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Continental Flight 3407

From Captain Bogs:

This is your Captain speaking…

Another accident, another quest to find the reason why, so we don’t do this again.

Except this time, we have already have had a chance to fix things so it doesn’t happen again. But the FAA will not take the actions necessary to fix the problem despite the fact that the NTSB pointed at this type of anti-icing system as the cause of an accident 15 YEARS ago. So 50 more people pay with their lives because the FAA does not want for the commuter airlines to have to pay for an effective anti-icing system. It always comes down to money vs. lives, and when the cost in lives gets too large, the FAA will act. I hope that balance has at last been reached.

Basic training. Anti-ice systems in use at the present time are a heated leading edge of the wing, used by all the larger (737 and up) jets. The turboprops in the commuter ranks use a system where the leading edge of the wing has a rubber coating covering a pneumatic tube (more like a network of tubes, actually). With this system, the rubber expands when the air is applied, and the ice is supposed to break off the wing.

Anti ice systems have to deal with three types of wing ice. There is clear ice, which is formed by large super cooled drops of water which freeze when they hit the airfoil. This type of ice is hard to see, but is normally smooth. The aerodynamic characteristics of the wing are basically unchanged as the large drops adhere closely to the wing. Weight builds up quickly, however, and this type of icing can build to inches of heavy ice before it is noticed. The pneumatic anti-ice system works well on this type of icing if it is seen and taken care of early before the ice gets to be so thick that the pneumatics are not strong enough to dislodge them.

Pneumatic systems do not work so well with either of the other two types of icing, mixed and rime ice. Both of these happen with smaller drops of water that make smaller ice crystals on the wing. The problem with that is that the ice layer can be very flexible, going out and back with the rubber boot, and eventually forming a covering that builds outside the range of movement of the rubber boot. This makes the pneumatic system ineffective when you need it most, as the mixed and rime ice are rough and cause the aerodynamic characteristics of the airfoil to degrade.

The expanding rubber is an effective system. Well, at least that’s what they try to tell us. I am much more inclined to believe Ernest K Gann, Airline Pilot, the author of a number of fictional books on aviation, but most importantly, the author of the nonfiction book, Fate is the Hunter. He tells us of an encounter with ice in a DC-2(!!), an aircraft that has the same type of pneumatically powered anti-ice systems. Didn’t work for him either, although he and his crew were able to land the old crate before the ice forced them down. That was in the early 1930’s, so this is not a new problem.

Both systems are designed to handle only light icing. Anything heavier can overwhelm the system no matter which type of anti-icing system you have. Then you will have increased drag, possibly degraded lift and a lot more weight right when you have less lift to keep you in the air. Too much of this, and you stall your wing. This is what just happened, and we are all horrified at the result.

Each time an aircrew gets into ice they are presented with the facts that they have a degraded wing, increased weight, decreased power (both systems bleed air off the compressor of the turbine, taking power away from the engines) and an unknown type of ice. Each encounter has to be handled on an ad hoc basis, especially if you have a rubber boot system. You apply the anti-icing and try to evaluate its effectiveness.

As soon as you are in ice you become a test pilot, because no one has taken your aircraft into this exact icing event. This is even more important when you have to change the configuration, either by putting out flaps or dropping the gear. Anything like that changes your environment from where you are and have handled to something you know will be different but you know will require more power. (All configuration changes in the landing sequence increase drag, which must be overcome with more power.) How much more power? Enough, but not more. Or less. Again, this is what just happened. They were where they needed to lower flaps to prepare for landing. The movement of the flaps changed their aerodynamic characteristics enough to increase the power required more than they were ready for, and they stalled right into the ground from 2000 feet up.

The crew knew they were in icing. They had their anti-icing system on. They were doing what they were trained to do. It wasn’t enough.

When I flew the Jetstream 2000 it had a rubber boot on the wing as its anti-ice system. I never trusted it. I made sure that the anti-ice went on only when we had enough ice on the wing that it would break off in large chunks no matter what kind of ice we had encountered. One time we had clear ice, and there was so much ice on the wing when we noticed it and turned on the system that we popped up 100 feet as the ice flew off. It made a sound like a pistol shot. Scared the hell out of both of us, and that was the crew. I can only imagine what the passengers thought! The other times we had to use the anti-icing the ice flew off the wing and we turned the system off until we had enough ice on the wing to make the ice brittle so the system world work. That is the only way that system will work with mixed and rime icing. It is NOT the way the airline (and indeed all the airlines with this type of pneumatic system) trained their pilots to use the system. They said to turn it on and leave it on. They are wrong. The Canadian FAA says that the anti-ice system should be turned on before the aircraft gets into any known icing. This will work with a heated wing, but it will not work with rubber boots. I wonder if they have any pilots in their regulators. It doesn’t look like it.

All in all, an avoidable accident. Inexcusable! Either we need to learn how to use the boots and train our crews on how to use them in a way that will at least give them a chance, or we need to consign the rubber boots into the trash can and put what the big boys use on their jets, the heated wing. I knew about the problems the rubber boots cause long before I was a pilot. (I read Fate is the Hunter in middle school.) The ICAO (International regulators) and the FAA need to start putting safety and the lives of the crew and passengers above cost of an effective anti-icing system.

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