Calculated risk of a mid-air

[Bruce Tuncks]

For years, I have been impressed with how big the sky is compared with the size of our planes. In fact, it is hard to meet up with another plane when you are trying. Here's what has happened to me more than once:

 

" CC this is CY at 6000 feet over Burra, where are you?"

 

"CY this is CC also at 6000 feet over Burra , I can't see you"

 

We both do a few fruitless scanning circles....

 

"I can't see you either"

 

So one day I sat down to try to work out the odds of two aircraft having a midair if there were 100 airborne over the wheatlands of Australia.

 

I made the assumption that none of them were looking out the windscreen because I didn't know how to incorporate this in the calculation.

 

Well I worked out that, in the absence of any concentrating factor, there would be a midair once in about 22,000 years. If the lookout reduced this by a factor of 3 then it will be one every 66,000 years.

 

No wonder it doesn't happen much ... anybody care to do another calculation independent of mine?

 

 

[Bruce Tuncks]

Yes I am well aware that concentrating factors mean that the risk of a midair should not be taken lightly. A new and subtle concentrating factor is GPS navigation ,where the accuracy puts aircraft on the same rout on the same path. The vicinity of airfields is another one, but not new. Also cloudbase and airspace edges.

 

 

[turboplanner]

That's the classic academic's report, like the one where the academic himself drowned in a creek of average depth 1 metre.

 

 

[dsam]

Yes I am well aware that concentrating factors mean that the risk of a midair should not be taken lightly. A new and subtle concentrating factor is GPS navigation ,where the accuracy puts aircraft on the same rout on the same path. The vicinity of airfields is another one, but not new. Also cloudbase and airspace edges.

I am inclined to agree that the accuracy of GPS combined with following "VFR recommended routes" adds to the risk of collision, making "see and avoid" plus "communicate" even more vital. ADS-B in, has also been a big help to me when finding traffic nearby. It seems a perverse outcome of advanced technology that an air-to-air collision is somewhat more likely these days!

 

 

[Geoff_H]

Some years ago I read of a similar study in Great Britain. Theirs was 1 every 400 years, smaller country more aircraft. However near an airport I believe that the probability increases greatly for obvious reasons.

 

 

[Cobalt]

Nearly had one on my first area solo. Just took off from caboolture in a skyfox gazelle heading east toward bribie island bridge, i gave a departure call and leveled off at 1500ft, heard another aircraft call "bribie bridge 1500 tracking south for beachmere" but as i was still 6 or so nautical miles from the bridge i didnt believe this to be an issue so i continued tracking for bribie, a few miles later as i was approaching ningi township i saw a small flicker of light out of the left corner of my eye i turned my head to see a cessna coming directly at me at the exact same altitude, without even thinking i jammed the stick forward and dove down as i did i looked up through the skylight of the gazelle to see the cessna pass directly over the top of me, i looked back to the right and the cessna never climbed or altered course in any way.

 

Which then brings me to last weekend when i was doing some training in the foxbat, we just finished doing some steep turns over central bribie at 2500ft and were heading west toward donnybrook to do some forced landing practice, the airspace over bribie was really busy that day radio calls galore, constant scanning and spotting aircraft passing beneath up and down the coast, but while scanning i looked back over my left shoulder to see a cessna passing behind us at exact same altitude wouldnt have been more than 100 meters which is still a little close for comfort if you ask me. I guess thats why its a danger area.

 

 

[onetrack]

People win 1st prize in OzLotto every couple of weeks, too - and the chances of winning Division 1 are 45,379,620 to 1.

 

The problem with calculations associated with number of aircraft VS area of the sky is that, so often, many aircraft are converging to a point that is an area of concentration of aircraft numbers - so the chances of a MAC then increase enormously.

 

 

[facthunter]

I don't know what you are basing your facts on. If we all flew random heights and tracks we would be safer but we concentrate on almost exact heights and tracks we increase the likelihood massively of having a close encounter of the wost kind. In a "controlled" airspace environment with digital monitoring of collision factors if designed well you might approach 100% surety if all aircraft movements and positions are known with a high degree of certainty. Even TCAS hasn't stopped all collisions with properly installed systems as the human factor can still get involved. BIG SKY is misleading as a concept. We got away with it this time means little. I've had more close calls than I wish to think about so I fly right of track by about 10 miles and give traffic information on the local frequency when passing cross traffic areas and any other sensible way of avoiding the LIKELIHOOD of encountering traffic. Go where the traffic isn't as long as it's legal. A miss is as good as a mile isn't correct. If you were relying on luck rather than skill or sense one day you won't have it going for you. In flying, to a large extent YOU make your OWN luck. Nev

 

 

[Bruce Tuncks]

I agree that we need to be especially vigilant for knowing when we are in a concentration area, the east coast is a good example. The Caboolture/ Bribie island area is busy I know.

 

But if you are rational, you will be influenced by actual risk. For example, I have saved a lot of money over the years by NOT buying lottery tickets.

 

Now that I've turned 70, here is my risk profile: Yours will be the same if you last that long and are overweight too.

 

Mortality ( all causes) 25 /1000 per year

 

Mortality( flying risk) 1/1000 per year

 

Mortality risk ( 9kg overweight ) 5/1000 per year

 

So I have a 31/1000 risk of dying in the next year, and a 31/100 chance of dying in the next ten.

 

Why does our wonderful government spend disproportionally on the small flying risk?

 

 

[facthunter]

Because CASA make a career of it (Empire building). Nev

 

 

[onetrack]

W]hy does our wonderful government spend disproportionally on the small flying risk?

Because their aim is to eliminate that industry, and that risk, by crushing it with regular major increases in costs, and over-regulation. They are probably pleased with their success, so far. Once GA and RA air movements are immeasurable, they'll be besides themselves, it will be an achievement like getting smoking down to 0.1% of the population.

Any risk factors will have been totally neutered, and all the bureaucrats will be happy, because all the stats and graphs look fantastic, and they will be able to claim all their risk-reduction measures have been proven to have worked.

 

 

[Cosmick]

Nearly had one on my first area solo. Just took off from caboolture in a skyfox gazelle heading east toward bribie island bridge, i gave a departure call and leveled off at 1500ft, heard another aircraft call "bribie bridge 1500 tracking south for beachmere" but as i was still 6 or so nautical miles from the bridge i didnt believe this to be an issue so i continued tracking for bribie, a few miles later as i was approaching ningi township i saw a small flicker of light out of the left corner of my eye i turned my head to see a cessna coming directly at me at the exact same altitude, without even thinking i jammed the stick forward and dove down as i did i looked up through the skylight of the gazelle to see the cessna pass directly over the top of me, i looked back to the right and the cessna never climbed or altered course in any way.Which then brings me to last weekend when i was doing some training in the foxbat, we just finished doing some steep turns over central bribie at 2500ft and were heading west toward donnybrook to do some forced landing practice, the airspace over bribie was really busy that day radio calls galore, constant scanning and spotting aircraft passing beneath up and down the coast, but while scanning i looked back over my left shoulder to see a cessna passing behind us at exact same altitude wouldnt have been more than 100 meters which is still a little close for comfort if you ask me. I guess thats why its a danger area.

Bottom of Bribie to Beachmere (9nm from Caboolture and 7.5nm from Redcliffe) is a more dangerous place to play at 1500' being a busy laneway to and from Redcliffe and to add to the dilema both busy airports have their own CTAF.

 

 

[facthunter]

Lanes of entry would have to rate as some of the most dangerous places to be. Nev

 

 

[damiens]

I am inclined to agree that the accuracy of GPS combined with following "VFR recommended routes" adds to the risk of collision, making "see and avoid" plus "communicate" even more vital. ADS-B in, has also been a big help to me when finding traffic nearby. It seems a perverse outcome of advanced technology that an air-to-air collision is somewhat more likely these days!

The other side of the technology being TCAS. I have been flying frequently the last year with an aircraft that has a traffic awareness system (Skywatch). I have been stunned how many aircraft I can't and don't see, but I know they are there. Around places like Bankstown, I am starting to realise how handy TCAS can be. Nothing beats your eyes in the circuit though.

 

 

[Bruce Tuncks]

Yes damiens, gliders now have an avoidance system called FLARM and it certainly alerts you to gliders you would not otherwise have seen. It uses a GPS, a 2 way radio and of course a computer on each unit . They communicate with each other and display where to look to see the other glider. They cost about $700 and work well.

 

One day mine went into the alarm stage ( urgent noises and flashing red lights) before I saw the other glider. It would have missed, being a few hundred feet away and about 50 ft higher, but I appreciated the warning.

 

In this case the concentrating factor was a nice looking cloud street.

 

 

[facthunter]

If you have a situation where there are a large number of aircraft in the area, you must get "clutter" and reach appoint of saturation, surely.

 

IF your system doesn't interrogate ALL aircraft. you have to be looking for the ones you don't pick up. Time spent looking inside the cockpit isn't good for the visual aspect. You have to train to do an effective visual scan, and you still have the stationary in the window effect. You mind fills in as a blank a part of the sky you move over too fast. There can be quite prominent objects you just don't see, because you are not actually looking there. Nev

 

 

[onetrack]

The optical illusion of the 12 black dots you can't see all at once, makes you realise that our vision is actually a pretty imperfect system, and a lot of what we actually see, is the brain doing calculations, not the eyeball actually seeing the object!

 

Here's why you can't see all twelve black dots in this optical illusion

 

As a result, any assistance device we can develop and install, to help us see other objects that we need to see, can only be of great benefit.

 

 

[Bruce Tuncks]

yes onetrack, our eyes are poorly "designed" with the light-sensors upside down. It's one of the best examples of how there was no design, just blind evolution. Evolution can't retrace steps.

 

And Nev, the flarm sees lots of other flarms. When you are in a gaggle the whole display is lit up. Of course, in a gaggle your head is swivelling about anyway.

 

Funny thing, as I get older and my life is worth less,( in terms of years left), I am more fearful than when I was young. So I tend to leave gaggles these days.

 

 

[dsam]

If you have a situation where there are a large number of aircraft in the area, you must get "clutter" and reach appoint of saturation, surely.IF your system doesn't interrogate ALL aircraft. you have to be looking for the ones you don't pick up. Time spent looking inside the cockpit isn't good for the visual aspect. You have to train to do an effective visual scan, and you still have the stationary in the window effect. You mind fills in as a blank a part of the sky you move over too fast. There can be quite prominent objects you just don't see, because you are not actually looking there. Nev

A few weeks ago I was established in a cruise with ideal VFR conditions, and OzRunways showed a "target" 500 feet below on an oncoming 45 degree intersecting path some 5 miles away. I decided to test my see-and-avoid capability & deliberately watched the area with visual scanning technique etc. I was astonished that even with this intense vigilance on the area, the "target" aircraft was nearly 30 seconds away before I saw it against the terrain below. It crossed directly underneath me. I consider my vision to be very good (and it tests this way too). Who knows what other traffic I've missed seeing over the years with less intense vigilance?? Human vision is well known to be imperfect!

30 seconds isn't much time if one has a tendency for too much "head-in-the-cockpit"... (definitely not recommended as we all know). Perhaps an affordable TCAS system is truly the best solution for our modern GPS & ADS-B equipped sky?

 

 

[Yenn]

It is hard to see some aeroplanes because they blend into the background. I painted my first plane yellow so that it would stand out against a blue sky. Result it is hard to see. My second is white on top, dark green underneath and very easy to see. If you want to see other planes the best place is to be lower than they are. All the aids in the world won't be any use if there are more than about 3 planes in your immediate area. Just go to a busy fly in if you don't believe me.

 

 

[turboplanner]

A few weeks ago I was established in a cruise with ideal VFR conditions, and OzRunways showed a "target" 500 feet below on an oncoming 45 degree intersecting path some 5 miles away. I decided to test my see-and-avoid capability & deliberately watched the area with visual scanning technique etc. I was astonished that even with this intense vigilance on the area, the "target" aircraft was nearly 30 seconds away before I saw it against the terrain below. It crossed directly underneath me. I consider my vision to be very good (and it tests this way too). Who knows what other traffic I've missed seeing over the years with less intense vigilance?? Human vision is well known to be imperfect!30 seconds isn't much time if one has a tendency for too much "head-in-the-cockpit"... (definitely not recommended as we all know). Perhaps an affordable TCAS system is truly the best solution for our modern GPS & ADS-B equipped sky?

That was a great exercise to show how hard an aircraft is to see when it's below you; unless he/she has used a radio, or electronics are involved, you really don't know what you haven't seen.

 

A practical disprover of Bruce's academic calculation is the airfield training area.

 

With city airports such as Archerfield, Bankstown, Moorabbin, Parafield, Jandakot, you are effectively flying through a multilayered ants nest with aircraft and helicopters of all types flying in all directions at all levels.

 

Every one of those aircraft in the training area "box" will have a degree of difficulty seeing some of the aircraft below a lot of the time, and some of the aircraft above, behind, and at rear angles to the side.

 

So the risk will increase dramatically if you spend a lot of time in the training area.

 

Living underneath the Moorabbin TA, I see near misses (not necessarily dangerous ones) where as many as three aircraft converge and pass within a hundred metres of each other, with no banking, or course correction indicating they saw each other at the last minute.

 

At those airfields the training has always been very strong on eyeballing as much sky as you can before you do everything, and that has worked very well for decades.

 

 

[pmccarthy]

An interesting thread. As a pilot I often see and point out birds such as eagles or flocks of ibis to passengers who never notice them even though they are looking out and about. But they are not scanning the way a pilot does.

 

 

[Mike Borgelt]

"Because CASA make a career of it (Empire building). Nev"

 

Bingo ! We have a winner.

 

Avplan and Oz Runways both have a facility to report your position and latitude to a website. I did suggest to someone close to the Avplan people that it would be nice if all this information was available on both websites but have not heard anymore about it. This would be a very low cost traffic awareness aid independent of transponders, radar and ADSB.

 

 

[Old Koreelah]

...Funny thing, as I get older and my life is worth less,( in terms of years left), I am more fearful than when I was young...

Well put, Bruce. As a bullet-proof youth I had the same attitude: those slow old farts are almost dead anyway- why are they being so careful? The memory of some painful spills now increasingly controls my impulses.

 

 

[Old Koreelah]

A few weeks ago I was established in a cruise with ideal VFR conditions, and OzRunways showed a "target" 500 feet below on an oncoming 45 degree intersecting path some 5 miles away. I decided to test my see-and-avoid capability & deliberately watched the area with visual scanning technique etc. I was astonished that even with this intense vigilance on the area, the "target" aircraft was nearly 30 seconds away before I saw it against the terrain below...

Most of our club members now use OzRunways. On trips we talk on the numbers and know each others' altitudes and locations. Even with a screen full of nearby aircraft, looking up at cloud haze or down over bland crop land I almost never see them, even when passing within a km. (My distant eyesight is near-perfect).

 

But wait, there's more: there's always a couple of members who don't have their OzRunways on, or who refuse to use it. Sobering.