The Flight: Landing and Taxi In: Airplane and Airline FAQ

STANDARD CALLOUTS

The surest way to make a good landing is to make a good approach. Having everything stabilized and “in the slot” while descending on a final approach is a must. Gear down, flaps down, on course, on speed, tower clearance to land, before landing checklist complete. At 1000 feet above the ground, flying at 140 knots (161 mph), you are a little over a minute from touchdown.

Passengers can tell they are at 1000 feet above landing by the addition of power. If you have been flying with the engines at or near idle, they need to be “spooled up.” Turbofan engines are slow to accelerate. To be sure that instantaneous power is available, the thrust levers are increased from the flight idle position. Frequent small power adjustments can be heard to maintain the exact predetermined approach “bug” speed. Too slow is unacceptable. Too fast and you will use additional runway. If any deviations are observed, the pilot not flying will call them out.

In low visibility the transition from flying solely by instruments to making a visual landing is difficult. On an instrument approach it is the responsibility of one pilot to stay solely on the gauges. The ILS instruments are so sensitive that a descent below the glide slope will first be noticed electronically. Two hundred feet above the lowest altitude you can descend for the approach, the pilot not flying calls out, “Two hundred above, no flags”—meaning no malfunctions. Next he calls out, “One hundred above, no flags.” “Decision height,” is announced, and the pilot flying states either “Runway in sight” or “Go-around.”

DECISION HEIGHT—MINIMUM DESCENT ALTITUDE

At the decision height (DH) for an ILS approach, or the minimum descent altitude (MDA) for an approach without an electronic glide slope, the decision has to be made whether to descend to the runway or go-around. The criteria is simple. Do you see the runway? Are you in position to land? Yes to both, and you can continue lower.

At this point you are cleared to land, but not committed to do so. Cleared to land means you temporarily own the runway. Whether or not you use it is ultimately up to the pilots. If you were slightly high, and concerned whether you would land in the touchdown zone, the safest alternative would be to go-around. The control tower can also rescind a landing clearance at any time. If the plane ahead was slow to exit the runway, the control tower would be required to issue a go-around. Even though the plane has flown below the decision height, it’s not yet committed to land.

Surprisingly, once touched down on the runway, the plane is still not committed to land. Any time before the pilot deploys the spoilers and selects reverse thrust, a go-around is possible. In fact there is a training maneuver called a “touch and go,” where you purposely touch down, roll for a short distance down the runway, and take off once again.

GO-AROUND / MISSED APPROACH

The terms go-around and missed approach are synonymous. There are many misconceptions about a go-around. Some feel it is an emergency procedure. It is not. Others think the pilots must have made an error and need another chance. No again.

The most common reason for a go-around is that the plane that proceeded you to the runway was slow in clearing. Since two aircraft cannot be on the runway at the same time, your landing clearance is withdrawn. If two aircraft begin getting closer than is normal on the approach, ATC will first ask the second aircraft to slow to his minimum speed earlier than normal. This should increase the separation. If not, ATC will alert you to the possibility of a go-around, but still let you continue. ATC is aware that low altitude go-arounds, though rare, are not dangerous. Go-arounds are time consuming for the passengers and expensive for the airline. Once around the pattern can cost upward of $500. Letting you continue in the expectation the first airplane will make the early exit can save time and expense without sacrificing safety. Of course, if the first plane is not able to make the first turnoff, then a go-around is mandatory.

Whether begun at 50 or 500 feet, the procedure is exactly the same. In fact, it takes less power to make a go-around than to make the initial takeoff. You are already at flying speed. The only requirement is to stop the descent and begin a climb. The descent rate is only about 700 feet a minute, much less than the 2000 to 3000 feet a minute at altitude. The climb rate will be better than the rate at takeoff because the plane weighs less. Think of a go-around as an extra takeoff.

An additional reason for a go-around—besides not enough visibility, an unstable approach below 1000 feet, or someone still on the runway—might be an unprepared cabin. Twenty minutes from touchdown the flight attend ants are signaled by the seat-belt light to discontinue cabin service. If all the galley equipment is not stowed and passengers not buckled in, the regulations require a go around. Go-arounds have been made because passengers refuse to come out of the bathrooms and return to their seats. Also, a problem on short final makes a missed approach likely. Short final is no time to be troubleshooting. Let’s say a landing gear unsafe light is flickering, or both bulbs have simultaneously burned out. There’s no risk in the air. So a go-around, a simple maneuver, is initiated, and the problem investigated where the plane is in its element.

A plane is handed off from the approach control to the tower control frequency about five to seven miles from touchdown. If in that two- to three-minute time frame the tower fails to issue a landing clearance, no matter how clear the runway looks, a go-around is also mandatory. In the remote case of a radio failure, the control tower can issue a landing clearance with color-coded light signals. Steady green and you are cleared to land. Fortunately, this good idea rarely has to be used.

THE LANDING

Large white rectangular boxes are painted on the runway on both the right and left sides. Located 1000 feet from the threshold, these mark the touchdown aim point. If you are flying an electronic glide slope, this is also the point where it intercepts the runway. The pilots sit in a cockpit up to two-thirds of a football field in front of the tail. They aim for the runway from their vantage point. If from their perspective they touch down exactly abeam the 1000-foot marker, the main landing gear will be safely on the runway. Aiming for the very beginning of the runway would not allow any margin of safety for landing short. From your window seat you can tell that the plane passes over the beginning of the runway while still 35 to 50 feet in the air. It’s not high. This is by design.

Just after passing the threshold, the “flare” begins. The flare is the round-out portion of the landing where the descent rate is decreased from 700 feet per minute to very nearly zero at touchdown. That’s the goal, at least. As you flare, the nose is raised farther than its nose-up pitch on the approach. Increasing the pitch increases the lift and slows the descent. At the same time, the power is reduced to idle. The airspeed over the “numbers”—the runway identification numbers painted just past the threshold—was a mini mum of 30 percent over stall speed. In the flare, extra power this close to the runway translates to additional runway needed. There are times when you will hear the power increase fairly rapidly just prior to touchdown, and then pulled to idle. There are two ways to stop your descent rate. The first is raising the nose. The second is an increase in power. Many times they are used in conjunction. Airplanes are built to withstand a maximum landing rate of 600 feet per minute. At first that doesn’t sound like a lot, but it is nearly equivalent to a static drop of 10 feet. Since the plane is moving forward, its downward force is never completely vertical, leaving a huge margin of safety for the occasional “firm” arrival.

The last few feet before touchdown requires excellent depth perception. At the controls of a 767, the crew is nearly 36 feet in the air when the main gear touches down. Experience helps learn the touchdown “picture.” Just like parallel parking your car, the second time is easier. To help the pilots learn the correct perception, the two radio altimeters can be used for guidance. The new ones read to the nearest two feet, but a slightly mis-calibrated radio altimeter would make a poor excuse for a hard landing. Landings during the day are easier. At night, and during restricted visibility, you draw more from experience.

TOUCHDOWN

Touchdown occurs first on the main gear. The last several inches makes all the difference between a “grease job” and an “arrival.” Given a runway of infinite length, a grease job could be accomplished nearly every time. The power would be reduced very slowly, the pitch adjusted in minute increments as you inched your way down step by step.

But such infinite runways do not exist. Since runway length is a consideration, you try for the perfect touch down, but you don’t waste excess runway doing so. Floating beyond the touchdown zone is not calculated in the landing distance figures. Passengers do not always appreciate a firm arrival, but there are times that it is the correct way to land. If a runway is wet and/or slippery, the quicker you land, the faster you can begin to stop. Gusty wind conditions some times necessitate “putting it on.” Foggy conditions, where the other end of the runway is not visible, lends itself to touching down with a minimum of fuss. Or if the plane behind you is a little too close, ATC might request “mini mum time on the runway” to prevent his go-around.

After the main gear touches, the spoilers are deployed. Those over wing panels do what their name implies—spoil the lift. The approach speed was 30 percent over stall, so even after touchdown there is still enough speed to fly. In fact, some planes do. Aircraft with a manual spoiler extension can skip on landing. The touchdown is smooth, but this extra available lift can cause a slight bounce back into the air. Automatic spoilers remove this possibility. On main gear touchdown, the panels are automatically raised, dumping all this excess lift. The downside is that the panels can dump the lift so quickly, a smooth touchdown can be made firm as the landing gear struts are rapidly com pressed.

After main gear touchdown, the nose gear is lowered to the runway. A smooth landing of the nose wheel is desired also, but similar to the main gear, there are times that this is not possible.

CROSSWIND LANDINGS

It is desirable to land an aircraft as directly into a headwind as possible. Touchdown with an airspeed of 130 knots into a 10 knot headwind means the ground speed is 120 knots. This 10 knot reduction in ground speed translates into a shorter landing roll after landing. Landing under opposite conditions would mean a 10 knot tailwind, increasing the ground speed and increasing the landing distance required. To ensure that your landing performance figures are accurate, a maximum 10 knot tailwind limit is imposed.

Most of the times a tailwind is not a factor. A tailwind landing one way is a headwind landing the other way. Tailwinds become a factor at noise-sensitive airports. After midnight at Los Angeles International Airport, all arrivals approach over the Pacific and land east. Normally, the prevailing winds are from the ocean, so a tailwind can be expected when the winds are not calm. If the tailwind limit is exceeded, the “airport must be turned around.” It’s not the most desirable situation for the airport’s neighbors, but it’s a legal responsibility.

Most of the time the wind is not straight down the runway, so a crosswind component figure is calculated. Actual winds are given on the ATIS weather tape, and by the control tower. Taking the actual wind, we can deter mine how much of the wind is acting as headwind and how much as a 90 degree right or left crosswind. If a wind was reported 45 degrees off our right at 20 knots, the headwind would be half, 10 knots, and the direct crosswind component the same 10 knots. (The math is only this simple with a zero, 45, and 90 degree wind).

Landing in a crosswind is different than landing into a headwind. All commercial aircraft must be able to land with a crosswind component of at least 25 knots. Most are certified with 29 to 39 knot, direct 90 degree crosswind limits. During the approach, the plane will be level, but the nose will not be directly aimed at the runway. Aiming the nose upstream, toward the crosswind, will maintain a path over the ground straight to the runway. This is no different than boating with a water current from the side. This crabbing—from the ground it looks like you’re flying sideways—can be adjusted to take the plane precisely to the runway threshold, just as in a headwind.

However, the touchdown technique changes because of a crosswind. If this crabbing technique were carried out all the way to the runway, the aircraft would land directly on the runway center but cocked off to the side. This would put a great deal of sideways stress on the landing gear. Instead, just before touchdown, the plane is banked into the wind and the nose held straight with the rudder. What’s uniquely different is that because the airplane is in a slight bank at touchdown, the upwind landing gear will land first and be closely followed by the other main gear and then the nose wheel. This is a normal crosswind landing. Because one main gear touches down first, the automatic spoiler deployment may cause the other main gear to be firmly planted on the ground. Again, perfectly smooth does not mean perfectly safe.

AUTOLAND/AUTOTHROTTLE

When correctly programmed, the high technology air craft are capable of landing themselves. When the visibility gets below 1200 feet RVR—about a quarter of a mile—use of this autoland and autothrottle capability is required. On an autoland approach, three independent autopilots are working side by side in a fail operational mode. All three autopilots “talk” with each other and compare data. If the computers detect a malfunction with one autopilot, the other two can do the job. Loss of two autopilots is said to make the system fail-passive, and autoland capability is lost.

The autopilots fly the ILS localizer and glide slope. Descending through 1500 feet, a flare and roll-out mode is armed. An autopilot status display in front of both pilots clearly annunciates the condition of the complete autopilot system. Any flags, and a go-around will be made.

Because the legal visibility required is soon to be as low as 300 feet, the pilots may not see the runway before touchdown. An alert height at 50 feet above the ground serves as a “check all systems” altitude. Descending through 45 to 25 feet, the autopilots begin a gradual flare, and begin to retard the power just as if the pilots were flying. Up until five feet above the ground, when the roll-out mode is captured, a go-around can still be made. Of course, a go-around made at that altitude may involve runway contact, but the gear is down so runway contact is not a problem.

After landing, the auto roll-out feature continues to track the localizer—remember, the antenna is located off the far end of the runway—until you come to a complete stop on the runway. Most autoland aircraft have autobrakes also, which are set by the pilots for a specific deceleration rate. After coming to a complete stop, the autopilot is disconnected and the airplane taxies clear of the runway. Autolands have their greatest value when it is foggy and the visibility extremely limited. However, the autoland capability can be used in good weather, for two important reasons. First, by regulation, the system must be tested at regular intervals or it loses its autoland certification. Second, even though the pilots practice autoland approaches and very low altitude go-arounds during recurrent training, real airplane practice increases confidence in the system for when it’s really needed. Except for an announcement, passengers have no way of knowing if the plane was manually or automatically landed.

STOPPING THE AIRCRAFT

The basic way to stop an airplane is with the brakes. Multiple disc brakes are located on each main gear tire. Earlier models are made of steel, the latest design is a carbon brake. Widebody aircraft are capable of absorbing well over 60 million foot-pounds of energy, the equivalent stopping power of 6000 family cars. The brake pedals are actually the upper portion of the rudder pedals. The pedal pressure required is only slightly more than your automobile. Light to moderate braking is normally all that is required. Heavy or maximum braking is only used in emergencies and is capable of stopping the airplane in less than 2500 feet. The antiskid system allows the pilot to apply brake pressure, while the system itself applies and releases the brakes as necessary to prevent a skid on slippery runways. Newer aircraft have the traditional manual brakes and an automatic braking system that allows the pilots to preselect a certain after-landing deceleration rate. The rate can be changed during the roll-out.

Reverse engine thrust is also used to slow the aircraft after landing. Just after touchdown, a second set of thrust levers attached to the principal throttles are used to select reverse thrust. A common misconception about reverse thrust is that the engines turn in the opposite direction during its use. Actually, during reverse thrust, devices known as “buckets,” “clamshells,” or “cascades,” are un locked and moved aft behind the engines to redirect the exhaust air forward. This redirection of the air forward causes the deceleration. Reverse thrust is noisy because, just like on takeoff, the engines’ power is being increased.

Slowing between 80 to 60 knots, the engines will be taken out of reverse because of the tendency they have to blow debris forward, putting it in front of the engine, where it could be ingested. Of course, reverse thrust is available to make a full stop if needed.

HIGH-SPEED TURNOFFS

In an effort to maximize the number of takeoffs and landings an airport can handle per hour, high speed turnoffs are designed as exit points from the runway. Similar to a straight off-ramp on the expressway, an airplane can turn off the runway onto a high-speed taxiway still traveling in excess of 60 knots. Runways with only 90 degree right or left turn exits require the plane to be slowed to 10 to 15 knots before the turn can be made. Spacing between landing aircraft would have to be increased because the additional time each airplane would “own” the runway.

GROUND CONTROL/RAMP CONTROL

After taxiing clear of the active runway, the ground control is contacted. Similar to taxi out, he is in charge of coordinating all the aircraft movement on the ground. At times it can seem like a long wait before receiving clearance to taxi across another active runway, or to the terminal building, but it is the ground controller’s job to have the big picture and keep the flow going. There is nothing the pilot can do except wait if the taxiway leading to your gate is blocked.

Upon entering the ramp area at the larger airports, jurisdiction for ground control is transferred to the ramp controller. He is the one who knows exactly what gate each plane will be using, and if it’s open. If it is occupied but the delay is a matter of minutes, the plane will probably just wait for it. If the delay is more than a few minutes, another gate will be assigned. If none of your airline’s gates are open, a trip to the “penalty box” may be the order of the day. The penalty box is a specific location at an airport where you can sit and wait, without blocking any taxiways needed for the other inbound and outbound traffic.

AIRCRAFT SHUTDOWN/MAINTENANCE LOG

Parked at the gate, the engines are shut down, the seat-belt sign turned off, and a shutdown checklist completed Any maintenance items are noted in the aircraft log book. As the pilots gather their belongings and close up their flight kits, a mechanic will call on the interphone and ask, “How’s the aircraft?”

When this happens, the next flight has already begun.

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