Prop pitch, IFR clearance, icing, WX decisions

[nosehair]

...uh, was that for me??

 

[Vector4fun]

Vector4fun,


Had another ATC question. I reas an article on the FAA aeromedical website http://www.cami.jccbi.gov/aam-400a/FASMB/FAS/34.html that mentioned that 30% of all ATC transmissions are repeated. This sounds way too high to me. Could this actually be true? Let me know. Thanks.

I chuckle every time I see this guy's work. When I started in ATC, and for years later, one of the things we were graded on was "Combines transmissions". In other words, why make three transmissions, when you can make one? Now they realise we (ATC) do that all too well.

I think the number could be as high as 30% at times. I certainly try to stay under that. I probably have to repeat around 10% of the time on average.

 

[wings421]

The question about the 172 in ice.

I would say 2 inches of ice in a 172 and you'd be coming down, at a moderate pace. Thats A LOT of ice in any aircraft let alone a 172 with no boots, and the pitot tube that MIGHT get to room temp. I think that IMC in a "light" single in winter time is a gamble (in geographic areas). Ice is almost always forcasted in the clouds.

As far as the question about dual in the soup.

You only have 55 hours TT. I'm sure that, like others have said, you'd be along for the ride. Once you get close to your checkride, going up in the clouds is a GREAT idea. Perhaps not as low as what it was that day, but you NEED to get some actual before you go it alone in the clouds. Its much different than the hood. As far as your CFII's decision, always go on the side of cautious. Respect his/her decision and rest assured that they did what was best for you.

As for the other replies on this thread. You guys make me feel better about not wanting to go up in moderate to low IFR in a single again. I though I might be the only one. As I've moved up to more advanced equipment in my short career, I look back and think about things that could have gone wrong. Flying down to ILS mins in an Archer is crazy. Two wig wags and equipment that is all older than me. Great experience, but I don't want anymore of it.

 

[HMR]

Ice on the 172: Do you mean two inches on the wing? Remember, the ice forms in an inverse proportion to the size of the surface it's collecting on (I can't remember the exact formula). If you have two inches on the wing don't look back. There will be more on the horizontal stab. The tail will likely stall before the wing. If you've never stalled the tail before (maybe doing unusual attitude training) it's a creepy feeling. The prop in a 172 will most likely stop long before two inches can build on the wing. The prop is the first surface to ice up and performance drops significantly with just a small amount of ice. The performance drop from two inches on the wing would be far greater than full flaps. Add in the weight of the ice and you have a lawn dart.

I still have a twitch from an icing incident in a 182 a few years ago when I was a CFII. The plane stalled at 100kts. in the clouds as we were executing a 180 to get out of there.

 

[apcooper]

HMR,


My goodness! Tell me more about the 182 ice incident. While certainly the 182 stall speed in ice is a lot higher than Vso I'm amazed it was 100kts! I'd have thought maybe 75-80kts clean. Did you have the flaps deployed? If so that actually would INCREASE the stall speed! I am amazed at 100kts because in you've ever watched the NASA research video "Icing for GA pilots" if the beginning they show a Bonanza with a student and CFI that is at full power and 110kts and desc at 200fpm!! The plane seemed to fly OK at 110kt eventhough it was desc and later after they safely landed there was about 3-4 inches of ice on the wings in a nasty horn shape.

 

[Mr. Cole]

That should be a good real-life lesson on how weight (load) increases stall speed, something we should already know. Throw in a turn, even a shallow turn, and the increased load was enough to put them over the top. Especially if they were trying to maintain level flight. Also, the flaps would decrease the stall speed under normal conditions. With that much ice who knows what impact the flaps would have.

Dave

HMR,


My goodness! Tell me more about the 182 ice incident. While certainly the 182 stall speed in ice is a lot higher than Vso I'm amazed it was 100kts! I'd have thought maybe 75-80kts clean. Did you have the flaps deployed? If so that actually would INCREASE the stall speed! I am amazed at 100kts because in you've ever watched the NASA research video "Icing for GA pilots" if the beginning they show a Bonanza with a student and CFI that is at full power and 110kts and desc at 200fpm!! The plane seemed to fly OK at 110kt eventhough it was desc and later after they safely landed there was about 3-4 inches of ice on the wings in a nasty horn shape.

 

[Illini Pilot]

if somehow oil pressure was lost in the governor (not necessarily the engine), i believe that most piston twins' props would feather...at least this is what i recall from systems classes

 

[avbug]

Some propeller systems will automatically feather, most will not.

One should know one's system and have a good understanding of what makes it work, it's strengths, weaknesses, proceedures, and a solid understanding of what makes it tick.

There's no substitute.

 

[ROB-x38]

The typical light twins i'm familiar with use oil pressure to reduce the blade angle and are fitted with counterweights to overcome the centrifugal twisting moment.

So with a loss of oil pressure the prop tends towards coarse pitch.

 

[HMR]

APCOOPER,

That event really scared me and made me realize a 500hr CFII(yours truly) might not know much about weather. Here’s the Reader's Digest version: I flew this route often in small singles and twins. Strong westerly surface winds (30+KTS), CAVU. In the vicinity of Panoche VOR (PXN), just west of KSNS in a new C182 at 9,000' and 130KIAS, or whatever a 182 does flat-out, we entered the top of a fluffy white cloud that was forming on the ridge that runs along that area. There were no forecasts/reports of ice. We hit what is best described as a wall of snot. It was like flying through heavy rain except every drop stuck to the plane. We immediately tried to climb and the stall horn went off at 80KIAS or so. We could see blue sky but couldn’t get up the extra 100’ to get out of the cloud. We told ATC we were turning around. When we got back to 9,000’ again our airspeed was only 100KTS in level flight. Then the plane just kind of vibrated and dropped a wing. We recovered, kept a steady descent going and asked ATC for a turn east or west to get off the ridge and to a lower MEA. We popped out into severe clear over the Central Valley. The airplane looked like the one in the NASA video. All this took place in 5-10 minutes. The plane was vibrating badly and we kept trying to level off every 1,000’ or so but it felt like it was going to stall. We started looking for an airport but realized we couldn’t slow down and there was no way we were going to touch the flaps. We were able to maintain 3500’ and flew all the way to Bakersfield before the ice melted off and we felt we could land safely.



What I’ve learned since and I’m sure some Amflight or SkyWest guys can vouch for this: warm, moist ocean air getting shoved up and cooling that fast from unusually strong surface winds makes for bad ice. It also seems like the worst ice is in the tops of clouds (just personal observation). I went on to fly King Airs and now a jet and I’ve never seen anything like that. I’ve carried ice in the BE-20 over the Sierras, the Wasatch, Sawtooths, and Rockies but have never seen it build that fast again. Fly Safe!