JET AIRPLANE CRITICAL ENGINE

[piratepete]

It is well established that due to P factor a propellor engined aircraft, given certain prop rotation relative to the airplane body has a CRITICAL ENGINE for the failure case of one powerplant.However I have been asked, as an instructor on Jets, if the same concept applies to a Jet Airplane.I do not know of any reference to support this idea (Look at SKYBRARY.AERO for example, a very very good source of aviation knowledge), and asked how this question has arised.The universal reply was that certain Interview Panel Pilots in many airlines were asking this silly question and when the applicant said there isnt a critical engine on a jet aircraft they were told the answer is a definate "yes" and they had demonstrated poor technical knowledge! The only issue I can relate to this silly idea is if you have a significant crosswind then the UPWIND ENGINE if it fails might be considered the more critical failure as you have the weathervane effect coupled with the engine swing BOTH COMBINING thus requiring a larger rudder application to keep straight etc.However every manufacturer ive talked to said THERE IS NO SUCH THING AS A CRITICAL ENGINE on a Jet airplane, so the argument is not valid from these "PANEL EXPERTS", its rubbish.Any comments, thoughts?

[DaveReidUK]

However every manufacturer ive talked to said THERE IS NO SUCH THING AS A CRITICAL ENGINE on a Jet airplane

Hard to argue with that.

[planit]

The only one that is still operating ? I'd call that critical !

[TurningFinalRWY36]

only situation i can think of when you might have a critical engine is during a crosswind takeoff. Crosswind from the left, using left rudder to keep aircraft aligned with centreline, Right engine fails, less rudder travel available for the asymmetric thrust

[Current Limiter]

I have also been posed this question. Aerodynamically (apart from the crosswind mentioned before) there should be no difference. There is however a difference measured by what systems are supported by which engine. In some aircraft the hydraulic systems supported by each engine may result in a downgrade of the controlability if say the right hand engine should fail compared to the left hand one. This may be considered to be a critical failure as a result of some downgrading of your redundancy, or reduced controlability.

[wiggy]

However every manufacturer ive talked to said THERE IS NO SUCH THING AS A CRITICAL ENGINE on a Jet airplane

FWIW the last time I looked there was no mention of a "critical engine" in the 744 FCOM and there is no mention of "critical engine" in the 777 FCOM.

[FE Hoppy]

You are correct.
In certification terms there is no critical engine.
However, a quick search on here will uncover lots of knowledge from the horses mouth about the effect of crosswind.
If I were posed the same question at interview I would answer in two parts. Firstly certification standards for VMC and secondly the reality of crosswind in controllability. If it were a UK operator I would mention how the old UK standard did in fact consider crosswind (7kts if memory serves) but how that is no longer the case.

[lomapaseo]

there are more critical pilots than critical engines

[ImbracableCrunk]

Someone's been reading "How to Ace the Technical Pilot Interview" book again.

[Chesty Morgan]

There could be a critical engine in terms of systems loss and subsequent handling/performance factors.

[piratepete]

The context of the question regarding CRITICAL ENGINE on a Jet is with respect to a failure at V1.I dont see any way to validate the idea of a critical engine on a jet with respect to PERFORMANCE or aircraft handling (like on a prop),although im told if its say a 747 then systems loss due to engine number 1 causes problems, I dont know, I dont fly it, Peter.

[wiggy]

I'm told if its say a 747 then systems loss due to engine number 1 causes problems, ?....

Not quite.

I've not flown the 744 for a while so am open to correction but as I recall it performance aside a straight forward run down/ failure of number 1 ( or any one of the 4 for that matter ) shouldn't cause major problems on the 747 (400 anyway) since you shouldn't lose any major systems. I certainly wouldn't think of it as a "critical engine" in the context of this thread.

What you might have heard is that it gets a bit more interesting if for some reason you lose the #1 engine and the associated hydraulic system ( and to emphasise on a straight forward engine failure you shouldn't) since amongst other things the #1 hydraulic system is needed to raise the nose and body gear.

HTH

[Chesty Morgan]

The context of the question regarding CRITICAL ENGINE on a Jet is with respect to a failure at V1.

No, it isn't.

[DaveReidUK]

The context of the question regarding CRITICAL ENGINE on a Jet is with respect to a failure at V1.No, it isn't.

I think it's safe to assume that the OP does actually know in what context he was asked the question by his students. :O

I have been asked, as an instructor on Jets, if the same concept applies to a Jet Airplane

[Chesty Morgan]

It's also safe to assume that he didn't mention V1 in his OP. :O:O

[piratepete]

Just to remove any doubt about the context of the original question, it was ALWAYS asked with respect to an engine failure at or very near (just after) V1 for the continued takeoff case in conjunction with the correct meaning of both V2 and V3.Peter.

[FlightDetent]

From AB's Getting to Grips with A/C Performance: “JAR/FAR 1.1: 'Critical Engine' means the engine whose failure would most adversely affect the performance or handling qualities of an aircraft”, i.e. an outer engine on a four engine aircraft.

There are 26 instances of "critical engine" in that document, all of them being paste-copy quotes of regulations. Not a single mention that there is actually such thing, except from the very one I quoted above.

[FullWings]

I suppose the concept applies to jets as with a non-zero angle of the thrust line to the relative airflow, you will get p-factor effects from the fans. I assume that the magnitude of those effects is small compared to everything else, especially as the intake ducts probably reduce them considerably by ‘bending’ the airflow to be more perpendicular to the fan disc. Engines on commercial jets tend to rotate in the same direction, so the potential for slight asymmetry is there but appears to be disregarded.

It seems to me that there are two common usages of “critical” when it comes to power plants: One describes the intrinsic properties of an an engine + airframe combination and the other takes the operating environment into consideration as well, e.g. crosswinds.

If you really wanted to nit-pick the question, you could argue that at V1 you are still on the ground, so in many installations the thrust line is parallel to the airflow. It’s only during rotation that p-factor effects increasingly come into play and you would have hoped that you’d be nearer V2 than V1 by the end of the manoeuvre...

[Derfred]

only situation i can think of when you might have a critical engine is during a crosswind takeoff. Crosswind from the left, using left rudder to keep aircraft aligned with centreline, Right engine fails, less rudder travel available for the asymmetric thrust

Other way around?

[keith williams]

This question was included in the JAR ATPL POF question bank for many years and it is probably now in the EASA question bank.

In the case of airline interviews I suspect that the questioner is attempting to test whether the candidates knowledge and understanding have expanded beyond the basic propeller theory.

If the candidate only considers the term “Critical Engine” to be applicable to multi-engine propeller aircraft, then the questioner will probably conclude that he/she has not given sufficient thought to the effects of engine failure on multi-engine aircraft.

But if the candidate is aware that the generally accepted definition of the term Critical Engine is something along the lines of “The engine who’s failure would most adversely affect the performance and/or handling of the aircraft” then he/she should be able to discuss effects such as crosswinds and system layouts. A candidate who is able to do this is more likely to convince the questioner that he/she is the right one for the job.

[piratepete]

Keith, that is the most reasonable and sensible explanation ive heard, well done.Makes sense to me, and ive been one of those "interviewers" in the past.I have to say that I spend a lot of time educating myself on SKYBRARY.AERO its an awesome source of aviation knowledge, but I fail to understand how they make any money out of it, Peter.

[Capn Bloggs]

Outboard engine on the downwind side. :ok:

[Chu Chu]

Presumably gyroscopic effects will produce a yaw either into or away from the dead engine on rotation, depending on which fails (and the direction of rotation). I'm guessing not that significant, though.