Cockpit Confidential (9 page)

And then, yes, it's to lighten the load. The maximum weight for takeoff is often greater than the one for landing—for a few reasons, the obvious one being that touching down puts higher stresses on an airframe than taking off. Normally, a suitable amount of fuel is burned away en route. Now, let's say something happens after takeoff and a plane must return to the airport. If the trouble is urgent enough, the crew will go ahead and land heavy. But almost always there's time to get within landing limits, and rather than tossing passengers or cargo overboard, the easiest way of doing this is to jettison fuel through plumbing in the wings. (I once had to dispose of more than 100,000 pounds this way over Northern Maine after an engine malfunction, a procedure that took many minutes and afforded me a lavish night's stay at the Bangor Airport Hilton.) Dumping takes place at a high enough altitude to allow the kerosene to mist and dissipate long before it reaches the ground, and no, engine exhaust will not set the discharge aflame.

Not all airliners have this capability—just the bigger ones. The 747, the 777, the A340, and the A330 all can dump fuel. A 737, an A320, or an RJ cannot. These smaller jets must circle or, if need be, land overweight. For some, landing and takeoff limits are the same, in which case it doesn't matter.

Know that nine times out of ten, a plane dumping fuel and executing a precautionary return is not in the throes of an actual emergency. The term “emergency landing” is used generically by passengers and the press. Crews must formally declare an emergency to air traffic control and will do so only in situations when time is critical, there's the possibility of damage or injury, or aircraft status is uncertain. The great majority of precautionary landings, even those when fire engines are lined up along the runway, are just that: precautionary.

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.

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.

Photos of what are taken to be duct-tape repairs are periodically passed around through email and posted on blogs, putting people in a frenzy. It always looks worse than it is. The material isn't duct tape at all, but a heavy-duty aluminum bonding tape known as “speed tape,” used to patch superficial, noncritical components until more substantive repairs can be made later on. You'll see it on flap fairings, winglets, gear doors, and the like. Speed tape costs hundreds of dollars per roll and is able to expand and contract through a wide range of temperatures.

This is a great illustration of what I like to call PEF, or Passenger Embellishment Factor, the phenomenon that accompanies so many accounts of dodgy takeoffs, supposed near misses, and so on. Earmark this page for the next time you're subject to a water cooler tale like this one.

Not to belittle your powers of observation, but distances aloft can be hard to judge, and passengers have an
extremely
common habit of underestimating separation with other aircraft. During cruise, planes will always be a minimum of 1,000 feet apart vertically or three miles horizontally. Flights on the transoceanic track systems (
see oceanic routings
) frequently encounter one another more or less as you describe. It can be startling—a 747 is a big ship, and even from a thousand feet away it looks awfully close—but it's perfectly safe and routine. The rules are different for takeoffs and landings. With simultaneous approaches to parallel runways, for instance, planes can be at the same altitude and a mile or less apart—though they remain under the very close watch of ATC and must also maintain visual contact with one another.

As for seeing people through the windows, this is classic PEF and something that I hear all the time. Even when an airplane is parked at the gate, a few feet away and stationary, it can be difficult to see anyone inside. Aloft, you have never been remotely close enough to another plane to see its occupants, trust me.

People have a habit of embellishing even the basic sensations of flight. They can't always help it—nervous flyers especially—but the altitudes, speeds, and angles are perceived to be far more severe than they really are. During turbulence, people sense that an airplane is dropping hundreds of feet at a time, when in reality the displacement is seldom more than ten or twenty feet—barely a twitch on the altimeter (
see turbulence
). It's similar with angles of bank and climb. A typical turn is made at around 15 degrees, and a steep one might be 25. The sharpest climb is about 20 degrees nose-up, and even a rapid descent is no more severe than 5 or 6 degrees nose-down.

I can see your letters: you will tell me that I'm lying, and how the plane you were on was
definitely
climbing at 45 degrees, and
definitely
banking at 60, and how you
definitely
saw people through the windows. And you're definitely wrong. Sorry to sound so bossy, and I wish that I could take you into a cockpit and demonstrate. I'd show you what a 45-degree climb actually looks like, turning you green in the face. In a 60-degree turn, the G forces would be so strong that you'd hardly be able to lift your legs off the floor.

Bird strikes are common, and the damage tends to be minor or nonexistent—unless you're looking at it from the bird's point of view. As you'd expect, aircraft components are built to tolerate such impacts. You can see web videos of bird carcasses being fired from a sort of chicken-cannon to test the resistance of windshields, intakes, and so forth. I've personally experienced several strikes, and the result was, at worst, a minor dent or crease.

I should hardly have to mention, however, that strikes are occasionally dangerous. This is especially true when engines are involved, as we saw in 2009 when US Airways flight 1549 glided into the Hudson River after colliding with a flock of Canada geese. Modern turbofans are resilient, but they don't take kindly to the ingestion of foreign objects, particularly those slamming into their rotating blades at high speeds. Birds don't clog an engine but can bend or fracture the internal blades, causing power loss.

The heavier the bird, the greater the potential for harm. Flying at 250 knots—in the United States, that's the maximum allowable speed below 10,000 feet, where most birds are found—hitting an average-sized goose will subject a plane to an impact force of over 50,000 pounds. Even small birds pose a threat if struck en masse. In 1960, an Eastern Airlines turboprop went down in Boston after an encounter with a flock of starlings.

Your next question, then, is why aren't engines built with protective screens in front? Well, in addition to partially blocking the inflow of air, the screen would need to be large (presumably cone-shaped) and incredibly strong. Should it fail, now you've got a bird and pieces of metal going into the motor. The incidents above notwithstanding, the vast improbability of losing multiple engines to birds renders such a contraption impractical.

Ice or snow on an airplane is potentially very dangerous, especially when adhered to the wings. The devil isn't the added weight, but the way it disrupts the flow of air over and around a wing's carefully sculpted contours, destroying lift. You've also got slick runways to contend with and assorted other challenges.

Ice or snow piles up on a plane parked at the gate the way it piles up on your car. But while a cursory brushing is a safe enough remedy for driving, it doesn't work for flying, when even a quarter-inch layer of frozen material can adversely alter airflow around the wing—highly important during takeoff, when speed is slow and lift margins are thin. To clean it away, planes are sprayed down with a heated mixture of water and glycol alcohol.

While it appears pretty casual to the passenger, the spraying procedure is a regimented, step-by-step process. Different fluid mixtures, varying in temperature and viscosity, are applied depending on conditions, often in combination. A plane might be hit with so-called Type I fluid to get rid of the bulk of accumulation, then further treated with Type IV, a stickier substance that wards off subsequent buildup. Pilots follow a checklist to ensure their plane is correctly configured for spraying. Usually the flaps and slats will be lowered to the takeoff position, with the APU providing power and the main engines shut down. The air-conditioning units will be switched off to keep the cabin free of fumes.

When deicing is complete, the ground crew will tell the pilots which types of fluid were used, as well as the exact time that treatment began. This allows us to keep track of something called a “holdover time.” If the holdover time is exceeded before the plane has a chance to take off, a second round of deicing may be required. The length of the holdover depends on the kind of fluids used, plus the rate and type of any active precipitation (dry snow, wet snow, ice pellets; light, moderate, heavy). We have charts to figure it out.

Deicing fluid isn't especially corrosive, but neither is it the most environmentally friendly stuff in the world. And although it resembles apple cider or an apricot-strawberry puree, I wouldn't drink it; certain types of glycol are poisonous. At upward of $5 a gallon, it is also very expensive. When you add in handling and storage costs, relieving a single jet of winter white can cost several thousand dollars. Another method is to tow aircraft into specially built hangars equipped with powerful, ceiling-mounted heat lamps. In some ways, this is a greener technique, though it uses hideous amounts of electricity.

Snow will not stick to an airplane during flight. Ice, however, is another story. Owing to airflow and aerodynamic forces, it tends to adhere to the thinner, lower profile areas and not to larger expanses. It will build on the forward edges of the wings and tail, around engine inlets, and on various antennae and probes. Left unchecked, it can damage engines, throw propeller assemblies off balance, and rob the wings of precious lift. In a worst-case scenario, it can induce a full-on aerodynamic stall—the point when a wing essentially ceases to fly.

The good news is that all affected surfaces are equipped with devices to keep them clear. On propeller-driven planes, pneumatically inflated “boots” will break ice from the leading edges of the wings and horizontal tail. On jets, hot air from the engine compressors is used instead, bled to the wings, tail, and engine intakes. Windshields, propeller blades, and various probes and sensors are kept warm electrically. These systems use redundant power sources and are separated into independently functioning zones to keep any one failure from affecting the entire plane.

Airframe ice comes in three basic flavors: rime, clear, and mixed. Rime is the common one, appearing as a sort of white fuzz. The rate at which ice accretes is graded from “trace” to “severe.” Severe icing, most commonly encountered when flying through freezing rain, is a killer. It's also quite rare, and it tends to exist in thin bands that are easy to avoid or fly out of. On the whole, inflight icing is considerably more of a threat to smaller noncommercial planes than it is to airliners. Even in the heaviest precipitation, seeing more than a trace amount of rime on a jetliner is uncommon.

An icy runway is a slippery one, needless to say. Airports issue so-called “braking action reports” for each runway—even different portions of a runway—which pilots make careful note of, along with the latest wind and weather reports. Together, this data helps determine whether it's safe to arrive or depart. Because there must always be adequate rollout distance on landing, as well adequate room to stop following an aborted takeoff, operations are prohibited when braking reports fall below a certain value or when snow, ice, or slush exceed certain depths. Takeoff and landing speeds, as well as the power and flap settings to be used, are often different in snowy weather than they are in dry weather. And if you've ever looked closely at a runway, you'll see they are cut laterally by thousands of grooves spaced inches apart. This helps with traction, as do the sophisticated anti-skid systems found on modern planes.

I've made plenty of winter-weather landings. One thing that always surprises me is the way in which fresh snowfall can make a runway difficult to see and align yourself with. In normal conditions the runway sits in stark contrast to the pavement, grass, or whatever else is around it. When it's snowing,
everything
is white. Runways are outfitted with an array of color-coded lighting. Most of the time you pay only cursory attention to these displays. That is, until the moment you break from a low overcast, just a few hundred feet over the ground with a half-mile of visibility, and find yourself confronted with a landscape of undifferentiated whiteness. Those lights and colors are suddenly very helpful.