30 min Dry Run Capabilities
 

I have been thinking about this since it has been a hot topic on here on number of threads.

There is a requirement to either design a gearbox lube system such that is has an extremely remote chance of failure. I guess that means it is as reliable as the other systems and components in the gearbox. Happy with that. If not, a manufacturer has to demonstrate a 30 min dry run capability.

Why 30 mins? These certification requirements are being used for heavy twin engined helicopters which are used for extended range operations over hostile terrain. As oil goes further offshore, the ranges get bigger.

To demonstrate this ability, what conditions are the manufacturers using? Max cruise power?, Max AEO hover power? Power at Vy with MGTW? Certainly in my experience if you loose your MGB oil, you are to fly at Vy. So that gives you 35 - 40 nm still air.

Now as far as I can see, if a manufacturer is to demonstrate a 30 min dry run capability, you need a gearbox you are happy to destroy, you don't want to have to do it more than once, so you are going to find a reasonable gearbox and make sure that any emergency cooling/lub systems are working.

Do the test conditions therefore relate to us trundling along with a gearbox that may be close to life, an emergency back up system that is just about to get its major overhaul and not been tested for a while when the MGB Oil Pressure caption lights up? Are we sure that we can then fly for 29 mins 30 secs to get to somewhere safe and then pull 100% Tq to make a safe landing on a turbulent (but only) helideck.

My point here is that 30 mins seems pretty pathetic as a means to get you somewhere safe. So I am wondering if the dry run certification requirement is there to allow you time to make an immediate power on landing (ie ditching or finding a flat spot if over land) following a powered descent from say FL080 perhaps IMC?

Already this year two gearboxes have failed offshore and the final catastrophic phase of each has been sudden. So how much of the 30 mins should we be happy to use? The dilema: go for a deck/clearing 29 mins away on the basis of a one off lab test or make sure you make a controlled ditching/emergency landing?

Food for thought.

My vote would be, use the time available to get the aircraft to a point where a safe landing can be made (if onshore) or a ditching is survivable (well, as survivable as it can be), offshore.

407
 

I recall being told by my TR examiner that the 407 gearbox (which is Kiowa derived), could run dry at 105% max contin for 30 mins - no plans to check it out though. Something to do with the dimples holding enough surface oil, plus presumably some meaty engineering.

It will be interesting to see if anyone posts some official documentation on dry run capabilities. My personal view is that a lot of the facts and figures are urban myths.

From what I've seen on the mil side, the Aircrew Manual or equiv will provide guidance on the max power setting which can be used without detriment to the 30 mins, which in two cases I know of have been 'proven' by bench tests.

Good question! The crew would have to make up their minds based on how rough the sea is/how inhospitable the terrain/how seriously ill their cas is (eg if on SAR). 30 mins may seem pathetic but it's a lot better than nothing - is it realistic to expect a published capability much greater than this?

At Agusta experienced guys told me the AB412 MGB is FOR SURE have been tested for 30 min run dry- that is, have been cranked at 100% NR for 30 minutes without any oil inside, than stopped and inspected for damage assesment.
On the other side a friend of mine had all the MGB oil gone out the casing because of a bad inspection at the sump chip detector o-ring.
He was flying day VFR over the sea and managed to reach the shoreline in time to get the skids on hard; he went down low 100Ft@Vy and shutdown after 18' the caption went on.
It was winter and OAT was 5° Celsius at MSL, no pax on board.
After Agusta on site inspection the MGB continued operations for awhile producing some very little chips and thereafter changed with a brand new one.

Maybe the 30' requirements come from Vietnam era on the Huey?

Maeroda

Not sure what manufacturers use, but the FAA demonstration requires the minimum torque necessary to sustain flight at the maximum gross weight and the most efficient flight conditions. The torque is increased at 25 seconds remaining and at 10 seconds remaining to simulate the loads of a landing. A small amount of damage is allowed, as long as autorotation is not affected.

You do bring up a good point in that when flying beyond 30min of a safe landing spot, you're committing yourself to a ditching. However, there are other failure conditions in FW and RW flight where flight cannot be continued to a safe landing area. A risk that has to be accepted or the flight can't go.

Cheers,
Matthew.

I know a little bit about 407/412 MGB performance with no oil pressure and let me tell you, if the pressure is at 0 PSI, you do what the Flight Manual says; land as soon as possible. It does not say to land within 30 minutes.

Some have decided to continue flight to shore, low and slow, and are no longer with us today to tell us how unfortunate the ending was...:=

A battery is supposed to last 30 minutes - would you expect to actually get that? Nope - the same goes for gearboxes. My personal decision would be to get on the deck asap, which in reality would be several minutes even if you went for the surface below you (try it some time).

Phil

Model of chopper that crashed off N.L. failed first test by 20 minutes: FAA

The Canadian Press: Model of chopper that crashed off N.L. failed first test by 20 minutes: FAA

Regards
Aser

The comment by Sikorsky's Paul Jackson that 10 mins is enough because you can get from 15000 ft to the ground comfortably in that time is pathertic and shows that Sikorsky really don't give a sh*t.

There is clearly collusion between Sikorsky and the FAA to sidestep both the letter and the spirit of the law and both should answer to a senate committee or similar.

The business practices of Sikorsky make the city bankers look like honest folks in comparison.:ugh:

Crab,

Such disdain for the manufacturer of your next steed...:{

Why doesn't some bright spark design an emergency fuel feed to the MRGB, whereby, in the event of loss of oil, the remaining fuel can be cross fed into the MRGB? After all, Jet A is still an oil based coolant and would keep the gearbox running a little longer. I actually run a MRGB with JetA as the lubricant very successfully in an un manned helicopter.:ok:

Would that make any difference in your decision "Land ASAP"?

I don´t think so.....

I work as a MTP on Bell helicopters-the 30 min value is just a theoretical value-never experienced on a real flying helicopter, just on test runs...

Nobody can really assure that your MGB will run for 30 minutes without oil.....

If you loose your complete oil during flight, there is a major reason for that....so i wouldn´t risk my life.....

What if there is nowhere to land?

Some scenarios would be different. For example, you might be feet wet and 45 mins from land, at night and with plenty of fuel. Your MRGB runs dry so you decide to do what?
If you had the option to divert some of your fuel through the MRGB to keep the gears cool and wet, would you do it?.
Or would you prefer to just ditch?

Search the online FARs
 

To get the details of what the run-dry testing means, you can pull up the online FAR requirements and look at the guidance that explains how the test should be completed:
The 30-minute test is just a gearbox test that to demonstrate a standard of reliability an it is shown once before aircraft are certified. It does not imply that the aircraft can or should be flown for 30 minutes after loss of lube.


Here is the rule that the gearboxes are certified to:

From 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.
(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.

Here is the guidance material for this test (from AC-29)
(1) Section 29.927(c) prescribes a test which is intended to demonstrate that no hazardous failure or malfunction will occur in the event of a major rotor drive system lubrication failure. The lubrication failure should not impair the ability of the crew to continue safe operation of Category A rotorcraft for at least 30 minutes after perception of the failure by the flight crew. For Category B rotorcraft, safe operation under autorotative conditions should continue for at least 15 minutes. Near the completion of the lubrication failure test, an input torque should be applied for 15 seconds to simulate a minimum power landing following autorotation. Some damage to rotor drive system
components is acceptable after completion of the lubrication system testing. The lubrication system failure modes of interest are usually limited to failure of bearings, gears, splines, clutches, etc., of pressure lubricated transmissions and/or gearboxes. A bench test (transmission test rig) is commonly used to demonstrate compliance with this rule. Since this is a test of the capability of the residual oil in the transmission to provide limited lubrication, a critical entry condition for the test should be established. The
transmission lubricating oil should be drained while the transmission is operating at maximum normal speed and nominal cruise torque (reacted as appropriate at the main mast and tail rotor output quills). A vertical load should be applied at the mast, equal to the gross weight of the rotorcraft at 1g, and the lubricant should be at the maximum temperature limit. Upon illumination of the low oil pressure warning required by § 29.1305, reduce the input torque for Category A rotorcraft to the minimum torque necessary to sustain flight at the maximum gross weight and the most efficient flight conditions. To complete the test, apply an input torque to the transmission for approximately 25 seconds to simulate an autorotation. The last 10 seconds (of the 25 seconds) should be at the torque required for a minimum power landing. A successful demonstration may involve limited damage to the transmission, provided it is determined that the autorotative capabilities of the rotorcraft were not significantly impaired. For Category B rotorcraft, upon illumination of the low oil pressure warning light, reduce the input torque to simulate an autorotation and continue transmission operation for 15 minutes. To complete the test, apply an input torque to the transmission for approximately 15 seconds to simulate a minimum power landing. A successful demonstration may involve limited damage to the transmission provided it is determined that the autorotative capabilities of the rotorcraft were not significantly impaired. If compliance with Category A requirements is demonstrated, Category B requirements will have been met.

I know that it is hard to give up a helicopter-but everyone has to decide this regarding the actual situation.

During emergency, there is not only "black or white".
Whatever leads to success is right.....

Unfortunately, you don´t know if your MGB go on..
Any idea what can happen if the MGB gives up?

I have several hours offshore-and yes, i thought about several emergencies that could have come up while over sea..

I think that i would prefer ditching....but actually (and luckily) i have never been in that situation-and hopefully will never be.....

(My bold.)"That language is fully compliant with the ... requirement to prove 30 minutes of flight after detection of an oil leak," he said."(representative of SK)

The European regulators said the test showed a loss of oil would mean the helicopter could only stay in the air for "around 10 minutes," a finding Sikorsky does not dispute.
Sikorsky documents used to market the aircraft, dated August 2003, said the gearboxes of the S-92A have a "30-minute drive system after oil leak."
So the language complies !!! We are all right then :mad:
Semantics used to justify failings, with both manufacturers & regulator \ certification process.
I tend to agree with crab

At least with a premeditated ditching, there's time to steel oneself (and one's pax) for the coming ordeal, run through the ditching drills one final time etc - may prove more survivable than flogging the MGB to destruction especially as

Definitely no 'one-size-fits-all' answer to this dilemma!

I'm interested in gathering examples of the above (ie trying to make it, low and slow, and the MGB giving up the ghost) to pass on to young bucks learning the trade, to reinforce to them that this is a scenario they might face - anyone able to help?

I am glad some seem to think like myself and that a test bench demonstration of dry running for 30 mins is no guarantee of it doing that in the real world.

So what do the EOPs say for an aircraft with demonstrated 30 min run dry capability, Land ASAP within 30 mins, or Land immediately, power on?