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Cockpit Confidential: Everything You Need to Know About Air Travel by Patrick Smith.

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Why the annoying rules pertaining to window shades, seat backs, tray tables and cabin lights during takeoffs and landings?

Your tray has to be latched so that, in the event of an impact or sudden deceleration, you don’t impale yourself on it. Plus it allows a clear path to the aisle during an evacuation. The restriction on seat recline provides easier access to the aisles and also keeps your body in the safest position. It lessens whiplash-style injuries and prevents you from “submarining,” as it’s called, under the seat belt. Keep your belts low and tight. Nothing is more aggravating than hearing a passenger voice the theory that should a crash occur they are guaranteed to perish, so what’s the point? Most crashes do have survivors, and something as simple as a properly buckled belt could mean the difference between serious and minor injury.

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Raising your window shade makes it easier for the flight attendants to assess any exterior hazards – fire, debris – that might interfere with an emergency evacuation. It also helps you remain oriented if there’s a sudden impact – rolling, tumbling, etc. Dimming the lights is part of the same strategy. Burning brightly, the glare would make it impossible to see outside. And by pre-adjusting your eyes, you won’t be suddenly blinded while dashing for the doors in darkness or smoke.

During early climb, engine thrust is suddenly cut and it feels like the plane is falling. What is happening here?

The amount of thrust used for takeoff is always more than enough, so typically at a thousand feet or so, depending on the profile, it’s reduced to what we call “climb power.” This saves wear-and-tear on the engines and keeps the plane from exceeding low-altitude speed restrictions. The plane is neither descending nor decelerating; it’s just not climbing as rapidly.

It might surprise you to learn that despite the impressive roar and acceleration, airliners seldom take off at full available power. Maximum thrust is used when conditions (weight, runway length, and weather) dictate, but normally they don’t, allowing for a reduced setting. This is healthier for the engines, and the power is still there if you need it.

While at cruising altitude, I periodically hear a loud rumbling, as if engine power is being increased. This lasts for a few minutes, and then it dies down. It sounds almost like taking off, yet the plane doesn’t seem to be climbing. What is this?

This is either the gastrointestinal distress of the guy sitting next to you or what’s known as a “cruise climb,” whereby the plane is ascending from one cruising altitude to a higher one, be it for traffic, weather or better economy. Engine thrust is increased, resulting in a noisy rumble, but because the climb angle is a lot more gradual than it is on departure, you don’t necessarily feel it. This sound is most noticeable only to those seated aft of the engines. People in the forward rows might not hear it.

On every flight, we hear a series of dings or chimes. What do these signals mean?

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The chimes you hear are one of two kinds. The first kind is basically just a phone call. The flight attendant stations and cockpit share an intercom system through which any station is able to call another. When a call is made, the recipient’s phone will “ding.”

Chimes also are used by pilots as a signaling device for the cabin crew. On the plane I fly, we create this sound by cycling the seat-belt sign an appropriate number of times. Airlines have their own rules for how many chimes mean what and when they’re given, but the basics are the same: ordinarily, those after takeoff indicate the plane has passed through 10,000 feet, at which point passengers can use approved electronic devices and flight attendants may contact the cockpit without fear of interrupting a critical phase of flight. During descent, it’s equivalent to, “We’ll be landing soon, so please get the cabin ready.”

None of the signals, by the way, has anything to do with landing clearance. Often, after the second round of descent dings, you’ll hear a flight attendant announce, “Ladies and gentlemen, we have been cleared to land, so please put away …” I don’t know when this habit got started, but in reality the flight attendants have no idea when the plane is cleared to land. They’re using the term for convenience. Actual landing clearance, assigned by air traffic control, usually comes much later, sometimes only seconds prior to touchdown, and it is not something communicated between pilots and cabin crew.

For the record, it is not true that a runway must be vacant before a flight is cleared to land on it. Flights are cleared to land all the time with other arriving or departing planes still on the strip. It simply means that you may go ahead and land without further communications with the control tower. If the runway is not vacant in time, ATC will cancel the clearance and have you go around.

What happens when lightning hits an airplane?

Planes are hit by lightning more frequently than you might expect – an individual jetliner is struck about once every two years, on average – and are designed accordingly. The energy does not travel through the cabin electrocuting the passengers; it is discharged overboard through the plane’s aluminum skin, which is an excellent electrical conductor. Once in a while there’s exterior damage – a superficial entry or exit wound – or minor injury to the plane’s electrical systems, but a strike typically leaves little or no evidence. In 1963, lightning caused a wing explosion aboard a Pan Am 707 over Maryland. Afterward, the FAA enforced several protective measures, including fuel tank modifications and the installation of discharge wicks aboard all aircraft.

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In 1993, I was captaining a thirty-seven-seater when lightning from a tiny embedded cumulonimbus cell got us on the nose. What we felt and heard was little more than a dull flash and a thud. No warning lights flashed, no generators tripped off line. Our conversation went:

“What was that?”

“I don’t know.” [shrug]

“Lightning?”

“Might have been.”

Mechanics would later find a black smudge on the forward fuselage.

Sometimes when a plane is landing, I see a long trail of mist coming from the wingtip. What is this?

As air flows around a wing at high velocity, its temperature and pressure change. If humidity levels are high enough, this causes the cores of the wingtip vortices described in the previous question to condense and become visible, writhing behind the plane like gray, vaporous snakes. Moisture will condense around other spots too, such as the flap fairings and engine attachment pylons. You’ll witness what appears to be a stream of white smoke pouring from the top of an engine during takeoff. This is water vapor caused by invisible currents around the pylon. Other times, the area just above the surface of the wing will suddenly flash into a white puff of localized cloud. Again, this is condensation brought on by the right combo of humidity, temperature and pressure.

What does “doors to arrival and crosscheck” mean?

Example: “Flight attendants, doors to arrival and crosscheck.”

Occasionally heard as “disarm your doors and crosscheck” and announced by the lead flight attendant or purser as a plane approaches the gate. The intent is to verify disarming of the emergency escape slides attached to the doors. When armed, a slide will automatically deploy the instant its door is opened. Disarmed, it needs to be deployed manually. On departure, the slides are armed to facilitate an emergency evacuation. (You might hear this as “doors to automatic.”) Upon docking, they’re disarmed to keep them from billowing into the boarding tunnel or onto the apron during servicing. Crosscheck is a generic term used by pilots and flight attendants meaning that one person has verified the task of another. In the cabin, flight attendants crosscheck one another’s stations to make sure the doors are armed or disarmed as necessary.

Excerpted from Cockpit Confidential: Everything You Need to Know About Air Travel by Patrick Smith. Published by Sourcebooks. Reproduced with permission from the publisher. All rights reserved.