Propellor feathering on light twin-engine aircraft
 

There wouldn't be a pilot who, during asymmetric training on his initial light twin-engine aircraft, that did not have the mantra drummed into him of: Pitch up, mixture up, power up, flap up, gear up, identify, dead side dead leg, throttle close to confirm identification then feather. Maybe not in exactly the same order depending on aircraft type and instructor preference.

Chances are for the rest of your career on light twins that order of actions will be stuck in your mind. It is almost certain your instructor in those early years would not have told you that the above sequence of actions take time and that you should never hurry them. Take your time Bloggs, lest you inadvertently identify the wrong engine and close down the good one.

That may be good general advice especially for a cruise engine failure but does the same order of things apply to an engine failure after take off where the cause of the engine failure could be a major mechanical fault; for example seizing bearings due to loss of oil?

Back in 1980, Aviation Safety Digest published the following article entitled Propeller feathering on light twin-engine aircraft. It introduced the article thus: The following article was produced as Aeronautical Information Circular 9/1979 by the Civil Aviation Authority, United Kingdom. It concerns the possibility of feathering difficulties with propellers fitted to light twin-engine aircraft. The message it contains is applicable anywhere in the aviation world

Most feathering propellers (hydraulically actuated, constant speed, such as the Hartzell and McCauley types) fitted to twin-piston engine light aircraft are designed in such a way that it is not possible to feather the blades below a certain low rpm (typically 700-1000 rpm). This is because at these low rpm centrifugal latches operate to hold the blades in fine pitch to ensure that when the engine is shut down on the ground, the subsequent restart is not made with the propellers feathered.

In cases where the normal windmilling rpm at low airspeed may fall low enough to prevent feathering, the Flight Manual, Owner's handbook or Pilot's Operating Handbook warns the pilot that feathering cannot be accomplished below a certain rpm. However, the full implications of the situation may not always be clear, and other factors of which the pilot should be aware of are:

(a) In the event of an engine failure caused by a major mechanical fault (e.g. seizing bearings due to loss of oil), the rate of deceleration of the engine can be rapid and it is thus imperative that the pilot take immediate action to feather the propeller before the rpm falls to the 1000 rpm region.

(b) On most twins the usual procedure when shutting down an engine which has failed is initially close the throttle of the inoperative engine. This serves to confirm which engine has failed before commencing the feathering actions. However, if the windmilling rpm has reduced towards the critical region where feathering may not be successful, then re-opening the throttle will usually increase the rpm slightly and improve the probability of being able to feather.

(c) In the event of an engine failure, it is important not to let the airspeed reduce below the scheduled engine-out climb speed. This will help ensure that the propeller continues to windmill at sufficiently high rpm for feathering to be successful. if optimum performance is required it is vital to achieve and maintain this best engine-out climb speed.

(d) The loss of performance associated with a stopped propeller in fine pitch or more importantly with a windmilling propeller is potentially serious. The additional drag will considerably reduce the single-engine climb performance from that available with a fully feathered propeller. The directional control will also be reduced, though adequate control should still be available down to the minimum control speed (Vmca), as Vmca is determined with the propeller in the condition existing prior to feathering action by the pilot (i.e. normally with a windmilling propeller). It will probably not be possible to trim the aircraft on the rudder trim at the best rate-of-climb speed and considerable foot force may have to be held to maintain heading. However, it cannot be over-emphasised that, if it is necessary to gain or conserve altitude, the best available performance is essential and for this the best engine-out rate of climb must be maintained.
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Paragraph (a) bears repeating: (a) In the event of an engine failure caused by a major mechanical fault (e.g. seizing bearings due to loss of oil), the rate of deceleration of the engine can be rapid and it is thus imperative that the pilot take immediate action to feather the propeller before the rpm falls to the 1000 rpm region.



Centaurus comment: Flying school instructors qualified to instruct on light multi-engine piston aircraft should bring the attention of their students to the above UK CAA AIC 9/179 and explain that with an engine failure shortly after take-off caused by a major mechanical fault, the subsequent actions prior to feathering may have to be modified in order expedite feathering before the rpm drops below a critical figure.

The current updated CAA advice can be located in the following link:

http://www.ead.eurocontrol.int/eadba...2005-12-08.pdf

There is no performance guarantee in light piston twins for Engine Failure After Take-off, and so looking for the best crash site is also up there on the "important" list.

Spend important time to correctly feather the engine, and then crash with a cry of surprised dismay because the aircraft is STILL descending, won't help you much, either...

I see a dilemma.

The article referenced by Centaurus makes a valid point.

However, the advice not to rush a feathering drill is also correct, and written in blood.

So, will you teach inexperienced pilots to do drills quickly, or methodically? In my experience, you can't teach both, even if you stipulate the different scenarios applicable. The brain doesn't work that way.

Given the accident rate and the type of accidents commonly experienced in GA, it seems to me that doing emergency drills methodically and diligently is the way to save lives.

That article can then be a discussion point (as Centaurus intends, I'm sure!) for commercial pilots who would like to expand their existing toolbox of life saving tricks.

Here begins the argument for four engines.

Every time Ive tried to rush in an aircraft it hasn't made things happen any faster (or easier). I also feel less effective and more stressed.

I get in the Sim at work as often as possible and spend the entire time in worst case scenarios. The more I practice the quicker and easier it becomes, and the more time I seem to find simply by being more proficient and confident with the procedure.

I also like what Bob Hoover said about airspeed and twin performance. Breaking it down he said If you've got and keep the former, then you'll get the latter. Im sure many of you will have seen this, but watch this vid for the way he's handling the feather and shutdown.

I find it helps to have selected any possible landing areas prior to the roll and Il mention them in the TOSB. There's usually a preferable way to turn even if its only a slight change to heading (terrain, buildings, wind etc) . Another time saver.

If I have an engine failure after take off and haven't reached blue line speed, what am I achieving by worrying about feathering?

Going to start this reply with the caveat, "Not every situation will be the same."

Very good point by Delta T (and in no way detracting from the OP's intent) in that you won't keep it under control below Vmca. You need to increase speed (most often by lowering the nose) if below Vyse, so if there is runway remaining, it would be wise to get it back on the ground. In between, you are in dangerous territory.
I would suggest that even going through the fence at 20-30 kts will have a much better result (ie. Less likely to kill yourself, disregard aircraft damage, that's what insurance is for) that trying to continue flying low and slow.

There is conjecture about utilising balanced field lengths when flying FAR23 certified aircraft with regard to a desicion point. Decision speed is therefore an alternative. FAR25 (heavier transport category) are guaranteed performance. FAR23 only guarantees control in the event of an engine failure.

Suggestion however wrt throttle confirmation of failed engine. If the engine is still producing any power (evidenced by a last minute change of noise during the final portion of the throttle closing, it is still in a better state than feathered. This will be more easily detected by slowly confirming with throttle rather than belting it into the closed position. A turbo failure for example will still produce ~75% power normally aspirated at sea level in a PA-31, but still give a noticeable yaw when the power reduces, possibly inducing the pilot to initiate a complete shutdown.

Again, not a one size fits all discussion.

Fixed it for you. :ok:

Forget about single engine climbing in a light twin - the height you have at engine failure is the most height you'll get, in 90% of cases.

Pontificating about responses to an engine failure after take off in an aircraft not certified under CAR 125 or equivalent is futile.
One response only - Are you above Vmca by a good margin? & Are you above V2 by a good margin?
If both apply,[and the numbers should be assessed pre take off ] - commit to continue - [my idea of a good margin is 20%].
IF NOT-, commit to an emergency landing in the best area ahead.
Statistics pretty much verify that loss of control is fatal.
Only test piots have the skill and "corporate knowledge" to operate at the boundaries!!

90% is a pessimistic figure. Single engine performance is largely a function of weight and density, of course some aircraft are more critical than others.
You should know the single engine limits of your aeroplane for weight/density before you take off (allowing for engine/airframe degradation of course). If you are outside the limits, take a single! Half the chance of engine failure and certain doom! :ok:

Very interesting article and does provide good food for thought.

I fall into the camp that aircraft like PA31s, in the Australian summer particularly, should more be considered like a powerful single, rather than a twin, below 'comfort' height (this 'height' depends on ALL of the circumstances).

Hey, forget about about the reduced ROC or power output with a failed turbo, or the like - I've been in PA31s (very well maintained ones too) that I've popped off the end of some runway in the apparent dead centre of the GAFA and have been convinced that neither turbo is working, despite seeing a healthy 40+" of MP! Anybody who's flown these things much, knows that feeling.

I always based my plan, in those conditions, that I would expect to get a couple of hundred fpm ROD rather than alt hold - on the basis of, plan for the worst - hope for the best.

These things, 40 years ago, when all nice shiny and new, were pretty much promised to do a few fpm ROC at 15c, with Bob Hoover behind the wheel.

Consider, the original P charts only show a SE ROC for a PA31 up to a max of 35C at sea level - hotter and/or higher than that - you are the test pilot. 35c in the GAFA in summer, would have you reaching for a jumper.

The 17 most popular ways to fall out of the sky video had a good line about light twins.

It was something along the lines of: "Unless you restrict the weight, you're essentially flying a single engine airplane with power divided into two packages. While you're chance of a failure in the first place is doubled."

Vmca -red line
Vyse - blue line

It might be possible to lower the nose build up speed to then be able to climb away...so therein a reason to feather, though if you are at that kinda height to achieve that the aircraft should be above blue line.
If you are so low as to be below below line, I put forward that spending time worrying about feathering the engine is a moot point and you are better closing the throttles and preparing for the crash landing ahead.

From memory in my training it was something like 300ft close the throttles landing ahead, above that and blue line then feather, and when above something like 1500ft continue the drills for basic troubleshooting.
As for knowing the speed specific for the weight, again if memory serves, in a light piston it is only a variation of some 5knts.

And therein lies the problem for a candidate undergoing dual instruction on his initial twin engine piston type. Every instructor has his own opinion or parrots what he was taught by his first twin instructor who in turn parrots what he too was taught and so on. Lots of opinions but few facts. We see that for example in the differing instructor opinions on minimum height for an asymmetric go-around; yet rarely is that mentioned in the manufacturer's handbook, AFM or POH. Most POH cover the basics of engine close down but nothing specific about the need to feather before the prop reaches a critically low rpm

The purpose of the opening post was to remind instructors that swifter than normal action is required to feather the propeller of a failed engine that has packed up due to a major mechanical fault. That applies during initial climb after lift off as well as at any other phase of flight.

Centaurus, you are right in principle, a seized prop isn't as good as a feathered one. but how exactly is one supposed to diagnose a 'major mechanical fault' before commencing any immediate action drills, particularly after takeoff?

Why risk botching it up and feathering the wrong engine?

The drills all the way through to feather shouldn't take more than 5 seconds for a well-practiced pilot. And getting the gear and flaps up is just as important as feathering the prop.

Why delay all these items to take the time to consider whether the prop will seize first? You simply can't train someone to knee jerk react with proper checks and drills as well as have them consider the possibility of having to feather immediately if the revs are dropping below min feather speed (somewhere around 700rpm or so I seem to recall from most I have seen). They are conflicting commands. You can either stop and think about it. Or do the checks. I'd rather fly the plane and do the checks immediately. If the prop stops that quick, there probably wasn't much I could do about it anyway.

As for in the cruise, well is a seized prop in fine pitch really that critical? You're going to have to come down anyway!

I have an extremely vague memory that back in the old days a check flight involved loading the aircraft to something like 75 or 80 % of gross. I know we used to load sand bags to do just that, but the practice was not continued for what ever reason.

Have once again extremely vague recollection that CASA required loading to some % of gross. Getting somewhat aged so failures of memory are excusable.

Talking to recent twin pilots, all they know is how the aircraft performs when empty on a check flight.

False training?

Nomde,
chances are a major mechanical fault is going to be one that has a hell of a bang, so you probably won't need to confirm much.

The gear up flaps up thing is a bit of a misnomer. Subsequent training/experience (tho not as extensive as many here) has taught me that If you are in the take-off phase and the airframe isn't cleaned up, or your speeds haven't been reached, then you are a single engine...Close both throttles and land ahead....at least you have control and can concentrate on your crash.

If on approach, you are going to continue the approach anyway regardless of alt. The only difference is going to be how much time you commit to getting that prop feathered.

a major fault may or may not manifest itself as spectularly as that. The whole mixture pitch power gear flap thing is basically just confirming everything is where it should be. I've seen many pilots unwittingly leave the gear down til 1000' or takeoff with the mixtures chopped for the taxi out. The key is to properly identify the correct engine then feather in a swift manner. Why you are feathering it has no significance except for when you are safely back on the ground!

If you are on approach feathering is the least of your concerns, just add a bit of power to pick up the slack of the dead one, bit of rudder and the aircraft will not know the difference. Go arounds are another can of worms as Centaurus mentioned.

In the case of Piper aircraft they usually include the minimum feather RPM in the checklist for feathering, as well as a description of it in systems. It would be very worrying if instructors today are not teaching this, as its vital to understand what the feathering locks are and how they operate, this in additional to how the prop control mechanism works, oil flows etc. I remember it used to be emphasised during the full feather demonstration where we would shut down the engine in flight, fly around for a while single engine to get a feel for it, do a restart, and in ages long gone, shut it down again and land feathered. Even if you are adverse to feathering engines you should do a sequence of simulated single engine flight at zero thrust including level, climbing, turning, climbing turns, to see the performance and how it can be improved.

Years ago we used to practice engine failures at 200ft (some lower than that) after take-off by cutting the mixture, ie you had a real failure, you would then climb away on zero thrust at blue line to circuit height to prove the aircraft can do it. All my training was done this way in everything up to a Navajo, mixture cuts included (not advocating mixture cuts but just that its is an actual failure, if you don't trust the throttle method actually replicates a failure). You should be close to blue line if not above by 50ft in most light twins, if not why not, by 100ft you should be above blue line and climbing away nicely. A PA-44 training is usually close to max weight most of the time anyway. Even most 6 seaters these days are only 4 seaters with max fuel because of all the toys they carry, so 2 up they're only 150kg off max, chuck in a little ballast and you're almost there.

The key here is you have to make a decision once the runway runs out, can you make it, depending on a lot of factors you should consider before take-off. Above blue line, without sufficient runway I would be thinking "go", control, clean it up(drills), assess whether my performance meets my expectations. If performance satisfactory, continue the "go" plan, if things look ugly, use what performance I have to follow the "stop" plan (includes knowledge of likely landing areas, similar to what you would think SE.

This process must be 100% methodical and not rushed, but that does not mean its is a slow process and it should not be delayed in any respect at any point of flight if there is oil issues or anything affecting the prop mechanism or engine that could possibly cause RPM below minimum feathering. On take-off the initial actions should already be complete, everything is just a confirmation 10-20 seconds and you are ready to feather, rushing will only save a few seconds that may lead to big mistakes and in the end will not change the outcome.

Where I've seen most cause for concern is engine failures late final, usually requires a good deal of power to overcome the loss of power and windmilling prop combo. If you have time I would always recommend identify and feather the dead, there's always a chance you might not have the performance to make the field from above 200ft on final. There are also a lot of accidents caused by pilots choosing not to feather and having to suddenly add power late final and losing control. It's also important to still follow the drill, without getting too distracted from flying, control, mixture, pitch and power up (to maintain glide path), then you are almost there to identify & feather anyway. In some aircraft in a descending turn at low power you can get the aircraft to yaw towards the live engine, if you follow the drill and power up it will remove any false yaw.

I also remember one pilot who had an engine failure turning final, he was high and fast, elected to do the drills after the turn to final complete and found he'd pulled a mixture back with the throttle (Beechcraft), power restored and now a normal two engine landing resumed.

I definitely discuss what the cenrifugal latches (I even have a set to show) do and how to deal with an engine that can't be feathered.
Consider Avro Ansons. There's one in the display case at Tamworth. They had fixed pitch props.:ok: