Tuesday, January 12, 2010

Icing and dangers of attempting to get on top by Don Wright

Columbia LC 42-550FG (2007)

Just received this post from fellow pilot flight instructor and Delta Captain Don Wright:

Hi Dick,

Congratulations of your new blog!

My two instrument students were asking about in-flight icing, and the Cirrus accident the NTSB attributed to ice came up. I don’t have the file in front of me, but, as I recall, the Cirrus pilot was flying at a pretty high altitude over mountains and reported that he could see the moon through breaks in the overcast. He asked for higher and shortly after disappeared from radar. The NTSB attributed the accident to airframe icing, but I have a different take on it.

Let me set the scene: You're cruising along at 15,000 feet or so in turbulence and picking up a little ice. Service ceiling is 18,000, but you're a little heavy for it according to the charts. You look up and notice the moon is peeking through breaks in the overcast. Damn! I'm almost on top, you think and ask ATC for 17,000 even though the POH says you can't maintain that altitude. You think you'll be on top in a few hundred feet, so you're not too worried about actually having to climb to 17,000. You can just cancel or go "wrong way" at 16,000. Anything is better than bumping along at 15,000. Clearance received, you pitch the nose up confidently expecting to be in bright moon light in a few seconds. WRONG! You're now at 16,000, still in the clouds with the IAS dropping toward the white arc. So close, you think. But 16,500 should do it, you think. Long before you get there the ADI rolls over on its side, the IAS goes off scale and in less than two minutes you are reduced to warm, red mush.

The lesson is this: Never, ever try to "zoom" the airplane up to a marginal altitude. If you must climb, do it like you’re milking a mouse--gently. Never ask the airplane to do more than it's capable of. You want 500 FPM? Make sure the airplane will do it. Better yet, don't ask.

Never try to judge the height of the tops from below. It always looks like you're just about to pop out into clear air. An old joke has it that John Glenn in orbit called Houston and said that if he could climb another thousand feet, he'd be on top.

One dark night on climb out from JFK, I watched a captain with 20,000 hours try to "zoom" a B-747 up out of turbulence. We popped up using Max Continuous Thrust to an altitude that we should have been able to sustain, but we were seriously behind the power curve. Normal climb is 300 knots to Mach .75, then maintain the Mach all the way to altitude. We were back to about Mach .55 with the nose up in the air and the throttles (Thrust Levers) firewall forward. As I remember, the 74 had a digital (well, Mechanical-Digital) airspeed indicator that clicked every time it changed it's display. I sat there listening to the IAS click down from Mach .55 to something less with the nose going higher and higher. The autopilot was telling us, "You want me to maintain this altitude? OK. I'll give you whatever it takes." We finally gave up and asked Center for lower. It took about 4,000 feet to get our airspeed back.

Yes, ice is a winter time concern, but stalling the airplane while trying to get on top will kill you just as quick.