Page 21 - TNTMay18

here to write the story, they must work pretty well.
It was mid-December and over the past several days there had been the typical winter low pressure system moving into the Washington State from the Gulf of Alaska. The weather at BFI was 1,400 overcast, visibility 3 in light rain. Temperature on the surface was 43 degrees F, and wind was 110 at 12. BOI reported a 1,500 overcast, visibility variable from 1 to 4 miles with occasional blowing light snow and a 28 degrees F surface temp. En route weather showed tops in the Seattle area at 17,000. Over the Cascades they are at FL210, and at BOI 10,000 feet. Winds aloft were from the west at 30 knots at 10,000 feet, and 50 knots at FL180. And as usual, light to moderate rime icing in clouds was forecast for the entire route, and pilot reports were confirming the forecast.
The flight distance was 350 nm, which given a TAS of 210 knots, plus a tailwind of about 60 knots, would take just under 1.5 hours in the C414. The airplane easily carries four hours of fuel plus the passenger load. Seemed like a pretty easy trip and not knowing any better, we filed IFR BFI direct to BOI just like we do in
the summer. Off we go. Some 20 minutes later, we are climbing eastbound on our direct routing to BOI with a TAS of 140 knots, and ground speed of about 200 knots. We have covered some 65 miles since takeoff, placing us well over the Cascade Mountains and be somewhere in the mid-teens on altitude.
We were right in the middle of the worst icing conditions, and the real sneaky problem we now faced is the combination of winds aloft, cloud tops of FL210, degraded aircraft performance and our position in the middle of the Cascades. The airplane will get up to FL210, but even on a good day and without any ice on the airframe, the climb rate in a pressurized piston twin will drift down to some 400 to 500 fpm once in the flight levels. With cloud bases at 1,500 feet, and the freezing level starting at about 6,000 feet, this means that as a minimum, we would be spending a good 30 minutes either accumulating ice, or with it clinging to the airframe. Seeing that is what caused our saliva production to stop.
Now, we were taught that even in a FIKI (flight into known ice) approved aircraft, the best strategy when encountering ice is to immediately do something to get out
of it. The simplest option when over flat country is to just descend into warmer air, but we were over mountains, and so that was not possible. Another option was to climb above the icing layer as fast the aircraft can. The layers where ice accumulation is at its worse, are usually only 3,000 to 4,000 feet thick, but at 400 to 500 fpm that is going to take a long time. And, even with all de-ice equipment working, residual ice on the aircraft could slow the climb rate down to nearly zero, so it was quite likely we simply don’t have the ability in this pressurized, piston- powered aircraft to “out climb” the ice.
Finally, the last option we are taught way back when, is to simply turn around. But given the winds aloft, that solution can be a death trap. To get back where we came from just 20 minutes ago with our tailwind and a groundspeed of 200 knots will now take nearly 45 minutes given the 60-knot wind from the west, plus the airplanes degraded performance. There was a fatal accident in the NW some years ago, wherein the groundspeed problem alone precluded the pilot from reaching warmer air and lower terrain before his impossibly iced-up twin, still
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TWIN & TURBINE • 19