Idling A Failed Engine To Continue The Flight???

[AeroTech]

Hi,
I read that it is permissible to idle a failed engine after certain anomalies if engine parameters are in the allowable limits in order to continue the flight.
If this statement is true, here are some questions:

-What are these anomalies?

-Is this valid for all aircraft (all airliners:twin, tri, quad)?

-Are there other factors (besides engine parameters in the allowable limits) that pilots should take in account to decide either to continue the flight or divert (land ASAP)?

-If pilot decide to continue the flight, can he maintain his altitude or the driftdown is necessary (let's say he is flying at altitude cruise in twinjet)?

Feedback appreciated. Thank you.
Best regards.

[Willit Run]

If the engine has truely "failed" it wouldn't be running. If you can keep an engine running, its probably producing hydraulics and electricity which is always a good thing. Aside from physical damage, there are two things that hurt engines; over temp and lack of oil. You certainly don't want to keep an engine running if its out of oil or has been over temped unless its a dire emergency.
Precautionary shut downs have different outcomes depending on whether or not you have 4 or 2 engines. if you have 4, no sweat, if you have 2 and shut one down, you now have to "land at the nearest airport in time to which you can make a safe landing.".
I'm sure more folks will provide you with more and probably better info to your very broad question.

[NigelOnDraft]

AT...
As AR says, your post is misleading with the phrase "failed engine". This covers many scenarios, but my broad interpratation of "failed engine" would be one that wouldn't run at all :ooh:
Certain problems with the engine might mean it can be run at idle, or low power. As AR says, this keeps certain ancillary systems going, so makes life easier for the FC. Of course, Engineering might not thank you if it leads to further damage, but that's their problem :(
However, certainly on types I have flown / company I work for, the engine is to be treated as "failed". So on a twin, it's a Land ASAP - so your statement "in order to continue the flight" is incorrect. Why? Well, if it will only run at idle, it's not a lot of use for approach or GA... and if the remaining engine failed you have no power.
As to what failures / aircraft / driftdown etc. consult your Airline / Aircraft Ops Manuals - I am assuming you are a pilot :hmm: If you are not, the answers are endless and variable, and best left at that...

[AerocatS2A]

Hi,
I read that it is permissible to idle a failed engine after certain anomalies if engine parameters are in the allowable limits in order to continue the flight.
If this statement is true, here are some questions:
-What are these anomalies?


A couple that I can think of from the Dash 8.

Oil pressure between 45 - 55 PSI is not enough to run the engine at flight poiwer settings but is ok if the engine is feathered and it can then run hydraulics. However, it is still an engine that's not developing any power (i.e, an engine failure), so you'd be heading off for a landing at the nearest suitable airfield.

Or a prop oversepeed where the prop could not be feathered, you leave the engine running at idle and land ASAP.

In neither of these examples do you "continue the flight" in any way other than finding somewhere good to land.

[Engineer]

Anomaly that fits your criteria would be the compressor stall situation on a turbo jet.
It is feasible to maintain the engine at min thrust and use as a backup in the event that it is not a lucky day and you lose another engine. Alternatively it could be shut down and then restarted if required. All ways good to leave your options open :8
But the AOM/FCOM/etc will also mention a caution that continued operation of an engine that exhibits stall tendencies must be done with extreme caution. If high EGT becomes evident or a rapid EGT rise occurs during slow throttle advance or an increase in vibration is noticed than these would require the engine to be shut down

[AeroTech]

Hi,

Thank you for your answers. I apologize for the delay regarding this post.

I should said engine having problems instead of a failed engine, like engine experiencing high EGT, and after reducing the power the EGT returns to the allowable limit and the engine is kept running at idle.

-I am wondering about another utility (besides the one mentioned previously in your posts) of idling engine after it is experiencing permissible problems :
The idled engine will reduce the trim between the normal operating engine and the idled engine (compared to the trim caused by one engine normaly operating at MCT in such case), therefore reducing fuel consumption. In addition the airplane will fly at at higher altitude with both engines compared to an altitude with one operating engine, so this will save more fuel for a diversion (according to the previous posts LAND ASAP, so it is not possible for a twin to continue the flight if the planned destination is not far from the divertion airport or may be even to opt for adequate and suitable alternate airport).
Is this statement true?

-If a permissible idling engine (in stead of shutting) in trijet or quad will save fuel as described above (for the twin and if it is true), is it possible to continue the flight for the planed destination (assuming we saved enough fuel by idling engine)?

-When the engine is set at flight idle or lower power settings, the EPR will probably be < 1, does it mean that the engine is not producing thrust?
Is there an EPR limit for a minimum thrust and/or providing electric, hydraulic and pneumatic power? (or may be minimum N1 if the aircraft is not fitted with EPR).

Feedback appreciated. Thank you
Best regards.

[NigelOnDraft]

AeroTech...
May I be somewhat forward, and ask where you are going with this? You are bringing up some potentially valid, but minor technical points, but missing the "big picture"?
A "safe" "commercial" flight is essentially based on the premise that any single failure will not unduly hazard the passengers. A twin engined aircraft therefore meets this criteria, since an engine failure can be tolerated at any stage of flight.
Having "lost" an engine, this premise no longer holds true. Failure of the other powerplant essentially leads to dead people. They may be lucky, and live, but it should not be down to luck. Therefore, having lost an engine, this risk is minimised by "Landing ASAP".
Fuel Consumption, Cruise Altitude, and "making destination" are 99% likely to be irrelevant. Any Crew taking these into account is asking for trouble.
Again, the EPR is not really relevant. Idling EPR < 1 is theoretically "drag" not thrust, but still less drag than shutdown. EPR has no relevance to producing hydraulics / electrics / pneumatics - these will be more RPM based - and N2 on most engines. On types I have flown, the only time above idle is needed is for pneumatics on the ground to crossbleed another engine.
For a 3 or 4 engine jet, the idle or shutdown will be more likely based on ancillary systems than fuel consumption. I have no figures, but doubt range / Crz Alt etc. are much different between idle and shutdown - the idling engine will (inefficiently) produce some thrust, but use some fuel. Whether it can make destination depends on the fuel plan at the time, and also asks many other questions - see the BA LAX-LHR threads :confused:
HTH NoD

[BOAC]

Memories are thankfully fading, NOD, but what was the outcome when a BA manager (IIRC?) 'continued' to destination on a flight in an Airbus with an engine at idle (due to oil problems?) a while back? Was a final safety report made available to the troops and if so did the company judge that to be an 'acceptable action'? What was the applicable BA QRH/ECAM action?

Assuming they did, and if we have heard nothing from the CAA on this, presumably it becomes an 'acceptable action'? This would make AeroTech's question interesting.

[NigelOnDraft]

Hi BOAC...
The Mgr concerned wrote an article to address the "rumours" :hmm:

As far as I recall, it was an "advisory", not a Warning / Caution. No actions were required, and all the advisory tells you (it was Lowish Qty) is that the Qty is likely to rise when power is reduced. Only when the Qty gets seriously low and/or (?) has Pressure/Temp associated implications are any actions required.

As far as I recall, he elected to reduce power, or even idle the engine. So I am not sure if it is relevant to this thread. There was no requirement to do anything other than monitor the engine, in fact not even that ;) and so the "idle" was purely at the crews' whim. It turned out there was a filter partially blocked that just restricted the Qty returning to the sump where the level measurement.

Therefore, IMHO the engine was not failed, faulty, unserviceable, and was able to produce full power if required, and there was no strict reason to believe that there was even a time limitation apparent - so he was technically correct, and could even be stated to have been "over cautious".

Please do not read into any of the above that I would have acted similarly. I do not know the full facts, was not in the situation, and as far as I know, there was no report published, other than his article, and doubt it got any further than an ASR.

[BOAC]

Thanks, NOD - as you say it appears to be outside the scope of this question.

[Cornish Jack]

Might be worth considering a specific case of engine vibration. Coming back to idle removed the problem. Flight continued to destination. Problem engine investigated ..... the fan securing nut was down to the last one and a half threads!!!!!!:uhoh: Think on't:suspect:

[GotTheTshirt]

Many an RB211 has operated at reduced power after clapper lock up.
As per the Manual. Reduce power until the vibration subsides

[PAXboy]

Reduce power until the vibration subsides
That wise advice is applicable on soooo many occasions ... ;) ;)

[ZQA297/30]

There could be other considerations too. ETOPS stats might be one. IFSD rates, and returns/diversions are always subject to scrutiny.