near 0 degrees and held steady, the ident booming through within a few more minutes. Some time later I learned that the Gizo NDB had an effective range of about 20nm...on a good day
We turned overhead the NDB 5 minutes ahead of my DR estimate and flew down the Slot under the glow of a fantastic moon and landed at Honiara. My new best mate now thought I walked on water.
Last I heard he now flies Airbus for Cathay and I fly Boeings for another airline.
Maybe an irrelevance today with handheld GPS virtually in every pilots navbag - but technology can fail and all you have left is your brain and the basics - to prove the point some years ago both my FMCs failed departing LHR - I reverted to VOR/DME/ADF and continued on to Dubai - we made up time and landed under burn - and most of all I had a BALL doing it. It turned a normally boring sector into a very interesting one.
Oh and the big tin boxes I couldn't look in?
Weapons - I had unknowingly taken a paramilitary hit team to the Solomons to sneak over onto Bouganville Island and attempt to kill the leader of the Bouganville Revolutionary Army. A week later I did a second trip over to drop off a ships captain and when I checked into the Mendana Hotel there on my bed was that days Honiara Star newspaper and it was all over the front page. They had been arrested in the Western Solomons.
We (same young fella in the RHS - hell I was only in my late 20s) checked out the next morning and departed back to PNG all the time expecting to be arrested - but were not even asked a single question.
Had we not altered course there is no land we would have spotted we would have droned out into the Pacific with no accurate idea where we were.
Ahhh the good old days
Once upon a time, some years before GPS came on the market, I was tasked with flying from A to B, at night, over the Solomon Sea from PNG to Honiara in a Beech Queenair. I had to track via an NDB on a small Island called Gizo (due IFR enroute navaid requirements) and then down The Slot to Honiara.
As an aside it was a PNG Govt charter and they required 2 pilots so a newbie, who arrived in PNG that morning, was tasked to warm the right seat. The pax were duly loaded, along with some locked large tin boxes (which I was not allowed to know the contents of) and away we went.
Our point of departure had a VOR/DME but terrain would ensure that we lost reception of those not far past TOPC. My plan was to fix my position before we lost those navaids and then do a 'Running Fix' (something I learned navigating yachts on coastal races as a teen (LONG before even Satnav let alone GPS) as I passed abeam an Island with an NDB that would be barely in range - but better than nothing. A Running Fix is when you take a note of the time your relative bearing to a place is 45 degree off and 90 off - if you know your speed then it is easy to calculate how far abeam you were at the 90 off and, therefore, whether you're on track/how far off track and do a 1/60 to resolve any issue. All based on an Equilateral Triangle.
Just past TOPC I gave the DME dist from departure and the time to my 'copilot' and we preceded on our merry way as the sun set rapidly behind us. Some hours later I tried to record the 45/90 off but never received the aid - it only surprised me slightly - this being the SWP navaids were always failing and going unreported for days. I asked my erstwhile companion for the dist/time I had given him before - "Dunno, I didn't write them down".
As I sat there pondering this something that I couldn't put my finger on but that had been bugging me since before we departed suddenly made itself manifest. I handed over control to the newbie (no autopilot - well except for the voice activated one in the RHS) and pulled out the weather reports and perused the forecast winds aloft which I had dutifully applied to the track we were flying giving us a heading. Memory dims but they indicated NW at about 15kts (our track being ENE). It suddenly occurred to me that this was the wrong time of year for NW winds - it was the SE Trade wind season and they typically blow at 15-20kts. In my defense I was a bush pilot who spent his days in the mountains flying VERY short legs between mountain strips and NEVER applied wind to a flight plan in the normal course of a working week...or month...in fact not for a few years.
I turned to my copilot and informed him I believed we were left of track - a long way...which was why we never got the Misima NDB. He sorta looked wide eyed as I explained my logic. Fair enough it was his first day using his brand new CPL.
I sat there with my chart and a pencil and calculated where I believed we were based on the heading I'd been holding (very carefully) and what I believed the real upper winds were. I then worked a DR 1/60 to track direct to Gizo figuring we'd only have to be within +/- 30nm to actually pick up the NDB and make a final course correction.
From memory the heading change I came up with was 40 degrees.
I don't remember what my copilot actually said - but the look on his face was a mixture of horror and 'you gotta be ****ting me'. He'd only met me for the first time 6-7 hours before.
I retook control, altered heading (with my heart in my mouth) and we droned on into the night - me with a very real sense of how Earhart had felt in this same area 50 years before.
Maybe another hour passed and I was really expecting to be well within the range of the Gizo NDB soon if not already - only a DR GS to work off but how far out could I have been? The ADF just swung lazily around the dial - plenty of Equatorial Night TSs around and it was doing its poor mans weather radar imitation.
About 20nm ahead was a line of TS - I intently watched a spot that stayed dark just a fraction right of the nose - maybe a nm or two off my new track - and aimed us through it - no weather radar. 5 minutes or so later we bashed our way through the line of storms and...there was an Island!!
Quite possibly the most beautiful island I have ever seen, bathed in moonlight and ringed by villages...maybe 20nm away. And right then the ADF sprang to a relative bearing of damn near 0 degrees and held steady, the ident booming through within a few more minutes. Some time later I learned that the Gizo NDB had an effective range of about 20nm...on a good day
We turned overhead the NDB 5 minutes ahead of my DR estimate and flew down the Slot under the glow of a fantastic moon and landed at Honiara. My new best mate now thought I walked on water.
Last I heard he now flies Airbus for Cathay and I fly Boeings for another airline.
Maybe an irrelevance today with handheld GPS virtually in every pilots navbag - but technology can fail and all you have left is your brain and the basics - to prove the point some years ago both my FMCs failed departing LHR - I reverted to VOR/DME/ADF and continued on to Dubai - we made up time and landed under burn - and most of all I had a BALL doing it. It turned a normally boring sector into a very interesting one.
Oh and the big tin boxes I couldn't look in?
Weapons - I had unknowingly taken a paramilitary hit team to the Solomons to sneak over onto Bouganville Island and attempt to kill the leader of the Bouganville Revolutionary Army. A week later I did a second trip over to drop off a ships captain and when I checked into the Mendana Hotel there on my bed was that days Honiara Star newspaper and it was all over the front page. They had been arrested in the Western Solomons.
We (same young fella in the RHS - hell I was only in my late 20s) checked out the next morning and departed back to PNG all the time expecting to be arrested - but were not even asked a single question.
Had we not altered course there is no land we would have spotted we would have droned out into the Pacific with no accurate idea where we were.
Ahhh the good old days
Last edited by Chimbu chuckles; 6th Aug 2009 at 17:05.
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Chimbu chuckles
Now that is navigation. Brilliant stuff.
Unfortunately my bug smasher has no VOR, ADF, DME, transponder etc. I have a compass & a PDA Memory Map GPS device which I hope will be enough. I am too old & too late in the game to aspire to such feats, but I admire those who have & do.
Now that is navigation. Brilliant stuff.
Unfortunately my bug smasher has no VOR, ADF, DME, transponder etc. I have a compass & a PDA Memory Map GPS device which I hope will be enough. I am too old & too late in the game to aspire to such feats, but I admire those who have & do.
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You need at least 3 identifiable features. One at the start of the track deviation, one for the off track fix and the third at the track regain fix although you could DR the last one with some loss of certainty of position.
The simple maths, when applied carefully, is brilliant!
Done the equivalent to a blank sheet of paper by flying over the top of a hundred miles of fog/low cloud. In my instructing days I loved finding a nice fog morning for my CPL students who couldn't trust headings & DR. New South Wales west of the dividing range in winter was a great time for that but I've also had charters to no-navaid airstrips in Queensland that had the same issue.
Flying across the deserts in outback Australia requires a good grasp of navigation & track correction/ground speed/ETIs. The lack of ground features meant planning track corrections to arrive on track at some miniscule feature that could be seen. Some of my most enjoyable navigational tasks were flying direct from NW. Western Oz to Alice Springs in Central Australia & then direct to Birdsville or Eastern Oz.
Fog & low cloud was a common problem flying in the Shetland Islands. TAS as heading rarely worked due to the gale force winds. Doesn't change the basics of navigation though.
Flying around the Bahamas dodging TS at low level is also an area where good DR & 1:60 skills are beneficial. Not always a convenient navaid in reach.
Flying across the deserts in outback Australia requires a good grasp of navigation & track correction/ground speed/ETIs. The lack of ground features meant planning track corrections to arrive on track at some miniscule feature that could be seen. Some of my most enjoyable navigational tasks were flying direct from NW. Western Oz to Alice Springs in Central Australia & then direct to Birdsville or Eastern Oz.
Fog & low cloud was a common problem flying in the Shetland Islands. TAS as heading rarely worked due to the gale force winds. Doesn't change the basics of navigation though.
Flying around the Bahamas dodging TS at low level is also an area where good DR & 1:60 skills are beneficial. Not always a convenient navaid in reach.
Last edited by Tinstaafl; 7th Aug 2009 at 03:30.
Long story, might have mentioned it, but I knew the Capt. who crossed the Arctic regions ANC to LHR part way, using two toothpicks stuck into 2 pieces of cheese chunks. Steered a constant Sun line - shadow of one toothpick over the other. He wasn't so much unsure of his positon as being without a reliable heading reference - i.e. a Compass. Sun moves around at 15 deg / hour. Used that to do the rest of the maths.
