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Takeoff is the most critical phase of flight because the greatest stress is imposed on the plane. The engines are running at full power. The airframe, including the landing gear and tires, are carrying their largest load. Also, any abnormality must be handled at low altitude.This is why a significant portion of recurrent training—the mandatory simulator checks required of pilots every six months—is spent learning to respond to takeoff emergencies. WHO FLIES THE PLANE? Under normal circumstances, the captain flies one leg of a trip and the co-pilot flies the next. Why do they rotate actual flying responsibilities back and forth? If the captain were to make every takeoff and landing, then the co-pilot would have no experience. Still, the captain, who has ultimate responsibility for the passengers and the plane, has final authority over whether he or the first officer flies the plane. Certain weather conditions, such as low visibility, require that the captain take the controls. LEGAL FOR TAKEOFF Before a plane can take off, three criteria must be satisfied: the pilots must be legal, the plane must be legal, and the airport itself must be legal. Of course, the pilots must have current FAA licenses, including their FAA physical certificate and FCC radio telephone license. They must also be up-to-date on their simulator proficiency and airplane line checks. Without these, they need not show up for work. But what it means for a pilot to be legal has to do with visibility requirements. No matter the co-pilot’s experience, when the visibility is less than 1600 feet, or a quarter mile, the captain must make the takeoff. The plane itself must also be legal. This means all the systems and their backups are functioning normally. The greatest variable in this equation is the airport being legal. Even different runways at the same airport can have different restrictions. Runway takeoff minimums, for example, contain numerous variables. RUNWAYS (AND WEATHER) Runways earn the lowest visibility requirement, currently 600 feet runway visual range (RVR), by having a complete set of painted runway markings clearly depicting such things as the runway’s center line. Runway lighting, which depicts the same things but is easier to see in reduced visibility, must also be available. Runway center-line and edge lighting is color coded: the last 3000 feet are amber, the last 2000 feet are red and white, and the final 1000 feet are all red so that it’s distinct. An RVR system that reads the specific visibility must also be operating. This system reads three zones: the touch down, which is the first one-third; the midfield, which is the middle third; and the roll out, which is the last third. The system must show that all three zones are above the 600-foot minimum. If any part of the runway is not operating correctly, from the center-line lights to one of the RVR meters, the takeoff minimum is raised. On a runway with paint-only markings, the takeoff minimum is one-quarter mile. Although snow, rain, and ice may not reduce visibility below the legal limits, they do create restrictions. All runways are crowned, meaning higher in the center, and grooved, meaning troughs are cut across the width every few inches, to allow rapid water runoff. Still, standing water can accumulate, so a legal limit of one-half inch maximum is mandated. Wet, slushy snow also imposes limits, since it retards acceleration on takeoff. Again there is a one-half inch maximum. Dry, powdery snow is different. As long as there is enough friction between the ground and the wheels to allow for normal acceleration and braking, a maximum of six inches of dry snow is allowed on the runway. Ice on the runway is never permitted. PRE-TAKEOFF BRIEFING Before taking the active runway, the cockpit crew discusses all the routine procedures as well as all the what-ifs they might encounter. Although pilots all go through the same training, if a quick decision has to be made, this pre-departure briefing helps to maximize the crew’s response. TALKING WITH THE CONTROL TOWER As the plane approaches the runway, ground control reconfirms its takeoff slot and instructs the pilot to contact the tower. The tower Air Traffic Controllers are directly responsible for all takeoff and landing clearances, any taxi clearances on or across an active runway, and traffic separation within the airport’s traffic area, a radius of approximately five miles. When a plane is number one in line for takeoff, one of three tower instructions will be transmitted: 1. If a plane is landing on that runway, the tower will say “Hold Short.” 2. If a plane has just landed but has yet to exit the runway, or a prior airplane is taking off but not yet airborne, the clearance will be “Taxi into position and hold.” This allows the plane to taxi onto an active runway but not depart. 3. The tower will say “Cleared for takeoff.” But several criteria must be met before a plane is cleared for takeoff. First, the runway must be completely cleared— which means no planes exiting or taxiing. Second, the preceding departure must be far enough in front that there is no possible chance of catching up to it. Departures behind so-called “heavy” planes, those having a gross weight in excess of 300,000 pounds, require added caution. All aircraft produce mini artificial tornadoes called wake turbulence—or wing-tip vortices—just like a speedboat leaves a disturbance in the water. Departing behind a “heavy” requires spacing of no less than two minutes or five miles. CLEARED FOR TAKEOFF Pilots can employ two different types of takeoff—either a static or a rolling takeoff. In a static takeoff, meaning from a stopped position, it is most common for the brakes to be released, power slowly applied, and the takeoff roll begun. It’s preferred when visibility is reduced or when a runway is not completely bare and dry. Also, if the plane is cleared to taxi into position and then hold, a static takeoff is the only choice. Rolling takeoffs are ordinarily made when the tower clears the plane for takeoff from the Hold Short line. Less power is needed to start the takeoff roll, which reduces the jet blast behind the engines. For this reason, at some airports where the runways are very near highways, rolling takeoffs are mandatory. Rolling takeoffs are also made because the less time each individual plane spends on the runway, the greater the airport’s capacity. But a pilot can request either a static or rolling takeoff, as necessary. LIGHTS While waiting for departure, the crew will turn off the plane’s lights, which are especially noticeable at night from window seats. Since most taxiways face directly toward the approach areas, any arriving planes would find the bright lights a nuisance. When cleared for takeoff, the full complement of lights, including the wing-tip strobe lights, are turned on. HOW DOES AIR TRAFFIC CONTROL SEE THE PLANE? In good weather conditions ATC can see a plane when it’s on the ground or near the airport simply by looking out the window. But to supplement this rather limited technique, every commercial airliner has a transponder and encoding altimeter. The pilot enters a distinct four-digit code into this cockpit instrument, which sends the aircraft’s exact location and altitude—to within 100 feet—to all ground stations within radio range. When the tower controller matches the specific flight with its distinct code, the two are tagged together the entire flight. Any ATC facility with radar, towers, approach and departure control at airports and the various en route centers can see the plane even if it’s not in direct voice communication. All aircraft—large or small, commercial or private—must have transponders when operating near airports with TCA’s (Terminal Control Areas) and when cruising above 12,500 feet. In the event the transponder should malfunction, an independent backup can be turned on. TAKEOFF Power is controlled by the multiple thrust levers— depending on the number of engines—located on the throttle quadrant between the pilots. Pushing the thrust levers forward increases power, pulling them all the way back to the stop decreases power to idle. Big turbofan engines take a few seconds to accelerate from idle, so to ensure that all the engines are developing power at the same rate, the thrust levers are first moved only partway forward. Asymmetric thrust would make initial directional control more difficult. Like a turbo charger in a car, a turbofan engine is slower accelerating from idle to 50 percent power, than from 50 percent to full power. Therefore, care must be taken not to overspeed—over-rev in your car—your engine. Newer planes have Electronic Engine Controls (EEC’s) that can automatically prevent overspeed, but do not yet have the capability of preventing excessive temperatures. Similar to initial taxiing, the sounds generated from the engine will begin with a deep rumble as the fan, compressors, and turbines spin up at slightly different rates, followed by the familiar whine of a stabilized and smoothly running machine. Full power must be set before accelerating through 60 knots. Immediately after applying full power, the engine instruments are thoroughly checked. The pilot not flying will verify that all the engine gauges are within specific parameters. A unique feature of the engine instruments is that all the gauges are designed so at full power all the needles point to the nine o’clock position. After the engines have stabilized during initial power application, the auto throttles are capable of setting the power with computerized precision. However, as a safety against a computer glitch causing the power to be reduced at an inopportune time, when accelerating through 80 knots the autothrottles drop into a “throttle hold,” or manual mode. This allows an increase or decrease in power to be made independent of the computer. Accelerating to liftoff speed, passengers—particularly near the front of the plane—hear and feel a thump-thump- thump. This is the tires going over the center-line lights. The center-line lights are raised slightly above the surface of the runway in order that they can be seen from great horizontal distances. If they were mounted flush, they would only be visible from directly overhead—not very useful for approach and landing. Tracking exactly on the center line, this slight bump every 75 feet can be felt. The lights are built to withstand a direct 300-ton load. Steering slightly left or right of center line will stop this inconsequential thumping. Passengers sometimes express concern to the flight attendants that the overhead interior panels seem to vibrate on takeoff. These panels, constructed of lightweight composite materials, are installed for cosmetic reasons only. Like a drop ceiling in an office, they cover up the plumbing, air-conditioning ducts, and the various wiring that runs the course of the plane. Their removal allows easy access for any required maintenance. The shaking and vibration is normal. Accelerating through 85 knots, the rejected takeoff automatic brakes that were previously armed become active. At this point if the thrust levers are retarded to idle, maximum braking will automatically be initiated. The one- or two- second reaction-time advantage the autobrakes have over manual braking by the pilots can mean a shorter stopping distance of several hundred feet. It also means that any aborted takeoff above 85 knots (98 mph) will be fairly dramatic, because unlike the pilots, the auto-brakes cannot tell how much runway remains. Approaching 100 knots (115 mph), a double-check of the engine instruments will be made, if it hasn’t already been done. Acceleration time can be compared to the predicted standards; zero to 100 knots usually takes between 20 and 30 seconds, depending on the aircraft’s weight. Passing V-1 —approximately 130 knots (150 mph)—the plane is committed to takeoff. At this point all the performance data guarantees acceleration to V-2 (140 knots, 161 mph), engine failure climb speed. At V-R (approximately 135 knots, 155 mph), the calculated velocity of rotation, the nose wheel is rotated skyward at 3 degrees per second. Slower rotations are acceptable, though they use additional runway. Faster rotations are avoided, because of the chance of a tail strike if the nose of the plane is rotated higher than 11 degrees before the main gear flies off the ground. In the unlikely event of a tail strike, the tail is fitted with a compressible tail skid that acts as a shock absorber. Initial climb is accomplished at V-2 plus 10 knots (or 150 knots, 173 mph), to maximize the initial rate of climb. GEAR UP Once airborne, the thump-thump of the runway is re placed by the smooth sense of flight. The airplane is finally in the environment for which it was built. Immediately after liftoff, passengers can sense the extension of the landing gear shock-absorbing struts. The landing gear is extremely heavy, and once the weight of the plane is removed, the struts are designed to fully extend. On bogie gear—landing gear with more than two tires—the entire mechanism tilts as well as extends. In this fully extended (and tilted) position, the gear fits into the wheel wells. The landing gear is a high-drag item and serves no purpose in flight. With a positive rate of climb indicated on the vertical speed instrument, and then called by the pilot not flying, the command for gear up is made. The gear handle is raised from down to the up position. The first sound heard by the passengers is the gear doors opening. With the doors opened, the gear is hydraulically raised into its wheel wells. During retraction, the main gear brakes are automatically applied to stop the tire rotation. Once fully retracted, the gear doors close again. There is one unique difference about the nose gear: Since that gear has no brakes, the tire rotation is stopped with a rubber snubber mounted in the nose-wheel well. This snubbing sound can be quite loud, but lasts only a moment or two. ABORTED TAKEOFFS According to a study completed in 1987, takeoff is aborted in about one in every 300,000 flights. This, however, does not give a complete picture. Some aborts are at speeds well below a critical speed, and most aborts are for reasons other than an engine problem. Those of most concern are at or near the critical V-1 accelerate-stop speed. High-speed aborts are difficult. If a warning light comes on, you have to assume the worst and abort if your speed is below V-1. There is little or no time to assess the situation. Consequently, aborts have been made for nuisance cautions and alerts. On newer aircraft this problem is being rectified. Unlike older planes, when the newer ships accelerate through 80 knots, the malfunction of a nonessential item will not be indicated by the usual caution lights, horns, or buzzers until 20 seconds or the first 400 feet of flight. If, for example, a fuel pump were to fail at or near V-1, there’s another fuel pump to do the job, making this a noncritical item during takeoff. Despite the failure, there is no need to abort takeoff. Instead of a high-speed abort, the safer procedure is to circle back and land. On these new high-technology aircraft, the computers have prioritized the warnings, reducing the need to analyze before acting. ENGINE FAILURE DURING TAKEOFF The most critical time for an engine failure is exactly at V-1, a moment before takeoff. Pilots know it, airline training departments train for it, airplane and engine manufacturers design for it, and performance data is figured with it. A worst-case scenario is always assumed. If an engine failed, the plane would circle once around the traffic pattern and return for landing. If the airport were closed, an alternate landing airport would have already been decided. Again, the airplane is able to fly just fine with an engine shutdown. It was designed to do so. But again, as a precaution, the flight attendants will brief everyone about the applicable emergency procedures. Suppose an engine caught fire? As a safety measure, aircraft engines (both wing and tail) are mounted on struts to isolate them from the main body of the plane. Fires can be extinguished, first, by closing multiple fuel valves with the pull of one fire handle and removing all the fuel going to the affected engine. Also, the engine can be starved of oxygen by discharging one or both fire extinguishers directly into the engine. This is done by rotating that same fire handle left or right. After the fire is out, the same engine failure procedures are followed. Hard as it is to imagine, birds can cause an engine shutdown. Not one, two, or three birds, but an entire flock. Airports, with their vast empty spaces, serve as convenient stopover points for migrating birds. The loud noise of the jet engines usually frighten them away before takeoff. However, at some airports remote mini-cannons firing blanks are needed to clear the takeoff zone. Birds in flight can sense the plane approaching, and make every effort to fly clear, but some occasionally do hit the airplane and bounce clear. The critical problem is when birds are ingested into the engines. Several birds at once, or many birds over a short period of time, will be chopped up quite completely and exhausted out the back of the engine with no damage to the aircraft. However, a flock of birds going through the engine at once can overload the engine compressor, nicking one of the blades, causing an out-of. balance vibration. A precautionary engine shutdown and return to the departure airport may be necessary. INITIAL CLIMB For passenger comfort, the initial angle of climb is limited to 18 to 20 degrees nose up, even if the airspeed accelerates beyond V-2 plus 10 knots. This rapid rate of climb is continued to 1000 feet AGL (above ground level). At 1000 feet AGL, the nose of the aircraft is lowered to approximately 10 to 12 degrees nose up, so the plane can be accelerated. At this point the power is reduced from takeoff to a climb power setting and can be heard. The amount of power reduction is dependent on the specific noise abatement procedure. With airspeed increasing through 160 to 170 knots (again depending on weight), flap retraction is started. The pilot flying calls for the appropriate flap setting, and the other pilot actually moves the flap level to provide an airspeed double-check. Flaps are raised from their takeoff position of 15 degrees to 5 degrees. Looking out the window, you can see the flaps retract, and you can hear the hydraulic motors operating in the wheel wells. As the airspeed increases further to the 180 to 190 knot range, the flaps are raised further, to a 1 or 2 degree position—essentially up—leaving only the leading edge slats deployed. Reaching the 210 to 220 knot range, the high lift devices—flaps and slats—are completely raised to the zero or up position. With the flaps and slats fully retracted, the airplane is said to be in the “clean configuration,” and any induced vibration from the additional drag will cease. Complete cleanup is accomplished during the first 3000 feet of climb—the first couple of minutes of flight. At 3000 feet above the ground, additional climb power may be added to increase the acceleration rate without violating the airport good neighbor policies. Acceleration is completed to 250 knots (288 mph), the maximum allowable ATC speed until climbing through 10,000 feet. Just like accelerating onto an interstate, a rapid acceleration allows more room for the planes following, increasing airport capacity. Sometimes on the initial climb to 3000 feet, the air is a bit choppy even though the wind is calm. Why? Just like swirling air currents created by tall buildings, convective air currents can be present. The large, open concrete expanse of an airport surrounded by industrial plants or other buildings can cause uneven heating of the earth’s surface, and mild chop. Air currents caused by the friction between the earth and the atmosphere as the earth rotates can also cause low-level convective air. In any case, with initial rates of climb anywhere from 1500 to up to 4000 feet per minute (with a light load), this low-level chop, if still present, is very short-lived. At 10,000 feet the speed limit is lifted, which means the nose will again be lowered to approximately 5 degrees nose up and the aircraft is allowed to accelerate to its best climb speed of around 300 to 320 knots. With the body angle of the plane reduced, and no choppy air forecast, the flight attendants will begin cabin service and the seat-belt light will be turned off. 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