Engine Shutdowns

[Snikers]

G'day,

I am from the marine world and would like to ask a question of any Pilots who have flown large commercial airliners. I am currently involved with a gas turbine installation with engines very similar to that fitted to large aircraft.

My questions are: -

- If, say, on take off or landing one of the aircraft's engines lost oil pressure to its bearings would the engine shutdown or would it continue to run until catastrphic failure ocurred?

- Can the Pilot override an engine shutdown in any circumstances?

Any information greatfully recieved.

[Avionker]

Not a pilot but an avionics mechanic who has worked on several types of aircraft from Jetstream up to 747, and some rotary wing also.

No aircraft I have ever come across, or even heard off, as any kind of auto shut-down system on the engines. If an engine shuts down in flight it is because the crew have decided to shut it down or because there has been a catastrophic failure that prevents the engine from operating.

I am ignoring the possibility of fuel starvation as that is a situation that really shouldn't occur unless human error is involved (BA 38 at LHR excepted).

[PBL]

Vague question, Snikers.

For one thing, are you talking about turbine bearings or, say, pump bearings.

Would you mean: lost 100% of oil pressure to all turbine bearings instantaneously? Physically impossible, so let's ignore it.

Would you mean: slowly lost oil pressure over a manageble period of time to some turbine bearing. One would hope the crew would be alerted and shut the engine down, for if it continued running then serious damage is very likely to ensue.

Or would you mean: lost some/most oil pressure over X period of time to various bearings Y,Z,W? Then we would want to know what engine you are talking about, what X is, and which bearings Y,Z,W you are concerned about.

There are, definitively, no shutdown mechanisms on any engine which trigger in all of the possible cases of bearing oil-pressure loss (that is, for all X, Y, Z, W).

[lomapaseo]

You can program the engine control to do what you would like regarding engine shutdowns for cause.

Of course that's not a good idea when you can't float without it.

Left to their own the engine will keep running (at least at idle) until the blade tips wear away or until the fuel system breaks down somehow.

I am aware of some newer engines today that having sensed an overspeed will latch the fuel control at idle (not withstanding the throttle position) and can only be reset by a restart. Other than that I can't think of a forced (no pilot involved) shutdown

I'm still confused by the question :confused: Is it a historical question or a technical how-to question?

[DERG]

Hiya Snickers

I can see why you are interested in the shut down..or not..of a gas turbine engine. There have been two recent incidents where a gas turbine was uncontrollable. One was the incident with the Rolls Royce A388 T972 engine and another was on the BP oil drilling rig in the gulf of mexico.

In both these events the engines could not be shut down.

Now as far as the critical phase of take off is concerned in a jet 'plane the best man to ask on this forum is TURBINE D.

[SNS3Guppy]

No aircraft I have ever come across, or even heard off, as any kind of auto shut-down system on the engines. If an engine shuts down in flight it is because the crew have decided to shut it down or because there has been a catastrophic failure that prevents the engine from operating.

Some turbine engines do have automatic shutdown features. This is common on certain APU's with automated start procedures,for example. A number of different switches that monitor various parameters will shut the engine down, from overspeed sense circuitry to oil pressure switches.

Some turbopropeller engines have a somewhat similar function, using an "autofeather" feature which doesn't shut the engine down, but feathers the propeller automatically if a torque loss is sensed on one engine. This is specifically a takeoff safety feature. The engine may actually be running at that time, but the system is designed to eliminate the drag of a windmilling propeller and feathers the propeller.

I've personally experienced a loss complete loss of oil in a motor, in which the engine kept running; according to the manufacturer, the engine has been demonstrated to run for a half hour with no oil. In that particular case, the failure occurred on a turbopropeller engine. The lack of oil pressure prevented the engine from "developing torque," in that while the engine was still providing power to the propeller, the propeller wasn't available to produce thrust.

Takeoff in an airplane is a little different than an operation in a boat. Generally on takeoff, we don't touch anything if there's an emergency until the aircraft is a minimum safe distance in the air. If the engine is producing useful thrust, we use it, whether it's out of oil or has some other problem. In a boat, you could use an auto shutdown circuit to protect the engine without too much concern about the dangers that an aircraft faces on takeoff; you could do more to protect the engine as your priorities may be a little different.

[Avionker]

I had actually avoided the APU auto shut down scenario intentionally so as not to muddy the waters. Auto shut down of an APU is more likely to be a nuisance to the crew than a safety issue.

I am assuming that the OP works on gas turbines in a marine environment, where having a control system capable of carrying out an auto shut down of the engine, if certain parameters are exceeded makes sense and is not likely to create a major safety issue. The turbines in these installations will tend to be running for more than a few hours at a stretch and auto monitoring will alleviate the need for someone to be tied to a control panel/terminal 24/7.

This clearly is not the case with aircraft where the crew, and not a electronic nanny, must be the ones to decide when it is safe and appropriate to shut down an engine.

[Ka8 Flyer]

Don't ERJ's engines auto-shutdown if they lose oil pressure? I remember hearing about this - I think its a FADEC function...?

[grounded27]

Don't ERJ's engines auto-shutdown if they lose oil pressure? I remember hearing about this - I think its a FADEC function...?

I would not like this, would prefer to trash an engine getting every last lb of thrust I can out of t to save lives.

Bottom line to the OT is that every turbine I know of will sieze if oil does not get to the bearings, even just one bearing could, would be catastrophic. Turbine shaft looses support warps and blades start to contact the case. For a marine turbine I would prefer an auto shutdown on low oil press or qty for obvious reasons.

[Exaviator]

Hi Snickers,

The decision to shut down an engine always rests with the aircraft's commander. There is no auto-shut down function. That decision is based on engine indications and the state of flight at the time.

In the example that you gave it would not be normal to shut the engine down on the basis of a single indication i.e. Loss of Oil Pressure as it could be only a indicator failure. If however it was accompanied by a rapid rise in Oil Temperature then a shut down would be considered.

The other option would be to operate at a reduced thrust setting and evaluate further indications.

I trust this helps, Cheers :ok:

[Snikers]

Gentlemen,

Thank you for your comments. I think I have an understanding of the questions I asked. The reason for the questions were as a result of some internal arguments with regards to engine shutdowns. In the normal course of events in reciprocating machinery we have shutdowns on low lube oul pressure, high cooling water temperature and overspeed of the engine. This is normal for a "ship" and canot be overridden by anyone.
It would appear to me from the various commnets, that no such dievice is fitted to aircraft. The Pilots making the judgment on whether or not to shut down the engine based on various circumstances. In my world there is no such thing, if the engine is in danger it will shutdown. Mind you, we can't drop out of the sky!
Thanks again for your valued assistance.

[barit1]

Free-turbine engines (where the LP turbine powers a generator, or a ship's screw, or an aircraft propeller or helo rotor) have another failure mode that must be accounted for: Namely, loss of load. (Prop goes to fine pitch, driveshaft breaks, powerlines severed, etc.) This can cause an extremely rapid overspeed, requiring automatic response to prevent uncontained failure (such as QF32 experienced).

In every such installation I'm aware of, there is an overspeed sensor - separate from the main control loop - that chops the core engine to idle, or maybe even to shutdown. I've worked on a half-dozen different such installations.

If you need details - PM me and I'll tell you what your engine is likely to have in this regard.

And I agree - while low/no oil pressure should ring alarm bells, shutdown should be left to the operator.

[Turbine D]

Snikers

I would really need to know more about the usage of the marine gas turbine installation you are involved with. But in general, these engines are monitored the same as the aircraft turbine engines from which they were derived. On board a ship, the gas turbine is used for both electrical power generation as well as providing the power to the props. As in any gas turbine, oil is consumed and usage is monitored to keep proper operating level as is vibrations that could indicate several things going wrong. In general, barit1 gave you a very good explanation of an important monitoring feature of these installations. Any complete shut down is generally in the hands of the operator although the control system may reduce the engine to idle while the problem is assessed.

[FE Hoppy]

CF34s fitted to the e-jets have an overspeed protection function which will flame out and relight an engine who's N2 goes beyond the normal limit by approx 2%. As the FADEC uses N2 as a control input the overspeed is an indication of the fadec failing to control the engine. If the engine overspeeds 3 times in 30 seconds the fadec shuts off the fuel and signals an engine failure.

Better secure it than let it overspeed to destruction.

Gas turbines can flame out for lots of reasons but loss of oil will normally lead to a seizure if the engine is left to run. That can be quite dramatic too. I vaguely remember an engine detaching itself due to a seizure. Which is why we shut them down for low oil pressure usually.

[Snikers]

Turbine D

We are using 2 x LM 2500's to power a 99m fast ferry. The craft should atain speeds of up to 50 knots. The LM 2500's will be rated at 22mW each. Each gas generator is coupled via fluid (exhaust gas) to a power turbine which is directly coupled via a clutch to a reduction gearbox and onward via a shaft to a thrust bearing and finally a large water jet. The power turbine is rated at max 3600 rpm driving the shaft at approximately 600 rpm. Engine control is via the power turbine. These engines will run on LNG gas and liquid fuel (gas oil), dual fuel. A world first for a high speed craft.

We have various shutdowns built in to the engine as well as slowdowns which return the engine to an idle state. Shutdowns will shut the engine down irrespective of the Captain's wishes to "save the engine". Shutdowns will include, low low lube oil pressure following an audible warning, overspeed following an audible warning, fire in the turbine enclosure, failure in part of the gas system, gas detection, gearbox low low oil level after a 10 sec delay etc etc.

If you would like more information please advise.

[DERG]

Please note well..

There is a set of circumstances where a marine turbine can run to overspeed. If there is a leaking source of methane or propane in the engine room the machine cannot be shut down if the engine is ingesting the gas.

The liquid fuel can be stopped but it will run to destruction. This could be said of any engine that burns hydrocarbons, and I guess ships have ducted air intakes from the decks. However...this scenario has happened recently.

So if you have any liquified gas anywhere on the ship make absolutely certain it is secure. It is heavier than air and will collect into the lowest part of the ship.

Wait one..."gas detection" Yes Yes this is the danger..I see they are well on top. The BP rig was not so lucky. The machines could not be shutdown.

[barit1]

Each gas generator is coupled via fluid (exhaust gas) to a power turbine which is directly coupled via a clutch to a reduction gearbox and onward via a shaft to a thrust bearing and finally a large water jet.

The "directly coupled via a clutch to a reduction gearbox" is my concern. Clutches can fail, as can shafts and reduction gearboxes. Be sure that the control system can tolerate these without permitting a destructive power turbine overspeed. Put these questions directly to the GE people, including any results of their loss-of-load tests.

Further, if both engines are driving a common gearbox, what happens if one engine is running, the other is shut down, and its clutch is dragging? Will the power turbine bearings in the shutdown engine be running dry while the shaft windmills?

GE has plenty of experience going back 4 or 5 decades with these issues, so they should have ready answers.

[Turbine D]

Snikers

Thanks for the additional information.

I think this application is the new catamaran high speed ferry being designed and built by Incat in Tasmania. The LM2500 engines and their accompanied waterjets are separately located in each hull. So I can understand the logic to automatically shut down an engine to save it. I would imagine each set operates independently of the other and there is no common gearbox. The duel fuel concept is very unique.

[Snikers]

Turbine D,

Excellent piece of detective work!