Midair Collision over Denver

I was camping near Whistler a few years ago and heard a bang. Looked up and saw falling debris and bodies. A wing landed not far from our campsite. Turns out a glider (low-wing monoplane) was descending and the tow plane (high wing monoplane) was climbing. They were each in each other's blind spots :(

Glad to see no fatalities here; I'm an aerospace engineer in the field of airworthiness and technical risk management so my work sees a lot of accident reports and flight safety incidents. I can say with certainty these folks (esp. the metroliner crew) are very fortunate.

"Big Sky Theory"

https://en.wikipedia.org/wiki/Big_sky_theory

>In aviation, the Big Sky Theory is that two randomly flying bodies are very unlikely to collide, as the three-dimensional space is so large relative to the bodies. Some aviation safety rules involving altimetry and navigation standards are based on this concept. It does not apply when aircraft are flying along specific narrow routes, such as an airport traffic pattern or jet airway.

>The Big Sky Theory has been mathematically modeled, using a gas law approach. This implies that collisions of aircraft in free flight should be extremely rare in en-route airspace, whereas operational errors such as violations of formal separation standards should be relatively common. Three critical parameters are the number of flying objects per unit volume, their speed, and their size. Larger, faster objects, flying in a traffic-rich environment are more collision-prone.

http://code7700.com/big_sky_theory.htm

>It seems that there are a lot of pilots out there that believe in the "Big Sky Technique." They think the amount of airspace out there is so wide and vast, and that they are so small, that the chances of hitting another aircraft is too small to worry about. And yet history begs to differ.

The Big Sky - Kate Bush

https://www.youtube.com/watch?v=sV7w5TaYjRA&ab_channel=KateB...

    They look down
    At the ground
    Missing
    But I never go in now

    I'm looking at the big sky
    I'm looking at the big sky now
    I'm looking at the big sky
    You never understood me
    You never really tried

Big Sky - Lou Reed

https://www.youtube.com/watch?v=Ug_Z-gu7u44&ab_channel=Naoyo...

    Big sky, big sky holding up the sun
    Big sky, big sky holding up the moon
    Big sky holding down the sea
    But it can't hold us down anymore

    Big sky holding up the stars
    Big sky holding Venus and Mars
    Big sky catch you in a jar
    But it can't hold us down anymore

    Big sky, big enormous place
    Big wind blow all over the place
    Big storm wrecking havoc and waste
    But it can't hold us down anymore

The Cirrus overshot the centerline of the runway it was supposed to land on. The common way for these situations is for the plane to be on an intercept angle towards the centerline. That's a max 30 degree angle for an instrument approach, but this was a visual approach so it could have been a sharper angle. All it takes to make this mistake in a Cirrus (and other G1000 avionics type small airplanes) is to forget 1 button on the autopilot mode. If it isn't set to capture the final approach track (either GPS or ILS) it will continue straight ahead which in this case means into the side of another airplane.

One thing that makes it more likely is that US air traffic control makes heavy use of visual approaches, and then it's allowed to point two aircraft at collision courses on the same altitude because they can see each other. The European way to do this is to have them intercept at different altitudes so if one overshoots they pass over/under. But it results in lower capacity per runway than the US system.

Planes going opposite directions on the same route are meant to be at different altitudes. Altimeters have been quite accurate for a long time.

It's the code for the particular airport they were about to land at. https://en.wikipedia.org/wiki/Centennial_Airport