Prop pitch, IFR clearance, icing, WX decisions

[apcooper]

A few questions for all you experienced pilots out there:

1) If flying a piston twin and you suddenly lose oil P and the engine seizes will the prop automatically spring into the feather position? Some have said it will go into flat pitch like when shut-down while others claim it will go into feather since that is obviously best while flying on one engine.

2) When given an IFR clearance, will the last waypoint given to you in your route always be either an IAF, FAF or feeder route for an insturment app at your dest arpt? If not, how does ATC expect you to transition from your last wypt to some waypoint on the app if you go lost comm?

3) I hope I never have to experience this, but if your were flying a 172 and you have picked up 2 inches of ice, would this deteriorate performance by as much as 30 flaps hanging out?

4) Lastly on Sat. I was schedueled for an insturment flight and my CFII felt uneasy about launching when the weather at home base was 600ovc (var 400-1000ft) and 2 1/2vis and no ice or t-storms around. The LDA app had an MDA of 620 and BDL 13nm to the N which has an ILS was 300ovc and RVR 5000. We had 5hrs fuel and even after flying to ALB (closest legal alternate 100nm) we'd still have 2-3hrs fuel. He was afraid to launch in the 172R even with 2 vac pumps, only one alternator and obviously one engine. He was concerned about the Attitude indicator failing and having to fly a PP ILS that low. Also he was concerned if the Alternator dropped off and also the engine quitting. I thought we could have flown safely with 2 proficent pilots and a GPS handheld for backup as well as lots of fuel and I certainly am a wimp when it comes to weather decisions, espically ice and t-storms. In your opinion would you have launched under those circumstances?

Thanks for the much needed feedback.

 

[C77MD80]

(1) The constant-speed props used on most single-engine general aviation aircraft use a very powerful internal spring to drive the blades to flat pitch, with governor oil pressure used to oppose that force.

In either case, a governor failure causes the prop simply to go to full low (flat) pitch, whereupon it becomes just another fixed-pitch prop (of the "power" type).

By contrast, the full-feathering props used on most general aviation twins work differently — almost the exact opposite, in fact. The hub of such a prop contains a very powerful spring (called the "feathering spring") that drives the prop towards "high pitch" ("low RPM" or "coarse pitch"), while governor oil pressure (and pitching moments) oppose this. This means that a governor failure — or loss of oil pressure — in a light twin will drive the prop towards low RPM (high pitch), and right on into feather, which is nothing more than extremely high pitch. The theory is that with a loss of oil pressure due to engine or governor failure, you'll want the prop feathered in order to keep flying on the other engine.

Many people get the two confused. If you make a career out of flying, know this area well.

A wonderful link http://www.avweb.com/news/columns/182082-1.html

(2) No. Suppose you were on a STAR, the star says “expect vectors to final”. Now you’re in the zone of ambiguity. Technically follow part 91.185. It gets tricky, you could have multiple scenarios. Ask a controller what he expects you to do?! Betcha you’ll get different answers.

(3) I have picked up two inches but not in a C172. That sounds about right though. The idea is just don’t get there but if you do don’t stay there.

(4) Personal minimums are just as important as legal minimums. Your CFII was correct with his/her personal minimums. Sometimes it gets a bit nerve racking when you are an instructor watching over a newbie with conditions such as that.

 

[hyper]

1.) IF you can get the prop lever back soon enough AND IF the prop can move to feather before the centrifugal pins that are kept thrown out by engine rpm drop in preventing the prop from completely feathering. (I assume we're talking typical trainers here, ie: Duchess, Seminole, etc.) If the engine seizes immediately, it's doubtful that it will feather.

2.) No. If not given in the route, you would transition from the en route enviro to approach and land in the most efficient manner you deem appropriate. (Assuming you're cleared to your destination.) Keep in mind, if you're nordo atc is clearing the airspace around you for miles. They want nothing more than you on the ground.

3.) 2" of ice on a 172? Have you ever seen a boulder fly?

4.) Aside from any other situation, launching any single-engine in low ceilings is a gamble. No decision made in the interest of safety is in err.

4.) "2 proficient pilots" At 55 hrs, especially considering instrument flying, the last thing you could be considered in that scenario is proficient.

Hope this helps

 

[Gulfstream 200]

1) Sorry no piston twin time

2) Not in my experience.

3) If you picked up 2 inches of ice on your 172 you are a moron. There is NO WAY to know what this will do to performance. Dumb question.

4) 55hr "proficient pilot" huh?? Oh boy....With 55 hours you really dont need to be going up doing low approaches. -not that you wouldn't get a little out of it- Your CFII would have been just taking you for a ride. Was that OK with you? or would you complain when your Private License cost 15K because of fun rides?

Nothing wrong with flying a 172 IFR. Nothing I care to do for kicks, but nothing truly WRONG with it. I did that kind of thing when I was a CFI because I needed the money and I had students with fat pockets.. I wouldn't do it now.

How well are these things maintained? Maybe he didnt trust that plane in low IFR. Out of the 10+ a/c at the school I taught at I would only fly ONE in low IFR.

Handheld GPS? WTF you gonna do with that? PLEASE...put that freakkin thing away. Nothing worse than climbing into the cockpit with techno-dork student who has the GPS, the Bose headsets, the "cloud level finder" etc...all wired up and still cant fly to save his balls. Lose the excess garbage in the cockpit.

Anyways, maybe he isn't as "wimpy" as you think. maybe he just thought his a$$ was worth more than the $25 he was going to make on that joyride..

You almost sound like one of those 55hr pilots who play way too many flight simulator games and know it all before stepping to the plate...enthusiasm is great, but sit back and learn from experience -- and this includes making GOOD SOUND DECISIONS -- like staying on the ground sometimes.

Want a hint?? next time ask him if he is willing to do this in the schools twin...

Good Luck and try to trust your Instructor.

 

[seethru]

From your 1st question,

If you're flying a light piston twin and one of the engines loses oil pressure and seizes, the propeller will NOT feather. This is due primarily because there is a lock-out device that engages below a certain RPM, around 900, and prevents the props from feathering (the actual name of this escapes me right now). This keeps the blades from feathering during normal shut-down procedures.

I believe in turbo-props they have an autofeather option which will feather the blades imediately if an engine fails. This is not the case with piston twins, which usually have to be feathered manually.

Greg

 

[DAS at 10/250]

Nice post by C77MD80.

I wil reply to question 4 only.

I respect your CFII for setting his/her own personal minimums and sticking to them. Personally, I will not fly a single at night or in IMC (trying breaking out at 300 OVC with no motor). I have talked to a couple of pilots who will not fly a single with less than 1000 ceiling. I also refuse to fly an aircraft of any type with only a vacuum/pressure attitude indicator. These type of indicators are the most worthless piece of equipment in the airplane. In my relatively low time I have lost two pressure attitude indicators (King on the KFC-200 and KAP 150) and one complete pressure pump failure (BE36).

Now, have I flown a single at night and in IMC? Yes. But now that I have the option I choose to eliminate that risk altogether.

What is legal is not always safe.

Good luck.

 

[guido411]

Coop,

Think I can help with your questions:

Concerning prop pitch in a piston twin, I can't answer positively for ALL prop models but the Hartzells that were on the Aztec and Navajo I used to fly definitely feathered after a loss of oil pressure. This happened to me while giving some dual in an Aztec, fortunately we had just landed. Engine quit (did not seize) and prop was in feather. Got the motor running again, prop would not unfeather and oil pressure would not come up off bottom red line. Solution: new motor. See, in this system engine oil pressure acted upon the aft side of a piston that is in the prop hub to push the prop towards low pitch (high RPM). Counteracting this force was an air charge on the fore side of this piston in the hub. By the governor modulating the amount of oil pressure that acted on the hub this controlled the RPM. Loss of oil pressure causes the air charge to push the piston rearward towards a low RPM condition. At this point there was a feathering spring in the Aztec hub that pushed the piston back even further causing the feathering action. In the Navajo the feathering was accomplished by flyweights that pulled the prop into feather by centrifugal force. On the flip side, a loss of the air charge inside the hub would cause an overspeed, or runaway prop.

About IFR clearances, read your lost comm procedures real close, 91.185. First off, no, the clearance you get will NOT always include a fix that is an IAF, FAF, or feeder fix. Some clearances will be so very simplified that it may read "Cleared from LAX Victor 123 JFK." If you loose comm under IFR, if at any point on the journey you can decend and land while MAINTAINING VFR, do so, have a Dr. Pepper and call ATC. If you are in IFR conditions and cannot land VFR. Proceed via the assigned route, in this case the airway to JFK. ATC will expect you to begin an approach to the destination airport at as near a time as possible to your proposed arrival time (figured by adding your proposed en route time to your actual departure time). So, should you get to the JFK VOR 15 mins early they'll expect you to hold for 15 mins then start the approach of youre choice. Have no fear, if you stick to these rules, the airspace in a huge radius will be cleared for you, don't worry about hitting an airplane but watch out for rocks. Very important to also note MEAs in route and adhere to them VERY strictly while crossing the countryside. That reg also says to maintain last assigned altitude or the MEA whichever is HIGHER, do this immediately. If you are off route (on a vector) climb to the sector altitude published on the grids on the en route chart.

On icing, I really have no idea on the numbers for a 172, or really ANY airplane on the effects of ice versus flaps when comparing deteriorated performance. What I can say is I have had 2 inches of ice on an airplane and not been able to climb PERIOD. But I know with 30 degrees of flaps in most small airplanes they are still capable of climbing at least a little bit. So I would venture to say that 2 inches of ice would be more hazardous than 30 flaps. If you got that much ice on a 172 don't even THINK about touching that flap switch. The change in airflow could cause all kinds of nasty problems, just ask those ATR drivers about tailplane stalls and so on. So it might not be that drastic but you can land on ALMOST any runway in the counrty with ZERO flap in a 172.

About your cancelled flight on Saturday, don't take any offense at this but with 55 hours, I'm assuming you only recently started IFR training after getting your private. If this is the case, congrats but don't go putting the carft before the horse. You need to spend your first 15 hours under the hood doing nothing but learning how to scan by flying climbs decents and timing turns, intercepting radials and bearings, and partial panel. I wouldn't have taken you up either in that weather. Frankly I would have been calling one of my students that was working on approaches and holds and gotten them some real world experience, then if you wanted and it was ok with the other student, I'd have let you sit in the back with a headset on. I am guessing that, unless you're one of those REALLY fast learning students, that your CFI would have spent most of the lesson just telling you exactly what to do, instead of figuring it out yourself. This is what happened to be when my CFI did it to me early in my training. Sure, I got all warm and fuzzy when the localizer led me to the runway, then later on I actually shot an NDB approach, but truth be told, I hadn't a clue how I ended up there.

As for your CFI's unwillingness to take you up in that weather, my biggest concern would have been being able to get back into my home field with the ceiling being variable to below the minimums. I cancelled lessons for this because it really IS a hassle getting stuck somewhere. Could you have afforded to be stranded all day? 2 days? Could somebody have picked you up in a car? If so who pays the bill for getting the airplane home when the weather gets better? About losing an Attitude gyro, and engine, and so on, people fly real world IFR in single engine airplanes that are less equipped than the one you're flying all the time. You run the risk of losing an engine every time you strap in. If the weather hadn't been marginal at home base, and you had been at a level that I felt confident in you having a positive learning experience, I'd have taken you in a heartbeat. There are always those CFIs that are more willing to fly on days like that, I always loved those real IFR days, but some hate it. Some people have flown twin and turbine airplanes with so much redundancy that is gives them the shivers to do it in a single anymore. Your CFI will probably do the same thing on future similar occasions, a student will NOT pressure a CFI to do something he doesn't want to do. If you feel you're missing out, find another CFI. If you really like your current CFI and he's done well for you in the past, tell him you'd like for another local CFI to take you up on days like that and he could probably reccommend a collegue to sub for him those days. Just remember, don't forget to learn the basics before shooting those approaches.

Hope I've been a help. Have fun up there.

 

[guido411]

seethru,

SOME turboprops have an autofeather device. Senses power lever position compared to actual power being developed. If it senses high power being commanded and the things is spooling down, bam, feather.

 

[avbug]

To answer your questions in order:

If flying a piston twin and you suddenly lose oil P and the engine seizes will the prop automatically spring into the feather position? Some have said it will go into flat pitch like when shut-down while others claim it will go into feather since that is obviously best while flying on one engine.

1. The answer is possibly. The type of propeller system in use, and the nature of the failure mean that it might, or it might not. Not all propellers will go to feather upon failure. If the engine siezes immediately, then there may not be time for the propeller to feather before the pitch stops prevent the travel to a feathered position. If it's a hydromatic propeller as found in older airplanes, oil must be available through a dedicated feather pump to drive the propeller to feather...you may well be out of luck.

Having said that, if the engine siezes and is not feathered, you won't see much appreciable performance difference between stopped and not feathered, and stopped and feathered. A windmilling propeller is where you see your drag; a windmilling propeller produces more drag than a plywood disc out there of the same diameter as the propeller. Stop the prop, most of the drag goes away, feathered or not.

Most light twins require manual feathering of the engine. The propellers will not automatically feather.

When given an IFR clearance, will the last waypoint given to you in your route always be either an IAF, FAF or feeder route for an insturment app at your dest arpt? If not, how does ATC expect you to transition from your last wypt to some waypoint on the app if you go lost comm?

2. Your instrument flight plan may be from any point to any point, and does not need to terminate at an airport. You may file IFR to a point in space, if you wish. That's not generally a common practice, but you may do it strictly as an IFR flight plan, or a composite IFR/VFR plan. Some recommend filing to a fix where an approach begins, I don't believe in that. File to the field. There's not much reason not to.

If you know your point in space, the fix to which you file, will be in VFR conditions, you can plan on cancelling at that point. If you don't know for certain that it will be VFR, then you're better off filing to a destination field. You always have the option of cancelling before that point if in VFR conditions.

I hope I never have to experience this, but if your were flying a 172 and you have picked up 2 inches of ice, would this deteriorate performance by as much as 30 flaps hanging out?

3. The short answer is that I hope you're smart enough to never experience it. Will ice reduce performance the same as flaps? What kind of ice? What kind of airplane. How did you have it configured before the loss? What kind of capability on the airplane do you have? Too many questions, no answers, and no way to answer it.

The short answer is that ice can have a tremendous impact on the aerodynamic performance of the airplane. Two inches of ice is a very large amount of ice. If you let an airplane go that long, especially one that isn't equiped for known severe ice, you're in a world of hurt.

Avoid ice. It's scary; it's a monster. It can quickly go beyond the airplane's capabilities; you can get in over your head and not be able to get back out.

As for what performance loss an airplane will experience with flaps, that really depends on the airplane. You can always raise flaps. Under many circumstances, you may not be able to shed ice. There's a big difference. Is it worth your life to find out?

Lastly on Sat. I was schedueled for an insturment flight and my CFII felt uneasy about launching when the weather at home base was 600ovc (var 400-1000ft) and 2 1/2vis and no ice or t-storms around. The LDA app had an MDA of 620 and BDL 13nm to the N which has an ILS was 300ovc and RVR 5000. We had 5hrs fuel and even after flying to ALB (closest legal alternate 100nm) we'd still have 2-3hrs fuel. He was afraid to launch in the 172R even with 2 vac pumps, only one alternator and obviously one engine. He was concerned about the Attitude indicator failing and having to fly a PP ILS that low. Also he was concerned if the Alternator dropped off and also the engine quitting. I thought we could have flown safely with 2 proficent pilots and a GPS handheld for backup as well as lots of fuel and I certainly am a wimp when it comes to weather decisions, espically ice and t-storms. In your opinion would you have launched under those circumstances?

4. Would I have gone? Absolutely not. Even with higher minimums. Some think me conservative, but a 172 makes a fine instrument trainer under the hood; it's not an airplane I would be spending time in the clouds with.

Then again, I can't think of any other single engine airplanes, especially piston airplanes, I'd care to do it with either. I don't do night single engine cross country work, either.

That may be academic to you. Perhaps after your tenth or so engine failure you'll begin to get the picture; it won't be theory to you any more. It's not academic for me; it is never a matter of if your engine will fail...but only a matter of when. It's gonna happen. Today? Tomorrow? Ten years from now? It's going to happen.

Instrument failures. Okay, you have redundant vacum pumps. Considering the extremely high failure for dry vacum pumps, that you have two of them means very little. Do you have a backup electrical attitude gyro, too? You have only one electrical source, and apparently feel that a VFR GPS makes a difference here. Making that flight would have been a foolish idea regardless of weather you carried around a handheld GPS (which isn't legal for IFR flight).

From the tone of your post, one might assume that you are an instrument student. You indicated that you believe this flight will be conducted with "two proficient pilots." With no information provided regarding the experience level of yourself or your instructor, one might question the value of an instrument student in IMC as a contributing "proficient pilot," but I can say this; never overestimate your ability or capability in instrument flight. Very experienced folks have been lost in IMC, even in very capable airplanes.

Remember that no matter how capable you are, you are powerless when conditions exceed either your own abilities, that of the airplane, or combine under circumstances that exceed either one. Partial panel work is tough enough, add to that turbulence, ice, other potential failures, carburetor ice or induction ice, etc...and you may quickly see the combination of circumstances that are beyond what you forecast or can handle. Or that the airplane can handle.

I lost an engine in a 182 in IMC once; carburetor ice that built very quickly, and a carb heat control that physically failed and came away in my hand. I landed without power on a gravel strip after exiting the cloud base. With 600' OVC, how much time will you have to exit the cloud base and set up for a successful forced landing? Speaking of which, how much experience do you have with that, and what is the underlying terrain like?

I think your instructor has the right idea...you can wear that view-limiting-device any day. You cannot resurrect and be reanimated any day following a tragic mishap.

There is NO flight which must be made.

 

[cheater1239]

just to provide a contrarian view, i found the training flights in real weather to be so much more valuable that i consider it a must to see real low wx before obtaining an instrument rating. the cfii formed his own opinion, and you will form your own when you instruct. but just consider what he used to decide not to go. if this than if this then if this... well then better not leave the house eh? also on your prop question you had some people stating " it will feather" which is not true. but they stated it as fact. you are in the early stages of your training, you will hear some many opinions, don't confuse them with facts...