![]() ![]() Air Traffic Control will give them time to reduce their speed slowly obviously, a plane can't fly at 300 knots until two miles out and then suddenly hope to slow down to between 150 and 160 knots right at the runway threshold without something going wrong. Pilots will know that they'll need to land with a specific approach speed. The descent rate depends upon the weight of the airplane, because it represents the safest, slowest possible speed that the plane can lose its thrust, stay on an angle, and maintain control. The way to do this properly is to calculate a descent rate from a particular spot close to the runway threshold. It's kind of complex, because you want to land at a specific spot, like, say, on a runway, where you can burn off all the excessive energy that the plane has in a way that doesn't kill anyone or wreck the thing. This does not mean that you lower the power and point the nose toward the ground. The way you get a plane to land is to reverse the process that generates the thrust. The way you get a plane in the air is to generate enough thrust to overcome its weight, so that the thrust plus the weight of air itself is higher than the weight of the plane. What does it mean that the "speed" was too slow? How would they know what the right speed was? So there were at least two cues - one electronic, and one visual, that the pilots were relying on. Is that's the case, your ground speed is sufficient to land in the touchdown zone properly. It'll get bigger and bigger, and bigger and bigger, but it won't move. It should be, relative to the rest of the stuff in your band of vision, at the same place it was when you first saw it. Is that the only way for a pilot to tell if she's going to land at the right spot? In any event, when you see the two-two configuration, you're good. If you're coming in too high, you ease back on the throttle or change the angle of the plane relative to the descent, pitching up a little. If you're coming in too low, it means that you need to increase the ground speed of the plane relative to the rate of descent, so you push the throttle forward a bit, or perhaps adjust the pitch. If he's coming in too low, he'll see three red lights next to one yellow light. ![]() If the pilot is coming in high, he'll see three yellow lights and one red light. The angle at which the pilot's eyes catch the PAPI is key: if the pilot is on the correct glidepath, he will see two yellow lights next to two red lights. The PAPI is a series of lights set to one side of the runway threshold. Runway 28L had a functioning PAPI, or Precision Approach Path Indicator. On a clear day with no visual distortions, there are other ways for a pilot to know if he's flying the correct approach path. So how did the pilots know how to stay on the right path? If the lines stay tight, you'll land precisely in the touchdown zone of the runway, which is usually about 1,000 feet in from the threshold, or the start, of the runway. Another beam provides lateral guidance, so you're using your rudder pedals to slightly adjust the yaw to keep the line as close to the horizontal center-line in the same indicator display. When cleared by the tower for an ILS approach to a runway, you tune your plane to the frequency of the glideslope emission you adjust your speed, using the throttle, and pitch, using the stick, to keep the glideslope line as close to the center-line of an indicator display in the cockpit as you can. A glideslope refers to a beam of energy that's part of the Instrument Landing System and keeps a plane on a vertical descent line. Potentially, very important - if the pilot really, really preferred to use this method. How important was it that the glideslope wasn't working? First, a few words: Associate pitch with moving up or down, the "stick" with pitch, yaw with left or right horizontal movement, rudders with yaw, and thrust with force and speed. ![]()
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