Feather and 12" MP for zero thrust?

[morno]

I don't really feel like wading through pages and pages of dribble with everyone's opinion, but can just one person, tell me what is wrong with simulating a failed engine using the mixture?

I have only ever had it done that way to me in every assymetric drill in various aircraft, by various instructors/checkies with varied levels of experience. I'm struggling to see why that's a dangerous procedure?

morno

[Trent 972]

Lycoming agree with you Morno, but the NTSB has a reservation about the procedure at low level.
Lycoming Flyer

The fatal crash of a light twin in which a flight instructor and an applicant for a multiengine rating were killed prompted the NTSB to issue an urgent warning to all pilots simulating an engine-out condition on multiengine airplanes. The Board’s investigation revealed that some flight instructors do use the fuel selector or the mixture control to shut down an engine to test a multiengine applicant. Although this is a recommended procedure, the urgent warning was aimed at flight instructors who were using this procedure at altitudes too low for continued safe flight.
The NTSB observed that use of such procedures at traffic pattern altitudes may not permit instructors enough time to overcome possible errors on the part of the applicant. The recommendation by the NTSB means that all simulated engine-out operation at the lower altitudes should be accomplished by retarding the throttle, and this should be done slowly and carefully to avoid engine damage or failure.
Many flight instructors down through the years used the technique of abruptly cutting an engine with a multiengine candidate to test his emotional reaction and judgment with this extreme technique. Big radial piston engines with short, stubby crankshafts could tolerate the abrupt technique. However, flat-opposed piston engines with their long crankshafts and attached counterweights could not as readily take the abuse of suddenly snapping a throttle shut, particularly at takeoff or climb power. Use of the latter technique would tend to detune crankshaft counterweights and could possibly result in a nasty engine failure.
Since it was common technique by flight instructors to terminate power abruptly to simulate an engine power loss, we had to protect the engine. As a result, we published in our Engine Operator’s Manual and in Service Bulletin No. 245, the recommendation that if the power was abruptly terminated, it must be accomplished with the mixture control. Of course, this was intended for the higher altitudes where a complete engine shut-down could be conducted safely. The student was to identify the dead engine by retarding that throttle to about 12" MP to simulate zero thrust, or similar to having the prop feathered. At that point, the instructor could immediately return the mixture to an engine-operating condition, and power would be available if needed.
In our publications, we then explained the reason for using the mixture to abruptly terminate power. By putting the mixture control in idle cutoff position with the throttle in a normal open or operating position, the pilot merely cut off the fuel, but allowed the air to continue to fill the cylinders with resulting normal compression forces that are sufficient to cushion the deceleration of the engine and prevent the detuning of the crankshaft counterweights.
However, any practice of simulated engine-out condition at low altitudes should be best accomplished by a slow retardation of the throttle in accordance with the NTSB recommendation. This careful technique will protect the engine, and at the same time, provide for instant power if it is needed.

[Centaurus]

I don't really feel like wading through pages and pages of dribble with everyone's opinion, but can just one person, tell me what is wrong with simulating a failed engine using the mixture?

In flight safety speak I guess you could call it`Risk Mitigation`.
One of the extracts in "pages of pages of dribble" as you so eloquently describe it, I think stands out as the answer to your question. It came from, and was titled, National Transport Safety Board Warning on Simulated Engine-Out Maneuvers. I was about to reproduce it here until I realised that Pprune reader Trent 972 has beat me to it, thank goodness, and gone to great trouble of quoting the NTSB warning.

It is well worth reading that report if you are serious about wanting to know the story of mixture cuts versus throttle closure. Don't bother however if you approach the subject with a closed mind. Especially if you happen to be a flying instructor on light twins -or even a student undergoing twin training.
Twice the NTSB uses the term `urgent warning`in that missive. It would be foolhardy to ignore that advice from such a well-informed government body as the NTSB.

[MakeItHappenCaptain]

Trent, who actually wrote that online POH?

I treat anything not produced by the manufacturer with a great deal of skepticism and that is definitely not a Beech checklist.
All the Baron manuals I have (55, 58, multiple models) spec 12"/min RPM.

Highway, I have revised all of my post 1980 piston twin manuals and cannot find any mention of the settings you mentioned. Do you have a reference for the three manufacturer's comments regarding full fine zero thrust settings?

Trent, thanks as well for the NTSB ref.
Centaurus, always an uphill battle. I am one of the converted, but all I can say to those who question the low altitude mixture cut debate with "but I've never had a problem" is,

Learn from other people's mistakes...
You won't live long enought to make them all yourself.

Does everyone think the NTSB are complete morons?

[Old Fella]

Asymetric training

Centaurus, your contribution as always is worth reading and digesting. I recall an earlier contribution where you related your early days as a QFI and the training on Lincolns. In that you mentioned the loss of the RAAF B707 as being attributed to loss of control during asymetric training. The accident certainly was avoidable, however it was not just as a result of asymetric training. The accident came about as a result of departing from established training demonstrations and published abnormal procedures. The accident, in my opinion, clearly and tragically demonstrated the need to operate within the envelope proven to be appropriate by the certification procedure and confirmed by those whom operated the type for over twenty years prior to the RAAF taking it into service.

[Trent 972]

MIHC, I do not know who wrote that POH, but you will see it is for a BE-55B (T-42A) registered N43657 to the USAF at Langley AFB, build year 1966, Construction Number TF-32.
Wikipedia T-42A

The T-42A Cochise is a military version of the Baron B55 for use by the United States Army as an instrument training aircraft. The Army Aviation School took delivery of 65 aircraft, a further five were bought for delivery to the Turkish Army.
By 1993, the Army's remaining T-42 aircraft had been transferred to the Army Reserve and the National Guard and were no longer in standard use.

[MakeItHappenCaptain]

Trent,
It's still a license built Baron and that checklist doesn't seem to be factory issued.


Highway,
You need to check your theory. Badly.
Sorry, missed your reply earlier, but actually, the blade counterweights (and air press/springs) are only there to reverse the centrifugal twisting moment for when oil pressure is lost to the hub. (Makes it easier to send to feather following engine failure. Even then, if YOU do not move the prop lever to feather, it's just going to keep windmilling unless you have an autofeather system.)
Whenever the engine is rotating (ie. windmilling), the high pressure pump (~290psi in McCauleys, 300psi in Hartzells) is supplying high oil pressure to the hub. How do you think the prop comes out of feather during an air restart? It sure as hell isn't rotating fast as those blades come out of feather and towards fine pitch.
When you close the throttle, oil pressure is still available. The governor is controlling the rpm by altering pitch with oil pressure. RPM too slow and the governor counterweights are in an underspeed condition, therefore, the valving routes more oil to the hub to send the blades towards fine, reducing the torque from the prop blades and increasing RPM.
In an overspeed condition, oil is allowed to bleed from the hub back into the engine. The arodynamic twisting moment (Cp of each blade being forward of the pivot) and the counterweights (with air pressure and spring assist) reversing the CTM (that in a non counterweighted blade would tend towards fine) send the blade towards coarse.
As the governing range is around 1800-2600 RPM (say), at low throttle settings, if you are not supplying enough torque from the engine to spin the prop fast enough, the governor's only option is to send the prop to fine to try and increase the RPM.
Unless you are travelling at a great rate of knots (most likely vertically downwards), there ain't NO WAY that prop is normally anywhere but the fine pitch stops when the throttle is closed.

[Jabawocky]

Perhaps the USAF came to realise that not all factory POH are created equal, and many are poorly written, thus had to write their own.

[MakeItHappenCaptain]

No dramas if this is actually USAF produced, they do have their own test pilots who know what they're doing, however, as I have said (and actually flown many hours using, they are correct btw) the factory settings of 12"/min rpm work (also work for senecas) and there are no markings (apart from this being a single serial model specific checklist) to indicate who actually wrote this.
I could knock up one of these in half an hour that looks pretty good but probably contains crap. Who'd know?

Maybe the big manufacturers should all sit up and take notice that simulated single engine manoeuvres actually have a limitation of two pilots as well?
(Actually not a bad idea considering some pilots I've flown with, but funnily enough, can be accomplished with only one pilot.)

Good point from Highway being that zero thrust settings also change with altitude.
Agreed, the Baron Manual has no allowance for this.

ps. Did find the 303 stuff, but think this is a one off. Still unconvinced that Piper, Cessna and Beech have all started saying all zero thrust settings should be at full fine.

Anyone got access to a G58 manual?

[FGD135]

Lumps,

I suspect you are misreading the procedure. From your post, it appears you are reading that the process has 2 steps, with step 1 being:

1. Propeller Lever - RETARD TO FEATHER DETENT
2. Throttle Lever - SET 12 in. Hg MANIFOLD PRESSURE

Then step 2 being:

The procedure should be accomplished by alternating small reductions of propeller and then throttle until the desired setting has been reached.

This is not how I read the procedure. I read "desired setting" as that achieved by the prop lever retard and 12" setting.

In other words, after you have retarded to the feather detent AND set 12" MAP, you have achieved "zero thrust" - there is nothing more to do.

... how is one supposed to know when you're at zero thrust without just taking the POH's word for it

You don't know. You have no choice but to take the POH's word for it. The Baron does not have the instrumentation to allow you to confirm zero thrust.

The DHC Caribou, however, does have instrumentation to show the amount of thrust being produced by each prop. I have never flown a Caribou, but I imagine this instrumentation could be used when setting zero thrust.

The Caribou had a set of pitot tubes (one behind the prop, the other free from the propwash) that measured the difference in air pressure and displayed this on a gauge in the cockpit as "thrust" (in units "inches of water").

Does the prop actually feather?

No. You must pull the lever past the feather detent to get it to feather.

A few misconceptions have been expressed in this thread about the prop pitch and blade angle.

At low power settings (and normal airspeeds), the prop blades will be on the fine pitch stops, so it does not matter where the prop lever is positioned. Moving the lever between the "full fine" (max RPM) position and the feather detent has no effect on the blade angle.

[john_tullamarine]

Perhaps the USAF came to realise that not all factory POH are created equal, and many are poorly written, thus had to write their own.

I'm not military but have had a passing acquaintance. I suggest that it's not so much that the civil manuals are poor cousins .. rather the style and purpose is different.

On the one hand, the civil POH tends to be tied to serial number ranges and a variety of configuration differences. Hence it is quite common to see a series of POH paragraphs relating to this particular build, followed by another series relating to a different build, and so forth.

The military folk, on the other hand, tend to prefer flight manuals which are tailored quite specifically to their aeronautical beast. To this sort of military mindset, the ifs and buts style of manual is quite disconcerting and there will be pressure to repackage the POH into a more military style of document.

[Old Fella]

Military Flight Manuals

Hi JT.

The comment re "tailored quite specifically to their aeronautical beast" is not always so. The RAAF C130A Flight Manual, and the accompanying Tech Publications, covered several C130 models, including the Ski equipped versions. My recollection is that the C130E Flight Manual covered more than one model also. The C130H was tailored specifically for the RAAF aircraft. On the other hand the B707, when first introduced into the RAAF, used the QANTAS Flight Manual with the only reference to it being a RAAF publication being the cover. Up until I left the RAAF in 1981 the Flight Manual remained unchanged, even to the extent of the pages having the QANTAS tag as a header. What transpired after that I cannot comment on.

[RHLMcG]

The comment re "tailored quite specifically to their aeronautical beast" is not always so.

Evidently horses for courses. A mate works down at 32SQN in Sale and he tells me that the RAAF "tidied" up the civil KingAir manual very early on to get rid of non-pertinent bits and pieces.

[27/09]

Regarding the exact Mp and RPM zero thrust settings.

Does it really matter exactly what they are, so long as the aircraft approximates the performance of having OEI.


Re the mixture V throttle debate

I have only ever had it done that way to me in every assymetric drill in various aircraft, by various instructors/checkies with varied levels of experience. I'm struggling to see why that's a dangerous procedure?

Same here. The big thing for me about using the mixture technique is that all the instrument indications are the same, in that MP and RPM act in exactly the same manner whether it be a simulation or for real. I believe this important for the student to see.

The crux of the matter so far as the NTSB is concerned is this sentence

The Board’s investigation revealed that some flight instructors do use the fuel selector or the mixture control to shut down an engine to test a multiengine applicant. Although this is a recommended procedure, the urgent warning was aimed at flight instructors who were using this procedure at altitudes too low for continued safe flight.

From my perspective it is very questionable that an engine failure no matter how it's initiated should be performed at these altitudes.

By the way using the fuel selector at any altitude to fail an engine isn't very smart.

[lilflyboy262...2]

Why do we still simulate them low level?
Why can we not simulate an approach to land and a go-around at altitude, with a failure on an engine on the overshoot? Go-around altitude of say 1,500'.

Do we need the trees to make it more realistic?

[MakeItHappenCaptain]

The human brain sometimes doesn't perform as well without some level of stress. Too much stress will overwhelm the student, but a failure at 400' where the student forgets to identify and feather the failed engine certainly reinforces the correct actions while the aircraft is losing height. Guarantee after one or two EFATOs where the trees are rising, the student starts to get it together.

The mixture cuts do allow the instructor to hide which engine they have failed with a sheet of paper, however I agree with the statement about only using this method at altitude. (Used to use mixture cuts at low alt, but have decided the manufacturers and NTSB know what they're talking about better than I do.)
Total agreement with not using fuel selectors.

Too high and normally aspirated engines won't perform anyway. Senecas won't climb at 5000', ISA and max weight on one engine. (Sometimes a blessing as it highlights the importance of correct speed and configuration.)

[Lumps]

FDG135 - I did misread it, as in move pitch to the feather detent (not through).

The stipulation that the procedure should be accomplished with alternating reductions I take as meaning you can't set one then the other then that's it - due to the inter-relationship RPM/MP have with each other. i.e.,, set 12" then reduce RPM, up goes the MP, adjust that, RPM drops a bit more, adjust again. Having not done this actual procedure on this type I am armchairing it here. Just curious.



Why it specifies reducing RPM then throttle has me beat. Is it assuming it is already 'failed' with the throttle? or mixture. or at cruise power?

[27/09]

I still fail to see why using the throttle is safer than using the mixture to simulate engine failure.

I've never had an engine fail to respond smoothly and promptly when the mixture is enrichened to restart, I sure as hell have had a few engines respond the less than the desired power and smoothness when using the throttle to simulated engine failure in singles for PFLWOP exercises. In my experience the mixture method is the better of the two.

[MakeItHappenCaptain]

Lumps
Again, some CSU theory.

Yes, manifold pressure will change with rpm, but unless you drop the manifold pressure enough to set the blade pitch onto the fine pitch stops, (ie. outside the governing range) the governor will continually adjust the blade angle so that prop torque equals engine torque at the desired rpm. (Or, Constant Speed!)

The small changes recommendation is more likely because large throttle reductions, if performed quickly enough, have the ability to inertially detune the crankshaft counterweights on the bigger engines.

27/09
So do you set zero thrust when performing PFLWOP? No. You have the throtle closed with an almost completely cooling engine and low enough rpm to possibly develop icing and/or spark plug fouling. This would be the reason you are supposed to introduce some power every 500-1000' of the exercise; so you don't get to 500' AGL with a cold engine, throw in full power and find you have to complete the landing.

Ask a few engineers what they think is more likely to cause problems. I was taught to and used to initiate all my failures with mixture, but some discussion as to the merits of each led to my current methods. If something goes south and you do bend an airframe (hopefully without fatality) what are you going to say to an investigator (or coroner) about any qualifications you hold (or don't) that say you know better than;

A) The manufacturer of the airframe and engines, who have test pilots and engineers that spend a hell of a lot more time than you to develop and refine these recommendations and procedures; and

B) The FAA, EASA, or any other regulatory authority who have been examining and making recommendations about accidents and fatalities for years before you or I discovered spoons make noises like aeroplanes.

Can you honestly say you won't attract at least partial responsibility for making up your own procedures when the recommendations are THAT strongly worded?

Thought.
The throttle lever pretty well just moves a butterfly in the intake plenum and mechanically adjusts the idle valve.
How many things in comparison are adjusted (or could potentially fail) when the mixture lever is moved (in particular to ICO)?
The complxity of the Auto Mixture Control which operates in parallel with the Manual Mixture Control, the Idle Cutoff Valve...
Which system is simpler?

[Lumps]

MakeItHappenCaptain - why are they so specific about reducing RPM then MP? (in small increments)