Nurse or feather that engine??

[ackattacker]

If it siezed, wouldn't the feathering pins extend, preventing it from feathering?

Fly safe!

David

Yes they would. However if it seizes due to low oil pressure it will feather on it's own due to loss of oil pressure to the prop hub well before the engine itself actually seizes. Even if it doesn't, if the engine is seized it is stopped solid, so who cares if it is stopped in a feathered or unfeathered position. The difference in drag is minimal. What you don't want is a *windmilling* engine.

 

[EMBATP]

i'll through my 2 cents in: i am like the other guys, never shut it down if its producing some power and you may need it, and don't worry about the costs of damaging the engine.

i know a guy that flies everything on the field...got checked out in a c-90 with basically no turbine time...takes off on a real long cross country.
enroute, sees oil pressure guage on one engine at zero...all other gauges show normal, engines running fine etc. ...whats this guy do? shuts down a pefrectly good engine for no reason, just because of lack of experience and worrying about the cost....poor judgement in my opinion

 

[deemee boosgkee]

I love the vigerous debate in this thread without the personal attacks. Keep it up! When discussions like this take place, everyone has the potential to better they're airmanship skills. I appreciate and welcome constuctive criticism here and anywhere believing it will make myself and others a safer pilot.


I am still a bit confused about whether or not the prop on a piston twin will feather if oil pressure is completely lost without intervention from the pilot. I know when oil P is lost everytime it is shut down on the ramp the prop goes into the low pitch/windmill position but can't seem to figure out how it will feather if oil P is lost in flight. How does it know the difference? Thanks.

 

[minitour]

i know a guy that flies everything on the field...got checked out in a c-90 with basically no turbine time...takes off on a real long cross country.
enroute, sees oil pressure guage on one engine at zero...all other gauges show normal, engines running fine etc. ...whats this guy do? shuts down a pefrectly good engine for no reason, just because of lack of experience and worrying about the cost....poor judgement in my opinion

What happened?

If all other gages were normal but low oil, I'd probably let it run...but then again I've got limited turbine experience.

ackattacker: that's a very good point about the windmilling prop. I just don't know what the difference in drag is between a stopped prop and a feathered one.

-mini

 

[MauleSkinner]

i know a guy that flies everything on the field...got checked out in a c-90 with basically no turbine time...takes off on a real long cross country.
enroute, sees oil pressure guage on one engine at zero...all other gauges show normal, engines running fine etc. ...whats this guy do? shuts down a pefrectly good engine for no reason, just because of lack of experience and worrying about the cost....poor judgement in my opinion

Personally, I wouldn't worry about the cost (about $250k in 1994 if you shut it down just as it gets to the 40 psi minimum red line, in case you were wondering. ) I'd evaluate it just like any other engine problem...how badly do I need the engine, and what would be the safety consequences if I tried to keep it running when it REALLY didn't want to. A properly conducted engine shutdown with subsequent approach and landing really a non-event in my experience.

If all other gages were normal but low oil, I'd probably let it run...but then again I've got limited turbine experience.

I was always told that the first indication you'd see would be prop rpm fluctuations, due to the loss of oil pressure to the governor. I never saw that, but the torque indications use oil pressure, and they started bobbing up and down pretty heavily by the time I shut it down.

ackattacker: that's a very good point about the windmilling prop. I just don't know what the difference in drag is between a stopped prop and a feathered one.

-mini

I had this on my computer...I THINK it came from Aerodynamics for Naval Aviators, but I'm not 100% sure.

Fly safe!

David

 

[minitour]

I had this on my computer...I THINK it came from Aerodynamics for Naval Aviators, but I'm not 100% sure.

Fly safe!

David

COOL!

-mini

 

[avbug]

It is easy to say what we would do in your position, having not been there!

Speak for yourself.

I am still a bit confused about whether or not the prop on a piston twin will feather if oil pressure is completely lost without intervention from the pilot. I know when oil P is lost everytime it is shut down on the ramp the prop goes into the low pitch/windmill position but can't seem to figure out how it will feather if oil P is lost in flight. How does it know the difference? Thanks.

That really depends on the propeller system. Some absolutely will NOT feather without oil pressure to drive it to feather. Others will feather on their own, providing the RPM doesn't drop low enough. In some turbine installations, the propeller must be moved opposite from feather, into beta, prior to shutdown, and may or may not feather on it's own, and yet other systems utilize autofeather systems which automatically feather one propeller in the event of a torque loss, and at the same time prevent the operating engine from feathering by disabling it's autofeather feature.

When you practice feathering your engine during the runup, you're dumping oil pressure from the propeller through the governor assembly.

Ever notice in your AFM a direction to feather before a minimum RPM is reached...else the propeller won't feather? Study your aircraft a little more, look for the reason that it won't feather below a certain RPM (generally about a thousand RPM), and you have your answer.

He said: IMC, temp. problem corrected with reduced power setting.

The temp was never the problem, just a symptom of the problem. The rough running engine, the low manifold pressure, and the low oil pressure were more immediate concerns. When you have low oil pressure, you already have a problem, and what about the drop in manifold pressure? We either have a blocked induction causing the drop in manifold pressure, a closed throttle, or a loss of boost if the pressure was high enough (ala seneca II). High oil temps come later...and in this case, he waited five minutes to see if the temps came down. We haven't been given the values of the oil pressure, but "very low" certaily sounds like a bigger immediate concern than the high oil temps.

Just as I was entering a hold he assigned the right engine ran very rough and lost about 7 in of MP. I looked up and saw the oil T pegged and the oil P very low. I was torn on whether or not to shut it down or simply reduce the power. I decided to reduce the power and wait to see if it cooled. About 5 min later the oil T was now down to 20 deg shy of redline.

The conversation has split into differing opinions regarding turbine engine failures and piston. I've experienced a number of failures in turbine and piston, both horizontally opposed and large radial recip, and in turbojet engines as well as turbopropeller engines. The most recent for me occured last summer at low level in terrain, when I lost all the oil in a TPE-331-10 engine an executed a forced landing shortly thereafter.

Over the years I've seen engine failrues that resulted in a variety of responses and indications, ranging from a very active fire to a wing and engine covered in oil, to strong yawing motions to no yaw force apparent at all. I've seen the engine surge from idle to full power and back again ever couple of seconds with a failing fuel control unit, and had engines begin exhibiting signs of a compressor stall. I've seen some exhibit a loss of manifold pressure while others did not, whereas others had an indicated loss of oil pressure, and others did not. I've flown behind propellers such as the ham standard hydromatic which required oil to feather, and which could not be feathered when the oil pressure was lost, when the drag resulting thereof had to be controlled by airspeed...you're taught early-on that flying a twin faster with an engine out results in better control, but this isn't necessarily the case with an overspeeding propeller, or merely a windmilling one. The circumstances dictate.

continued...

 

[avbug]

In the case presented in this thread, the poster is flying a piston engine airpalne to a landing. With a barely running engine or a feathered engine, if the poster is intelligent, he or she will not attempt a missed approach on one engine. When you approach in that piston twin, you're approaching for keeps. You're not nursing that engine; you're keeping a critical patient on lifesupport at a time when you need to devote your attention to flying the airplane. You're on an approach.

Several things to consider. When you have an engine failure, give some thought to the fact that what caused one engine to fail may very well soon cause the second engine to fail. Bad fuel? Same person worked on both engines? Sabotage? Evil instructor? Do you care about the reason? You need to be on the ground.

You're flying an approach. The engine is running rough. Is it causing assymetrical thrust problems? You might want to leave it alone. Is it operating outside acceptable parameters? You might want to shut it down. If the oil pressure is below the minimum, then shutting it down now is probably a good idea. Don't be in too big a rush...fly the approach, identify positively the engine you want, and double and triple check it before you shut it down. This isn't the time to be troubleshooting. Do you have an engine failure during approach checklist? You might want to be consulting it right now. In fact, you might want to know it cold before you ever take off.

If the engine needs to be shutdown when flying an approach, then cleaning it up is something you're probably going to do after you land. If you're flying this in a light piston twin with less than stellar capability on one engine, and you've considered the minimum climb gradient on your one good engine, hopefully you're smart enough to refuse to take the missed. Nail the localizer, nail the glideslope, nail whatever guidance you have, and land. High speed aborts are generally a bad idea, and single engine missed approaches in light twins are also a bad idea. Sometimes it's best to continue the takeoff with a bad engine, and sometimes it's best to continue the landing with one too. Remember that; it may keep you alive some day.

I used to fly a four engine airplane that couldn't hold altitude on three if the fourth wouldn't feather. True story. The engine that failed last year gave no indications of failure. I arrived at the bottom of a smoke filled canyon behind another airplane, pushed the power up, and saw the EGT gauge come up normally to a takeoff temperature, but felt no response. A quick glance back inside reveale that the torque was very low, about 15%, and that was all she wrote. For a brief moment the torque came up to nearly 56%, and I did one of the less intelligent things I've ever done; I entertained the idea of limping back to the airport on reduced power.

It wasn't to be. After three glorious seconds of partial power, during which time I jettisoned over half my weight and climbed to a lofty three hundred feet or so, the torque dropped to nothing. I was unable to feather, unable to get torque, I had nothing, and I made a right turn, and put the airplane down on a hillside. Temps were good; it was turning and still burning, but no torque, no feather, no NTS available (or needed), and oil pressure still reading up there. I was entirely without a clue as to why the engine wasn't giving me power; my best guess was that I had a sheared shaft, but it didn't look right for that. More importantly, I didn't care. I had a very, very short time before reaching the ground, and I knew that my best chance to achieve a feathered position was to push the power lever forward to the stops, which sent the EGT's through the roof with still no torque, and I touched down in that condition on the mountainside at 95 knots; best glide speed, or slightly less (as I'd used some of it to clear a last set of powerlines.)

Back to the piston on the approach; if it's running rough and may cause you problems, if you're high enough to hold and sort it out, that may be best. If you're established inbound, glideslope captured, or descending out of the FAF on the final segment, then caging it may be your best bet You don't have time to play mechanic and troubleshoot. Fly the airplane first, and if you have that under control, then devote a minimum of attention to handling your problem. Not necessarily solving it; you're not there to find out why it quit or build an airplane out of spare parts; you're there to fly the approach. Simplify. If the engine is giving you fits, get rid of it. You have more important things to worry about, and that's making this approach perfect, because you're not going to get a second try. You're landing either way, so make it a good one.

Doubtless a few will chime in and tout the merits of going missed on one...how about we just hear from those who have really done it, and see if they give the same counsel...especially in a light piston recip twin.

I remember very well my PIC checkride in the PB4Y. I flew a simulated mission with an experienced captain in the right seat and a government inspector standing behind us. After a number of approached to targets, I was set up to approach a coordinate which turned out to be a fence post in the southeast corner of a field in mountainous terrain. I was at 200', when my copilot said "low oil pressure, #3." I looked at #3, and it was fine. I continued with my thumb on the drop button. Again, "Low oil pressure, #3."

I again checked, nothing wrong. Quick scan of all the other instruments. Nothing wrong. Why would he be telling me that? He knows I know the airplane. He knows I'm a mechanic. He knows I'm on a checkride. He's an experienced captain, he knows better than...rats. That's it. It's part of the checkride. Transition to emergency jettison, egress downhille, exit. I did. I looked to my right to see an unhappy face, and glanced behind me to see an inspector shaking his head. "Head for the barn." he said. "You're done."

Done, busted, or so I thought. They made their point. Being a mechanic in the airplane, trying to troubleshoot when you need to be flying, will get you killed. If you can use the engine and it will serve you, keep it. If you need to simplify it and it's outside it's limits, then get rid of it. Make your life easier. You may be losing an engine, but you're also losing a distraction. Be prepared to quit your plans on the spot and accept that the landscape for you has changed. You might have been capable of a missed approach 1.2 seconds ago, but that was then, this is now. Recommmit to a new future. One that may have very different choices; know them before you launch, and adapt to them right away. That's why you train and prepare and plan.

 

[svcta]

Hey, bug. Good post, um, well thought out.

One thing. My man, I've known a lot of guys with 40 years of experience, 20,000+ hours, varieties of experiences and backgrounds, and none of them. NONE. have had to fly through the perils you routinely discuss. You need to find a new place to work.

 

[avbug]

Chances are that most of them spent their careers flying point to point with very little working of the airplane. If they'd spent much time flying large radials, they'd have engine failure experiences to discuss. More than a few. If they put airplanes in demanding environments, they'd have some interesting airplane stories to tell...hours of their own accord mean very little. I've met pilots who have gone much of their career without seeing a hiccup, and I've met others who have been there and own a vault full of tee shirts. Some of the equipment I've flown has had some of the best maintenance that could be had...airplanes are still mechanical objects and still subject to breakage. Put the airplane in an environment which is prone to breaking it, and it only equates to a LOT more maintenance required.

As far as a new place to work...lots of different places, lots of different types of aircraft, and certainly lots of different types of operations. Some are not your father's operation.

Just prior to that forced landing last year, another pilot flying for that operation also made a forced landing. In his case, he ran a tank dry and was unable to retart the engine. In a nutshell, he was an idiot. I saw him do other bone headed things, and in such cases, despite him having considerably more time in type than me, he invited problems upon himself by actually causing the problems. In the case I described above, the problem occured due to a very rare failure of the rear turbine bearing seal, allowing all my oil to exit the airplane; the engine ran like a top, but with no control over the propeller, and while it was producing power, I couldn't use it. Discussions with federal investigators and mx reps after the fact suggested that the engine may be capable of running for another half hour minus the oil, or nearly all the oil, before it gets to that condition, but should show low on the oil pressure. In my case, that didn't happen, and during the actual run to the target, I was in a canyon into the sun on a 3,000' descent in smoke, and primarily focused not on things in the cockpit, but on the rock walls around me.

I believe, based on the information I have now, from discussions with experts in that engine and with those who participated in the incident investigation, that it's very possible the problem might have been discovered sooner...such as when I started the run, which would have given me 3,000 of altitude or more to make a decision, rather than 150-300'. However, I had no indications, nor reason to suspect the problem...and when I spoke to an individual who's an expert in the engine type directly after getting on the ground, he had no clue what could have happened...let alone me trying to analyze it while operating under the conditions I did. Quite frankly, I was confused by what I was seeing in the cockpit; it made no sense, and I had a big neon billboard flashing in the front of my mind asking "what are you doing wrong, and how can you fix it?" It was answered by an equally large billboard that was one big question mark.

The only choice available, and the only prudent one to make, was to set it up as a forced landing and carry it through to completion. Because the way in which it unfolded made no sense to me, I had to believe that I was doing something wrong. There was no time for a checklist, no time for anything but jettisoning the load, making the turn, and reducing to the best glide speed prior to impact and to enable me to clear powerlines. The inner voice was yelling that this was all wrong, that because the scenario didn't match anything that made sense, I must have a good airplane and was about to put a good airplane in the dirt over nothing. I forced myself to push that voice aside; it wanted a theoretical discussion that I didn't have time for, and I made a wheel landing on the terrain straight ahead.

Again, for that reason, I submit that trying to analyze the problem when more immediate demands of flying the airplane exist, can lead to serious complications. In the origional post, I believe the engine roughness occured during a hold; this is a good time to make the decision and if appropriate, get rid of that engine and simplify...but only if the particular needs and the condition of the engine at the time dictate. If it's producing some power and you do need it, and you can tolerate the potential for it to go belly-up and complicate your life during a critical phase of flight (approach and landing), then you might consider keeping it. If the oil pressure is extremely low, the damage is probably already done, or about to be done. Take what you can get.

Conversely, engines do sieze, and some engines do need that oil pressure to feather, and you don't want a runaway propeller, either. A rapid siezure at high torque can cause an engine mount to fail, and some engines with excess heat and wear can cause other problems. Many engine cases are magnesium or mag alloys, as can be generator drives and accessory cases and drives...run these dry and create heat and you can also create a class D metal fire out there, and you definitely don't want that. Further, if you're pumping oil onto a hot engine (low oil pressure...is it going somewhere?) you're setting yourself up for a fire you won't be able to control by merely shutting down the engine.

Coming out of Lake City, FL one morning, I noted the #1 engine could only achieve barometric manifold pressure. I noted the #4 engine was covered in oil as was the wing...which meant the accessory section was full of oil, as well as the exhaust short stacks, which put out flame. I discovered this as we climbed on top of a layer. I didn't want to shut down both engines. The #1 was most likely a failed supercharger clutch, which could cause problems, but appeared functional for now. The #4 engine presented a definite fire hazard, and was losing oil at an undetermined rate, almost certainly through a cracked propeller governor stephead base...not unheard of in that installation. I elected to shut down #4, and monitor #1.

During the enroute portion to St. Joseph, MO, I went below and built up a new stephead motor and governor assembly, and prepared the necessary tools and gaskets. When we arrived, I repaired the #4 assembly, and cleaned the engine. I inspected #1. We performed ground runs, noted the lack of boost and only barometric on #1, and made a reduced power takeoff on all four, with a precautionary shutdown on #1 after takeoff for the remainder of the trip. As it turned out, after some very frustrating troubleshooting the next day, we had a cracked manifold pressure line; the engine was fine, but indicating low.

Evaluate what you have on it's own merits and make a decision; it may be different each time, as the circumstances will almost invariably be different.

After departure in a turbopropeller airplane, I experienced a power loss, albeit slight, on the left engine. I was flying with the company assistant chief pilot. We heard a slight muffled hooting sound, noted that the temps were higher on that engine with less torque. We were empty and repositioning and elected to continue the climb while we considered what we had. So far, nothing overly upsetting; a slight split in the engine gauges. The assist CP went aft and looked outside, came back and said he could hear the noise a little better...a hooting sound. Ahhh, compressor stall, but why? Lots of altitude, in the clear, now we had time to consider our problem. No applicable checklists yet. We levelled into cruise, and I went aft to see. I noted a splined object protruding through the bottom of the cowl. I opened an illustrated parts catalog and found the part; the only splined part in that nacelle assembly was part of an anti-ice door. With that information, and the part number I contacted the Director of Maintenance, and we discussed the situation. We elected to continue to a maintenance base downrange, where it could be inspected and repaired. On arrival, we found exactly what it appeared to be. A new design part from the manufacturer, an all-steel part that had replaced a carbon fibre part with steel inserts, had failed in two places, and had shifted to partially block the induction passage. The splined end I saw was part of the failed door assembly. When I knew what I had, I elected to fly with reduced power on that engine, and the moaning compressor sound went away. No more engine asthma...a common fix during a compressor stall involving mechanical damage. In this case, no engine damage, just a partial nacelle occlusion.

I knew based on the research I'd done, the engine wasn't going to ingest that door. Absolute worse case, we could evntually intentionally perform a precautionary shutdown, but we elected to operate it at reduced power, which solved the problem and actually extended our range. Had I been flying an approach, I wouldn't have thought twice about it, but would have reduced power based on the audible responses in the cockpit, and failing that as a fix, shut it down. If I'd seen something else entirely, such as low oil pressure or excessive heat, I'd have shut it down right away.