Comair Jet crash

[jon lynn]

Comair Jet Didn't Use Runway Assigned Before Crash

This was in the news here today. But I have a question for any real pilots out their.

In 1980-81, before I ran out of money, I finished 20 of my 40 hours of flight instruction, in a tiny Cesna 152. I seem to remember if an aircraft produces lift, and the wheels come off the ground, you are considered airborne. And should be able to sustain flight once lift is achived, and enough thrust.

If the jet crashed a mile from the end of the (supposed) short strip, I would say the pilot(s), were just unskilled, and the crash could have just as easily happened from the long strip.

I know a jet engine vs. a little old prop job, are two different worlds, but arent thrust-drag and lift-weight laws of aerodynamics still the same?

All I can think of is maybe they took off in the wrong direction of the wind? Can any real pilots gimmie a view here?

[Rocky Raab]

It's due to a phenomenon called "ground effect." If you are less than about a half wingspread from the ground, there is a cushion effect caused by air trapped between the ground and the wings. That cushion can mimic lift, and a plane can actually fly in ground effect at less than flight speed. It works dandy on flat, level surfaces, but introduce some vegetation or other objects, and the cushion effect suddenly disappears.

Now, in this instance, they had probably achieved two-thirds or three-fourths of liftoff speed when (out of the dark) they saw the end of the runway zip by. Way too late to stop and too slow to fly, but they had no choice. They probably yanked the plane off the ground and into ground effect. They'd still have been accelerating, but any attempt to raise the nose would have resulted in an instant stall. Sooner or later, they had to raise the nose to miss something - and that was that.

In jet aircraft, it's called "flying behind the power curve" where the drag caused by lift or configuration is greater than the thrust available. The only way out of that corner is down, but if there is no room for down...

[jon lynn]

As usual Rocky, you are a fountian of information, thanks!

[Hawkeye6]

I heard a professor emeritous of areonautics interviewed on the radio Monday. He said he could see skid marks on the runway that looked to him like th pilots had tried to rotae to a very steep angle of attack on realizing their error on the runway.

I don't know where they wre in the process when they realized it, but I wonder if it would have been better to cut the power, use the brakes, reverse thrust, whatever and jsut run off the end of the runway?

[Rocky Raab]

Hawkeye, slamming on the brakes is almost always the first thing a car driver thinks of - and does. That's perfectly normal, as that's about the only emergency procedure there is in a car.

But an airplane driver thinks differently. The entire object of a takeoff is getting off the ground. That's the default option, and that's what they'll attempt to do nine times out of ten if the plane is working correctly.

Two other factors come into play. One, it was dark, and they couldn't see what might be ahead of them off the runway (no obstacles in the sky, though). Two, planes have notoriously poor brakes and the smallest possible tires, made worse by the fact that the wings remove a lot of weight from the tires, and that further reduces braking power.

So, in their mindset, the solution to any non-airplane problem would be, "Get this mutha UP!" Trouble is, it doesn't always work...