Loss of power

[NM Doug]

Interesting flight tonight (!)

I was IFR from Brown Field to Gillespie, IMC from about 800 or so AGL. Initially had moderate-severe turbulence climbing out of Brown, but got out of that OK.

Heading out east to BARET, my C172 couldn't maintain airspeed when level at 7000. Even full throttle, I was dropping down to 80 kts (?) Still IMC in precip in the sim... Ice? Pitot heat was on since before takeoff, but maybe it couldn't keep up? Declared an emergency and got helpful and creative ATC getting to the field through IMC. Finally broke out and was cleared for the visual approach...but had a moment of unanticipated IMC on the way down - I hadn't seen a cloud between me and the field...maybe this was the moment X-Plane updated the weather (?) After that, I was well off speed and altitude coming in. My choice was to land long and risk going off the end, or go around...with an undiagnosed power situation. I chose the former. Second day in a row I've done a rotten approach . I did get on the ground though without hitting anything massive, so that's nice.

Boy, that was messy! I should know better than to try to fly after a long day at work and a big dinner.

Edit: I had X-Plane 10 on real weather from the net. I have to admit, for sim flying, I don't always check the weather.... I just now looked at the actual San Diego weather. Egad! Clearly not a night to take up a 172. The icing AIRMET makes me wonder if that's what was going on. Well, maybe that and the thunderstorms.

[arb65912]

Nice story, Doug. Thank you for sharing. I am anticipating responses about what would be the cause of the problem you described. Did you try the carburator heat?

Cheers, Andrzej

[Orest Skrypuch]

Yep, airframe and induction icing was definitely in the mix in LA yesterday, freezing level around 6000ft with precip.

* Orest

[NM Doug]

Indeed, this makes the most sense. I looked out at the strut and didn't see any ice accumulating (though that isn't a guarantee that there isn't any), and I double-checked pitot heat, but I simply did not think of induction icing. (The 172SP is fuel injected, but if I *had* thought of carb ice, I might have remembered the Alt Air, which would have almost certainly helped with my engine power situation.)

Of course, by this point, even with Alt Air helping the engine do its job, I would have been in an emergency situation for the very likely airframe icing, but I would have known what was going on and been in better shape. Depending on the visibility of the 1000 ft above the field, I might have done a gentle-turn go around at higher-than-normal airspeed. I wasn't in precip over the field and therefore wouldn't have been accumulating more ice.

Thanks for the insights,
Doug

[Orest Skrypuch]

Impact ice can be just as effective at sapping engine power.

All sims model pitot heat issues, but if pitot heat is ON, then I doubt that it would be overwhelmed in a sim. FS9 does not model airframe or impact/induction icing, FSX does sort of, I'd be intrigued to know if X-plane does or does not.

With airframe icing, of course you need more speed on approach (add 30+ knts to Vref), gentle rate-one-half turns, and don't touch the flaps. You are essentially a test pilot. If in a smooth (normally) low-drag aircraft like a Cirrus, watch out. An old Cherokee or Cessna is somewhat more tolerant of airframe icing. Job one is to get out of the icing, divert, climb (if you can), descend.

Always good to check the weather, eh?

* Orest

[NM Doug]

Thanks and yes to all points, Orest -

Yes, I should have written impact/induction icing.

As I was looking around online for definitions of each, I came across "Induction icing consists of any ice accumulation that blocks the venturi, air filter, ducting, and/or fuel metering device. Impact ice, a type of induction icing, can occur anywhere that temperatures are near to, or colder than, the freezing point of 0° C. Impact ice can block the air filter and rob the engine of air needed for combustion, even on a fuel injected engine. If you suspect impact ice, activate alternate air or carburetor heat as directed by your POH/AFM." This is from https://www.faasafety.gov/gslac/ALC/cou ... 33&sID=150

Given the airplane's symptoms, my guess would be that X-Plane 10 does model impact and/or induction icing

Yes about the weather checking (I do go into a fair amount of detail when flying r/w, but I just hopped on PE last night and off I went, with only an X-Plane METAR). The net result was a great (unplanned) learning experience...boy, do I remember what that Alt Air knob is for now!

Before I started trying out the I-1 rating on PE, I remember seeing a forum thread with various pilots describing their IFR prep for online flying. Just looked it up again: viewtopic.php?f=3&t=296 I'll give it a read again and probably be able to make more of it this time!

Cheers,
Doug

[Keith Smith]

Doug,

I might be mistaken but I'm sensing you're under the impression that if pitot heat and alternate air or carb heat will save the day and allow you to fly through icing conditions. The pitot heat will help preserve the operation of your pitot-static instruments and the alternate air will help with engine operation to some extent. Basically, you'll have a very accurate air speed indicator telling you that you're about to die The real killer is the ice building up on leading edge of the wing, turning your well-engineered airfoil into...who knows what? Similarly, your horizontal stab becomes a slab of ice and things just continue to get worse from there. The prop itself can accumulate ice and effectively change its shape, too.

If you're in visible moisture (clouds or precip) and the OAT is anywhere near or below freezing, you should exit those conditions as soon as possible unless you have an aircraft capable of FIKI (flight into known icing).

X-Plane does model the buildup of ice within various parts of the engine, the pitot tube, the airframe, prop and airfoils. Since it's using real world physics to calculate all of the forces, based on known info about your airfoil, you can bet that it's going to sabotage your efforts to stay alive. You can FEEL the power diminishing, and more importantly, the fact that at a given power setting, you don't get the lift that you were getting before, so you have to increase the angle of attack to make up for it, which leads to more drag...and before you know it, you're unable to maintain level flight even at full power.

I'd suggest wading through X-Plane's data input/output screen and outputting the ice states to the screen, then entering clouds when it's below freezing. That'll tell you what's going on Now, in reality, not every cloud will result in ice accumulation on the air frame if it's at or near freezing, but I think it's a certainty with X-Plane.

Keith

[Orest Skrypuch]

X-Plane does model the buildup of ice within various parts of the engine, the pitot tube, the airframe, prop and airfoils. Since it's using real world physics to calculate all of the forces, based on known info about your airfoil, you can bet that it's going to sabotage your efforts to stay alive.

I may just yet, have a look at X-Plane.

* Orest

[Keith Smith]

Most people dismiss it because the controls feel twitchy, the interface takes time to learn, and there is a stunning lack of basic terminal scenery. Get past those things, though, and the treasures that lay within are unsurpassed by anything I've seen in 30yrs of simming.

The weather depictions in XP-10 rival the visual systems in multi-million Level-D sims. It's a mind bender to be saying, "yeah, it's clear here, but look what's coming up ahead."

Then we have the lighting system...oh mama: http://www.x-plane.com/desktop/multimedia/

If I get some time, I'll upload some of the pics I've snapped from the weather lately. The lighting is nice, but the weather system has serious implications for pilot training.

[NM Doug]

Hi Keith -

I will indeed try out the X-Plane data output trial flight you suggest - that will be fun (under controlled simulation!)

I'm sorry if my posts conveyed that impression ...that wasn't my take ("that...pitot heat and alternate air or carb heat will save the day and allow you to fly through icing conditions"). I agree with you 200%: avoid the icing conditions in the first place, and then, if somehow in them anyway, get out very much ASAP. If I had had a big picture WX awareness (which I didn't), and had somehow run into icing conditions inadvertently, I would have had a sense which way to go to exit the icing conditions.

Once I recognized I was in a bad, though undiagnosed, situation (from not checking the WX and avoiding the flight - and so I thought I was "just" in precip, as opposed to icing conditions) - my goal was simply to get safely down by getting to the nearest field, which was behind me, as opposed to further ahead over even more mountainous terrain.

What I meant about the Alt Air was that, if faced with a similar problem again, I would turn Alt Air on *while* also working to exit the icing conditions as quickly as possible. That would give me the best chance of having a reliable source of power and not add a loss of power to an already perilous airframe icing situation.

But thank you very much for posting your comments - I appreciate your not wanting to take a chance at letting a dangerous misconception go uncorrected

- Doug