Helicopter crash off the coast of Newfoundland - 18 aboard, March 2009

[oldgrubber]

Does it have ELS?

I have looked at this thread for a while and as an engineer I am puzzled by one major point, Sikorsky designed Seakings are operated by UK armed forces with ELS fitted to the main gearboxes. This was due to need for aircrew to be able to land the thing if they lost all gearbox oil pressure and it does work, not 1/2 hour fly dry, but good enough for most situations. If the idea that the Seaking could lose all it's gearbox oil is not "remote" or "negligible" ( first hand knowledge!), why is it that, from what I've read here, by some very knowledgable people, the S92 has NO ELS? It seems to be like a car manufacturer inventing the seatbelt and then not fitting it in the latest model! If I missed the answer to my puzzle, I apologise and await your scorn! (newbie flaming)

[Phil77]

Welcome to pprune oldgrubber!

No intention of flaming a newbie, nor am I an expert in the S92.
However, my research (read: google search for "sikorsky ELS" - sometimes google is more effective finding stuff inside pprune than the build-in search function) led me to page 63 of this thread:
http://www.pprune.org/rotorheads/163...ations-63.html

...I know, an obvious place to look for, but the fellow resident experts elaborating extensively over the emergency lube issue in particular on that very page; just follow the link.

[oldgrubber]

Thanks for the link

Cheers Phil,

I see it's been done to death. I like the "indication" "operation" argument.
Thanks for the kind welcome, I'll try to be a bit more useful in future (laugh).

[riff_raff]

Outwest,

"Are you on drugs man???"

It's not me, it's the FAA. So lighten up.

"FAR 29.927.-
[(c) Lubrication system failure. For lubrication systems required for proper operation of rotor drive systems, the following apply:
(1) Category A. Unless such failures are extremely remote, it must be shown by test that any failure which results in loss of lubricant in any normal use lubrication system will not prevent continued safe operation, although not necessarily without damage, at a torque and rotational speed prescribed by the applicant for continued flight, for at least 30 minutes after perception by the flightcrew of the lubrication system failure or loss of lubricant."

Now I've been involved in a couple of MRGB design qualifications. And there is no way to show by (FMEA) analysis and/or with a qual test validation, that a typical single-fault-tolerant lube system failure can be shown to be an "extremely remote" event. Unless the S-92 MRGB has two totally isolated, independent, and functionally redundant lube systems (which it doesn't), then it must show by qual test that it has a 30 minute loss-of-lube capability, according to FAR 29. Not my requirements, it's the FAA's.

Plus, even though I'm obviously not intimately familiar with the S-92 MRGB design itself, I do understand that it is based on the UH-60 design which does have a firm requirement for a loss-of-lube condition per MIL-T-5955:

"G.6.9 Lubrication. It shall be demonstrated, either analytically or by
testing, that lubrication is suitable for all steady-state operational attitudes
with respect to gravity."

So what do you say now?

[Brian Abraham]

riff_raff, I'm afraid you are holding the stick by the wrong end, and not your fault, as like many others you obviously believe what you read in the professional aviation press. Search this thread for posts by HeliComparator and also the thread here http://www.pprune.org/rotorheads/163...ations-89.html for an education.

[Outwest]

So what do you say now?

I say go back and read your initial post again or refer to the section of your post that I hi-lighted in red.

like all other FAA certified rotorcraft MRGB's,

I'm pretty sure the following are FAA certified rotorcraft

BH206,204,205,212,412, MD500, AS350, etc,etc,etc.......

also pretty sure I won't be draining the oil out of any of them and expect to last 30 minutes.

Care to revise your post?

[Phil77]

[post deleted by me, since in hindsight it created more confusion than enlightenment as Brian clearly points out in the following post - Thanks Brian]

[Brian Abraham]

Phil77, perhaps not clear enough but I was referring to riff_raff's post,

The MRGB in the S-92, like all other FAA certified rotorcraft MRGB's, is qualified for operating in a 30 minute loss of lube condition while maintaining power levels sufficient for level flight. Thus the pilot has a 30 minute period after the HUMS gives an indication of loss of lube circuit pressure, in which to continue at level flight and/or perform an emergency landing. So that should not be a concern to you.

The fact is the 92 does not have a 30 minute capability as suggested by riff_raff, and as I said in my previous post he can not be blamed for having that view as it has been propagated erroneously by the professional aviation press as if it were fact. As I said, search for HeliComparator's posts on the subject.

HC, why are you leaving the job to this amateur, you're the professional?

[squib66]

I don't want to spoil a good rant but the same rule WAS introduced at the same time for Part 27 Cat A rotorcraft and has been sucessfully applied to MD900, EC135 etc.

Brian A is right that the issue has been covered extensively elsewhere.

Lets just say, there is a rule, the aircraft was certified, and as long as the heat exchanger and its pipework are the source of the leak, IF you follow the RFM action to activate the bypass in seconds AND watch the oil pressure like a hawk until it stabalises then you have time to seek a landing site. So far there have been no leaks from the external part of the system (GOOD!). There have been pump drive failures that have created similar symptoms and resulted in premature landings.

If the leak is from elsewhere then, unlike other types certified to 27/29.927, you will see the pressure drop below 5psi and you must Land Immediately. Leaks from the MGRB itself were claimed to be 'Extremely Remote' but have happened twice to date, about 1 every 100k hours (BAD). The outcome of failing to do that promptly is demonstrated by C-GZCH.

I'm sure those who voiced doubts about the certification 5 years ago will take no comfort that their worst fears have come true.

We can only hope the TSB get to the bottom of why this was allowed.

[500e]

rifaf
ch posts 384 385

[JimL]

Svenestron,

That is an extremely interesting contention!

How did you manage to establish that the event was 'extremely remote'; empirical knowledge would have been difficult to provide as it would have had to show that there had been no failure of any lines, fittings, valves, coolers, etc. over a period of 10,000,000 to 1,000,000,000 hours.

The very fact that, as squibb66 has pointed out, there were two 'loss of oil events' to the S92 type over a period of six months would indicate that making such judgements is fraught with danger.

I cannot imagine that the regulator would be sympathetic to such contentions in the future.

My interpretation of the intent of the rule would be no more accurate than yours but I would consider it to be 'unless such failures can be established to be extremely remote'. However, that was before the S92 accident; it might be difficult, since the accident, to contend that such failures are 'extremely remote'.

'Semantics' is not the way to address engineering issues:

Sematics: The individual meanings of words, as opposed to the overall meaning of a passage.

Jim

[victor papa]

svenestron, that approach costs money and we all know Eurocopter parts are ridiculously expensive! Makes me wonder why?

[widgeon]

As a matter of interest is the EC135 tgb made by Zahnradfabrik Friedrichshafen. I know the 105/117 Inter and tail were ?

[tecpilot]

widgeon, yes it's made by ZF.

Svenestron,

as i believe you know some years ago a BO 105M (Army version) from ECD (MBB) killed the two persons onboard while chrashing due to a tail rotor gearbox failure. In the TRGB the oil level wasn't correct filled after maintenance work.

As i remember the crash occured within 15-20 min after take off.

[squib66]

I'm sure a few old 61/Sea King hands will remember many oil leaks from casings seals and even filter housings. I think the point of Svenestron's post is that other manufacturers would not even have dreamed (hallucinated?) of doing the test the unique and less demanding way that Sikorsky finally did (and yes a more robust gearbox does cost).

Just days after the Cougar accident EASA took action to make its opposition clear to a Sikorsky 'Safety Advisory' issued immediately after:-

EASA cautions S-92A operators over Sikorsky letter

The European Aviation Safety Agency (EASA) today cautioned operators of Sikorsky S-92A helicopters that a recent Sikorsky all operators letter issued in the wake of the Cougar Helicopters S-92A crash on 12 March could appear to suggest using flight manual changes not approved by the US Federal Aviation Administration (FAA), a possibility Sikorsky denies.

Sikorsky issued the note on 14 March to update owners on recent safety bulletins related to the S-92A, but not connected with the accident. The letter, provided to Flight International by Sikorsky, reminds operators of all safety bulletins issued in the previous 90 days, including at least one dealing with the main gearbox.

EASA says a 26 September 2008 SSA (SSA-S92-08-006), not specifically called out in the 14 March letter, informed owners of impending rotorcraft flight manual (RFM) changes for the S-92A based on service difficulties with the aircraft’s main gearbox lubrication system. “This advisory document refers to RFM changes that have not yet been approved by the FAA,” the regulator continues. “In fact, the SSA specifies the ‘corrective action’ as ‘Ensure all flight crews become familiar with the RFM changes when received.’”

Flight has learned that SSA-S92-08-006 discusses methods for detecting and responding to single and multiple indications of main gearbox problems and an impending transmission failure.

EASA says it published today's information bulletin "to ensure that all owners and operators of affected rotorcraft, registered in the European Union member states or associated countries, are aware that the procedures specified (in Sikorsky's September SSA) have not been approved by the FAA or EASA. The relevant emergency procedures in the approved RFM must be observed,” EASA states.

Sikorsky officials tell Flight the 14 March letter was sent to remind operators to comply with existing rules, not proposed changes to the RHM.
"The Sikorsky Safety Advisory referred to in the EASA bulletin (SSA-S92-08-006) had been issued as notice to operators that a change might be forthcoming. Sikorsky's practice is to provide operators with transparency and to supply information as it becomes available. This bulletin was simply notice of a proposed change, with no directive to comply either then or now pending all required approvals per normal procedures," Sikorsky says.

A few days later the FAA were forced to issue a humiliating note:-

FAA: Sikorsky S-92 gearbox safety alert ?premature?-19/03/2009-Washington DC-Flightglobal.com

The FAA admitted they agreed with EASA and said that:-

The information in the Sikorsky safety advisory (SSA) was premature and may not be appropriate

That information, obtained by Flight International, was relayed by Sikorsky to operators in SSA-S92-08-006 on 26 September. The SSA points out that “some of the indications for an impending gearbox failure currently listed in the rotorcraft flight manual (RFM) are not representative of the main gearbox (MGB) performance/capability during a malfunction. As such, Sikorsky will be removing these items as indications of an impending gearbox failure."

The SSA was based on Sikorsky's investigation of “recent events” involving the S-92 MGB lubrication system. It's not clear what current indications are "not representative".

Sikorsky clearly indicates in the SSA that the revised guidance was being provided “in advance” of the RFM revision. It later states that the RFM changes would be forthcoming to “formally document (the guidance).”
That guidance includes suggestions for how to handle an impending transmission failure, which Sikorsky says can be manifested by an increase in power required at a constant collective setting; yaw kicks and unusual vibrations or unusual noise. “Multiple symptoms are a very strong indication of an impending failure,” Sikorsky adds.

“If an impending failure is suspected, the primary consideration is to land the aircraft before the failure progresses to a gearbox seizure or loss of drive to the main or tail rotor,” the SSA continues. Sikorsky writes that a “single” indication of a MGB problem (pilots receive MGB temperature, pressure and chip detection system readings) dictates that the helicopter should land “as soon as practical”. Multiple indications, Sikorsky notes, “dictate that the helicopter should land as soon as possible,” while an impending transmission failure “would necessitate that the helicopter land immediately.”

In addition to descending to an “altitude from which a landing can be quickly made with minimal power changes” if pilots suspect an impendng failure, Sikorsky also recommends flying at an airspeed “for which minimum power is required”, avoiding “rapid or frequent” changes to power, and performing descents at a reduced power setting “but with enough torque to drive the transmission.”

It is believed the 'recent events' mentioned above were the emergency landings in the jungle of Brunei of two Shell S-92s in January & May 2008 (connected with the pump drive failures mentioned in my last post) and this SSA was issued after pressure for Sikorsky to respond to those two events before an aircraft ditched with a surivable pump failure. The authors of the SSA did not apparently consider the July 2008 oil loss in Australia and the need to land immediately in those cases because such failures are not protected by the bypass system. Perhaps Sikorsky was starting to believe its own hype.

Rotor and Wing have been on the S-92's case since April and showed that after 20 years of production Sikorksy were still having casting problems with the UH-60 box and that the S-92 casing had a life limit imposed by AD:-

Rotor & Wing Magazine :: Program Insider: S-92 Main Gearbox Under Scrutiny in Cougar Crash

Sources in the industry said that the S-92A’s MGB was not known for its "robustness." But what does that mean? Again, facts are sketchy, but here’s what we have.

Some of the S-92A’s technology is derived from the Sikorsky UH-60 Black Hawk. In a December 17, 2006 interview with Sikorsky president Jeff Pino, the Connecticut Post reported that the Pentagon had sent Sikorsky a "Level III: Corrective Action Requests" letter after "...the Army discovered the walls were too thin on main gear box housings on Black Hawk helicopters...." Sikorsky declined to specifically comment on the Pentagon letter, but Pino defended the company’s commitment safety.

Sikorsky spokesperson Paul Jackson denied that the UH-60’s 2006 problems revealed any fundamental flaws in its MGB housing. "What really occurred is the local DCMA [Defense Contract Management Agency] did spot-checking and found some units not in conformance," he said. "We took corrective action, and no aircraft were grounded. This was not a design or engineering issue, but a manufacturing escape (sic) with some units." Note: The accident aircraft, serial number 920048, was built in 2006.

Doubts about the UH-60’s MGB are just that; doubts. But according to the FAA, there is a problem with the S-92A’s MGB housing. The proof: On July 26, 2006, the FAA issued AD 2006-15-19, which applies specifically to "Model S-92A helicopter, with main gearbox (MGB) upper main housing assembly (housing assembly), part number 92351-15110-042, installed, certificated in any category."

AD 2006-15-19 reads: "To prevent fatigue failure of the MGB housing, loss of MGB lube oil, loss of main and tail rotor drive, and subsequent loss of control of the helicopter, do the following: (a) Before further flight, replace each MGB housing with 2,700 or more hours time-in-service (TIS) with an airworthy MGB housing with less than 2,700 hours TIS. (b) This AD revises the Airworthiness Limitations section of the maintenance manual by establishing a new retirement life for the MGB housing assembly of 2,700 hours TIS."

These are not the only UH-60 gearbox problems as recounted here:-

http://www.pprune.org/rotorheads/163...ml#post3904718

The multiple main gear box issues with the original UH-60 2800 SHP boxes which one writer referred to were traced to a ring gear failure of ring gears from a particular manufacturer. SA got rid of those gears.

There were two planetary gear carrier fatigue crack induced failures that I learned about. Neither involved a complete failure of the planetary gear, and see immediately below for the story.

The one planetary carrier failure of a 3400 SHP gear box was caused by a fatigue crack and subsequent investigation disclosed that this customer ( non US Army ) was flying a GAG ( Ground-Air-Ground ) cycle powerwise that was way beyond the power ( should have said torque ) usage that formed the basis for the main box TBO . That failure did in fact result in deformation of the carrier plate, allowing it to contact an aluminum shim, generating lots of aluminum chips and clogging the filter, eventually shutting off oil flow. A precautionary landing was made without incident. No chip detection reported. The TBO for this operator was reduced in keeping with the power/time-at-power spectrum that he was in fact flying.

I did not get the history behind the single planetary carrier failure of a UH-60 2800 SHP main box, but based on the investigation of the 3400 SHP box event, assume it was a fatigue crack initiated thru usage far beyond the power/torque/time-at-power spectrum for which that TBO was formulated.

Sikorsky boasted about the run dry capability of the S-92 gearbox just after certification, the then S-92 Program Director, Nick Lappos posted here:-

http://www.pprune.org/rotorheads/163...ml#post1744337

In addition to its civil helicopter capabilities, the rotor system and dynamic components are designed to meet the UH-60 BLACK HAWK ballistic tolerance requirements and all gearboxes are capable of running 30 minutes after loss of oil.

He has also said:-

http://www.pprune.org/rotorheads/163...ml#post3901911

[quote][the S92 transmission is a true modular trannie, designed with structural partitions and independence of lube so that a section can be shot away (yes, shot away) and not compromise the ability of safe operation of the remaining sections./QUOTE]

Really? Like the filter?

The S92 trannie design is the precise opposite of the early 1960's designs where the entire box is a single entity

So more joints and leak paths?

The S92 transmission is bigger, taller, beefier and heavier that the Black Hawk transmission by almost precisely the amount of extra power that it transmits.

So more power and therefore torque than the UH-60, so therefore 'beefier'. Is it 'beefy' enough?

Just days after the Canadian Globe & Mail 'revealed' that actually the test failure (common knowledge on PPRuNe to those not blinded by the hype) and how the JAA resisted certifying the S-92 for over 18 months after the FAA certification on this and related issues:-

POLEMIC & PARADOX: S92 FAILED RUN DRY TEST

Certification documents show that the S-92 couldn't meet a specification that calls for the main gearbox to run for half an hour without oil – a requirement known as “run dry.” The specification is designed to give pilots extra time to make a safe landing if the gearbox loses its oil.

This was picked up by other newspapers and a debate started in Canada on the Sikorsky Cyclone, an S-92 based naval helicopter, that apparently will have to pass the test with no oil:-

The Telegram - St. John's, NL: Local News | Specs for new chopper include crucial gearbox requirement: Defence

Specifications for Canada’s new naval helicopters include a requirement that the gearbox be able to run in the event of a serious oil leak, the Defence Department says.

The department says its Cyclone helicopters will have to have a “run-dry” capability before they will be accepted from Sikorsky.

“The run-dry capability requirement for the CH-148 gearboxes, as stipulated in the solicitation document, is included in the maritime helicopter contract,” a department spokesman wrote in an email.
Sikorsky won the helicopter contract in 2004. A series of delays have put off the first delivery to 2012 from 2010. The initial delivery target was 2008.

Defence says the U.S. manufacturer is still working on the gearbox system.

News reports say the civilian S-92 won an exemption from the “dry-run” requirement by submitting evidence that the likelihood of a catastrophic oil loss was extremely remote.

Then in June the lawsuit of the Cougar familes charged Sikorsky with also giving and allowing to go uncorrected what they knew to be misleading information on the robustness of the gearbox to be circulated:-

Lawsuit claims Sikorsky knew of the S-92 flaws… S-92 Facts

Flawed mechanical design and dishonest marketing led to a helicopter crash that killed 17 people off the coast of Newfoundland this winter, according to a lawsuit filed by the families of the victims.

The lawsuit charges that Sikorsky sold its $15-million S-92 as “the safest helicopter in the world,” even though it was aware of a serious problem with the machine’s all-important main gearbox – a component that has emerged as the likely cause of the March 12 crash.

The lawsuit, filed in Pennsylvania, alleges that Sikorsky marketed the S-92 on the basis of its compliance with an advanced safety standard that calls for a helicopter to fly for at least 30 minutes after losing the oil in its main gearbox (also known as “MGB”), giving pilots time to make a safe landing. The lawsuit says that the S-92 did not actually meet the standard, but customers were led to believe that it did, creating a fatal misperception by pilots – including the Cougar Helicopters crew who died in the Newfoundland crash along with 15 passengers…

… The lawsuit argues that the pilots would have attempted a controlled landing on the surface of the ocean almost immediately had they been aware of the S-92’s true capabilities. “Within seconds of being alerted to the rapid loss of oil pressure in the MGB, the pilots turned the aircraft towards a safe landing site, which was close enough to be reached within the purported 30-minute ‘run-dry’ capacity of an S-92 helicopter. Because of the defendants’ misrepresentations and misstatements, the pilots were not aware that complete loss of operational control was imminent, and therefore, they did not attempt to set the craft down immediately on the water while the pilots still maintained control of the helicopter.”

The S-92’s run-dry capabilities have been at the centre of an ongoing dispute within the aviation community. The helicopter was certified to an advanced safety standard known as FAR Part 29, which calls for the extended run-dry time. A Globe and Mail investigation revealed that the S-92 failed the run-dry test, but was certified after Sikorsky showed that the chance of losing gearbox lubrication was “extremely remote.”

Sikorsky has argued that the S-92 meets the standard, and that pilots should have been aware of the need to land immediately in case of an oil leak. But the lawsuit charges that Sikorsky completely misrepresented the gearbox’s durability in a widespread campaign. “In addition to stating in their product literature and technical bulletins that their S-92 helicopters had a ‘30 minute run-dry capacity,’ the defendants knew that aircraft references, including Jane’s All the World’s Aircraft , innocently repeated the defendants’ representations.… Pilots would detrimentally rely on these misstatements, lulling them into a false sense of safety.”

The lawsuit alleges that Sikorsky “trivialized” the risks posed by oil loss, and failed to highlight it in the S-92’s flight manual, even after a series of incidents. (This week, the U.S. Federal Aviation Administration ordered changes to the S-92’s flight manual, instructing pilots to land immediately if a gearbox oil leak is detected.)

A few days after this the TSB revealled how the Cougar tail rotor take off gear (shown right as compared to a new on the left) disintegrated as the crew attempted to ditch:-

http://www.tsb.gc.ca/eng/medias-medi...6/A09A0016.asp



They added that:-

The Sikorsky S-92A Rotorcraft Flight Manual (RFM) has been reviewed regarding MGB oil pressure loss below 5 pounds per square inch (psi) and the need for pilots to land immediately. An RFM revision has been approved by the FAA and Transport Canada.

And that brings us to today and yet more cracking:-

FAA to mirror EASA S92 emergency directive

The US Federal Aviation Administration plans issue an airworthiness directive calling on Sikorsky S-92 operators to repetitively inspect the helicopter's main gearbox mounting feet for cracks, defects that could lead to gearbox detachment and loss of control of the helicopter.
The FAA mandate will follow an emergency airworthiness directive issued by the European Aviation Safety Agency on 23 October after reports that cracks had been found in the feet, pads and foot ribs on main gearboxes during inspections. "In one case, the mounting foot was completely severed from the gearbox," says EASA. "Other cases include cracks at the fore and aft mounting bolt location on the right-hand side of the mounting foot."

With the FAA delaying apparently because as they:-

waited for Sikorsky to submit a failure analysis for the main gearbox mounting feet and other information. The FAA says the cracking phenomenon, while seen in the North Sea, has not been experienced by operators in the USA and Gulf of Mexico.

So much for the 100,000 pages of engineering reports mentioned here:-

http://www.pprune.org/rotorheads/163...ml#post1744342

Just a few days after the FAA made this statement about the cracking being a North Sea problem and their AD was issued:-

http://www.canadaeast.com/news/article/844479

HALIFAX, N.S. - A hairline crack has been found in the main gearbox mounting feet on a Cougar Helicopters chopper based in Halifax. The St. John's, N.L., company announced that Cougar engineers found the crack on a Sikorsky S-92 during an inspection that followed a routine training flight Monday.

It is again worth turning to the words of the Program Director just after FAA certification:-

http://www.pprune.org/rotorheads/163...ml#post1744340

It was the fastest, cleanest certification anyone at Sikorsky can remember. The first certification data flight was made last December, the FAA got on board in September, and we were done with all flights exactly one year later, Dec 12. The data was all processed in real time, so the FAA was ready to sign on Dec 17 (Wright Brothers day!) so they did.

In many ways the S-92 gearbox saga has some echoes of the two NASA space shuttle disasters and NASA's failure to anticipate and plan for the worst, properly act on the early o-rings and tile problems promptly or listen to those who did voice concerns. The only difference is more people died on Cougar 491 than in Challenger and Columbia combined.

So what will happen next?

[HeliComparator]

squib - excellent post thankyou

Sven - yes you are missing something, the cracking thing refers to the MGB attachment feet cracking, a new phenomena since the Cougar crash and not related to it as far as we know.

HC

[squib66]

HC is correct - the newest cracks are of the big highgly loaded gearbox feet (the right hand one in particular) rather than the small fliter studs.

I forgot to mention the gearbox mounting bolts were also changed out earlier this year too (just like the filter studs the first material choice was poor) and are now a nickle based steel.

Svenestron there WAS no alternative way to pass the test until it was 'invented' by Sikorsky and I doubt anyone even thought of the meaning you did when teh words were written.

I hope no other OEM is stupid enougth to use the S-92 as a precedent to try the same thing, but I doubt any regulator would let them.

I now understand the significance of JimL's comment about semantics and missing the meaning of the whole rule by focusing on the meaning of a couple of words. However it would be good if the words 'extremely remote' were taken out of the rule.

[Shawn Coyle]

squib66:
If I understand you, by eliminating the 'except if it can be shown to be extremely improbable' you'd like all gearboxes to demonstrate 30 minute run dry capability??
Good idea!

[rjsquirrel]

squib66 said: However it would be good if the words 'extremely remote' were taken out of the rule.

It might not be obvious to ppruners, but every new helicopter takes use of that phrase for gear box design and approval in many ways. Erase that rule, and all helos will undergo major new design efforts.
That is because the same FAR/JAR paragraph is used to cover the tail and intermediate gear boxes, which are qualified by showing that they "cannot leak" and the housings are highly reliable structure.

[Mars]

It may be of interest to see when and why the words "Unless such failures are extremely remote" were inserted into the rule. Below you can see the rule as proposed in NPA 84-19, followed by the justification for the change that occurred in the final rule:

Proposal 3-46. The notice proposed several amendments to Sec. 29.927. Paragraph (c) is changed by revising and extending the rotor drive system lubrication failure test requirements for Category A rotorcraft and by clarifying the corresponding test requirements for Category B rotorcraft. Category A aircraft must have significant continued flight capability after a failure in order to optimize eventual landing opportunities. However, indefinite flight following the lubrication system failure is not expected. The changes to the Category B rotorcraft drive system lubrication failure test requirements are largely for clarification and are not substantive.

In NPA 84-19, issued on 10/10/84, this was the proposal:

(c) Lubrication system failure. For lubrication systems, the function of which is required for operation of the rotor drive system, the following apply:

(1) Category A. It must be shown by tests that each rotor drive system, where the probable failure of any element could result in the loss of lubricant, is capable of continued operation, although not necessarily without damage, for a period of at least 30 minutes at a torque and rotational speed prescribed by the applicant for continued flight, after indication to the flight crew of the loss of lubricant.

(2) Category B. It must be shown by tests that the rotor drive system is capable of operating under autorotative conditions, although not necessary without damage, for 15 minutes after indication to the flight crew of the loss of lubricant.

Following consultation, the Final Rules, Docket No. 24337, was issued on 08/26/88. The text had been amended with the following justification:

A commenter notes that paragraph (c), as proposed, could be interpreted to preclude credit for auxiliary lubrication systems or to require consideration of lubricant failures to self-lubricated bearings. This was not intended, and the wording of paragraphs (c)(1) and (c)(2) has been revised to eliminate this possible ambiguity.

The final rule being:

(c) Lubrication system failure. For lubrication systems required for proper operation of rotor drive systems, the following apply:

(1) Category A. Unless such failures are extremely remote, it must be shown by test that any failure which results in loss of lubricant in any normal use lubrication system will not prevent continued safe operation, although not necessarily without damage, at a torque and rotational speed prescribed by the applicant for continued flight, for at least 30 minutes after perception by the flight crew of the lubrication system failure or loss of lubricant.

(2) Category B. The requirements of Category A apply except that the rotor drive system need only be capable of operating under autorotative conditions for at least 15 minutes.