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Accident S92 de Couguar

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Poncho (Admin)
Whisky Charlie

Accident S92 de Couguar

Message par Poncho (Admin) le Jeu 25 Juin 2009 - 18:31

Bonjour à,

Quelques nouvelles du crash du S92 de Couguar ici

http://www.flightglobal.com/blogs/as-the-croft-flies/2009/06/feds-sikorsky-too-little-too-late-on-cougar-s-92-crash.html

Avec de belles photos ne pas hésiter à aller faire un tour sur le clic


Feds, Sikorsky: Too little too late on Cougar S-92 crash
By John Croft on June 24, 2009 1:44 PM | Permalink |ShareThis
Safety Investigators in Canada have determined that pilots of a Cougar Helicopters Sikorksy S-92 that crashed in the Atlantic Ocean off the coast of Newfoundland on 12 March, resulting in the deaths of 17 of the 18 on board, were likely trying to autorotate the heavy twin helicopter after a tail rotor drive failure, precipitated (my words, not theirs) by a loss of main gear box (MGB)`lubrication fluid. After the helicopter hit the water, the floatation system, for reasons unknown, failed to inflate. Pictured above is the reconstruction of the crash helicopter by the Transportation Safety Board of Canada (TSB).

Though the details of how successful that autorotation maneouver turned out to be are yet to be determined -- initial data shows the helicopter hit the water with a force of 20Gs -- what is clear is that the problem that initiated the deadly chain of events in the first place might have been flagged up before the helicopter was certified by the US Federal Aviation Administration.

Though the analysis is not yet complete, the evidence strongly suggests that two cracked titanium mounting studs used to hold an external oil filter for the helicopter's main gear box (MGB) cracked and allowed the transmission oil to quickly drain out. Picture below, from TSB, shows a one of the missing oil filter studs on the right side...

An emergency airworthiness directive after the fact required the replacement of those studs with steel equivalents throughout the fleet. Sikorsky earlier had given operators a year to do the changeout, a suggestion spawned by similar but non-lethal failures in the fleet.

Once that oil drained, the rotating machinery had no cooling. In picture below, also from TSB, damage to the tail rotor pick-off gear (connected to the MGB to power the tail rotor) is obvious when compared to a new pinion on the left...

In the aftermath of the crash, the Transportation Safety Board of Canada (TSB) says the FAA and Sikorsky "are working to identify all the modes of failure that might lead to Sikorsky S-92A MGB oil loss, determining their probability of occurrence, and developing appropriate mitigation strategies."


Huh? Shouldn't such a failure modes and effects analysis (FMEA) be done BEFORE certification?

Apparently not...

Though under Part 29 certification rules for rotorcraft, failures that result in the loss of lubrication to the drive train, in this case the MGB (the mechanism that takes in power from the S-92's two turboshaft engines to drive the main rotor, tail rotor, power systems, etc), must allow for 30 minutes of flight time after the crew receives an indication of the problem in the cockpit, there's an escape clause of sorts in the regs... If a failure mode is determined to be "extremely remote", the 30 minute rule no longer applies...

It's not clear in the case of the Cougar crash whether pilots, through tribal knowledge, assumed there was 30 minutes to get back to shore despite emergency guidance material for such anomalies. The helicopter ultimately went into the water about 10 minutes after losing its lubrication oil.

And why didn't the "30 minute rule" apply?

"Based on the applicable guidance material at the time of certification, the lubrication failure modes of interest were limited to the failure of external lines, fittings, valves, and coolers," writes the TSB in an 18 June update on the accident.

"This practice was consistent with industry experience, which had found that loss of lubrication tended to be associated with external devices. Therefore, the possibility of a failure at the oil filter was considered to be extremely remote. As a result of the fracture of the filter bowl mounting studs, resulting in the loss of a large quantity of oil, the certification guidance material is being reviewed."



J'étais personnellement resté sur cette histoire de 30 min sans lubrification... appliquée aux origines des hélicoptères...

Des réactions ?

bonne journée


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vonrichthoffen

Re: Accident S92 de Couguar

Message par vonrichthoffen le Ven 26 Juin 2009 - 14:10

Pour quelques grammes de trop. Il faut espérer que la leçon sera retenue, même si le gain de poids s'effectue sur l'ensemble des composants (comme pour le sac-à-dos d'un alpiniste). On ne perdra rien sur la charge utile en montant du 8.8 .

Poncho (Admin)
Whisky Charlie

Re: Accident S92 de Couguar

Message par Poncho (Admin) le Ven 26 Juin 2009 - 14:24

Bonjour Vonrichthoffen.

Comme vous dites... l'acier a encore quelques vertues !

Ce qui est troublant c'est cet abandon en "douce" de la notion des 30 min sans lubrification et la manière dont l'info a été transmise aux pilotes...

Je pensais que ce principe était gravé dans le marbre, sachant que si on savait le faire il y a 50 ans, il ne devrait pas y avoir de problème à le faire maintenant...


Enfin, ce n'est qu'un avis de non initié

Bonne journée


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@avia.poncho

alain57
Whisky Quebec

Re: Accident S92 de Couguar

Message par alain57 le Ven 26 Juin 2009 - 14:27

Bonjour surtout que la différence de poids doit repressentais quelques grammes. et peut être qu'au dernier entretient le mécano n'a pas respecté le couple de serrage préconisé.....

Vector
Whisky Quebec

Re: Accident S92 de Couguar

Message par Vector le Ven 26 Juin 2009 - 14:38

Bonjour à tous,
Le problème du titane est la fragilisation par la phase Alpha, qui est indétectable avant la rupture. Si je me souviens bien, les 30 minutes de lubrification sont assurées par un bloc de cire qui fond et graisse les engrenages, mais cela n'évacue sans doute pas la chaleur dégagée...

Poncho (Admin)
Whisky Charlie

Re: Accident S92 de Couguar

Message par Poncho (Admin) le Ven 26 Juin 2009 - 14:54

Bonjour vector,

Je ne le connaissais pas coup du pain de cire... je pensais que c'était 30 min à sec !
Quelqu'un peut-il confirmer ?

Bonne journée


_________________
@avia.poncho

Vector
Whisky Quebec

Re: Accident S92 de Couguar

Message par Vector le Ven 26 Juin 2009 - 15:09

Voici un forum de discussion où ils parlent du "dry run time" du S-92. Il semble avoir pas mal de divergences d'opinions : certains parlent de "no dry run", d'autres disent 30 minutes, j'ai même vu 1 heure.
C'est troublant qu'un élément aussi fondamental ne soit pas mieux protégé et ce ne serait pas très compliqué d'avoir un réservoir se vidant par gravité.

forum

alain57
Whisky Quebec

Re: Accident S92 de Couguar

Message par alain57 le Ven 26 Juin 2009 - 15:27

Admin a écrit:Bonjour vector,

Je ne le connaissais pas coup du pain de cire... je pensais que c'était 30 min à sec !
Quelqu'un peut-il confirmer ?

Bonne journée

je confirme la lubrification par pain de cire, la cire commence a fondre au delà d'une certaine température (normalement jamais atteinte si présence d'huile) et apporte une lubrification par brouillard et contact direct (gouttes) sur les pignons et roulements...

30 minutes a sec, me parais bien long, vu les contraintes d'une telle transmission,
il existe certes des additifs a base de téflon qui apporte un gain en cas de rupture du film d'huile et permette un fonctionnement plus long, mais je ne pense pas qu'ils tiennent 30 minutes, sauf si présence d'un réservoir qui approvisionne en continue...... mais la on augmente le poids....

Poncho (Admin)
Whisky Charlie

Re: Accident S92 de Couguar

Message par Poncho (Admin) le Ven 26 Juin 2009 - 15:29

Merci Alain...

C'est rusé le coup du pain de cire !

De toute manière pour moi les 30 min c'était avec le sacrifice quasi complet de la boite de transmission bonne à mettre à la poubelle après un tel coup...


_________________
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alain57
Whisky Quebec

Re: Accident S92 de Couguar

Message par alain57 le Ven 26 Juin 2009 - 15:33

exact Poncho, après un fonctionnement, même de quelques minutes a sec, la boite et bonne pour la casse, si une réparation et en principe possible, en remplaçant les éléments les plus marqué, on ne peut prendre ce risque sur un hélico, pour des raison financière.....

Vector
Whisky Quebec

Re: Accident S92 de Couguar

Message par Vector le Ven 26 Juin 2009 - 15:38

Il est évident que la BTP qui a atteint le point de fusion de la cire n'est pas destinée à être réutilisée. Le rôle de ce système est de retarder le plus longtemps possible le grippage complet. Par contre, la durée du "sursis" devrait être établie lors de la certification et clairement indiquée dans le manuel de vol. Dans ce cas, l'équipage a tablé sur 30 minutes et a perdu.

Poncho (Admin)
Whisky Charlie

Re: Accident S92 de Couguar

Message par Poncho (Admin) le Ven 26 Juin 2009 - 15:44

Je suis chanceux, et les autres membres aussi !
2 réponses intéressantes pour le prix d'une !

Merci !


_________________
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Vector
Whisky Quebec

Re: Accident S92 de Couguar

Message par Vector le Ven 26 Juin 2009 - 15:53

Poncho, j'aurai probablement à traduire le rapport final du BST canadien (Bureau de la sécurité des transports), malheureusement cela se fait généralement avec un certain retard, alors, ça m'intéresse particulièrement.

jullienaline
Whisky Charlie

Re: Accident S92 de Couguar

Message par jullienaline le Mar 26 Jan 2010 - 23:57

Bonsoir à tous,

Une conséquence de cette rupture de la BTP par suite d'une fuite d'huile provenant du filtre à huile.
L'EASA, par un AD, exige le remplacement dans les 60 jours ou les 100 h de vol , à partir du 9 février, de la cuve du filtre à huile en une pièce par une autre en deux parties.
La FAA devrait édicter la même consigne demain.
Les essais ont montré que l'ancienne pièce s'abime facilement lors des montages et démontages effectués pour l'entretien de l'appareil.

EASA mandates Sikorsky S-92A gearbox modification

The European Aviation Safety Agency (EASA) today mandated that operators of Sikorsky S-92A helicopters replace the twin-engine 19-passenger helicopter’s main gearbox (MGB) oil filter assembly with a new design that is less prone to leaks.
“Investigation of recent incidents with S-92A helicopters has shown that loss of oil from the MGB filter was a factor in the sequence of events,” says EASA in the airworthiness directive (AD).
The most high profile MGB oil loss occurred on a Cougar Helicopters S-92A that crashed off the coast of Newfoundland in March 2009. Seventeen of the 18 passengers and crew onboard died as a result of the crash. Sikorsky earlier this month reached an out-of-court settlement for an undisclosed amount with the survivor and other families to close out a lawsuit filed against the airframer.

Preliminary information from Canadian investigators revealed that damaged oil filter mounting studs was a likely cause of the oil leak that ultimately downed the helicopter after the gearing for the tail rotor drive portion of the MGB failed.
Both the FAA and EASA issued several directives related to the MGB in the aftermath, including a mandate to immediately replace the mounting studs, and a December AD to inspect the oil filters for installation damage caused in part by incorrect part numbers in the Sikorsky maintenance manual.
EASA is requiring operators to replace the existing single-piece oil filter with a two-piece design developed by Sikorsky within 100 flight hours or 60 days of 9 February.
The US Federal Aviation Administration (FAA) tomorrow will issue a proposed rulemaking that would require US operators of the helicopter to make the same changes within 60 days once finalized.
“This proposed AD is prompted by tests indicating that an existing MGB filter bowl assembly can fail under certain loading conditions including those associated with a damaged MGB filter or mounting study resulting from high frequency maintenance tasks,” says the FAA.
“Testing of the improved MGB filter bowl assembly demonstrates a significant increase in strength and durability over the existing filter bowl.”
Along with installing the two-piece filter bowl, outlined by an 18 December 2009 Sikorsky service bulletin, operators of 22 US-registered helicopters would also have to inspect oil filters for damage and replace the mounting studs if the directive is finalized as written.
http://www.flightglobal.com/articles/2010/01/26/337647/easa-mandates-sikorsky-s-92a-gearbox-modification.html

Amicalement


_________________
Jullienaline

Poncho (Admin)
Whisky Charlie

Re: Accident S92 de Couguar

Message par Poncho (Admin) le Mer 9 Fév 2011 - 23:50

Bonsoir à tous

Pas trop le temps de développer, ce soir, mais le sujet est fort intéressant...
Où l'on voit que quand une transmission ne tient que 11 min à sec ... certains préfèrent, en accord avec les autorité de certification, démontrer qu'il est impossible de perdre tout l'huile de lubrification. Je ne porte pas de jugement.

http://www.flightglobal.com/articles/2011/02/09/352993/canada-takes-faa-to-task-for-rotorcraft-run-dry-exemption.html


Canada transportation safety officials are calling on the US FAA to remove from helicopter certification standards a clause that allows manufacturers to bypass a traditional 30min transmission run-dry capability for "extremely remote" failures.
The clause is a central feature in the Transportation Safety Board (TSB) of Canada's final report on the 12 March 2009 ditching of a Cougar Helicopters Sikorsky S-92A off of Newfoundland. Seventeen of the 18 on board did not survive.
The final report, issued today, highlights 16 factors in the accident, which began when titanium studs holding the main gearbox (MGB) filter bowl broke, allowing all of the transmission oil to leak out. The Flight 91 ditched 11min later after pilots lost tail rotor control due to stripped transmission gears. An animation provided by the TSB shows how events unfolded.

Recommendations to Canadian regulators include prohibiting certain over-water helicopter operations "when the sea state will not permit safe ditching and successful evacuation", and making available underwater breathing apparatus.
Mark Clitsome, TSB's director of air investigations said during the meeting that the 30 minute run-dry timeframe was originally a requirement for military helicopters, but that the FAA when it developed its Part 29 rotorcraft certification rules, "believed that civilian aircraft could also meet this."
"However, when it came time to perform the run-dry test [for the S-92A], there was a catastrophic failure after just 11min," says Clitsome. "Following the failed test, Sikorsky and the FAA reviewed the rules and decided that a total loss of oil lubricant would only happen if the oil cooler system failed. Any other source of total oil loss was seen as-and I quote-'extremely remote.'"
"For this reason, [Sikorsky] chose to redesign the main gearbox's lubrication system to include a bypass valve for the oil cooler instead of taking steps to redesign the gearbox," Clitsome says. "What they did not consider was a failure in the main gearbox oil filter bowl-or its titanium studs. This is exactly what happened to Flight 91."
He notes that while the titanium studs for the S-92A have been replaced with steel studs via an emergency airworthiness directive, the S-92A gearbox remains the same.
"In the event of a sudden loss of oil, there would still be only 11min before the gearbox fails," says Clitsome. "The S-92 is the only helicopter to be certified using the 'extremely remote' provision," he continues.
"In fact, since that rule came into effect, [EASA] has certified four helicopters as capable of meeting the 30min 'run dry'. The FAA and Transport Canada also certified one each. So, we know it's possible for civilian aircraft to meet this requirement.

Le S-92 est l'hélico qui avait été retenu pour le SAR au royaume-uni dans le cadre de la délégation de service public récemment passée en Appel d'Offre et annulée cette semaine pour des raisons pas très glorieuses pour le gagnant désigné... (accès d'un des partenaires à des données que les autres concurrents ne pouvaient avoir).

Le S92 devrait avoir droit à une nouvelle transmission

bonne soirée


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Contenu sponsorisé

Re: Accident S92 de Couguar

Message par Contenu sponsorisé Aujourd'hui à 2:52


    La date/heure actuelle est Ven 9 Déc 2016 - 2:52