Discovery Channel's Inside a Jet Crash | Hacker News Reader

Discovery Channel's Inside a Jet Crash

usatoday.com

70 pointstwakefield22 comments

Interesting article. For me the two most surprising takeaways were that most people survive an accident, and the other was how cheap the plane was.

They paid $400,000 for the plane. By comparison they paid $150,000 each for each of 3 test dummies in the plane. The test dummies cost more than the plane!

It is a little known fact that fully depreciated planes (like the 727 in the example) are cheap, its operating them that is expensive. Adding up the costs of mandatory maintenance, repairs, upgrades, consumables (gas, tires, hydraulic fluid, etc). That is what bites you.

And the 'most people survive' is something of a misnomer. Start trolling through http://www.ntsb.gov/investigations/reports_aviation.html and you will see that accidents you would expect to be modestly survivable (low altitude takeoff and landing issues) are, and ones like the Air France jet falling out of the sky over the Atlantic are not.

Other factors that make aircraft like this one dirt cheap are that older aircraft (especially the 727) are very loud which makes it difficult to use them in commercial service to areas with noise restrictions. Hush kits are available but they're expensive and don't quiet the aircraft enough to operate some sensitive jurisdictions.

If the aircraft is also near the point where it has to undergo a D-check -- the most expensive kind of maintenance check where the aircraft is very nearly completely disassembled, inspected, and re-assembled -- it would make more economic sense to sell it for scrap than it would to continue operation. The BBC has a great documentary on a BA 747-400 D-check that has been posted on Youtube: http://www.youtube.com/watch?v=x_yHtfGH0nI

And the 'most people survive' is something of a misnomer.

So, if we consider only the accidents that are least likely to be survivable (which are a tiny percentage of all accidents), we find that they're not likely to be survivable?

Well, you could pull out two accidents out of the list where everyone died and say "most people die in plane crashes", which would be incorrect as well. Hence the term misnomer :-) As an engineer I would be inclined to say "if you find yourself in a survivable crash, the following things help increase your odds, ..." which keeps the cool bits about back of the plane vs first class, exits vs non-exits, but side-steps the probability question of surviving a gross malfunction in a commercial jet.

I assume they chose a 727 because it's not very useful these days and is therefore available for cheap. It's a decent airplane, but I believe it proved prohibitively expensive to make it meet noise regulations that are getting more common around big airports, and so they're relatively rarely used these days.

The article mentions that the 727 has a rear stairway that one can use to parachute out of the plane during flight, which the pilots did in this crash test. Random trivia: the famous hijacker DB Cooper picked a 727 for the same reason - he parachuted out the back of the plane with ransom money and was never seen again. For the interesting story, see http://en.wikipedia.org/wiki/D._B._Cooper

The article references the Sioux City Crash, aka United Flight 232. If you've never read it, this speech by that flight's captain (Al Haynes) is spellbinding:

http://www.clear-prop.org/aviation/haynes.html

Sioux City: United 232 heavy, winds currently 360 at 11, three sixty at eleven, you're cleared to land on any runway.

UAL 232: You want to be particular and make it a runway, huh?

------

http://www.youtube.com/watch?v=-l4pywdqvK4&feature=relat...

In that video, you hear the captain actually laughs before asking the traffic controller to be particular. Its absurd these guys can stay as calm as they do in these situations.

Its absurd these guys can stay as calm as they do in these situations.

Hayes credits the radar controller for helping with that: "If you have a serious problem like we did, and you need the kind of help that does not add to the tension level, a voice like Bauchman's, as calm and as steady as he was, certainly was an influence on us and helped us remain composed." [1]

Another fun factoid: "Subsequent simulator tests showed that other DC-10 crews were unable to repeat the effort of the crew of 232." [2]

[1] http://www.airdisaster.com/eyewitness/ua232.shtml

[2] http://www.airdisaster.com/special/special-ua232.shtml

Interesting that they seem to be confirming previous analysis that shows that the rear of the plane is indeed the safest part of the plane.

> flying in first class would have been fatal. Passengers in the middle of the cabin might have suffered concussions and broken ankles, while those in the rear could have walked away

which agrees with this analysis http://www.popularmechanics.com/technology/aviation/safety/4... which says

> the trend was clear: The rear cabin (seats located behind the trailing edge of the wing) had the highest average survival rate at 69 percent. The overwing section had a 56 percent survival rate, as did the coach section ahead of the wing. First/business-class sections (or in all-coach planes, the front 15 percent) had an average survival rate of just 49 percent.

Except that article you link does a terrible job of presenting this. They look only at a small sample (20 accidents), made up only of accidents which had both fatalities and survivors.

When what you want for a real risk assessment is to consider first the accident rate among commercial flights, then the percentage of accidents which have fatalities (and also the rate at which those accidents have any survivors).

Please link to the single page version:

http://m.usatoday.com/article/news/1606749?preferredArticleV...

> The plane was going 140 mph at impact, which is close to regular landing speed. But the 727 was descending at 1,500 feet per minute, much faster than the 10 to 20 feet per minute of a typical airliner landing.

I have to imagine that they were thinking seconds instead of minutes. coming down from 35k feet would take quite a long time if that was not the case. (20'/min would take ~30 hours)

For a standard 3-degree ILS approach, the descent rate is 318 ft per nautical mile. With a ground speed of 150 knots, that would be about 750 ft/minute. At higher altitudes and before the ILS, descent rates are usually higher, sometimes up to 3'000 or 4'000 ft with a default rate of 1'500 ft per minute.

I don't necessarily disagree, but it's possible that they were talking about the rate of descent at the point of impact, rather than the the rate of descent over the whole course of descending from cruising altitude to landing.

I think they were talking about touchdown. An aircraft that is landing approaches the ground quickly, levels off, and touches down at a couple of feet per second. An aircraft descending at 1,500 ft/min which no longer has control impacts the ground at 25 ft/s.

If you don't flare before touchdown and are not flying a Navy plane built for carrier landings, you will break your aircraft pretty badly when you slam into the runway at your normal descent speed.

Who would've thought. Ironically, flying economy might someday save your life (if Economy Class Syndrome doesn't kill your first that is).

Great, now if I ever get to fly first class I won't be able to enjoy it.

Glad to see the advertising dollars from Honey Boo Boo went towards something useful!

The Nissan advertising before the crash video was funny.

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