Propellor feathering on light twin-engine aircraft

[A Squared]

Originally Posted by Oktas8

I think he was actually referring to Centaurus' scenario of catastrophic bearing failure leading to a seized propeller. Like you, I'm not aware of any scenarios like that in recent years.

Additionaly, my impression is that a stopped, but not feathered propeller is not a huge drag source, obviously feathered is best, but the *big* thing is to get the windmilling stopped, as a windmilling prop creates a huge amount of drag, far out of proportion to the form drag of the prop blades themselves

Anyone have actual test data comparing the drag of a feathered prop to a stopped but not feathered prop?

[MakeItHappenCaptain]

Quote:
Secondly - can someone please tell me the last time an Australian registered twin had an engine failure shortly after takeoff where failure to feather quickly was the cause of loss of control and crash? I can think of NONE in twenty years.

PA-31-350 went in off East Point in Darwin on 6 Feb 2009. Seem to remember some conjecture on this site as to the contributing circumstances.

Another PA-31 IHR was buried just short of Mt Isa on 17 Jul '08 with no fuel in auxies, but full mains. Didn't follow all failure drills, but granted, not an EFATO event.

[Slippery_Pete]

I just wrote a big long winded reply, but *($#& iOS8 on my iPad dumped the lot as usual.

Tee Emm... Oktas8 and others are completely correct in that you have missed the point of my post.

I wasn't referring to EFATO, I was referring to EFATO where shortly after becoming airborne the engine seizes quickly, but still generates sufficient oil pressure, resulting in pitch lock and inability to feather. NONE of your scenarios demonstrated this.

Whether it is a VH rego or not has nothing to do with the subject.

It does. I was making a point of comparing pitch lock = failure to feather scenarios with other accidents in Australia to make a point about the statistical probability. If you want to consider international feathering accidents that's fine, but you'd need to compare this to international inadvertent IMC/fuel exhaustion accidents etc.

Incident #1 - Just piss poor instructing (and perhaps poor CFI oversight and mentoring to instructors). Failure to feather due to delay causing pitch lock, nope. Just failure to realise that mixture cuts at low altitude are idiotic.

Incident #2 - The manufacturer data indicated it may have been possible to keep the aircraft flying in this scenario had everything worked as it should have. And I quote from the ATSB " However, when the landing gear failed to retract on the first attempt, any possibility of the pilot being able to attain the required aircraft performance was lost."
Had the pilot ignored the gear issue and left it down and then promptly feathered the engine, it still would have crashed. BOTH of those things - gear up and feathering - needed to occur.
No mention of rapid prop speed loss and pitch lock engagement causing inability to feather.

Incident #3 - Just a complete loss of prioritisation as alluded to by others. Didn't matter if he feathered it fast, or after a 5-10 second drill. He just never feathered it at all. Game over.

Incident #4 - I'm not terribly familiar with this, but then it seems pretty straight forward. A failure above blue line should have provided ample time to complete an identification drill and then feather it. The pilot didn't feather it AT ANY STAGE.

illustrate the importance of prompt feathering following engine failure.

I never argued against feathering an engine efficiently and without unnecessary delay.

I simply stated that an EFATO, with a rapid engine seize, where the engine is developing oil pressure, with a short delay running an identification drill, leading to pitch lock, and subsequent inability to feather, and resulting loss of control - as an impossibly rare occurrence.

None of the incidents you linked to show evidence of this.

And in fact, the C404 incident in Scotland is in fact a very good example against your case. The INABILITY TO CLIMB was caused by the failure to feather, but the aircraft was controllable. What happened then, was the incorrect engine was feathered leading to loss of control and fatal crash. Perhaps the incorrect engine was feathered because the pilot rushed the shutdown through fear of the dreaded "pitch-lock"

History is scattered with rushed shutdowns of the operating engine. It is not scattered with pitch lock induced inability to feather.

Anyone have actual test data comparing the drag of a feathered prop to a stopped but not feathered prop?

The turboprops I used to fly had this data. From memory, the resultant drag from a windmilling prop was relative to an increase in aircraft weight of about 30%. So if you departed at a 20,000kg MTOW for example, and suffered an engine failure and the propeller was allowed to windmill, with MCP set on the live engine, the aircraft performed as if it was 26,000kg... ie 6000kg above MTOW, and well outside any guaranteed single engine performance.

EDIT: Sorry, missed your point on this. No, haven't seen this data before. I remember reading an aerodynamics text book at uni saying windmilling drag was equivalent to a solid disc the same diameter as the prop, but can't remember which text it was. You are right however, a completely stopped prop in fine pitch would have a mere fraction of the drag of a windmilling one.

Perhaps Centaurus' concern also is with those folk who take far too long generally in doing the identification exercise regardless of the nature of the failure ?

Thanks JT. You got it in one

Well that's fair enough Centaurus, but don't blame "pitch lock". And regardless, I still think there'd be at least as much (if not more) evidence of incorrect shutdowns causing fatals than "feathering too slow" causing fatals - but I admit I don't really know and that's just an educated guess.

If you have a light twin and want to polish your skills with an instructor, go and do some night circuits at a black hole aerodrome, practice some UAs in a synthetic trainer, or get an instructor to induce the leans for you.

I stand by this comment, and the data supports it.