How close is a near miss?

antiskeptic

I spotted this forum just now and thought to ask..

I was on a tourist flight to Tenerife a couple of years back and had a seat by the window, forward of the wing. Somewhere towards the latter part of the flight whilst looking out the window a similar sized passenger plane to the one I was in (a 737 I suppose) - twin engined too - came hurtling by, and I mean hurtling, in the opposite direction.

He was just below us and going nearly 180 degrees in the opposite direction. I could see that there was just 'clear air' behind the engines for a couple of engine lengths or so, then a cloud of dense black 'smoke' for a bit then the familiar white vapour trail.

The speed it went by at was breathtaking - what would it be, a 1000mph or so combined? Yet you could see all the detail, the windows, markings etc.

On the ground I looked at other 737's taxiing around and guesstimated the distance between our jet and the other to be 2-300metres or so, with the vertical distance between the two planes at around a plane length (stood on it's nose).

Was this a near miss? And if so, how near a miss was it?

EchoIndia

antiskeptic wrote: »

I spotted this forum just now and thought to ask..

I was on a tourist flight to Tenerife a couple of years back and had a seat by the window, forward of the wing. Somewhere towards the latter part of the flight whilst looking out the window a similar sized passenger plane to the one I was in (a 737 I suppose) - twin engined too - came hurtling by, and I mean hurtling, in the opposite direction.

He was just below us and going nearly 180 degrees in the opposite direction. I could see that there was just 'clear air' behind the engines for a couple of engine lengths or so, then a cloud of dense black 'smoke' for a bit then the familiar white vapour trail.

The speed it went by at was breathtaking - what would it be, a 1000mph or so combined? Yet you could see all the detail, the windows, markings etc.

On the ground I looked at other 737's taxiing around and guesstimated the distance between our jet and the other to be 2-300metres or so, with the vertical distance between the two planes at around a plane length (stood on it's nose).

Was this a near miss? And if so, how near a miss was it?

The minimum permitted vertical separation is 1,000 feet and as all commerical aircraft carry the TCAS avoidance system it is highly unlikely that the aircraft mentioned here was any closer than that. Trusting your eyesight is not a reliable guide, especially given the sort of closing speeds involved. I like the description "hurtling", as though the aircraft was somehow out of control, when pretty clearly it was travelling a straight line and in level flight!

diverdriver

It's five miles horizontal or a thousand feet vertical. A thousand feet does look awfully close. Closing speeds are spectacular, hurtling is a good word for it. It could have been a loss of separation but probably wasn't. It's difficult to judge distances without some form of reference. In clear air at altitude too, objects can appear a lot closer.

It does however give a sense of how important maintaining separation is. A collision at those speeds doesn't bear thinking of. :eek:

Steyr

If you say the latter stages you may also have been in busy airspace seeing aircraft that have just commenced a descent into an airport or have just taken off and you may have entered a stack.

pclancy

A dash-8 flew overhead me 1000ft above and probably 200 kts faster recently and my god did I get a shock. I'd heard his clearance and been told he'd be passing overhead but it still felt very close and that was at 3000ft. I was probably only doing 90kts or so but the closing speed (once I finally seen him) was quite dramatic.

highlydebased

Slightly off topic, but on a nice night flying east on the ocean other aircraft on paralell NATS can be seen easily, its quite interesting

dennistuam

the 11 30 ryanair stockholm to dublin meets a easy jet london to glasgow flight over cool

antiskeptic

diverdriver wrote: »

It's five miles horizontal or a thousand feet vertical. A thousand feet does look awfully close. Closing speeds are spectacular, hurtling is a good word for it. It could have been a loss of separation but probably wasn't. It's difficult to judge distances without some form of reference. In clear air at altitude too, objects can appear a lot closer.

It does however give a sense of how important maintaining separation is. A collision at those speeds doesn't bear thinking of. :eek:

Am I right in assuming there's some kind of sliding scale between horizontal and vertical then - this guy was about 30 degrees below horizonal?

Whilst taking your point about judging distance I'd note my referencing off a sense of how much aircraft fitted in my window frame at various points of it's flyby. If, for example, a mental snapshot sees the nose touch windowframeleft just as leading edge of the tailplane appears at windowframeright ...and replicates that 'photo' on the ground against a similar aircraft, then you'd have a reasonably close approximation of linear distance.

Happily, like a car crash, it happened too quickly to even think of getting a fright - so I had the chance to enjoy the sheer majesty of it all.

irishatco

antiskeptic wrote: »

Am I right in assuming there's some kind of sliding scale between horizontal and vertical then - this guy was about 30 degrees below horizonal?

Not when applying radar separation.

The standard rule is 5nm lateral or 1000ft vertical, not a mix of the two.

That standard rule is amended in certain airspace, for example in the Dublin TMA the lateral separation is reduced to 3nm. In other areas where radar coverage may not be 100% reliable the lateral requirement can be increased.

antiskeptic

irishatco wrote: »

Not when applying radar separation.The standard rule is 5nm lateral or 1000ft vertical, not a mix of the two

So what happens when an aircraft is 30 degrees low? He's neither vertical nor horizontal..

highlydebased

antiskeptic wrote: »

So what happens when an aircraft is 30 degrees low? He's neither vertical nor horizontal..

What do you mean by 30 degrees low?

irishatco

antiskeptic wrote: »

So what happens when an aircraft is 30 degrees low? He's neither vertical nor horizontal..

Vertical separation does not just apply to an aircraft that is exactly above or below another. Lateral (horizontal) separation does not just apply to an aircraft at the exact same level as another.

Imagine an aircraft sitting on the ground. Now draw a circle 5nm radius with that aircraft at it's centre. That is the standard lateral separation required in a radar environment for ATC.

Now climb that aircraft instantly to FL100 (10,000ft on standard pressure). That circle still remains, but now you add in vertical element:extend your circle up 1,000ft, and down 1,000ft.

Now you have a cylinder, 5nm radius and 2,000ft in height, which acts as a buffer zone protecting an aircraft.

In ATC (in the provision of radar control in controlled airspace), no other aircraft can enter the space occupied by that cylinder.

The parameters may change (3nm/10nm lateral separation, or 2,000ft vertical in non-RVSM airspace) but the principle remains the same.

antiskeptic

Neon-Circles wrote: »

What do you mean by 30 degrees low?

30 degrees below horizontal - in the sense of me having to drop my gaze 30 degrees down from horizontal in order to look directly at him.

antiskeptic

irishatco wrote: »

Vertical separation does not just apply to an aircraft that is exactly above or below another. Lateral (horizontal) separation does not just apply to an aircraft at the exact same level as another.

Imagine an aircraft sitting on the ground. Now draw a circle 5nm radius with that aircraft at it's centre. That is the standard lateral separation required in a radar environment for ATC.

Now climb that aircraft instantly to FL100 (10,000ft on standard pressure). That circle still remains, but now you add in vertical element:extend your circle up 1,000ft, and down 1,000ft.

Now you have a cylinder, 5nm radius and 2,000ft in height, which acts as a buffer zone protecting an aircraft.

Gotcha. Thanks

This cylinder would look like something like a coin:: 61,110ft in diameter and 2,000ft tall. Assuming he was indeed 30 degrees low then he'd have to have been 2000ft away from me so as not to be intruding on my buffer zone - twice as far as estimated on the ground.

yhwh

Think you might be confusing yourself there mate, The aircraft has to be either 1000ft above or below your aircraft or if that is not the case then it has to be 5 miles away from your aircraft minimum. Forget about 30deg below or above or whatever, that does'nt come into it.

As long as two aircraft are seperated by either 1000ft in height or 5 miles in distance then they are deemed seperated and that's all you need to remember.

In certain airspace those distances might change due to more accurate radar or traffic levels but in general that's the seperation standard.

It's also highly unlikely that these two particular aircraft were any closer than that as they would have got an RA which would have put the aircraft into avoiding action and trust me you would have felt it if they did

antiskeptic

antiskeptic wrote:

This cylinder would look like something like a coin:: 61,110ft in diameter and 2,000ft tall. Assuming he was indeed 30 degrees low then he'd have to have been 2000ft away from me so as not to be intruding on my buffer zone - twice as far as estimated on the ground.

yhwh wrote: »

Think you might be confusing yourself there mate, The aircraft has to be either 1000ft above or below your aircraft or if that is not the case then it has to be 5 miles away from your aircraft minimum. Forget about 30deg below or above or whatever, that does'nt come into it.

I don't think I am - at least not if this 5nm/1000ft buffer cylinder gig is the way things work.

Draw a line from my window downwards at an angle of 30 degrees from horizontal and make it 2000ft long. At the end of that line place the second plane. The vertical distance between us is 1000 ft - as per requirement. Incidently, the horizontal distance between us would be a mere 1700ft - less than a third of a mile.

As long as two aircraft are seperated by either 1000ft in height or 5 miles in distance then they are deemed seperated

As per above calculation: 1000ft height separation.

It's also highly unlikely that these two particular aircraft were any closer than that as they would have got an RA which would have put the aircraft into avoiding action and trust me you would have felt it if they did

Fair enough. A ballpark calculation put it at about 1000ft but I suppose it could have been (at least) twice that - given the speed it all happened at.


(interesting handle that 'yhwh' - the Hebrew word for God )

yhwh

Basic trigonometry does'nt come into it mate,

If the aircraft is 1000ft below you then we're not concerned with how far away it is laterally, it's deemed seperated so the horizontal distance is irrelevant and visa versa if your using lateral seperation.

In other words your line 2000ft long at 30deg down angle would be irrelevant, a controller or pilot would not be concerned with that as long as they have 1000ft vertical so why bring it up?

As I've mentioned already 1000ft vertical or 5 miles horizontal and that's it, there aint anything more complex then that

God has many names

antiskeptic

yhwh wrote: »

If the aircraft is 1000ft below you then we're not concerned with how far away it is laterally, it's deemed seperated so the horizontal distance is irrelevant and visa versa if your using lateral seperation.

In other words your line 2000ft long at 30deg down angle would be irrelevant, a controller or pilot would not be concerned with that as long as they have 1000ft vertical so why bring it up?

Because

a) 2000ft is the minimum distance a plane at 30 degrees low would need to be in order to lie outside the 1000ft vertical limit and..

b) that (2000ft) is twice the distance I estimated there to be between the plane and me - indicating that I had a near miss.

But it would appear near misses are very unlikely (say folk here) making it more likely that I didn't have a near miss but estimated the distance incorrectly

yhwh

antiskeptic wrote: »

Because

a) 2000ft is the minimum distance a plane at 30 degrees low would need to be in order to lie outside the 1000ft vertical limit and..

b) that (2000ft) is twice the distance I estimated there to be between the plane and me - indicating that I had a near miss.

But it would appear near misses are very unlikely (say folk here) making it more likely that I didn't have a near miss but estimated the distance incorrectly

WTF????

antiskeptic wrote: »

a) 2000ft is the minimum distance a plane at 30 degrees low would need to be in order to lie outside the 1000ft vertical limit

This is incorrect and it seems you are seriously confusing yourself, there is no 2000ft minimum distance to lie outside any vertical limit., I have no idea where your getting that from????

Maybe your not understanding this so I'll try and explain it as simply as I can because it seems like your spatial awareness is pretty poor. The other aircraft could be 1000ft directly below you and it's seperated from your aircraft. The other aircraft could be 5 miles away and at the same flight level as you and it's seperated from your aircraft.

The situation you described indicates that the aircraft was a 1000ft below your aircraft vertically, forget about this 30deg angle business because it does'nt matter what angle you saw it at, the two aircraft always had 1000ft between and so are deemed seperated.

antiskeptic wrote: »

b) that (2000ft) is twice the distance I estimated there to be between the plane and me - indicating that I had a near miss

This is also incorrect as there was never any indication as you put it of a near miss (Airprox) as the aircraft were legally seperated. This happens thousands of times a day over Europe and while it may appear frightning to a layman such as yourself, to people who work in the industry it is perfectly normal so you indicating that you had one is just plain wrong.

I suggest nxt time you fly just sit back and enjoy the ride instead of sensationalizing what is in fact a trivial matter.


Now what part of that are you not understanding

antiskeptic

yhwh wrote: »

You are seriously confusing yourself, there is no 2000ft minimum distance to lie outside any vertical limit., I have no idea where your getting that from????

Au contreau ... it's basic trigonometry. For example..

Maybe your not understanding this so I'll try and explain it as simply as I can because it seems like your spatial awareness is pretty poor. The other aircraft could be 1000ft directly below you and it's seperated from your aircraft. The other aircraft could be 5 miles away and at the same flight level as you and it's seperated from your aircraft.

And an aircraft that is neither directly below me nor level with me? Let's take an example where the aircraft is 1000ft below me but not directly below me - it happens to be off horizontally to one side by 1700ft. In this case he also happen to be 2000ft away from me - along a line running at 30 degrees below horizontal stretching between me and him (says basic trigonometry).

Point being? The point was that I estimated an aircraft was 1000 ft away at an angle of 30 low. Which would mean near miss. In order for it not to have been a near miss it'd have to be at least 2000ft away.

So, we either have a near miss or me getting my distance to aircraft estimation wrong by a factor of 2. Quite possible by the sounds of it.

Now what part of that are you not understanding

Why someone, who goes by the name of God, is missing the point

yhwh

antiskeptic wrote: »

Au contreau ... it's basic trigonometry. For example..




And an aircraft that is neither directly below me nor level with me? Let's take an example where the aircraft is 1000ft below me but not directly below me - it happens to be off horizontally to one side by 1700ft. In this case he also happen to be 2000ft away from me - along a line running at 30 degrees below horizontal stretching between me and him (says basic trigonometry).

Point being? The point was that I estimated an aircraft was 1000 ft away at an angle of 30 low. Which would mean near miss. In order for it not to have been a near miss it'd have to be at least 2000ft away.

So, we either have a near miss or me getting my distance to aircraft estimation wrong by a factor of 2. Quite possible by the sounds of it.





Why someone, who goes by the name of God, is missing the point

Actually mate it seems like You are missing the point even though I have tried to explain it to you 3 times now.

As I've already mentioned in a previous post, basic trigonometry does not present a factor in this case (And it is very basic trigonometry mate so dont assume your impressing me with your use of something I learned in first class maths)

I gonna try and explain this one more time although I have no doubt that you will be unable to except it and admit you are incorrect.

"And an aircraft that is neither directly below me nor level with me?"

The aircraft has to be neither directly below you or level with you and in most case's would not be, if your looking out the window and you see an aircraft 30deg's at a down angle to your aircraft, as long as the horizontal plane it's flying on is 1000ft below the horizontal plane your aircraft is flying on then they are seperated.

"The point was that I estimated an aircraft was 1000 ft away at an angle of 30 low. Which would mean near miss. In order for it not to have been a near miss it'd have to be at least 2000ft away"

No it does'nt have to be at least 2000ft away from you as vertically it is 1000ft below the aircraft you are travelling on and is seperated, do you understand this concept of vertical seperation???

So it was not a near miss, again do you understand this point???

It does'nt matter that the aircraft was 30 deg down angle as this is not taken into consideration for seperation, the aircraft always had 1000ft vertical and so this point that you make while accurate as far as your maths in concerned, is irrelevant.

To clarify, Whatever angle you observed the aircraft at does not matter nor does your "at least 2000ft away" argument. As long as the aircraft is 1000ft below yours on a horizontal plane then it is seperated.

Now I have no doubt but that you'll want to argue your point and not admit that you are incorrect in saying this was a near miss when it clearly was'nt so I would suggest you maybe take a visit to the ATC centre in Dublin or Shannon where they can show you the seperation's I'm talking about because clearly you need to see this in operation as it seems you cant get your head around it from what I've tried to explain to you 4 times now.


All I can say is I glad your not a pilot or controller

irishatco

yhwh wrote: »

Actually mate it seems like You are missing the point even though I have tried to explain it to you 3 times now.

I think you're the one missing the point to be honest.

antiskeptic wrote: »

b) that (2000ft) is twice the distance I estimated there to be between the plane and me - indicating that I had a near miss.

The thread starter's original estimation of the distance between the aircraft (not the vertical or the lateral, simply the distance measure between point A being his aircraft and point B being the passing aircraft, measured in the diagonal) was 1000ft. Extrapolate from that using trigonometry, you are essentially dealing with a right angle triangle with angles of 90, 60 and 30 degrees. For separation to have occurred, the shortest side of that triangle had to have been 1000ft long, which means the hypotenuse would have to be 2000ft diagonally if the OP's estimate of the angle is correct.

Do the sums here:

http://www.1728.com/trig.htm

Rotate that triangle 180degrees in an anti clockwise direction to give yourself a better picture of the situation if needs be.

antiskeptic wrote: »

making it more likely that I didn't have a near miss but estimated the distance incorrectly

The thread starter clearly understands the concept of radar separation, he just underestimated the relative distances. It happens at high speed to an untrained eye, no need to rant at him.

yhwh

irishatco wrote: »

I think you're the one missing the point to be honest.



The thread starter's original estimation of the distance between the aircraft (not the vertical or the lateral, simply the distance measure between point A being his aircraft and point B being the passing aircraft, measured in the diagonal) was 1000ft. Extrapolate from that using trigonometry, you are essentially dealing with a right angle triangle with angles of 90, 60 and 30 degrees. For separation to have occurred, the shortest side of that triangle had to have been 1000ft long, which means the hypotenuse would have to be 2000ft diagonally if the OP's estimate of the angle is correct.

Do the sums here:

http://www.1728.com/trig.htm

Rotate that triangle 180degrees in an anti clockwise direction to give yourself a better picture of the situation if needs be.



The thread starter clearly understands the concept of radar separation, he just underestimated the relative distances. It happens at high speed to an untrained eye, no need to rant at him.

Have you even read any of my previous post's????

The op never indicated that his original estimation of the slant distance was 1000ft nor does it matter what the hypotenuse distance is.

If they had a thousand feet vertical they are seperated so what does it matter what the slant distance is.

From what the original poster mentioned it sounds very much like that's exactly what they had.

Making out that it's a near miss when it is'nt in my opinion reckless to be perfectly honest

irishatco

yhwh wrote: »

Have you even read any of my previous post's????

The op never indicated that his original estimation of the slant distance was 1000ft nor does it matter what the hypotenuse distance is.

I beg to differ:

antiskeptic wrote: »

On the ground I looked at other 737's taxiing around and guesstimated the distance between our jet and the other to be 2-300metres or so, with the vertical distance between the two planes at around a plane length (stood on it's nose).

antiskeptic wrote: »

Fair enough. A ballpark calculation put it at about 1000ft but I suppose it could have been (at least) twice that - given the speed it all happened at.)

There's potential for confusion in the way the guy explained his calculations, I'll grant you that, but if you calmed down for a second and absorbed what he was saying you'd have your knickers untwisted and you'd see what he was trying to get across.

You'd also see him accept the explanations given by a number of people that is was not an air miss.

yhwh

Dont patronise me fella,

Making assumptions about distances for something as serious as an airprox is not something a layman with no knowledge of the facts should be doing. Something as serious as such is not based on what if's. This is how the tabloids report such instances and it makes me furious when I see such inaccurate reporting on these matters.


Granted the aircraft may have looked close and probably felt a little scary to someone with no knowledge of how the system works but at no time was anyone in any danger and claiming that you might have had a near miss when you were neither the pilot or controller involved and without any facts but a few liberal estimations can be dangerous.

Delta Kilo

I see what yhwh is saying, the length of the hypotenuse desn't matter diddly squat and I think antiskeptic is over complicating things.

From my basic knowledge of atc, and I may be incorrect on this but isn't there a system where northbound traffic is at an even number and southbound traffic is at an odd number. eg. a plane going from London to Paris would be at 25,000ft and a plane travelling from Paris to London would be at 26,000ft, therefore maintaining the legal separation.

antiskeptic

deleted.

Thanks all for the info and discussion

pclancy