PREPARING FOR FLIGHT: THE PREFLIGHT INSPECTION
When you board an airliner, you've probably glanced into the cockpit and noticed the pilots intently engaged in some activity. If you've wondered what exactly they're doing up there, we'll demystify the process by highlighting some of these tasks as part of our series on flying.
The preflight inspection consists of two major parts: the internal preflight and the external walkaround. While both are vitally important parts of the pilots' preparation, we'll concentrate on the internal portion for this post. Prior to pushback, airline crews must complete several steps to ensure the aircraft is safe and legal for the upcoming flight.
Aircraft/Maintenance & Flight Logs
After reading through the Flight Release (see previous post), pilots will refer to the Aircraft Log (sometimes referred to as the Maintenance Log) and the Flight Log. In the Aircraft Log, the crew is checking to ensure that all required inspections are up-to-date and properly documented. Additionally, they'll verify that any inoperative equipment complies with the Minimum Equipment List (MEL) and is properly placarded. If everything appears satisfactory, the captain will sign the Aircraft Log to accept the aircraft. If anything requires attention, (s)he'll coordinate with the airline's maintenance department to address the issue(s).
The Flight Log maintains a record of the aircraft's utilization. In this document, the flight crewmembers record their names & positions, as well as the duration of all legs they fly. This log also keeps track of aircraft & engine cycles (number of engine starts and number of landings). On many modern aircraft, some of this information might be entered and stored electronically. As with the Aircraft Log, the captain will sign the Flight Log when accepting the aircraft.
Panel Scans and Checklists
If you've noticed pilots actively pushing buttons, flipping switches, and moving levers as you've boarded an airplane, you've seen them running their panel scans and checklists. Before each leg, both pilots complete a checklist to verify the position and operation of the plane's systems. Each pilot has his own "cockpit flow", a type of memorized checking procedure, he performs to review the systems he's responsible for. For the first flight of the day and/or each crew's first leg in a particular aircraft, the panel scans are especially thorough. For subsequent legs, certain items may be abbreviated.
When these scans/flows are complete, the crew will refer to a checklist to verify they've covered all necessary items. Any faulty equipment will be rechecked for proper operation. If maintenance is required, the crew will notify company mechanics. Occasionally, the flight will be delayed or a new plane will be assigned. For minor issues, it's often possible to MEL the item and continue the flight.
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Weather and Clearance
Shortly before pushback, the crew will obtain the departure airport's latest weather observation. This info may be manually recorded or generated automatically, depending on the airport's weather reporting system. Pilots use this data to supplement/update the weather information in the Flight Release and to verify the legality & performance parameters of the upcoming takeoff. When they contact Air Traffic Control (ATC) for taxi instructions, they'll let the controller know they have the latest weather info by stating the phonetic identification (Alpha, Bravo, etc.) of the most recent broadcast.
After obtaining the latest weather report, crews will contact ATC to receive their clearance. The clearance is a game plan for the flight leg. It includes the initial altitude to climb to after takeoff, the subsequent altitude to expect, the route of flight/heading to fly, the radio frequency to use after takeoff, the transponder identification code, and any other pertinent information. The clearance is obtained before pushback to allow the crew to set up their radios and navigational equipment prior to departure. Doing so minimizes workload during taxi and takeoff, which helps enhance safety.
As you can see, airline pilots have a significant workload to prepare their aircraft for each flight. In the next sections, we'll examine additional crew responsibilities and how each contributes to the safety and comfort of the flight.
PREPARING TO LAUNCH: THE FLIGHT RELEASE
In this section, we'll begin looking at the duties and responsibilities commercial airline crews undertake prior to beginning each flight. As you've probably guessed, airline personnel are responsible for numerous tasks before a given flight can actually leave the gate. One of the first steps airline pilots take is to look over the flight's paperwork. The main document airline crews consider is known as the Flight Release.
The Flight Release, also known as the Dispatch Release or simply, The Release, is the master plan or blueprint for the entire flight leg. This document is prepared by the airline's dispatch department and transmitted to the crew at their departure airport. The release contains vital information on the route, weather, fuel requirements, maintenance/equipment, and any other information pertinent to the flight. The Pilot in Command (the Captain) must determine if, based on the info in the release, the proposed flight can be completed both legally and safely. If everything appears satisfactory, the captain signs both copies of the release and leaves the station copy with gate personnel at the departure airport. The crew retains the other copy for use during the flight.
Flight Plan
A major part of the release is the flight plan section. This portion outlines the proposed route of flight, cruise altitude, alternate airport(s) (if necessary/requested), weather reports & forecasts, temporary flight restrictions (if applicable), pertinent Notices to Airmen (NOTAMs), and any other relevant data. From this information, the crew is alerted to possible adverse weather, probable air traffic control (ATC) routings, estimated trip duration, and other reasonably foreseeable information. Though helpful for planning, routing and altitude are ALWAYS subject to change, particularly in busy airspace and during bad weather. In such instances, the crew can expect to receive ATC instructions, while they may also request preferred routing/altitudes.
Fuel Requirements
The fuel section is an extremely important part of the release. This section lets the crew know how much fuel they need in order to legally depart. This specified minimum includes fuel for engine start, taxi, takeoff/climb, cruise, descent, landing, and taxi to the gate. If alternate airports are required, the necessary fuel to fly those routes is included. In addition, all flights are required to carry additional fuel (usually at least 45 minutes' worth) as a cushion for possible delays. At times, flights may choose to depart with more fuel than is legally required. However, such practices aren't common, as airlines prefer the increased performance & payload capacity afforded by carrying only the necessary fuel.
If the captain notes that the aircraft is under-fueled, (s)he must request & receive enough additional fuel to arrive at the legal minimum. In addition, if the pilots determine that (despite having the legally required amount) they would prefer extra fuel, they will coordinate with dispatch and ground operations to acquire the amount deemed necessary. In all instances, the captain has the final authority for the flight's operation.
Equipment (Inoperative/Restrictions on Use/ MELs)
Due to the vast amount of equipment carried aboard commercial aircraft, it's extremely common to have certain items inoperative on any given flight. For such instances, the airline has a Federal Aviation Administration (FAA) approved list, called a Minimum Equipment List (MEL), which specifies items that may be inoperative under certain conditions. Any inoperative equipment will be listed on the flight release. The pilots must then refer to the aircraft's MEL, determine possible effects of the inoperative equipment, establish how long the equipment has been inoperative, note how long the equipment may legally remain inoperative, and verify that any necessary placards/maintenance forms have been properly completed. If any inoperative equipment threatens the safety/legality of the flight, the crew must request maintenance be performed or a new aircraft be provided before beginning the flight. In some instances, the flight will be delayed or canceled while maintenance is performed.
Airline pilots are responsible for overseeing every aspect of the flights they operate. The flight release is the main document that facilitates coordination of all requisite tasks. Through the release, the pilots can assess the demands of the upcoming flight and take all necessary measures to ensure the safety of their passengers.
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PREPARING TO LAUNCH: PREFLIGHT INSPECTION, Part 2
Previously, we highlighted many of the cockpit tasks airline pilots perform prior to each departure. Now let's head outside the airplane to examine the external aircraft walkaround. This preflight procedure is equally important to all pre-takeoff cockpit checks and is a mandatory part of each flight leg. Through the walkaround, pilots are able to further enhance the safety and comfort of their passengers.
Why the Walkaround?
Throughout the aviation industry, safety is the paramount concern. Much of the airline industry's stellar safety record is achieved through minimizing/eliminating foreseeable risks. The external aircraft preflight is a highly effective method of risk minimization. Unlike with ground-bound modes of transport, aviators can't just pull over to the side of the road in the event a mechanical issue arises. For this reason, a detailed examination of the aircraft's structure and systems is necessary to reduce the chances of an in-flight malfunction.
Tires and Landing Gear
Though used for only a fraction of each flight, the landing gear system is a vitally important safety component. Think about it: airliners are multi-ton monoliths larger than most houses. Additionally, even at their relatively slow approach speeds, they're still travelling faster than anyone outside of the NASCAR circuit ever drives. The stress of several landings a day means the landing gear and tires have to be ridiculously tough to handle those weights and speeds. A malfunction here could make for a very memorable landing. On the walkaround, pilots observe such factors as the tread, inflation, and wear of the tires. They'll also examine gear struts, hydraulic lines, brake components, nuts/bolts/fasteners, and anything else noteworthy for their model. "Anything" appearing out of the ordinary will be addressed before the crew will consider departure.
Engines
As you've probably guessed, the powerplant is the heart of the plane. Without fully functioning engines, a state-of-the-art airliner becomes a very expensive glider. To avoid this undesirable possibility; pilots look for leaks, signs of scorching, evidence of foreign object damage (FOD), worn/overstressed components, and anything else that appears irregular. In some cases, maintenance personnel assist with the inspection, due in part to the engines' often-unreachable height. These external inspections are then cross-referenced with cockpit indications to ensure full engine functionality.
In case you're wondering; all commercial aircraft are rigorously tested and certified capable of taking off, flying, and landing with an inoperable engine. Should an unlikely engine failure occur, the other engine(s) are capable of sustaining flight.
Lights
Despite their massive size, at times airliners can be difficult to see; especially under low visibility conditions and at night. In these instances, external lights go a long way towards helping the aircraft show up. Navigation lights and anti-collision lights are among the most common lights used to make the aircraft stand out. On the walkaround, pilots check to ensure these required lights are operational. Additionally, at night and during low visibility conditions, external lights greatly assist the pilots in seeing the airport environment.
Landing lights and taxi lights are the most common lights that aid in seeing outside the aircraft. For winter weather, some planes have ice lights, which assist the crew in detecting ice accumulation on the wings. Pilots verify proper operation of these external lights when conducting the exterior preflight.
Airframe
Throughout the walkaround, the pilots inspect the various sections of the airframe. From nose to tail, they look at the fuselage, wings, and empennage for any indication of damage or defects. Depending on the airplane model, other items that might be scrutinized include: flaps, spoilers, ailerons, static wicks, static ports, pitot tubes, antennas, radar pods, pneumatic deice boots, and countless other model-specific parts. Any components appearing suspect are further evaluated to ensure safe operation.
The demanding environment in which airliners operate requires all systems to perform flawlessly. An external preflight inspection helps pilots detect possible deficiencies and minimize the chance of malfunctions aloft. Through their preflight walkarounds, pilots are able to reduce risk and enhance the safety of their passengers.
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PREPARING TO LAUNCH: ROLES OF SUPPORT CREWS
In the previous sections, we discussed the internal and external preflight inspections airline pilots conduct prior to departure. In addition to those important tasks, pilots must coordinate with a variety of support crews to ensure the aircraft is ready for pushback. While these support teams are largely capable of completing their respective tasks independently, the captain is ultimately responsible for assuring that each team's operations are conducted safely and legally.
Flight Attendants
For airline passengers, the cabin crewmembers are the most visible support staff. Flight attendants (FAs) are responsible for taking care of nearly all passenger needs. In addition to serving snacks and beverages, FAs supervise passenger safety. In this role, they conduct a thorough safety briefing, confirm that all passengers are wearing safety belts, make sure carryon luggage is properly stowed, and attend to special needs passengers. Additionally, cabin crew members conduct the passenger count and make sure it matches the flight's manifest. At some airlines, FAs assist with weight & balance calculations. As a passenger, the cabin crew members will be your point of contact once you've boarded the aircraft.
Gate Agents
Think of gate agents as the pre-boarding flight attendants. They'll be your point of contact for all matters prior to boarding and after deplaning. In their role, gate personnel oversee the boarding process and ensure only ticketed passengers enter the plane. They confer with the pilots & FAs to verify their passenger count matches the number of travelers aboard. Gate agents also make arrangements for special needs passengers (arranging for wheelchairs, interpreters, etc.) and chaperone unaccompanied minors (UMs).
Should you miss a connection or lose your luggage, the gate personnel are the people who will sort out the mess. In their role, gate agents greatly assist the crew by streamlining the boarding process to the furthest extent possible.
Baggage Handlers
Baggage handlers do more than just load your luggage. They assist the pilots in keeping the plane within its weight & balance limits. Rather than just blindly tossing bags into the cargo hold, baggage handlers maintain a precise record of exactly what goes into each cargo bay. This includes regular size bags, oversize luggage, and sometimes hazardous materials (HAZMAT). They ensure that everything loaded into the plane is properly secured and may legally be carried. At times, it's necessary to rearrange or offload cargo to remain within weight & balance limits. While the pilots ultimately determine what must be done, the baggage crew carries out the request to load the aircraft within the proper parameters.
Ground Crew
Ground personnel carry out the fueling of the airplane. After the pilots & dispatchers determine the requisite fuel load, the ground crew uploads the proper amount of fuel to the aircraft. During winter, they also apply deicing fluid to remove ice & snow from the plane. Additionally, the ground crew loads water, food, and beverages onto the aircraft. When it's time for pushback, they operate the tug that moves the plane away from the gate and maintain proper clearance from obstacles around the plane. Upon arrival at the destination, ground personnel guide the plane into the gate. For both departure and arrival, the ground crew are the people who connect the plane with the terminal.
Company Operations
Company Ops are the people on the other end of the microphone. In addition to recording the arrival & departure times, they coordinate their airline's flights with all ground support teams. When the pilots request fuel, deicing, maintenance, baggage, or assistance with passenger needs, Ops personnel pass the request along to the appropriate team. They also keep the crew apprised of any delays or updates relevant to the flight. Of all the ground-based crews, Ops is the team that brings everything together. As you can see, each airline flight requires a significant amount of planning and input before it's ready to leave the gate. While the captain is ultimately responsible for the safety and legality of the entire operation, the various support teams play an integral part in preparing the flight for departure. The next time you have a hassle-free airline experience, remember the part the supporting crews play in its outcome.
PUSHBACK TO RUNWAY
Once the passengers are loaded, the paperwork is completed, and the plane is preflighted, it's time to leave the gate. At this point, many passengers just want to get in the air. For the curious bunch, some important steps actually occur between the gate and the runway. With this section, we'll examine what's going on up front just prior to takeoff.
A Concrete Maze
Most passengers who've flown into a major airport have probably noticed that an astonishing amount of confusion can be crammed onto the airport's real estate. Besides the enormous terminals and the runways, an awful lot of additional items are cluttering up the airport. There are taxiways, signs, lights, navigation & weather equipment, ground vehicles, maintenance materials, and other airplanes between the gate and the departure runway. Ever wondered how pilots manage to get where they need to be? Follow me.
A Method to the Madness
Despite the frequently ridiculous layouts of massive airports, there is a systematic method in place to sort through the chaos. For starters, runways are numbered in reference to their magnetic direction. With this system, pilots have the benefit of the compass to aid with orientation. In addition, this numbering method is universal, meaning international crews won't have to learn a new system. As airplanes always want to take off into the wind, flight crews can often anticipate the departure runway based on current wind conditions.
Getting Directions
Unlike some macho motorists, pilots have no trouble asking for directions. Let's look at some of the options at their disposal.
Taxi Diagrams
These incredibly useful charts give a bird's eye view of the airport property. All runways, taxiways, terminals, and other noteworthy structures are labeled for easy reference. These diagrams are available in paper & electronic form and are a must for large airport operations.
Signage
Navigating an airport is a lot like navigating the interstate. Airports contain a plethora of signage to assist aviators in maneuvering on the surface area. Signs denote runway & taxiway locations/directions, provide information relevant to the airfield, identify areas to avoid/ exercise caution, and even reveal runway length. These signs and their characteristics are universal, and they provide a wealth of pertinent information to pilots.
Pavement Markings
Pavement markings provide additional info to pilots and help supplement airport signs. These markings are also universal and denote runways, taxiways, areas to avoid, locations to exercise caution, and loads of other useful info. As these identifiers are painted onto the airport surfaces, they are most visible/helpful during daylight hours.
Lighting
While hub airports can be confusing during the day, the possibility of disorientation magnifies after sunset. To minimize the potential for chaos, all airport lights are standardized based on color. If you've never seen a commercial airport at night, it's quite comparable to the Vegas strip. The slew of colorful lights helps pilots identify runways (and sometimes their lengths), taxiways, thresholds, and even their approach angle to the runway. Based on color alone, a string of airport lights can tell flight crews a lot about their position/status at the aerodrome.
The Human Element
As immensely helpful as visual aids and magnetic orientation can be, the most valuable assistance comes from air traffic control (ATC). In fact, one segment of the ATC workforce deals exclusively with aircraft (and some vehicles) moving on the airport's surface. This division, called "ground control", is the ATC entity airplanes call at pushback. Ground control then provides taxi instructions to the appropriate departure runway. Ground also monitors potential surface traffic conflicts and issues alerts when necessary. If an airplane becomes lost or disoriented during taxi, ground can provide "progressive taxi" instructions, which consist of turn-by-turn guidance to the plane's destination.
After arriving aircraft land and exit the runway, ground provides them with taxi instructions to their terminal, gate, or other destination on the airport. Though ground maneuvering comprises a small percentage of each flight, it can be a confusing segment with a large potential for error. By effectively utilizing the resources outlined above, pilots minimize potential risks and streamline the journey to the departure runway.
TAKEOFF & CLIMB
Thus far, most of our discussion has looked at the steps leading up to takeoff. Now we'll examine what happens once the plane departs "terra firma". While the takeoff and climb legs might appear simple and self-explanatory, both involve important steps that greatly contribute to the safety of each flight.
V1: A Critical Airspeed
Although we previously reviewed the need to calculate speeds & power settings, one speed in particular deserves special attention. V1 is defined as the critical engine failure recognition speed or takeoff decision speed. Whenever you fly, it's a sure bet your pilots are discussing V1 while they taxi towards the runway. Attaining V1 is a top priority during takeoff. Any abnormal developments below this speed mean the crew will abort the takeoff. At or above V1 the issue will be handled in the air, whether or not the plane has actually become airborne yet. Due to a variety of factors, it's actually safer to continue the takeoff run (once at or above V1) than to try to stop the aircraft. Pilots are keenly aware of this, and thus place special emphasis on monitoring airspeed during takeoff.
Alternates and Contingency Plans
Another discussion pilots have before takeoff involves alternate plans of action. These plans address issues that arise immediately after takeoff, while enroute, upon approach to the destination airport, and any other situation that might require an alternate airport/landing site. In some instances, mainly due to low ceilings/visibility or geographical restrictions (i.e. high terrain), airplanes are unable to return to their departure airport following takeoff. In these instances, pilots & dispatchers choose a "departure alternate", a (relatively) nearby airport the plane can divert to following an abnormal occurrence. In extreme instances, the crew might have to choose an off-airport landing site. Remember Capt. Chesley Sullenberger and US Airways Flight 1549 that he graciously landed in the Hudson River? While the outcome was indeed miraculous following the flight's double engine failure, the happy ending was largely due to the contingencies developed by Capt. Sullenberger and his crew.
Noteworthy Climb Altitudes
Throughout the climb to cruise altitude, pilots monitor a few key altitudes. These altitudes serve as milestones the crew uses to perform essential tasks.
400 ft: After liftoff, the crew's immediate priority is to reach an altitude of 400 feet. This altitude is widely used to transition from max performance climb to cruise climb. Why 400? This number is used because, by 400 ft, the plane will have climbed above most nearby obstacles. With a little altitude between the plane and the surface, the crew transitions to a cruise climb, at which a higher airspeed and slightly shallower climb angle are adopted. Any flaps used during takeoff will be retracted once reaching 400' and accessory items (like pressurization), which slightly decrease engine power output, are activated.
10,000 ft: Think your pilots are discussing last night's ballgame during climb? Absolutely not. Below 10,000 ft, "sterile cockpit" rules apply, meaning only essential communication is permitted. At lower altitudes, the crew is busy performing after-takeoff & climb checklists, communicating with air traffic control (ATC), monitoring instruments, and configuring the airplane. Additionally, airspace below 10,000' frequently contains a large amount of air traffic, particularly near airports. Above 10,000; things tend to settle down and traffic usually thins a bit. At this point, idle chatter is permitted and items like landing lights (used to increase the plane's visibility) are turned off.
18,000 ft: This altitude marks the lower limit of Class A airspace. Class A is off-limits to visual traffic and is the realm of airliners and business jets. At 18,000 ft, all aircraft set their altimeters to 29.92 in. Hg (atmospheric pressure), which allows for a uniform standard for high-altitude operations. Below 18,000 ft, aircraft utilize local airports' pressure readings. Throughout takeoff and climb, pilots are busy planning, monitoring, anticipating, and adapting to both expected and unexpected occurrences. This thorough dedication to safety has made airline travel the safest transportation system in the world. The next time you fly, rest assured your crew is prepared for and capable of handling nearly any possible situation.
THE CRUISE ALTITUDE SELECTION
Previously, we highlighted the cruise altitudes available to pilots depending on the type (VFR/IFR) and direction of flight. With this post, we'll take cruising altitudes a step further and examine how to choose the best altitude for existing circumstances. As you might imagine, a variety of factors affect the altitudes pilots and dispatchers ultimately decide on. Let's get started.
The Tropopause: Finding the Sweet Spot
Have you noticed how so many airliners tend to level off near 35,000 ft (F[light] L[evel] 350 in aviation parlance)? This popular flight level is far from coincidence. The most congested altitudes for en-route airliners result from the performance advantages associated with the Tropopause.
The Tropopause is the boundary between the Troposphere, the lowest atmospheric layer, and the Stratosphere. Its height varies with the earth's curvature, ranging from around 24,000 ft at the poles to approximately 56,000 ft near the equator. In the Contiguous 48 US States, the average Tropopause height is roughly 36,000 ft. A few benefits of operating near this altitude include lack of general aviation (slow) traffic and the ability to summit most weather. However, the performance advantages of Tropopause-area flight are the primary reasons for the deluge of jets at these heights.
Atmospheric Pressure
As you probably know, atmospheric pressure decreases as altitude increases. This decrease in pressure diminishes engine performance, but results in two significant advantages: 1. Total aerodynamic drag on the aircraft decreases, and 2. The lower the air density, the less fuel is required by the engines. Operating in these fuel-efficient altitudes saves airlines several million dollars each year in fuel expenses alone.
Temperature
While I've stated that decreased atmospheric pressure does diminish aircraft performance, this engine-robbing reduction in pressure is partially offset by the cooler temperatures aloft. Cold air, with its relatively low energy, tends to condense. As temperatures decrease with increases in altitude, the natural tendency of this cool air to compress helps counteract the overall rate of decreasing atmospheric pressure. This cooling of air with increases in altitude is a significant benefit for jets, but is only an option up to the Tropopause.
The Game Changer
Besides marking the top of virtually all weather, the Tropopause also denotes the end of decreasing temperatures with increases in altitude. Above the Tropopause, temperature actually increases with altitude, which rapidly diminishes aircraft/engine performance. Above the Tropopause, significant performance reductions eliminate virtually all benefits to be found at higher altitudes. Overall, the Tropopause is the sweet spot for airline operations. Reduced aerodynamic drag, low fuel consumption, minimal (if any) weather, and the absence of slow aircraft all increase the efficiency of flight at this level. With this many benefits, it should come as no surprise when your captain announces, We'll be cruising along today at 35,000 ft.
Additional Considerations
While the Tropopause usually offers the best overall conditions for airliner flight, at times it's impractical/unwise to climb to the altitudes around FL 350. Let's look at some reasons why it's occasionally better to choose altitudes not in the neighborhood of the Tropopause.
Winds: Winds have a general tendency to increase with altitude. Depending on the direction of flight, this can be a huge blessing or a significant curse. As a tailwind, performance and speed work in the flight's favor. As headwinds, Jet streams (often in excess of 100 knots) lengthen flight time and burn significantly more fuel. With strong headwinds aloft, it's often better to seek a lower altitude without the gales.
Length of Flight: Short flights often negate the advantages of going high. For instance, airplane engines burn more fuel while climbing than in cruise. It doesn't make sense to spend 30 minutes at climb power to spend 10 minutes in cruise. In many cases, the lengthy climb easily erases any performance savings of the short cruise. For passenger comfort, a period of level flight will also be more tolerable than a flight profile that resembles an inverted V. Pilots and airline dispatchers usually have many options when deciding on a cruise altitude. For the reasons outlined above, the Tropopause is often a good choice. However, at times conditions make flight at lower levels much more practical.
COLLISION AVOIDANCE 1
If you've spent much time as a commercial airline passenger, you've no doubt noticed the large number of airplanes that operate into and out of each hub airport. Perhaps you've wondered just how all those airliners avoid each other, as well as all other forms of air traffic, when airborne. With this post, we'll explore some of the procedural safeguards in place that help keep aircraft a safe distance apart.
SIDs and STARs
In busy terminal airspace areas, air traffic controllers (ATC) utilize "standard instrument departures" (SIDs, also known as "departure procedures" {DPs}) and "standard terminal arrival routes" (STARs) to streamline the flow of departing and arriving traffic, respectively. Unlike ground-based vehicles, which are largely limited to following roads, aircraft can arrive at a given point from any of the 360ÌŠ around the location. Such chaos would certainly compromise safety and make for an ATC nightmare. With SIDs and STARS, controllers are able to funnel traffic flow in a logical and safety-enhancing manner. Virtually all hub airports have several SIDs and STARs available to arriving and departing traffic. SIDs/STARs are published in textual (and often graphical too) form and instruct pilots of the headings, courses, & altitudes to fly when operating to/from each hub airport.
Depending on the general direction the aircraft is departing to/arriving from, ATC will give that plane a SID/STAR to/from that direction. These procedures also contain "transition routes", which allow aircraft to transition over a wider directional range when a safe distance from the airport (and the most congested airspace). As SIDs/STARs are published, ATC need only inform pilots to fly departure/arrival, transition. Pilots then know exactly which headings, courses, & altitudes to fly along their route. By following these routes, aircraft get in line behind other traffic, allowing an orderly flow in the most crowded areas.
Preferred IFR Routes
"Preferred IFR Routes "(IFR meaning "instrument flight rules", under which ALL commercial airline flights operate) are very similar to SIDs and STARs. In fact, Preferred IFR Routes are essentially a SID, a STAR, and the cruise portion of a flight all rolled into one. These procedures are common when the departure and arrival airports are located relatively close to one another, as well as for air traffic that transits congested airspace. These routes are, as the name implies, preferred because they streamline traffic and permit an orderly flow of aircraft within that airspace. If you've ever flown in the New England region, you've almost certainly flown on a Preferred IFR Route.
IFR/VFR Cruising Altitudes
For the cruise stage of flight, when not otherwise directed by ATC, aircraft utilize VFR & IFR cruising altitudes. VFR stands for "visual flight rules", and refers to traffic that navigates primarily by visual reference (mainly personal, general aviation aircraft). Cruising altitudes are determined by the magnetic course each aircraft is flying, as well as whether it's operating under IFR or VFR. For eastbound traffic (0ÌŠ through 179ÌŠ) IFR aircraft operate at odd, thousand foot intervals (7000, 9000, etc.) and VFR traffic fly at odd thousand foot intervals + 500 feet (7500, 9500, etc.). For westbound aircraft (180ÌŠ through 359ÌŠ), even numbered altitudes are flown (6000, 8000, etc for IFR; and 6500, 8500, etc. for VFR). This method ensures all aircraft will be vertically separated by at least 500 feet while in cruise. As you can see, the national airspace system has several procedural safeguards in place to keep air traffic safely separated from other aircraft.
Bear in mind that these are just the basic, operational methods pilots and ATC use for traffic separation. In a future post, we'll discuss additional safeguards built into the airspace system. These include ATC separation standards, airspace classes and the associated entry requirements, and the multitude of electronic equipment aircraft use to detect and avoid each other. Until then, breathe easy and know that whenever you fly, numerous safety procedures are working to keep your plane a safe distance from other aircraft.
COLLISION AVOIDANCE, Part 2
In a previous section, we highlighted some of the procedural safeguards used to provide adequate separation between airborne aircraft. With this post, we'll examine other methods to ensure aircraft remain safely separated from each other. All these procedures, methods, and equipment work together to maximize the safety of the national airspace system.
Electronic Equipment Transponder
The most basic form of electronic collision avoidance equipment is the transponder. This device emits an electronic signal that allows air traffic control (ATC) to locate an aircraft's position with radar. For the past several years, transponders have been capable of providing aircraft altitude as well (known as "Mode C", or "altitude encoding"). If aircraft get too close to one another, ATC receives an audiovisual warning. Controllers can then relay a traffic alert to the aircraft involved. Over time, transponders have continued to evolve and have paved the way for newer forms of electronic traffic avoidance.
TCAS
Additionally, all large aircraft are required to possess a "traffic collision avoidance system" (TCAS). TCAS is a form of portable radar, which works independently of ATC's ground-based radar. TCAS detects the transponder signals of other aircraft and, when traffic is nearby, issues alerts. These alerts may include "traffic advisories" (TAs) and/or "resolution advisories" (RAs). TAs are a kind of heads up to advise aircraft of a possible conflict. RAs announce when a conflict is imminent and evasive action is required. RAs even tell aircraft what type of maneuver to execute and, when received, supersede all ATC directives. Though established ATC procedures are usually sufficient to maintain separation, TCAS is great for belt and suspenders reinforcement.
ADS-B
"Automatic dependent surveillance-broadcast" (ADS-B) is the latest technological marvel for air traffic separation. ADS-B, through its use of both a highly accurate GPS receiver and a datalink, allows an equipped aircraft's position, speed, and altitude to be broadcast to other ADS-B equipped aircraft, as well as to ATC, in real time. Think of ADS-B as a highly accurate version of TCAS and radar combined. In fact, ADS-B is slated to replace traditional ATC radar. Though the technology is available now, future mandates will further enhance the safety potential of this system.
Airspace Requirements
The national airspace system is itself designed to promote aircraft separation. All controlled airspace requires all IFR ("instrument flight rules", which includes ALL airline traffic) flights to maintain radio contact with ATC. This enables controllers to notify aircraft of potential traffic conflicts. Additionally, airports with operating control towers require EVERY aircraft to establish radio communication in order to operate in their terminal airspace. The larger/busier the airport, the more traffic separation rules are in place.
Class D airports, the smallest tower-controlled fields, require all aircraft in their airspace to establish radio communications. This requirement permits ATC to supervise all types of flight operations in the airspace, as well as to issue traffic advisories/alerts. Medium size airports, located in Class C airspace, require both radio communications and an operable Mode C (position + altitude reporting) transponder in order to enter the airspace. As these airports generally have more traffic than Class D, the transponder requirement adds another layer of traffic separation safety. Additionally, the Class C airspace is larger than Class D, which keeps unqualified/non-participating aircraft farther from the airport. The nation's busiest airports are surrounded by Class B airspace.
In addition to the requirements for radio communications and a transponder, all aircraft must have a specific clearance to operate within Class B. This keeps many small, private aircraft from transiting the area near the major airport. Class B has even larger dimensions than Class C, which ensures more maneuvering space for the greater amount of traffic. While we've just glossed over the basics of the airspace & equipment characteristics, additional details further enhance the safety procedures for air traffic separation. In addition, ATC can and does address issues that the equipment, airspace, and procedures we've discussed cannot. Though we've spent two posts covering numerous traffic avoidance issues, the national airspace system still contains additional safeguards. If you've ever heard that it's safer to fly than to ride in a car, it's true!
READ MORE: Causes of flight delays
IN-FLIGHT NAVIGATION
So far, we've highlighted airline pilots' duties from pre-takeoff to leveling at cruise altitude. Up next we'll examine a major component of the cruise leg: navigating from Point A to Point B.
Unlike with ground-bound modes of transport, flight crews can't rely on a solid network of roads or rails. However, vast as the wild blue yonder might be; the national airspace system offers several types of navigational assistance.
Methods of Navigation
Air Traffic Control (ATC) The best-known method of navigational aid, ATC provides radar & communication services to all "instrument flight rules" (IFR) aircraft, which includes all airline traffic. Through transponder and/or ADS-B signals (see "Collision Avoidance II"), ATC can easily identify aircraft and provide navigational assistance. Many times, controllers instruct aircraft to fly to a known point using onboard navigation. At other times, they'll provide pilots with directional headings to fly, a method known as "vectoring" traffic.
Electronic Systems
VOR: The "VHF omnidirectional range" (VOR) network has been the backbone of America's air navigation system since the 1960s. This network consists of hundreds of VHF stations scattered across the country (and abroad). Each VOR emits a signal that can be used to navigate to/from the station on any of the 360 (1ÌŠ each) radials surrounding the unit. Many VORs are also equipped with "distance measuring equipment" (DME), and thus provide mileage as well as bearing to/from the station. While VORs are multifunctional and easy to use, this antiquated network is not without its drawbacks. Chief among its limitations is the finite range of VOR signals. Of the three classes of VORs, the maximum guaranteed range (with certain exceptions) is 130 nautical miles. While that might sound like a significant range, many airliners can cover that distance in about 15 minutes. The second major drawback is the need to operate directly to/from VOR stations (in most cases). While such navigation is simple, navigating by VORs rarely results in a direct course from departure to destination. Despite these shortcomings, VORs have reliably upheld the national airspace system for more than half a century.
GPS: Since the mid 1990s, the "global positioning system" (GPS) has significantly modernized aerial navigation practices. GPS lacks the range limitations associated with VORs while also allowing point-to-point (i.e. direct) navigation to virtually anywhere on earth. Additionally, after continual improvements over the years, the GPS network now permits pilots to fly instrument approaches without the aid of any secondary navigation systems. In fact, aircraft can now navigate from takeoff to touchdown entirely by GPS. As future upgrades continue to enhance the system, additional GPS benefits will undoubtedly refine air navigation practices. Although GPS permits direct-to navigation with the push of a button, ATC procedures and air traffic congestion usually prevent aircraft from flying directly from their departure airports to their destinations. Instead, airplanes are often instructed to fly to "waypoints", points in space that can be determined through navigation systems. Often these waypoints mark the beginning of a "standard terminal arrival route" (STAR, see "Avoiding Other Aircraft") into the destination airport. Though not as efficient at direct-to flight, waypoints often shave off many air miles that would otherwise be flown with VOR navigation.
INS: Limited mainly to airliners, the "inertial navigation system" (INS) is unique in that it is a completely self-sufficient system. Through the use of a computer and motion-sensing components (chiefly accelerometers and gyroscopes), the INS is capable of calculating its own speed, location, and orientation without external reference. As such, INS is great for supplementing other systems or for backup navigation. The system does, however, require an external source of position & velocity data (pilot, GPS, etc.) during initialization. In addition, small calculation errors will, with time, lead to increasingly greater speed/position errors (known as "integration drift"). However, INS's shortcomings are generally minor and unlikely to affect flight safety.
Although pilots still carry maps ("aeronautical charts"), most modern navigation is done through a combination of electronic sources and ATC. As technology continues to advance, future navigation procedures will likely become more efficient and reliable, further increasing the safety of the national airspace system.
THE DESCENT
Regardless of the distance traveled or the time spent aloft, all airplanes must eventually return to earth. For passengers, the descent leg means the flight is almost over. For the crew, the descent phase involves communication, coordination, planning, and even math. Let's examine some of the highlights your pilots deal with after leaving cruise altitude.
Econ Descent
In the section Selecting the Best Cruise Altitude, we discussed how fuel consumption decreases as altitude increases. For airlines, reducing fuel consumption whenever it's safely possible is a major goal. As it happens, the descent phase is the most fuel-efficient airborne leg. To maximize fuel savings, the aviation industry has developed procedures for what's called "economy descent". Economy descent, or econ descent, is the practice by which airplanes descend at idle power. At idle, the engines consume the least possible amount of fuel, which the airlines love. The goals of econ descent are to: 1. Remain at the fuel-efficient cruise altitude as long as possible 2. Descend at idle power for the entire descent (if possible). Ideally, the descent leg would be one continuous glide down from cruise altitude to the runway. Due to air traffic constraints, this is rarely feasible. However, industry authorities continue to evaluate possible procedural updates to accommodate econ descent improvements.
Noise Abatement
As you know, airports are noisy places. Airplanes create an incredible amount of noise, which is a significant source for complaints from airport neighbors. In many areas, noise abatement procedures have been established to enforce against unwanted sound. To avoid unnecessary disruption, pilots try to minimize the noise impact of their aircraft. The major techniques to reduce engine noise are to: 1. Gain/maintain extra altitude after takeoff/before landing 2. Reduce engine power settings/rpm. 3. Alter course to avoid populated/noise sensitive areas. As you can see, econ descent procedures incorporate noise abatement tactics. In addition, some approach courses and arrival routes are tailored to avoid noise sensitive areas.
Coordination with Support Teams
Another important pilot task prior to arrival is to report in range. The In Range notification, which can be completed via radio or electronic message (or a combination), notifies gate personnel and company ops of assistance the arriving flight will need at the gate. The in range call relays fuel status, unique passenger needs (wheelchair, interpreter, etc.), maintenance/equipment needs, and any other relevant information. This call is often made 10-20 minutes before the estimated arrival time, which allows supporting staff to line up necessary personnel, equipment, and/or fuel. At times, when the plane will be departing soon after arrival, the crew can arrange for a quick turn procedure to speed up the requisite gate tasks.
Approach & Landing Prep
Professional flight crews also use descent time to prepare for the approach & landing phases. These flight stages are often high-workload situations that require advance planning to ensure safety requirements are met. During the approach briefing, the crew will set up navigation equipment, tune radios, and analyze the characteristics of the destination airport. They also review the expected instrument approach procedure and calculate approach & landing speeds. By preparing ahead of time, the pilots are then able to concentrate once entering the terminal environment.
Traffic and Clearance
The closer to the airport the plane gets, the more congested the airspace becomes. Flight crews maintain extra vigilance near the airport, which involves watching for potential traffic conflicts and visually locating planes they're to follow to the runway (sequence behind). During this phase, you've probably heard your pilots advise flight attendants prepare for landing over the cabin speakers. An important final step is to receive clearance to land. While this might seem obvious, it can be easy to overlook amid the activities in the cockpit and the traffic out the window. Each aircraft must receive a landing clearance for the appropriate runway before touching down. Failure to receive clearance can potentially compromise safety. For ALL tasks required during descent, crew members refer to the appropriate checklists and company procedures. In the future, we'll cover some of the specifics for configuring the plane for landing. Until then, please fasten your seatbelts and stow your tray tables.
APPROACH AND LANDING
In "A Look at the Descent Leg", we discussed some of the steps pilots take upon vacating cruise altitude. With this post, we'll go into more detail about the final portion of the descent segment: the approach and landing. As you probably know, this final segment is one of the most vital of the entire flight and requires the crew's full attention. Let's examine some of these duties your crewmembers perform.
Approach Speeds
The airspeeds used by airliners vary depending on temperature and aircraft weight. Prior to commencing the approach, pilots will calculate three (sometimes more) relevant speeds. The first, referred to as "approach speed", is the speed flown during the latter stages of the final approach to just short of the runway threshold. This relatively slow speed permits a stabilized approach with the aircraft fully configured (landing gear and flaps extended). At times, approach speed will be adjusted for strong, gusty winds or when other than normal flap settings are used.
The second common speed, VYSE, provides the best climb rate with an engine inoperative. While engine failure during approach is extremely rare, flight crews always prepare for the worst-case scenario. Should a powerplant failure require an aborted landing, the crew is prepared with the requisite climbout speed. VREF, the lowest of the three speeds, is the target airspeed when crossing the runway threshold. Once the aircraft is fully configured and the landing is assured, pilots will reduce power to achieve VREF. This speed is desirable because it reduces landing distance and stress on the landing gear & tires, and yet still maintains a safe margin above stalling speed. All three speeds are calculated and marked with speed bugs, which facilitate easy identification by the crew.
Configuring the Airplane
An important prerequisite for landing is to ensure the landing gear is extended and locked into position. How do the pilots know when to do this? Gear extension, flap deployment, and all other necessary tasks are specifically outlined in the landing approach profile. Your pilots will ALWAYS refer to checklists to verify these steps are completed correctly, but it's a good bet most pilots also have these procedures memorized. The landing gear and flaps also have their own V speeds, which indicate the maximum velocity they may be operated and/or remain in the extended position.
During approach, pilots will slow the aircraft below these V speeds and deploy landing gear and flaps incrementally. You've probably seen the flaps extend during the approach, as well as heard a "clunk" as the landing gear locked into place. Rest assured, these extensions are far from arbitrary and are specifically spelled out for all conceivable types of approaches. What happens if the gear fails to extend? While this possibility is rare, the aircraft manufacturers have built in numerous safeguards and backup extension plans. Your pilots have also trained "ad nauseam" to handle such problems. If, worst-case scenario, the gear still fails to extend, a safe landing is still probable. Usually, the crew will inform airport personnel to foam the runway, which reduces friction/sparks and the chance of fire. In addition, it's a sure bet they'll have fire trucks and ambulances standing by. When a belly landing is necessary, such an event is almost never fatal and any injuries received are usually minor.
Descent Angle
Airplanes normally descend at a 3 degree angle and receive guidance from both electronic and visual aids. At most commercial airports, airliners will fly an ILS (instrument landing system) approach, which gives lateral and vertical guidance. Though designed for instrument weather, nearly all crews still utilize this approach system in visual conditions. In many cases, they'll let the autopilot fly most (sometimes all) of the approach. Next to the runways, external light systems also provide information on the aircraft's approach angle to aid crews if adjustments are necessary. The combination of these systems can guide aircraft virtually to the pavement. While the approach segment can be a nervous time for some passengers, the pilots have been thoroughly trained in every possible aspect of this phase. If something unexpected does occur, your crew is adequately prepared to handle the event. On your future flights, rest easy knowing you're in the safe hands of an experienced crew.
TAXIING TO THE GATE
When the tires squeak (or slam) onto the runway, many air travelers think the flight has ended. For pilots, an integral stage of the process still remains; one prone to confusion and with a notable risk for error. In a prior section we discussed the confusion and hazards of taxiing at large airports, as well as the tools pilots have to assist them with the taxi process. In this section, we'll cover taxiing on the other end of the flight, once the plane has landed and is ready to unload.
Clearing the Active Runway
After touching down and sufficiently slowing the airplane, the crew's next objective is to exit the runway. Per air traffic regulations, only one aircraft (with limited exceptions) can be on an active runway at a time. However long a just-landed airplane remains on the runway, no other planes can use that runway to takeoff or land. At commercial airports, with hundreds of operations per hour, every second of delay can potentially clog an already congested aerodrome. Therefore, pilots look to minimize the time they remain on the runway after landing (without sacrificing safety).
To aid aircraft egress from the strip, major airports usually have high-speed taxiways next to the runways. These wide taxiways are constructed so they turn off at a gradual angle, thus permitting planes to exit the runway at a fairly high speed. High-speed turnoffs are so effective that controllers often instruct landing planes to continue to the high-speed, even though another turnoff may be nearer.
If no high-speed taxiway exists, pilots are (unless otherwise instructed) expected to turn off at the nearest taxiway (ahead of the airplane) once the aircraft is adequately slowed. While exiting the runway in a timely manner is favorable, pilots will delay if necessary in the interest of safety.
The Maze and the Aids
Upon exiting ("clearing" in aviation jargon) the runway, pilots contact ground control for taxi instructions. At this point, taxiing is essentially identical to the process discussed in the section above, albeit in reverse order. The airport layout is oftentimes confusing, and pilots will utilize taxi diagrams, lights, signs, pavement markings, and ground control for assistance. As always, certain risks are inherent to the taxi phase, and your crew members follow established procedures to minimize these risks to the extent possible.
At the Ramp
Upon reaching the terminal ramp, most airliners are given one of two instructions: taxi to the gate or hold for a gate. When no gate is available, the plane will be directed to a ground holding area, commonly referred to as the penalty box, until a gate becomes available. Once a gate is ready, the crew will taxi to the directed gate to begin the parking process.
Parking the Bird
Parking an airliner requires a high degree of attention and planning. During this phase, ground tugs, conveyor belts, fuel trucks, baggage trams, food trucks (if you're lucky), airstairs, and ground personnel might all be moving around near the jetway. Your pilots must ensure they don't hit any of these moving targets while also controlling a multistory, megaton vehicle. In addition, airliners have lengthy wings protruding from both sides, another challenge to consider.
To aid with obstacle clearance, ground crews include wing walkers. Wing walkers don't actually stroll along the airfoil, but rather advise (from the tarmac) the crew of the wings' relation to nearby obstacles. For this, the wing walkers use hand signals, often with the aid of bright orange batons.
Once lined up with the parking tee, the crew proceeds "slowly" toward the signalman. Just imagine; a massive airliner can do some extensive damage if it accidentally taps the terminal, so pilots take every precaution to avoid such an outcome. Once signaled to stop, the Captain will set the brakes, shut down the engines, and review the parking checklist with the first officer.
Though a short flight segment, the final taxi phase consists of several essential factors. Your crew is well aware of each step's importance, and thus doesn't consider the flight over until they exit the aircraft. Next time you fly, think about your crew's responsibilities during the taxi to the gate.
READ MORE> Cockpit Operation
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