Cruise (aeronautics)

When cruising (german cruise ) is in aviation refers to that phase of flight that begins after reaching the planned cruise altitude and continues to descent. If you change the altitude or flight level during cruise, this is referred to as " cruise climb " ( engl. cruise climb ) or " Reisesinkflug " ( engl. cruise descent ).

• 3.1 Cockpit Crew
• 3.2 Cabin crew

• 4.1 Health risks
• 4.2 aviation -related risks
• 4.3 Effects on the environment

Importance

With the exception of round flights where the flight ends at the aerodrome of departure, and very short flights, the largest share of the flight is completed in cruise flight. Therefore, aircraft manufacturers optimize the aerodynamics and engines of commercial aircraft to operate in the normal cruising altitudes. Higher cruise altitudes have the advantage of being faster can be flown without the frictional resistance of the air rises excessively. In addition, storm clouds and mountains flew over, used the jet stream and the traffic can be avoided through secondary airports.

Before the start of each flight a flight altitude is determined during the flight planning, which is considered the most appropriate considering the maximum cruise altitude and the airspace structure for this flight. The planned cruising altitude is authentic specify in the flight plan, which the air traffic controllers of the Air Traffic Control (ATC ) is passed.

Due to the different performance of the various actuators used in aerospace vary the planned cruise altitudes of about 9,000 feet above sea level (german mean sea level, MSL, roughly 2,740 m) and 43,000 feet MSL, converted 13105.97 m. The performance of piston- powered recreational aircraft decreases with increasing density altitude from strong, while a modern turbofan engine 9143.70 m is highly effective even than 30,000 feet MSL.

For the calculation of the maximum cruising altitude of a commercial aircraft three main characteristics of the respective aircraft type to be used:

• The maximum structural cruising altitude. It is found during the acceptance by the aircraft manufacturer and is usually due to the strength of the hull to stresses by the pressurized cabin.
• The limited by the engine power maximum altitude. At this altitude, enough engine power for the implementation of a climb at a fixed rate of climb must be present.
• The limited maneuverability by the altitude. It must in-flight cross layers with a tilt angle of at least 33 degrees (FAA ) and 40 degrees (JAA, EASA) without the occurrence of stalls be possible.

In the flight planning the cruise altitude is striven to put as close as possible to the optimum altitude ( engl. Optimum Altitude ). It is in most cases approximately 2,000 feet below the maximum altitude and is based solely on economic factors. The fuel costs are compared with the flight time-dependent cost of the flight. Flight Time-dependent costs are maintenance costs and personnel costs incurred by flight time-dependent maintenance and regulation of working hours (for example, overtime control) of the flying personnel. Although a high cruise speed causes high fuel costs, but reduced by shortening the flight time, the flight time-dependent costs. The coefficient of fuel costs and flight time-dependent costs is referred to as "cost index" and can be calculated individually for each flight.

Special circumstances in cruise

Cruise climb, step climb

The minimum fuel consumption per unit distance of an aircraft is almost independent of the height, but the speed at which it is obtained is proportional to the mass of the aircraft and inversely proportional to the air density. That is, the heavier the aircraft and the higher it flies, the faster it needs to be.

In order to bring their customers as quickly as possible to their destination and to the expensive aircraft to exploit as much as possible, the airlines have the desire, as high as possible and thus to fly as quickly as possible. However, there is for the flight altitude, speed limitation, namely, the speed of sound. If they reached, an aircraft that is not designed to crash because of uncontrollability. That is, the best flight altitude is the greatest height at which the optimum speed is a bit lower than the speed of sound. However, the speed of sound increases with increasing altitude due to the decreasing temperature of the ambient air up to about 295 m / s (about 1060 km / h ) in the tropopause at about 11 km altitude from.

If the aircraft is more easily through the fuel consumption, it may rise slightly higher before its optimum speed is in the vicinity of the speed of sound.

In theory, would be the most economical variant of a cruise climb, in which the aircraft is during the entire flight in a very slight climb. For reasons of flight safety, this is not possible because an aircraft usually only receives the release for a particular altitude.

Only the de Havilland DH 106 ( Comet ) had in 1952 as the first jet airliner in the world still enough room for a continuous cruise climb in the still relatively empty airspace. After starting the first cruising altitude was 35,000 ft. The Comet then increased with decreasing weight steadily to 40,000 ft. The other road machines of the time were propeller planes, they did not fly in this altitude. Propeller aircraft had to be expected from higher altitudes no improvement in performance, but rather a performance degradation.

This freedom was repeated at the Concorde, which was put into service in 1976. Due to their small numbers they could during their transatlantic flights in cruise continuously 500 600 ( 50.000ft ft to 60,000, about 15 km to about 18 km altitude ) from FL to FL to rise. The Concorde got it from the air traffic control block shares for an altitude range of 10,000 ft. This was not a problem since the Concorde during cruise flight flew higher than the rest of aviation. This cruise climb it reached the maximum altitude just before the beginning of the approach.

But this climb is done for the usual air traffic gradually in the course of the flight because the pilot is bound to be laid down by the air traffic controller flight levels. So the cruise climb is running as a step climb ( step climb ). Also the step climb again naturally creates coordination problems and additional costs for air traffic control, and is not always possible in the crowded European airspace.

Weather

In the Earth's atmosphere most weather phenomena, in particular clouds, within the troposphere are possible. Directly to the troposphere limits the tropopause, the beginning of weather -free zone of the atmosphere, which is the larger by far. A distinctive, localized wind development, the jet stream forms at the border with the tropopause. It is up to 100 kilometers wide and three kilometers high wind streets with the highest average wind speed of about 200 kilometers per hour at its center. Already wind velocities were measured over 500 km / h.

The jet streams are caused by the rotation of the earth and the exchange of air masses between the regional high and low pressure areas. You are not predictable in the long term, but are recorded in its current appearance by weather balloons and other meteorological measurement method. They can be exploited when planning a route, to improve the speed of an aircraft. There are planning examples in which the flight route was somewhat diverted to go into the center of the jet stream. As a result, although prolonged the insurmountable distance, the speed increase but made ​​sure that the destination was reached more quickly and with less fuel consumption.

A byproduct of the jet streams are Clear Air Turbulences (CAT ). Under certain circumstances form at the edge of a jet stream turbulence, similar to the water eddies in a river between mid-river and riverbank. Are these turbulences known to meteorologists, they are shown as CAT areas on weather maps for aviation. Pilots can fly into these areas or avoid them, depending on their assessment of the severity of the turbulence. The term clear air comes from the fact that the turbulence suddenly occur without visible warning in the form of a cloud into clear air. At the center of the jet stream, it is usually quiet.

Thunderstorms also provide regularly to ensure that pilots have to deviate from the planned route, to avoid being confronted with dangerous turbulence, hail and lightning in a thunderstorm. Thunderstorms are regionally and seasonally varying height. The highest will be thunderstorms in the tropical convergence zone around the equator, they there reach a height of up to 16 kilometers and can not be overflown by ordinary commercial aircraft. In direct crossing of storm clouds could, apart from the danger of a lightning strike, the aircraft take structural damage caused by the strong turbulence inside the thundercloud. The pilots are encouraged for this reason, always keep a safe distance from storm clouds.

Duties of the crew

Cockpit Crew

As a rule, the cockpit crew of an airliner from two pilots who share the tasks in each phase of flight appropriate. During the pilot not flying ( PNF) typing, does the ATC and other administrative activities, the pilot flying (PF ) is responsible for the handling of the aircraft, in particular its control. This includes the monitoring and operation of the automatic pilot, which is normally activated during the entire trip flight. Both pilots are, however, responsible for the continuous monitoring of the air space in order to avoid a collision. For routine also includes the regular visits of weather information on the possible Notlande or alternate aerodromes and aerodrome of destination as well as the observation of the on-board weather radar for the detection and avoidance of storm cells. For several communication systems are available: ATIS, VOLMET radio service of weather stations and ACARS.

Furthermore, at specified intervals, the fuel reserves checks, as so-called fuel check. The preparations for the landing approach to be done during cruise, in particular the programming of the onboard computer, the settings of the navigation receivers and the approach briefing, must be discussed with the point by point the end of the landing approach and a possible throughput Start maneuver.

Cabin Crew

The cabin crew usually starts with the service before reaching the cruise altitude, after turning off the Anschnallzeichens by the pilots during the climb. In addition to the provision of food and beverages, the cabin crew watches over the health well-being of the passengers. Frequently occur during cruise to unforeseen medical emergencies that requires the performance of first aid, the exclamations of a physician and coordination with the pilot in terms of an emergency landing for medical reasons.

Economic activities such as the sale of duty-free goods and other goods come when time permits, do so. The cabin crew is usually by turning on the Anschnallzeichens by the pilots noted that the cruise is over and the descent was initiated. This represents an important information for the classification of work cabin

Flight attendants in aircraft for the transport of goods or live animals are responsible for supplying the cockpit crew during the flight in the first place, but also for the supply of the transport of animals accompanying keepers.

Risks in the cruise

Health risks

The technique of modern commercial aircraft cabin pressure leads to dehydration of the respiratory air in the aircraft cabin. The body loses fluid through the exhaling humid air. This circumstance can be used both in the crew as well as passengers lead to health problems ranging from poor concentration due to dehydration to blood clots ( deep vein thrombosis ).

Most injuries caused by turbulence occur also in cruise flight. This applies especially to the flight attendants that can protect against injuries caused by poorly sudden turbulence during Serviervorganges.

When the passengers cardiovascular disorders are the most common cause of medical emergencies during cruise, the degree of pre-existing conditions or pre-damage plays a significant role. This means that only a small proportion of these emergencies are causally related to the situation in cruise related, in most cases brings the passenger into the cabin with the disease without being adequately prepared for the flight.

Relatively unexplored is the impact of exposure to cosmic radiation as applied in increasingly high altitudes and near the polar caps to crew and passengers. It is possible to computationally determine the radiation dose that is received during a particular flight. Airlines are encouraged increasingly by law to record the radiation exposure of their employees, provided that these about one millisievert ( mSv ) per year, and to include this factor in the design of the service plan.

Medical emergencies during cruise cause the cabin crew to call a doctor. In consultation with the doctor, the cabin crew and the passenger the pilot shall decide whether an unscheduled stopover carried out or continuing the flight to the destination. One study of over a thousand medical emergencies during flight (English inflight medical emergency, IME), according to the main causes were for unplanned stops in this context, heart problems (28 percent), neurological disorders (20 percent) and food poisoning ( 20 percent).

For the performance of the first aid crew is a first-aid kit available that includes medical equipment such as blood pressure monitor and defibrillator, and its completeness must be verified and documented prior to each flight.

Aviation -related risks

The danger of a collision between two aircraft at cruising altitude is relatively low, but nevertheless had sporadically in the past clashes. The reasons for this are highly dependent on the individual circumstances. It is necessary a whole chain of errors, for admitting this event. In principle, the air traffic controllers are responsible for the spatial separation ( separation) of the monitored aircraft through them, but also the pilots are committed to continuous air space surveillance and collision avoidance. Technical support for this is provided by secondary radar and traffic alert and collision avoidance system.

When flying at high altitude, there is the risk of sudden or slow pressure drop, which requires an emergency descent (emergency descent ). The cause may be damaged due to material fatigue aircraft outer skin or a defect in the compressed air supply through the compressors of the engines or their control (pressure unit). This crew and passengers in the short term deficient supply of oxygen, which can lead to problems caused by hypoxia. By rules of the aviation authorities aircraft cabins shall be equipped with oxygen masks which are automatically released from the bracket above the passenger seats with a pressure loss in the cabin and release oxygen for a certain time. For the cockpit crew 's oxygen tanks and masks are available, which are designed as full face masks and with the grip of a hand can be quickly pulled over the nose and mouth (Quick doning Mask).

Through the thin air at high altitude airliners advised during cruise to their aerodynamic maximum speed, which is given by the Mach number. The Mach number indicates when the air is so compressed at the leading edges of the wings and the fuselage by the dynamic pressure that a shock wave is formed. Mach 1 is the speed of sound. Most commercial aircraft move in cruise at Mach 0.7 to Mach 0.9. The Mach number can not be read by a barometric instrument, but must be determined by an arithmetic operation using on-board computer. Transport aircraft are usually equipped with this instrumentation.

A special aerodynamic characteristics of flights at high altitude is the so-called Coffin Corner, directly translated: Coffin Corner. Thus, an aerodynamic situation is described in which an increase in speed meant a Mach number is exceeded, while a reduction in speed would lead to stall at the same moment. This situation can be represented graphically by the intersection of two curves, the intersection forms a corner, hence the term coffin corner. Both Mach number is exceeded (high speed stall ) and stall (low speed stall ) lead to the loss of lift and in the worst case to crash. A tactile precursor of the high speed stall is the high speed buffet, a low-frequency vibration, which is generated in the transition from subsonic to supersonic region on the wings by short successive small compression shocks. If the aircraft not energized at this stage, it slows itself off by the shock wave generated by the high air resistance and returns to subsonic flight.

Through the use of autopilot and autothrottle (automatic controlled power lever ) in conjunction with the onboard computer incidents related to the coffin corner are extremely rare today.

Fatigue of the pilot during cruise occasionally leads to concentration errors that still trigger in itself not a disaster, but represent a disturbance of air operations. These include the failure to hear calls by air traffic control to change the radio frequency to the next air traffic control sector. If you can not report the pilots in the air traffic agency, whose territory they fly, the flight shall be deemed " not identified " ( unidentified traffic). This can draw a Abfangeinsatz by the air forces of the country to stand for around the clock alarm Rotten of the Air Force in Germany ready for a so-called " Quick Reaction Alert" ( QRA, mutatis mutandis, to German " fast reacting alarm use " ) are ready. The identification is primarily used for the collection of route charges and to verify the overflight permission.

After the publication of a leading aircraft manufacturer, the statistical risk of a crash during cruise is relatively low. The death rate is higher than in all other phases of flight, as it is unlikely to survive a fall from a great height.

Effects on the environment

The fuel consumption of the modern airliner at cruising altitude of 500-3000 kilos of fuel per hour and engine. A twin-engined aircraft with a seating capacity for about 200 passengers consumes about 2500 kg of fuel per hour cruise. Carbon dioxide emissions from this process loads the carbon dioxide content in the atmosphere to some extent. Also, get soot and other combustion residues into the atmosphere.

The extent of the contrail of commercial aircraft at high altitude is dependent on the relative humidity of the ambient air. The air that is expelled by the jet engines, is deflected by the sudden expansion, cooling, and when the temperature reaches the dew point of the ambient air, contrails form. The visible water vapor itself does not endanger the environment. In heavy air traffic over certain tracts of land over which intersect several airways, it can be observed that the contrails of the various planes merge into a high cloud veil and so measurable lead to reduced sunlight exposure these lands.

New Technologies

Due to the utilization of the existing air traffic control units and the increasing congestion of the current airspace structure is researched continuously for more efficient methods of air traffic control. In addition to the desired long-standing intra-European unification computer systems to support the ATC also largely automated, supported by networking and digitization models have been developed. A massively funded by the major airlines model is known as Free Flight. This completely eliminates the need for air streets and uniform flight levels. The planes fly the direct line to the destination airport and adjust their altitude continuously to the current flight weight of which is reduced due to the fuel consumption.

The twin-engine airliner Boeing 787 comes up with a new technology for pressurized cabin. Instead of the compressor of the engines to produce the breathing air for the cabin two independent electrically driven oxygen - aggregates. This aims mainly lower fuel consumption of the engines, but also provides a way to enrich the breathing air with water vapor and thus to reduce the health consequences of inner dehydration. In addition, the cabin pressure was from the currently common in commercial aircraft normal condition of 8,000 ft ( 2,438 m) altitude to 6,000 ft ( 1829m ) increased. Other technical innovations are electronically dimmable cabin windows and a system for suppressing the effect of turbulence. The strongest selling point is an expected reduction in fuel consumption by 20 percent over current, equal-sized airliners. Airbus offers the A350 to a comparable advanced design.