Airplane and Airline FAQ: Preflight Planning

An airline is a highly technical labor-intensive, service- oriented business. More than 100 person-hours are spent preparing for every one hour a pilot spends flying.

A major airline employs approximately 60,000 people. Of those, 12 percent (or 7500) are pilots; 22 percent (or more than 13,000) are flight attendants; and 7 percent (5500) are mechanics.

The other 34,000 employees are equally as vital, but are not always given equal credit.The reservations staff, marketing personnel, passenger service agents, crew schedulers, dispatchers, central load planners, cargo and baggage handlers, fuel servicemen, cabin service, training instructors, lawyers, secretaries, etc. are all an integral part of a safe and reliable airline. In fact it takes more than 150 employees to operate just one aircraft. The larger airlines operate more than 400 aircraft.

A major U.S. domestic airline will schedule roughly 2500 flights daily, departing around the clock every day of the year. It doesn’t sound all that impressive until you realize that works out to nearly one departure every thirty seconds.

Equally impressive is that, even when you take into account weather and mechanical cancellations, the airline completes nearly 98 percent of its published flight schedule.

WHERE DOES YOUR FLIGHT BEGIN?

Two hours before each and every flight at one central location—usually near the corporate headquarters—the dispatch department begins planning your flight. One hundred dispatchers, who, like pilots and mechanics, are licensed by the Federal Aviation Administration (FAA) are responsible for the preliminary planning of your flight. This includes the route, cruise altitude, fuel load, and coordinating your flight plan with Air Traffic Control (ATC).

CHECKING THE WEATHER

The dispatcher’s first step is to check the weather. They review and compare reports from both the airline’s own meteorological department and the U.S. National Weather Service, which monitors weather at over 600 locations in the domestic U.S.

The dispatcher looks for forecasts of hazardous or severe in-flight weather that must be avoided, including thunder storms, squall lines (groups of thunderstorms), hail, tornadoes, hurricanes, severe ice, windshear, and moderate to severe turbulence.

In pilot parlance, forecasts of severe weather are called SIGMETS. The National Weather Service issues SIGMETS and transmits these forecasts to the airline’s meteorological and dispatch department—as well as to pilots in-flight—as they become available.

After checking for possible extreme weather, the dispatchers compare the en route forecast with the actual weather received from satellite photos, radar images, and actual pilot reports (called PIREPS). Among pilots, PIREPS are the next best thing to being there.

In the absence of hazardous weather, additional attention is given to the forecasted en route winds, including the location and intensity of the jet stream. The jet stream is wind of 75 knots (86 mph) or greater, spanning a distance of 300 miles or more. Occasionally it can get up to 200 knots (230 mph). (To convert knots into miles per hour, multiply the figure by 1.15.)

As a tailwind, the jet stream can shorten en route time considerably. In most cases, when it is turbulence free, it is a time- and fuel-saving asset. As a headwind, the opposite is true.

The dispatcher will next have the meteorological department locate the tropopause: the layer of atmosphere separating the troposphere (the layer located nearest the earth’s surface) and the stratosphere, the uppermost atmosphere. In the winter it begins in the mid-30,000 foot level, and in the summer it’s located in the 50,000 foot range.

Above the tropopause the temperature is fairly constant at approximately —56 degrees. Since temperature changes are the main ingredient for the formation of all weather, it follows that above the troposphere there is basically no weather.

The surface weather and forecasts at both the departure and destination airports will be reviewed next. The dispatcher’s surface weather analysis will also include any airport alerts—such as construction or ongoing maintenance that would alter the useful length of the runway— and field condition reports, which would include such things as standing snow or ice.

SELECTING A ROUTE

The next step: How is the plane going to fly from point A to point B?

The criteria are: safety first, passenger comfort second, and cost third. The adage within the industry is “Maximum safety at minimum cost.”

Because the first rule in picking a route is safety, weather is always a primary consideration.

However, the second consideration in selecting a route is working within the Air Traffic Control (ATC) system. For both takeoff and arrival there are ATC predetermined routes called SIDS—Standard Instrument Departures— and STARS—Standard Terminal Arrival Routes. Think of them as freeway on-and-off ramps in the sky. These published routes are depicted on navigational charts carried by all airline pilots.

When planes depart an airport, they follow SIDS. There may be as many as eight to ten SIDS per airport, depending on the size of the airport. All planes flying to their destinations on the same general compass heading—no matter how close or far their destinations may be—will be on the same SID. Aircraft with destinations in a different general direction will be on another published SID. These departure corridors end at particular points, where planes then join en route airways (highways in the sky).

Those arriving at airports are following STARS. These arrival routes sometimes begin more than 200 miles away from the airport. At this point Air Traffic Control begins lining up the aircraft on these off-ramps in the sky and sequencing them for landing. Some STARS allow for long, gradual descents at the discretion of the pilots. Other STARS, particularly if there is more than one major airport in close proximity, dictate specific speeds and crossing altitudes (exact altitudes at exact locations). Usually the time you reach the arrival gate for the STAR is also the time the flight attendants need to prepare the cabin for arrival. The seat-belt sign is turned on at this time.

PICKING AN ALTITUDE

The first two considerations in selecting an altitude are weather and winds, which have already been discussed. The third criteria is the performance of the aircraft.

Each plane has a maximum altitude it can fly. For instance, a Boeing 767 can cruise up to 43,000 feet. However, when the plane’s weight is taken into account, the optimum altitude for fuel economy may not equal the maximum altitude. The goal is to fly as close to the optimum altitude as possible.

The fourth and sometimes the overriding component in picking a cruising altitude is the ATC-mandated separation between aircraft.

When flying on an easterly heading—0 to 179 degrees— planes cruise at odd-numbered altitudes: 23,000; 25,000; 27,000; and 29,000 feet. When flying in a westerly direction—180 to 359 degrees—planes fly at even altitudes: 24,000; 26,000; and 28,000.

Above 29,000 feet, aircraft are required to maintain a 2000-foot vertical separation.

To maintain altitude separation between aircraft flying in opposite directions, the easterly heading “odd” altitudes are defined as 33,000, 37,000, 41,000, and 45,000, feet. The westerly heading “even” altitudes are defined as 31,000, 35,000, 39,000, and 43,000 feet. If your optimum altitude is other than a cardinal altitude, the safety of aircraft separation takes precedence over aircraft economy.

PICKING A CRUISE SPEED

The consideration is minimum cost at a minimum time. Optimum cruising speeds average 460 knots, which is 540 mph. This works out to about nine miles per minute. A proposed cruise speed is filed with ATC before the flight, and a deviation of plus or minus 10 knots must be reported. Why? Because many planes are flying the same routes, and any change will affect the departure and arrival gates as well as the separation between airplanes on similar routes.

Maximum speeds are higher than 460 knots, closer to 500 knots (or almost 600 mph). But as little as a 4-knot variation from optimum cruise speed will increase the fuel flow from one to two percent, which increases the fuel cost. Since the cost of fuel makes up nearly 45 percent of the per hour cost of an airplane and 20 to 25 percent of the total operations expense, flying faster or slower can be expensive.

SELECTING A FUEL LOAD

The two factors absolutely critical in aviation are fuel and weather. They are monitored continuously.

The fuel load is determined in a straightforward manner. First, trip fuel—the amount needed to get the plane from departure to its scheduled destination. By law, trip fuel takes into account numerous variables, including increased flight times due to forecasted headwinds, weather that must be circumnavigated, the actual route—not always the shortest distance between two points—and any anticipated delays.

Second, enough fuel is planned in case it becomes necessary to take an alternative route. This takes into account bad weather. If the weather at the flight’s destination is forecasted to be less than a 2000-foot cloud cover and less than three miles visibility, then there must be enough fuel to fly to the most distant alternate.

Third, the plane must have “hold fuel” for unforecast delays. Most airlines will carry one to two hours of hold fuel, though the FAA does not require the airlines to do so. In terms of cost, the penalty for carrying this fuel is not nearly as great as having to divert to another airport to refuel.

Reserve fuel is the fourth consideration, and the Federal Aviation Regulations (FAR’s) dictate a minimum of 45 -- lutes of reserve fuel. What this means is, if you flew to our destination and circled in a holding pattern waiting ..: the airport to open, which it never did, then flew to your most distant alternate and landed—when the engines are shut down and passengers deplaned, there will still be a minimum of 45 minutes of fuel in the tanks. Most airlines are more conservative and use a minimum reserve fuel of one hour and fifteen minutes. Ninety-nine percent of the time, there is much more than that, because to land with only reserve fuel assumes you used all your holding fuel at both your primary destination and alternate airport, then flew to the most distant alternate instead of selecting a closer suitable airport to refuel.

Fuel weighs 6.7 pounds per gallon, and the penalty for carrying too much fuel is extra cost. For every one percent the plane’s weight is increased, the fuel burn is increased by one and one-half percent. For example, carrying 10,000 pounds (1500 gallons) of extra fuel increases the aircraft’s weight such that nearly one-third of that 1500 gallons is used just to carry itself. This is a significant cost.

ALTERNATE COURSES IN CASE OF EMERGENCY OR WEATHER CHANGE

For every flight plan, there is an alternate course in case of emergency.

Visibility requirements for takeoff are generally less restrictive than for landing. Therefore, if the weather is such that a plane can take off from an airport but, in the event of a major malfunction—say, engine failure—could not return to land, there must be a predetermined alternate airport within 320 miles for two-engine aircraft and 700 miles for 3- or 4-engine aircraft.

If there is no alternate airport within the required distance, and the visibility at the point of departure is below minimum landing requirements, the plane will not be allowed to take off.

Landing alternates are also preplanned. There may be one, two, or more landing alternates selected prior to takeoff, and those might not be the airports closest to the destination. Why? If sixty airplanes were inbound to Dallas-Ft. Worth Airport, and DFW closed, it would be impossible to reroute all sixty to Houston. There wouldn’t be enough jetways, fuel trucks, or catering supplies to handle the load.

When the dispatcher plans alternates, he tries to find suitable alternates for every flight. Of course, the pilot has the ultimate say. The captain can, at any time, change the takeoff or landing alternate.

COORDINATING WITH AIR TRAFFIC CONTROL (ATC)

After the calculations have been made to determine the route, fuel load, altitude, and alternate courses of action, a flight plan has to be filed with Air Traffic Control. A specific ATC flight plan is filed for each and every flight.

All flight plans are filed as requests into a central computer at FAA headquarters in Washington, D.C., and they are either approved as filed or amended and returned. Air Traffic Control’s main responsibility is traffic separation. Of course, there is a great deal of repetition every day. It’s only when weather comes into play that gate-holds, flow- control restrictions, and spacing between aircraft cause delays.

Dispatchers are required to monitor the entire flight, from takeoff delays to arrival. Regular progress reports are made from the pilots directly to the company every hour. A dispatcher is usually required to monitor ten or more flights at a time while continuing to work on upcoming departures.

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