Peter wrote:
I heard recently that if you cycle rubber boots at low temps e.g. -40C you will destroy them. Is that correct?
Yep. Limitation on the Mustang for using the boots was -30. The rubber gets brittle and shreds. Of course at those temps you never get icing so it doesn’t matter.
I was speaking to the owner of a large turbine maintenance shop in the US the other day. He told me that this is the most frequent $45k mistake pilots make. Gives them a constant stream of revenue. Expand your boots once at FL300 and you’re in for a complete replacement.
Same thinking around the inertial separator on a PT6. By turning it on, you avoid compressor damage due to ice particles but you also increase your ITT and risk an even costlier temperature exceedance. Therefore you want to turn the inertia separator off when there is no longer a danger of icing, even if you’re still in IMC.
Liquid water only exists from 0°C to -15°C or so, sometimes -20°C. It seems that -25°C is a common rule of thumb for when to turn off boots/TKS and inertia separators.
Now this could solve all our problems:
achimha and Peter thank you, yes there is a typical limitation for operating pneumatic boots outside of a +/-40oc range
Flying from Lyon to Fairoaks today, there was an embedded front with forecast of turbulence and moderate icing up to FL180; I duly started turning into an icicle from 6000 feet (0C) up till FL140 (-15C), the boots did their job but it took a while (in icing in a PA46 you have to keep 135KIAS, and it’s already not a great climber at 125KIAS – I’m talking about the piston variant) and I picked up some airframe icing, making things slow and somewhat stressful. From FL140 no more ice, although we were still in cloud. From FL190 we could see we were close to the tops, but we were only climbing at about 300FPM.
I was talking to Paris Control, and was flying a route where you have to be at FL200 mini (going over Roissy). They called me and said “reports of severe icing from FL200 to FL230”. I acknowledged but was a bit puzzled; there was no convection forecast, no precipitation on radar, and I’ve never, ever had icing below -15C outside of a TCU. As soon as we reached FL200 though, with blue skies tantalisingly close, my windshield (which was on max heat) started to ice up and the very leading edge of the boots got covered with what looked like 0.5cm of solid, semi-translucent ice. I immediately asked and got a descent to FL190; stayed there for about 30 minutes; asked for any further reports – there weren’t any so we climbed again and finished the trip at FL200, soon in glorious sunshine.
Have others experienced something like this? I’m particularly interested in hearing about icing below -15C.
in icing in a PA46 you have to keep 135KIAS, and it’s already not a great climber at 125KIAS – I’m talking about the piston variant
I have some experience with this slow cruise climb and in the ice I switched to full power climbs. It will not happen very often and in my experience risiking to get stuck in the climb is not worth the little reduced load on the engine.
I used to do that but I have 4 new cylinders, still in break-in, trying to not brutalise them too much!
denopa wrote:
I’m particularly interested in hearing about icing below -15C.
This -15C thing seems to be more theoretical than definitive. I got moderate icing (so bad that the entire windscreen was whited out, and the heated panel wouldn’t shift it) going into Resolute Bay with an OAT of -40C to -30C.
denopa wrote:
I used to do that but I have 4 new cylinders, still in break-in, trying to not brutalise them too much!
Aren’t you supposed to fly new cylinders with as much power as possible for break-in? I heard at least 75 % power, but more is better?
