Another twin crash that does not make sense

[MountainDude]

I am puzzled by the fact that the prop cannot be feathered below 800 rpm. Seems like a huge safety issue.

 

[WDD]

You know, I just saw that video this afternoon and the same thought occurred to me.

Don’t know if it would have changed this specific outcome though.

 

[saddletramp]

The Twin Comanche only has 0-320 engines so not a lot of power to begin with. The props are feathered by old pressure from the engine. At only 800RPM there's not a lot of oil pressure to make feathering happen. He should have just landed on 04 but he seemed fixated on the engine issue. It was a very tragic crash.

 

[hindsight2020]

It's just a lockout mechanism so that it won't feather on the ground, and thus can be restarted. Very common system on all piston twins.

The presumption behind the system is that a windmilling prop inflight will windmill at higher than 800RPM, thus making the concern behind the pilot not dumping the oil pressure quickly enough before the centrifugal pin locks out the prop springs from being able to feather the blades, not a concern. I don't remember what kind of flight idle RPMS I was getting when faking those OEI scenarios on the PA-44, but I don't remember getting a low enough RPM to lockout the springs being an issue inflight.

 

[BigBadLou]

When an engine gives you trouble, entertain more options than what's on the checklist. I once had an engine failure where reducing throttle, albeit utterly counterintuitive, afforded me some power. Had the PIC had time to check engine gauges, he could have maybe advanced the throttle on the overly rich engine to match the fuel flow and at least keep the engine running. I know, I am Monday morning quaterbacking. But I want this to serve as a reminder to know your aircraft systems intimately so that you can make informed decisions in case of emergency and hopefully save your life.
Fly safe.

R.I.P. Joe and Patti.

 

[MauleSkinner]

When an engine gives you trouble, entertain more options than what's on the checklist. I once had an engine failure where reducing throttle, albeit utterly counterintuitive, afforded me some power. Had the PIC had time to check engine gauges, he could have maybe advanced the throttle on the overly rich engine to match the fuel flow and at least keep the engine running. I know, I am Monday morning quaterbacking. But I want this to serve as a reminder to know your aircraft systems intimately so that you can make informed decisions in case of emergency and hopefully save your life.
Fly safe.

R.I.P. Joe and Patti.

It’s also about understanding the limitations of the systems. Knowing that letting the RPM decrease too much while troubleshooting an engine failure can result in inability to feather is part of the decision making process, and should be taught for a multiengine rating.

 

[mandm]

RIP

 

[mandm]

The video said the G5s didn’t have memory cards, can you put a basic memory card in?

 

[Plano Pilot]

"Multi-Engine Propeller Considerations

Feathering

To fully feather the propeller, the propeller control is brought fully aft. All oil pressure is dumped from the governor to the oil sump, and the counterweights drive the propeller towards feather. So if oil pressure leaving the governor pushes blades toward feather, why do the propellers not feather on engine shutdown?

The answer is there are lock pins in the propeller hub which prevent feathering below 7-800 RPM to prevent the propeller from feathering during start and shutdown. During normal operations, centrifugal force retracts the locks, allowing the propeller to feather, but you must remember to feather a failed engine before the locks engage. Both feathering and starting a feathered engine are not recommended due to excessive stress and vibrations generated."

From: https://www.nashvillecfi.com/multiengine/propellers.cgi

 

[MauleSkinner]

Similarly, from the Airplane a flying Handbook…

 

[RussR]

It's just a lockout mechanism so that it won't feather on the ground, and thus can be restarted. Very common system on all piston twins.

The presumption behind the system is that a windmilling prop inflight will windmill at higher than 800RPM, thus making the concern behind the pilot not dumping the oil pressure quickly enough before the centrifugal pin locks out the prop springs from being able to feather the blades, not a concern. I don't remember what kind of flight idle RPMS I was getting when faking those OEI scenarios on the PA-44, but I don't remember getting a low enough RPM to lockout the springs being an issue inflight.

Like any other MEI who worked in a Seminole, I've done hundreds of engine shutdowns, real and simulated. Never once had the engine rpm drop to a point where it wouldn't feather. Normal windmilling rpm is way above 800 rpm.

@MountainDude , normally you'd have to try hard to get the rpm that low (by flying slow, like getting close to stalling). And if you did, that means you've had the engine windmilling for a while, when you should have feathered it long before as part of your memory items or troubleshooting (depending on altitude). (Note - I haven't watched the video yet to see what caused the low rpm scenario.)

 

[hindsight2020]

Though the deceased didn't have the benefit of knowing it was a [presumably] overrich idle condition due to debris contamination giving him trouble, we can still generally offer the tried and true "undo what you just did and see if it gets less bad again" as a way to mitiage these untimely distractions. You can't get channelized and let the airspeed out of your cross check however.

 

[Kristin]

The props on a Twin Comanche use oil pressure to push the blades to a low pitch/high rpm. Feathering shuts off the oil and springs and a nitrogen charge in the dome pushes the blades into feather. I haven't seen the rpm ever get slow enough on one of these props to engage the lockout pins and prevent feathering. They I have never tried to feather while hovering around Vmc either.

As often happens, particularly when the technology acts up, the pilot's brain gets sucked into the cockpit. Had he remained focused on landing on rwy 4, he would have just run the power up on the good engine and almost certainly makes the runway.

 

[WDD]

Thinking about this some more; what can I learn and use in the future.

Maybe a key takeaway: If I get behind the air plane when flying in a critical phase of landing (slow and low), go around if possible and ask for help. Help may even be "Tower, help me line up for the runway here". Better to embarrassed and end up safe on the ground than written about by the NTSB.

 

[iamtheari]

The video said the G5s didn’t have memory cards, can you put a basic memory card in?

There is a micro SD slot in the G5, but I don't know if it will record anything to a card if you insert it or if the card slot is only for software updates.

 

[Daleandee]

Maybe a key takeaway: If I get behind the air plane when flying in a critical phase of landing (slow and low), go around if possible and ask for help. Help may even be "Tower, help me line up for the runway here". Better to embarrassed and end up safe on the ground than written about by the NTSB.

Not long ago @Ed Haywood made a simple yet profound comment that I believes fits here:

"Don't be in a hurry to crash."

RV-12 Fatal Crash - Control Failure 6/6 Auburn, WA

Based on the photos it looks like the other side had started to loosen up as well.

www.pilotsofamerica.com

 

[texasclouds]

Though the deceased didn't have the benefit of knowing it was a [presumably] overrich idle condition due to debris contamination giving him trouble, we can still generally offer the tried and true "undo what you just did and see if it gets less bad again" as a way to mitiage these untimely distractions. You can't get channelized and let the airspeed out of your cross check however.

Yea, wonder if increasing thrust would have got that engine restarted. Did the report show the lever positions?

I wonder if there were electrical issues also causing distractions.

 

[nauga]

There is a micro SD slot in the G5, but I don't know if it will record anything to a card if you insert it or if the card slot is only for software updates.

It records data from itself and other log-compatible stuff connected to it - like other Garmin boxes.

Nauga,
carded

 

[Ed Haywood]

Not long ago @Ed Haywood made a simple yet profound comment that I believes fits here:

"Don't be in a hurry to crash."

RV-12 Fatal Crash - Control Failure 6/6 Auburn, WA

Based on the photos it looks like the other side had started to loosen up as well.

www.pilotsofamerica.com

Unfortunately my comment was wrong in the context of that thread. That poor RV pilot had disconnected ailerons and began an uncommanded roll. His plane was in a hurry to crash on its own.

But I appreciate the shout out. Even a blind squirrel finds a nut sometimes.

 

[Zeldman]

Wow... In flight school, before even getting in an airplane, I was taught that airspeed is life. It really pained me to see the airspeed get slower and slower.

 

[Pinecone]

There is a micro SD slot in the G5, but I don't know if it will record anything to a card if you insert it or if the card slot is only for software updates.

It will log. You have to turn on a setting.