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Hi Capt Lim,
Your site about plane and flying is superlative! An actual chance to communicate with a real airline pilot. Which airline do you fly for?
I have a few of questions for you. When turbulence occurs, what is the explanation for the sinking feeling and the momentary weightlessness? Also, how often are the planes checked for loose nuts and bolts? How fast does the fastest airliner travel?
Regards,
Tim,
Boston
Hi Tim,
I am currently flying for a major airline which I would not wish to disclose for personal reason but I do not mind answering questions that are of general interest to the air travelers.
1. The sinking feeling and momentary weightlessness you experienced are basically the effect of air turbulence. I have wrote about this topic as well as in various answers to previous queries. Air turbulence are created by any number of different conditions, including thermals, jet streams, mountain waves, cold or warm fronts, thunderstorms or micro-bursts. For example, if thermals (hot air due to solar heating) continue to develop, it would produce turbulence. When different types of surface are located in the proximity of one another, thermals develop and intensify at different rates, which intensifies the scale and effect of the thermals. Typically, the slower warming areas will become the sinking column of air, and the faster warming areas will form the center of a sustained upward thermal.
Turbulence is felt when an aircraft flies through thermals into areas of stable or sinking air. A light chop may be felt when flying through numerous thermals with diameters smaller than the size of the aircraft, but light or moderate turbulence may be experienced if the diameter exceeds the size of the aircraft. The vertical velocity of the thermal is an important factor in determining the severity of the turbulence.
This vertical velocity or momentary weightlessness you felt, is what some erroneously referred to as air pocket. When you stand on a bathroom scale, it measures your weight because gravity pulls down on you and the scale. Because the scale is resting on the ground, it pushes up on you with an equal force. This equal force is your weight. If you were to jump off a cliff while standing on a bathroom scale, both you and the scale would be pulled down equally by gravity. You would not push on the scale and it would not push back against you. Therefore, your weight would read zero and you are thus in a state of weightlessness. In fact, NASA use the KC-135 airplane as a flying laboratory to create weightlessness conditions for astronauts training.
2. How often are the planes checked for loose nuts and bolts? Well, all airplanes are physically checked by the pilot and the ground engineers before and after each flight. Then every three to five days, they inspect the plane’s surface controls (eg. flaps and rudders), landing gear, fluid levels, oxygen systems, lighting, and auxiliary power systems. Thereafter, every eight months, the internal control systems, hydraulic systems, and emergency equipment within the cockpit and cabin are thoroughly inspected. Crews open up the aircraft every 12 to 17 months and use sophisticated devices to probe for wear, corrosion, and cracks that can’t be seen with the naked eye. Finally, every three to five years, each airplane basically is taken apart and put back together, with major components and systems replaced as needed. So, if there are any "loose nuts and bolts" discovered, they would be rectified during any of the above inspections.
3. How fast does the fastest airliner travel? The fastest airliner was the Concorde. It cruises at Mach 2 (twice the speed of sound) or 2,200 km/h (1,350 mph) at around 60,000 feet. Unfortunately, British Airways is the last Airline to operate this supersonic airliner and its last flight was on the 24th of October 2003. That leaves the Boeing 747-400 as the fastest airliner today. Its cruising speed is Mach 0.86 or around 575 mph (930 kph) at 35,000 feet.
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Air Turbulence 
