Prop pitch, IFR clearance, icing, WX decisions

[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!