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Asiana Crash Investigation

Old 31st Jul 2013, 20:18
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Asiana Crash Investigation

Safety Surprises from Asiana Crash Investigation

By Guy Norris
July 15, 2013

Source: Aviation Week & Space Technology

While NTSB investigators look closely into the actions of the flight crew for potential causes behind the July 6 Asiana Airlines Boeing 777-200ER accident, safety experts working on the other side of the cockpit door are already learning valuable new design lessons for crash survivability.
Although all but two of the 307 passengers and crew survived the ordeal, more than 180 were injured, several of them critically. Therefore, while looking into why the crash occurred in the first place, the investigation is focusing just as closely on why these injuries and deaths were sustained, and it has already unearthed troubling concerns about the functionality of the aircraft's main exit escape slides.
Video and eyewitness accounts testify to the violence of the aircraft's brief passage along San Francisco International Airport's Runway 28L before coming to an abrupt halt to the south side of the strip, adjacent to the touchdown zone markers some 1,500 ft. from the threshold. Although the aircraft did not cartwheel in the same devastating way as in the 1989 DC-10 crash in Sioux City, Iowa, it was massively damaged by an initial impact with the seawall and the displaced runway threshold, during which parts of the main landing gear and the entire empennage were ripped away. Traveling at over 100 mph, the aircraft departed the runway at the touchdown markers where it became partially airborne again, pirouetting in a complete 360-deg. circle around its nose section.
During this high-speed ground loop, the aft end of the tailless fuselage momentarily pitched up at around 40 deg., causing passengers and crew in the back section of the cabin to fall vertically as much as 100 ft. when the aircraft came to a rest with its nose pointed back toward the runway. Despite this pummeling, the fuselage structure remained substantially intact with the extensively damaged wings appearing to have borne the brunt of the impact loads. Although the forward two-thirds of the fuselage was gutted by the post-crash fire, the overall structural integrity of the cabin section was not immediately compromised by the impact itself, with significant buckling only evident in two zones: forward of the wing root and aft by Section 47/48 where the empennage was broken off.
The NTSB says the fire was caused by oil leaking from a ruptured tank onto the damaged remains of the No.2 (starboard) Pratt & Whitney PW4090 engine, which was ripped from its wing mountings and lay beside the fuselage. The left engine was detached during the initial ground roll and came to rest on the north side of the runway, just under 2,000 ft. from the threshold. While the fire makes it more difficult for investigators to assess the post-crash condition of the forward and mid-cabin sections, the intact aft cabin is yielding information about the survivability design aspects of seats, interior paneling, overhead bin structures, seat tracks, cabin floors, exits and escape slides.
Images released by the NTSB of the aft cabin, close to the buckled section by Doors L4 and R4, show how the seating, cabin floor and ceiling in some areas, were significantly damaged and dislodged. Already weakened by the initial impact and loss of belly skin and structure below Section 47/48, the bulk of the aft cargo hold and lower lobe structure beneath the floor of the aft cabin appears to have been either ripped away by the slide along the runway or crushed by the vertical impact that ended the ground loop.
Nevertheless, despite massive damage, investigators say the surprisingly small number of fatalities and relatively intact interior present a very survivable picture, with much of the internal trim, ceiling panels and sidewalls still in place. This is partly thought to be due to Boeing's internal design concept, in which the tie rods supporting the arch of the secondary support structure (which holds the interior of the cabin ceiling panels and overhead bins to the fuselage monocoque) transfer loads above 46,000 lb. and withstand loads of up to 9g. Tie rods were built to absorb up and down loads, while truss-type sway bracing structure support the ceiling laterally. The seats are designed to meet the 16g crash load certification standard, while the seat tracks were originally designed to cope with stresses of 9g.
However, San Francisco hospitals that dealt with the injured report an unusually high number of spinal injuries, the worst of which include crushed vertebrae and torn ligaments, testifying to the excessive lateral and vertical loads sustained during the accident. Although safety experts say assuming the crash position would have limited jolting to the spine, passengers appear to have received little or no warning of the impact. According to Randy Scarlett, board director of the California Brain Injury Association, “there were significant spinal cord and traumatic brain injuries with the first wave of patients. More subtle concussions and spinal cord injuries were in the second wave of those patients coming to San Francisco General [Hospital].” Scarlett expects that while 80% will fully recover, “20% will be affected for a significant time in their lives.”

Commenting on the safety implications, former NTSB Chairman Jim Hall questions the adequacy of the current 16g dynamic seat standard. “I believe that it is time to update aviation seat standards to take a stronger G force, especially in light of the many recent spinal and head injuries,” he says. The regulation requiring all newly developed transport aircraft to use 16g-capable seats was issued by the FAA in 1988, superseding rules at the time which mandated a static 9g standard with no occupant injury criteria.
From a systems perspective, investigators are focusing on the performance of the safety systems, door operation and emergency inflatable slide deployment. “We're taking a very close look at survival factor issues, including emergency doors and exits, and to see if there were any malfunctions,” says NTSB Chairman Deborah Hersman. The most serious of these occurred during the evacuation, when two cabin crew were “pinned” against the cabin side by escape slides that inflated inside the aircraft at Doors 1R and 2R. At least one flight attendant had to be rescued by the relief first officer who helped deflate the device. “We need to understand why that happened, and if it happened inadvertently,” says Hersman.
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Old 31st Jul 2013, 21:16
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So, a 16 g seat on a 9 g seat track? Makes sense to me!
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Old 1st Aug 2013, 00:08
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About ten days ago, when the HQ pictures of the wrecked a/c were posted in the Asiana crash thread, I thought that most of the learning from this accident should (hopefully) result from a study (and hopefully, recommendations) around survival aspects.

It would seem that a lot of the other lessons that might come from the accident have already been noted, then forgotten.
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Old 1st Aug 2013, 03:29
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aisle width at bulkheads

Don't disagree with the report.
Airlines can increase post crash survivability and fast egress tomorrow by widening the aisle at bulkheads and galleys from the legal minimum of 20 inches.

It would seem that a lot of the other lessons that might come from the accident have already been noted, then forgotten.
History repeats...

In late 1980 JAA considered recommendations from UK AAIB into the 1985 Manchester B737 accident about the narrowing aisles caused by bulkheads and galleys, thus restricting egress.
Not to be confused with a similar width down the aisles between seats, where there is plenty of free space between seatbacks.

Following research at Cranfield, in 1996 JAA proposed an amendment to change JAR 25.813, so aircraft with 110 passengers or more the width between rigid structures with side of an aisle should be at least 30 inches.

In 2006, (21 years after the B737 accident) a "Rulemaking Group" was set up to examine width between bulkheads.

The options identified were
1/ Do nothing
2/ Voluntary Implementation
3/ Further research and/Analysis
4/ Rulemaking option

They decided that further research was not necessary and that bulkheads were not a serious issue, that the effect of rule 2 was same as rule 1 so they went with "do nothing" option

So whilst the Cranfield tests indicate a 30 inch width is safer most airlines go with the current legislation FAR 25.815 which is 20 inches.

This report details the above.

The video shot in the '80s at Cranfield clearly shows the difference in passenger mobility between varying galley aisle widths, a shame then that what seems like such a common sense change will apparently only be implemented by a more statistically relevant body count.

Last edited by mickjoebill; 1st Aug 2013 at 03:30.
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Old 1st Aug 2013, 07:46
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There were also numerous recommendations made after comprehensive study into survivability aspects of the British Midland crash at Kegworth. These again came from the medical profession as well as industry professionals, Cranfield, Farnborough etc.

While some were taken up (looking at the brace possition for example,) others were not. While improved brace possitions will help if the crash is expected, as noted here, if the incident is sudden and unexpected, survivability will depend upon the aircraft structure and layout, including cabin and seats.

One of the subjects that came out of Kegworth and was hotly debated was the subject of rear facing pasanger seats. Standard on some purpose built military transport aircraft for many years. (Not on those converted from civil types in recent years.)

In an impact, the entire weight of the body, including head is taken by the seat structure. This reduces whip lash injuries, and the decelleration forces are absorbed by a much larger area. Currently, the entire forward force is absorbed only by a lap strap. In modern cars, that crash at lower speeds, 3 point harnesses are standard, as are airbags. Why in aviation, where although accidents are a lot more rare, are we still using just a single strap? The result is that in many accidents, passengers survive the crash, but pelvic injuries (and lower limb injury caused by legs hitting the seat structure in front,) prevent a successful unaided evacuation of the aircraft.

Time to look at this again?

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Old 1st Aug 2013, 07:56
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Over 50 years ago, the RAF concluded that crash survivability in passenger aircraft was significantly increased by having rear-facing seats.

It is clear from train design that this is not a turn-off for passengers, although this is usually given for adopting it in airliners. Not, of course, that then they could be stronger (and heavier)...

(Descend to what height has pre-empted me while I was writing!)

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Old 1st Aug 2013, 08:45
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It is a turn-off for some passengers. My wife refuse to sit rear facing in a train. Not all the seats are rear facing, so you can choose. BTW, there are no, as far as I know, seat belts on trains, and they crash too.
Put [email protected] at the controls of any moving device, and accidents will happen.
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Old 1st Aug 2013, 09:00
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not just a turn-off - I'm probably not the only one who gets sick then. Dunno why. Cars, trains, buses, whatever.
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Old 1st Aug 2013, 09:00
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So, a 16 g seat on a 9 g seat track? Makes sense to me!
Well, it sort of does. Seat tracks and parts of the floor structure are prone to corrosion, so they have plenty of margin for blendout. Additionally the fllor structure is designed for the most dense seating arrangement. In perfect condition they stand much more than 9g, which is the limit load criteria. Ultimate load is at 13.5g and above, often even exceeding the 16g. The seats on the other hand are tested for their dynamic behavior at 16g, without margin.
I think the Asiana crash shows more collapsed 16g seats than broken 9g floor structure. But it will be nevertheless interesting to follow the investigations and to learn from it. This crash will make it into text books, for pilots and for engineers, end evertually into the rules as well.
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Old 1st Aug 2013, 09:10
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Bear in mind there is also a flying object hazard in a crash, and the seat backs of forward-facing seats do provide some protection against objects flying forwards and hitting passengers as the cabin decelerates rapidly. Rear facing isn't perfect, and it is important to bear in mind the assumptions on how well-secured loose objects are. Military transport may be able to control their passengers' belongings better than civil transport.
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Old 1st Aug 2013, 09:15
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Fitter - I remember reading that and on the Trident 2 we had a row of rearward facing seats which were popular amongst dead heading crew...except for on take off where you literally hanging on the straps.
After the Airtours Manchester disaster there were trials with a water sprinkler system but again costs came into it.
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Old 1st Aug 2013, 10:29
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I dimly remember reading a paper (might have been about Kegworth but I can't locate it online), where survivability was postulated to decrease above a certain strength of seat. The argument was that having the seat controllably deform under extreme loadings reduced the peak g experienced and took some of the energy out of the equation. If you built a seat that could withstand 50g, the seat would survive but the occupant wouldn't...
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Old 1st Aug 2013, 10:46
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rear facing seats may work on trains, but that is forgetting one important difference between trains and planes.

trains don't take off.

from the back it already feels like we are climbing at 45' or more, being pushed into our seats. Imagine now hanging in your belts, with projectile vomit flying through the cabin.
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Old 1st Aug 2013, 11:33
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OK. So 16G's is not enough. How about 20G's or 30G's. Hell with it, design for 50G's. 20" aisles not wide enough, make them 50" wide. Could it be that the problem is all of the obese people out there? As someone earlier said, put idiots behind the controls and all of this doesn't matter. Want a perfect safety record, park all of the aircraft in the hangar and lock the doors. When this is all said in done the bottom rine(not a typo) is going to be that a perfectly good aircraft was crashed due to incompetence among many other factors that are confined to the cockpit. Trying to take the flies off the bride by moving the emphasis onto ancillary items is typical when political correctness takes over for objectivity. One can only hope that the NTSB maintains its non-political status and does not give in to outside pressure in publishing the real cause(s) of this accident. It is long overdue that the lights were turned on in the kitchen exposing the cockroaches. Rant over.
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Old 1st Aug 2013, 13:05
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After the Airtours Manchester disaster there were trials with a water sprinkler system but again costs came into it.
The Manchester air disaster was British Airtours not Airtours. Different company, absolutely no connection, British Airtours was owned by BA.
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Old 1st Aug 2013, 13:15
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While some were taken up (looking at the brace position for example,) others were not. While improved brace positions will help if the crash is expected, as noted here, if the incident is sudden and unexpected, survivability will depend upon the aircraft structure and layout, including cabin and seats.

Yes, having flown a couple of months ago after a decade or so not doing so, I was conscious that the seat pitch and fixed seat back ahead didn't give me, or even my much shorter partner, space for the "brace position" as indicated on the procedures card. As said, aircraft layout is important.
The other cabin safety item is the huge size of many "carry-on" (or rather "wheel-on") bags and the thought that, even if there is a size limit, they have no weight limit and what load are the overhead bins designed round?
I also remember the aft-facing seats of the BEA Tridents and the "hanging from the lap-strap" feel of the take-off which, as said above, was what put people off.
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Old 1st Aug 2013, 13:29
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It would seem that a lot of the other lessons that might come from the accident have already been noted, then forgotten.
Like having a prescribed minimum height with which to cross the threshold!
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Old 1st Aug 2013, 16:02
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Why in aviation, where although accidents are a lot more rare, are we still using just a single strap?
Are you kidding? It's hard enough to get them to fasten a lap belt, let alone anything else!

While we're at it, why not have them all adopt the brace position for takeoff and landing? Normalise it, and it won't freak people out... however... modern air travel is such that it doesn't (to most people) inherently FEEL dangerous, therefore they are far more lax about their own safety as passengers. For example, parents who wouldn't dream of driving with their baby on their lap in the car feel perfectly fine passing it across the aisle or letting it walk around in turbulence because they can't feel/see the speed, unlike in a train or car.

I agree, cabin luggage needs to be looked at. The amount of unnecessary [email protected] that people bring on these days is astounding. Had a woman the other day bring on a hold-sized suitcase and then get tetchy when told it was too big. "But it fits in the overhead" was the response. "Yes but the overhead is limited to 20lbs and you;re not the only person with a bag!"
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Old 1st Aug 2013, 16:18
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The fact that the fuselage remained intact after the mistreatment of the crash landing is a testament to how modern aircraft design has advanced. Earlier aircraft designs would have crumpled on that type of impact. So it does seem a little unforgiving to start ratcheting up the requirements. However, it does raise some issues that should be investigated but have not really been raised here.

Rear facing seats/four point seat belts. These are always proposed after a crash. However, had the pax been in rear facing seats or been wearing 4 point seat belts it is probable that there would have been many more spinal crush injuries. The 'ejection seat posture' is one that has to be learned and even correctly in that posture ejectees regularly have spinal injuries even from the more gentle ejection seats which are less than 16g instantaneous load. A bent forward brace position might for a vertical deceleration be a more survivable posture. What is the most common g loading on an occupant of a crashing aircraft?

Seat pitch. This brings us to seat pitch the brace position leaning forward onto your thighs hands over head is a good posture but totally infeasible in most aircraft where the beancounters put seats far too close for a brace position to be feasible - a half brace position may well be the worst of both worlds in a vertical deceleration.

Crumple Zone Seats. As some have pointed out here - a seat that survives while the occupant does not is not really useful. However, it should be possible to design seats that absorb some of the deceleration so that the peak load on the occupant does not exceed a survivable level. So a peak/instantaneous 25G seat with a 10G peak for the occupant perhaps.

Of course as always the choice of internal fit is an airline responsibility usually from choices available from the manufacturer. However, the manufacturer will not develop fits that nobody will buy.
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Old 1st Aug 2013, 16:57
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Ian W, that's an interesting point about rear-facing seats.
In a past life, encouraged by many trooping flights in an even older life, I did quite a lot of work in the late '70s on the feasibility of converting a fleet of F27-600s to rear-facing seats, of which there was a suitable 9G non-reclining model available.

The operational impact was a loss of 2 seats to restore the APS+passengers+baggage weight to what it was with 44 forward facing seats. The space would have been used for a netted cargo/baggage/mail overflow area, in the front of the cabin. The capital cost spread over the seat life was very, very low in seat/mile terms.

The aircraft were used by oil companies for personnel and cargo around their oilfields. We also used them for some low volume/short scheduled services.

The oil companies' aviation experts simply said that losing the 2 seats (they rarely, if ever, had more than 33/44 passenger load in passenger configuration) would be a deal-breaking breach of contract, and who gives a shit about the safety aspects, and the company's FD said that losing 2 revenue seats would be a disaster. This was only partly true; the aircraft, as well as some thin services, operated a short sector shuttle service at 100% load factors with the highest seat/mile fares in the world; losing 2/44 seats would have reduced the net route contribution from about 400% to maybe 380%.

I do not believe that much has changed; seriously effective (ie expensive) safety measures will usually be kicked into touch by the finance people, and regulators have insufficient balls to change that. So we will go on nibbling ineffectually at the problem. In a related case; are we holding our breath for effective and prompt regulatory action to prevent another fire and/or its outcome like the UPS tragedy at Dubai?

But after all that, it comes as a shock to learn that rear-facing seats are not necessarily such a good thing! Can that be so?

Last edited by old,not bold; 1st Aug 2013 at 17:08.
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