VFR on top
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VFR on top
Flew a short trip a few days ago, and we were VFR at 3000 on top of FEW 1200. the flight was uneventful, but it got me thinking...
What sort of legal limits are in place for VFR on top. Looked in my AirLaw book and it says a PPL with no IMC or IR, must remain in sight of the surface.
Does this mean that you could fly VFR on top, in BKN cloud, provided you had the surfact in sight?
(Sorry if this has been asked before, I did perform a seach but nothing came up.)
What sort of legal limits are in place for VFR on top. Looked in my AirLaw book and it says a PPL with no IMC or IR, must remain in sight of the surface.
Does this mean that you could fly VFR on top, in BKN cloud, provided you had the surfact in sight?
(Sorry if this has been asked before, I did perform a seach but nothing came up.)
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Yes it's been covered before 
First thing to remember - cloud can break up, or it can close in. Licence privileges clearly state "Clear of Cloud and in sight of the surface". So - with those two factors thought about the best rules of thumb are:
If it's FEW or SCT then no problems - providing the holes are big enough to descend through (they will be if that's the cloud cover - SCT being no greater than half sky covered)
If it's BKN then DON'T risk it. The holes won't be big enough to fulfill your legal obligation, plus if they fill in you're going to get caught out above, with the ensuing IMC descent that's going to require.
OVC - self explanatory really
First thing to remember - cloud can break up, or it can close in. Licence privileges clearly state "Clear of Cloud and in sight of the surface". So - with those two factors thought about the best rules of thumb are:
If it's FEW or SCT then no problems - providing the holes are big enough to descend through (they will be if that's the cloud cover - SCT being no greater than half sky covered)
If it's BKN then DON'T risk it. The holes won't be big enough to fulfill your legal obligation, plus if they fill in you're going to get caught out above, with the ensuing IMC descent that's going to require.
OVC - self explanatory really
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Chilli has it absolutely right.
Understand the difference between "legal" and "safe". "Legal" is in sight of the surface, and you can satisfy that by peering down through a tiny hole.
"Safe" will vary depending on your experience and training, and the aircraft's equipment. You have to consider a) how you will navigate, b) whether you will still be legal 10nm further on, and c) how you wil get back down underneath the clouds.
(Another example of "legal" but not "safe" would be flying cross-country in 3km viz. I have flown in this kind of viz several times, flying IFR and navigating using navaids, but I've attempted (just for fun) to fix my position visually, and it's pretty difficult. Not impossible if you use the correct techniques, but not something to try by yourself for the first time.)
FFF
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Understand the difference between "legal" and "safe". "Legal" is in sight of the surface, and you can satisfy that by peering down through a tiny hole.
"Safe" will vary depending on your experience and training, and the aircraft's equipment. You have to consider a) how you will navigate, b) whether you will still be legal 10nm further on, and c) how you wil get back down underneath the clouds.
(Another example of "legal" but not "safe" would be flying cross-country in 3km viz. I have flown in this kind of viz several times, flying IFR and navigating using navaids, but I've attempted (just for fun) to fix my position visually, and it's pretty difficult. Not impossible if you use the correct techniques, but not something to try by yourself for the first time.)
FFF
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Last edited by FlyingForFun; 29th Jan 2006 at 17:46.
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Thanks for your replies, I'm a pretty low hours PPL so I would probably think twice about flying above a SCT layer, and BKN would definitely be out of the question. but I was just interested out of curiosity really.
I would imagine VFR in 3km would be very challenging! I've flown in the local area with a vis of 9k and that was unnerving!
I would imagine VFR in 3km would be very challenging! I've flown in the local area with a vis of 9k and that was unnerving!
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The legality is one thing, the practicality is another.
A UK PPL can fly down to 3000m vis but he can't navigate using the methods he's been taught.
A UK PPL can fly above an overcast layer provided there is a bit of the surface visible somewhere.... but he also can't navigate using the methods he's been taught.
Most other countries allow a PPL to fly out of sight of the surface, so I wonder why the CAA did this. It does allow less nav training, of course.....
Of course I can't resist saying that a UK PPL with the IMC Rating is allowed to fly VFR out of sight of the surface in any airspace where this is allowed, outside the UK (even though the IFR privileges of the IMCR are UK only).
The trap in flying above clouds is obviously not getting back down, or not getting back down legally
A UK PPL can fly down to 3000m vis but he can't navigate using the methods he's been taught.
A UK PPL can fly above an overcast layer provided there is a bit of the surface visible somewhere.... but he also can't navigate using the methods he's been taught.
Most other countries allow a PPL to fly out of sight of the surface, so I wonder why the CAA did this. It does allow less nav training, of course.....
Of course I can't resist saying that a UK PPL with the IMC Rating is allowed to fly VFR out of sight of the surface in any airspace where this is allowed, outside the UK (even though the IFR privileges of the IMCR are UK only).
The trap in flying above clouds is obviously not getting back down, or not getting back down legally
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Originally Posted by IO540
A UK PPL can fly down to 3000m vis but he can't navigate using the methods he's been taught.
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A UK PPL can fly down to 3000m vis but he can't navigate using the methods he's been taught.
Why could you not navigate using the methods taught at PPL level? If you're flying something like, for example a Luton Minor, that poodles along at 60mph and you have a bit of experience, there should be no great problem, or have I missed something?
SS
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Shortstripper,
I agree with you that it is easy to navigate in poor viz in, say, a Luton Minor - but I think IO540 is correct that the techniques taught at PPL level don't work in this viz - even more so at low speed. As I see it, there are two problems with flying in very low viz - navigation, and control of the aircraft.
First, navigation:
The ded reckoning techniques which are taught at PPL level will work perfectly well in any weather, including in IMC.
However, ded reckoning is only as good as the wind forecast you have to work with. If the forecast is not accurate, you have to back the ded reckoning up with some other means of navigation - map reading being the one which is taught at PPL level, and which should always be the primary one for VFR flight.
The techniques are based on the idea that if you follow your ded reckoning plan, you will be close enough to your track to be able to see features which are on or near your track, estimate how far off track you are, and make corrections. As the viz decreases, a number of problems arise. First of all, if you are not within a couple of miles of your track, or easily recogniseable features near your track, you will not see those features. The slower you travel, the more effect the wind will have on you, therefore the further off-track you might be if the wind forecast is wrong - so I would guess this particular aspect of navigation would be more difficult in a slower aircraft. (I believe that fast jet pilots have very few problems ded reckoning because they go so fast the wind has very little effect on them whatsoever, but maybe someone else can confirm?)
Also, it is more difficult to possitively identify features, because it is not so easy to compare a feature to its surroundings and see combinations of features when the surroundings and nearby features are further away than the limits of the viz - this, though, I don't think is affected by speed.
So what we need is an alternative method of navigation. The easiest way, I find, is by using line features. (I'm quite lucky in that right now I fly near a very big line feature called "the coast", which makes life very easy!) My first choice option is to follow line features. If that's not possible, then I would fly towards a line feature, making sure I keep to one side of where I would like to reach the line feature - typically to the right hand side. That way, when I reach the line feature, I know I have to turn left to arrive at my destination. In contrast to ded reckoning, this technique does work very well at low speeds, which is why if I'm anything much faster than a Luton Minor I would put some flaps down and use a "slow, safe cruise". The other thing I would do when planning a trip in this weather is make sure I am very aware of any obstructions along the way, and either fly at a height above the legal IFR MSA (even though I am VFR), or if that's not possible, find another way of definitely staying out of the way of the obstructions (e.g. knowing that the obstruction is to the north of the motorway, so remaining south will keep you clear.)
The second issue of how to control the aircraft without a horizon is a completely different one, and comes down to a combination of visual flying and instrument flying, very similar to what you do at night.
FFF
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I agree with you that it is easy to navigate in poor viz in, say, a Luton Minor - but I think IO540 is correct that the techniques taught at PPL level don't work in this viz - even more so at low speed. As I see it, there are two problems with flying in very low viz - navigation, and control of the aircraft.
First, navigation:
The ded reckoning techniques which are taught at PPL level will work perfectly well in any weather, including in IMC.
However, ded reckoning is only as good as the wind forecast you have to work with. If the forecast is not accurate, you have to back the ded reckoning up with some other means of navigation - map reading being the one which is taught at PPL level, and which should always be the primary one for VFR flight.
The techniques are based on the idea that if you follow your ded reckoning plan, you will be close enough to your track to be able to see features which are on or near your track, estimate how far off track you are, and make corrections. As the viz decreases, a number of problems arise. First of all, if you are not within a couple of miles of your track, or easily recogniseable features near your track, you will not see those features. The slower you travel, the more effect the wind will have on you, therefore the further off-track you might be if the wind forecast is wrong - so I would guess this particular aspect of navigation would be more difficult in a slower aircraft. (I believe that fast jet pilots have very few problems ded reckoning because they go so fast the wind has very little effect on them whatsoever, but maybe someone else can confirm?)
Also, it is more difficult to possitively identify features, because it is not so easy to compare a feature to its surroundings and see combinations of features when the surroundings and nearby features are further away than the limits of the viz - this, though, I don't think is affected by speed.
So what we need is an alternative method of navigation. The easiest way, I find, is by using line features. (I'm quite lucky in that right now I fly near a very big line feature called "the coast", which makes life very easy!) My first choice option is to follow line features. If that's not possible, then I would fly towards a line feature, making sure I keep to one side of where I would like to reach the line feature - typically to the right hand side. That way, when I reach the line feature, I know I have to turn left to arrive at my destination. In contrast to ded reckoning, this technique does work very well at low speeds, which is why if I'm anything much faster than a Luton Minor I would put some flaps down and use a "slow, safe cruise". The other thing I would do when planning a trip in this weather is make sure I am very aware of any obstructions along the way, and either fly at a height above the legal IFR MSA (even though I am VFR), or if that's not possible, find another way of definitely staying out of the way of the obstructions (e.g. knowing that the obstruction is to the north of the motorway, so remaining south will keep you clear.)
The second issue of how to control the aircraft without a horizon is a completely different one, and comes down to a combination of visual flying and instrument flying, very similar to what you do at night.
FFF
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A UK PPL can fly down to 3000m vis but he can't navigate using the methods he's been taught
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"If you're flying something like, for example a Luton Minor, that poodles along at 60mph and you have a bit of experience, there should be no great problem, or have I missed something"
At 60mph yes, watching out for pylons, towers, etc. But as FFF says, DR navigation will be correspondingly harder because the slow airspeed will give rise to huge wind (heading) corrections, say 30-40 degrees, for typical values of wind aloft, but the poor vis will make it hard to make the corrections.
Also 3000m vis will invariably mean no horizon. In the UK, it is either due to very heavy rain, or (more often) due to haze. In the latter case, you are flying in IMC in all but name. It's like being in an aquarium that hasn't been cleaned for a year. From say 3000ft, you can see the surface but only just, so unless you have instrument skills you have to be down (say 500-1000ft) and then you can't see far ahead to navigate.
During my PPL training, I was with an instructor who was a bit of a cowboy. He liked to demonstrate things like stopping the engine totally and gliding (C152). But he taught me a few good things, like flying in 3000m vis in drizzle, low down, between hills, and you quickly realise it's an easy way to die. It's easy to see how getting into that situation quickly becomes a fight to just stay away from terrain. DR nav, with its high workload, will go straight out of the window. If the poor vis is due to rain, there will very likely be low cloud (say OVC007) and then a pilot without instrument skills is stuck between ground and low cloud, with poor vis. I've heard it on the radio a few times and it is quite scary.
Like a lot of things in flying, it's OK in a familiar area, and this is the unstated perspective which a lot of people are writing from. If you did a survey of typical trip radius for 60mph planes, you'd see this
A GPS is the best way to navigate. VOR tracking is also fine (and is sort-of mentioned in the PPL) but if one is low down the reception might not work, so one has to fly higher and then (in 3k vis) you won't see much of the ground so you need reasonable instrument skills. DME reception disappears particularly fast when low down.
At 60mph yes, watching out for pylons, towers, etc. But as FFF says, DR navigation will be correspondingly harder because the slow airspeed will give rise to huge wind (heading) corrections, say 30-40 degrees, for typical values of wind aloft, but the poor vis will make it hard to make the corrections.
Also 3000m vis will invariably mean no horizon. In the UK, it is either due to very heavy rain, or (more often) due to haze. In the latter case, you are flying in IMC in all but name. It's like being in an aquarium that hasn't been cleaned for a year. From say 3000ft, you can see the surface but only just, so unless you have instrument skills you have to be down (say 500-1000ft) and then you can't see far ahead to navigate.
During my PPL training, I was with an instructor who was a bit of a cowboy. He liked to demonstrate things like stopping the engine totally and gliding (C152). But he taught me a few good things, like flying in 3000m vis in drizzle, low down, between hills, and you quickly realise it's an easy way to die. It's easy to see how getting into that situation quickly becomes a fight to just stay away from terrain. DR nav, with its high workload, will go straight out of the window. If the poor vis is due to rain, there will very likely be low cloud (say OVC007) and then a pilot without instrument skills is stuck between ground and low cloud, with poor vis. I've heard it on the radio a few times and it is quite scary.
Like a lot of things in flying, it's OK in a familiar area, and this is the unstated perspective which a lot of people are writing from. If you did a survey of typical trip radius for 60mph planes, you'd see this
A GPS is the best way to navigate. VOR tracking is also fine (and is sort-of mentioned in the PPL) but if one is low down the reception might not work, so one has to fly higher and then (in 3k vis) you won't see much of the ground so you need reasonable instrument skills. DME reception disappears particularly fast when low down.
Why do it if it's not fun?
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One thing worth noting about navigation aids in this kind of weather: Yes, they are extremely useful, and you should make full use of them. But there is a real danger that if you spend too much time heads-in watching the navaids, you will inadvertantly enter IMC.
As long as you are aware of this, and make a concious effort to focus your attention outside with only occassional glances at the navaids to confirm you position, any navaid will be a great help, but without being aware of the potential danger you might find you're worse off with the navaids than you would have been without them.
(This obviously doesn't apply so much when VFR-on-top as it does in poor viz.)
FFF
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As long as you are aware of this, and make a concious effort to focus your attention outside with only occassional glances at the navaids to confirm you position, any navaid will be a great help, but without being aware of the potential danger you might find you're worse off with the navaids than you would have been without them.
(This obviously doesn't apply so much when VFR-on-top as it does in poor viz.)
FFF
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If you can't navigate in 3 Km visibility then clearly you are not being taught the correct techniques!! The VFR minima is 1500 metres! The UK doubled that for UK issued licences but the holder of a foreign PPL can fly to the 1500 ft minima and MUST be able to navigate! I certainly teach my students to, they may not be able to do it but then they add their "personal allowance"
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Taking 1500m vis, the correct technique would be?
(Assume completely unfamiliar territory, no obvious landmarks i.e. within PPL privileges)
You call it "adding personal allowances".
I call it "not being trained adequately for the licence privileges".
(Assume completely unfamiliar territory, no obvious landmarks i.e. within PPL privileges)
You call it "adding personal allowances".
I call it "not being trained adequately for the licence privileges".
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Originally Posted by dwshimoda
This may be a stupid question, and if it is I'll apologise now, but if you are on top and out of sight of the land, is this logged as IFR?
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There is no way that i would want to be up in 1500m vis at all.
Thats getting to the point that you will be struggling to see the runway in the circuit, if at all. I dont care if it is legal in other countries. It just isnt safe!
Id rather sit down, have a brew and read my mag
Thats getting to the point that you will be struggling to see the runway in the circuit, if at all. I dont care if it is legal in other countries. It just isnt safe! Id rather sit down, have a brew and read my mag
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but the holder of a foreign PPL can fly to the 1500 ft minima
With 1500m vis you have a circle of view of 3k (1.6nm). At 90kts this means you are potentially uncertain of your position every 1 minute if using ground features and dead reckoning. Keeps you busy in the cockpit! Fly over a featureless patch for 1 minute and your guessing (or hoping) really.
If you can't navigate in 3 Km visibility then clearly you are not being taught the correct techniques!!
A GPS is the best way to navigate
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A GPS is the best way to navigate.
Quote
Don't agree with that one.
Stirring the old GPS pot again then. Ok - give me just three reasons why GPS isnt the best way - and please exclude it might just stop working because so might any of the radio navigation aids - and we are discussing navigating not flying an apporach.
A GPS is the best way to navigate.
Quote
Don't agree with that one.
Stirring the old GPS pot again then. Ok - give me just three reasons why GPS isnt the best way - and please exclude it might just stop working because so might any of the radio navigation aids - and we are discussing navigating not flying an apporach.