LOSING LIFT
It is somewhat odd that just weeks after the miraculous landing of U.S.Air Flight 1459, ditched in the Hudson River after losing thrust in both engines following bird strikes, that another commercial flight has crashed in New York. Two very different circumstances, but both shedding light on what is sometimes the fragile nature of flight. The publicity surrounding Captain Sullenberger of the U.S. Air flight,the level of interest and the interviews on major networks, have demonstrated to the general public that flying airplanes is anything but "routine" when something goes wrong.
When the Wright Brothers first flew, barely over one hundred years ago, it opened a door to science that has been unrivaled since. Flight. Before I indulged my lifelong interest in airplanes back in 1989, attending flight school and getting my ticket, I never understood, really, how airplanes fly. As it turns out, "lift" is a remarkable thing. Created, quite simply, by the flow of air over the curved, top portion of the wing. The more flat, bottom portion of the wing, allows air to pass by quicker, the slower air travelling further over the top of the wing, reduces pressure, and lift is produced. Every wing is curved on top, flat on the bottom, and every wing will create a certain amount of lift at a given airspeed and "angle of attack", the angle of the leading edge of the wing relative to the direction of airflow.
It is amazing in its simplicity. Small airplanes fly quite easily, that is, there is a lot of wing relative to the weight. Large, commercial planes fly more by brute force, faster airspeeds, bigger wings, but they don't glide far, or well. These are the dynamics that made the safe ditching of Flight 1459 so remarkable. Very little time, very little altitude to trade off for airspeed and time, and a large airplane that does not fly well "dead stick". Truly remarkable, and as written here in a prior column, an ultra-experienced pilot.
Now, a Continental Connection flight, number 3407, crashed in upstate New York, killing all 49 aboard. It is being reported today that the crew had noticed significant ice build-up on the wings and windshield. It was widely reported that there was snow and wind in the area as well. Snow and wind are pretty much non-factors for commercial planes, even a Bombardier Dash-8 which is a 74 seat commuter, is large in my book. Ice is something else. It has been a factor in many crashes, though this plane was surely fitted with de-ice equipment on the plane, and probably got the glycol treatment at Newark before departure. It will be a long time before the NTSB releases a finding, but given the accounts so far, ice would be, in my opinion, the leading culprit.
It's not the weight of the ice, it's the rough surface on the leading edge and top of the wing that disrupts the airflow, not allowing the flow to "stick" to the top of the wing. Like a wave of water, it fragments . I always find it amazing that ice, indeed even frost on small airplanes, will leave a wing unable to produce lift. The account of flight 3407 released today says that when they deployed the first installment of flaps, preparing to land, that the airplane pitched and rolled extremely. Clearly, they were unable to recover from that upset at only 2,300 feet msl. The airplane fell like a rock. The weather conditions probably made it difficult for the pilots to "feel" the ice building up, the airplane slowing and getting sluggish in control response, and the introduction of flaps caused an immediate stall, as the ice had brought them to the edge of their minimum flying speed envelope.
It is a sad reminder that flying is not guaranteed. There are many elements of physics at work, not the least of them, the battle between gravity and the lower air pressure above the wing. Sadly, lift requires a clean wing, a certain airspeed and a wing that is pointed in the right direction. Gravity requires nothing. It's "on"...24/7.
Karl From New Hampshire