CRUISE PERFORMANCE

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CRUISE PERFORMANCE
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Cruise Control

• Many corporate and regional jets spend their days
  flying shorter domestic routes.
• These short routes generally consist of a
  takeoff, climb, descent, and landing.
• In this case cruise planning isnt as critical.
• For larger jets operating on long transoceanic
  flights cruise control is critical and dependant
  on a number of factors.
• Altitude
• Fuel load
• Aircraft weight
• Weather
• Buffet boundaries

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Cruise Procedures

• High-speed cruise cruise at the maximum
  indicated airspeed or constant mach number.
• Provides the quickest en-route time, but
  sacrifices fuel efficiency. (not normally used by
  airlines)
• A variation of high-speed cruise is adopted by
  some operators where speed is reduced slightly to
  provide an additional Mmo buffer.
• Long-range cruise cruise mach number is varied
  with altitude and weight for maximum economy.
• Provides the best fuel economy for given flight
  conditions.
• Relative to lift/drag ratio for weight and speed.
• Thrust setting must be continually adjusted
  (reduced) as weight decreases throughout the
  flight in order to maintain optimum speed.

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Range Calculations

• Specific Air Range(SAR) Nautical air miles per
  pound of fuel burned. (SAR increases as weight
  decreases)
• SAR(NAM/lb)TAS/Fuel Flow
• Specific Ground Range(SGR) Nautical ground miles
  per pound of fuel burned.(provides an indication
  of the most efficient cruising altitude taking
  winds into account.
• SGR(NGM/lb)GS/Fuel Flow

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Example

• Find the best altitude for range under these
  conditions
• FL310, Track 270T, TAS 330kts, Winds
  270T/30kts, Fuel Flow 1100lbs/hr
• FL350, Track 270T, TAS 310kts, Winds
  270T/60kts, Fuel Flow 950lbs/hr
• Best altitude for range is FL310
  300/11000.27NGM/lb (FL3500.26/lb)

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Fuel Conservation

• Rising fuel costs have initiated change
  throughout the commercial aviation world.
• The higher fuel costs get, the more they affect
  an airlines bottom line.
• The price of jet fuel has doubled since 2003.
• American Airlines fuel bill was 5 billion
  dollars in 2005.
• By implementing fuel conservation techniques the
  airline saves 155 million dollars a year.
• All airlines have made fuel conservation
  practices a priority and pilots are expected to
  operate accordingly.

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Aircraft Handling

• Pilots can have a huge impact on fuel savings by
  being conscious of fuel conservation methods.
• Dont start the engines until you are ready and
  assured taxi for takeoff.
• Taxi on one engine. (company policy)
• Adhere to company fuel conservation schedules in
  cruise.
• Resist the urge to tanker fuel. (the increased
  aircraft weight increases fuel consumption)
• Request direct routings when possible.
• Diligently monitor changes in wind and modify
  altitude accordingly.
• Delay descent to maximize high altitude flight.

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Tanker Fuel

• The importance of contingency fuel is obvious no
  one wants to run out of gas.
• On transoceanic flights it becomes even more
  critical.
• If the destination weather deteriorates alternate
  options are limited.
• Carrying this contingency fuel increases aircraft
  weight and fuel burn.
• It takes careful planning in order to balance
  safety and fuel conservation. (In most cases a
  strong trust in the dispatch team)
• The only time it makes sense to tanker extra fuel
  is if destination fuel prices are high enough to
  offset the extra fuel burn.

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Mach Number

• The speed of sound varies with temperature.
• Sspeed of sound in knots
• KKelvin (C273)
• S39vTemp K
• The speed of sound at 15C is 39v288662kts
• Mach number is the ratio of true air speed of the
  aircraft to the speed of sound. Mach 0.8 is 80
  of the speed of sound.
• Mach number TAS/S
• An aircraft traveling at a TAS of 370kts when the
  temperature is 15C has a mach number of 0.56

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Critical Mach Number MCRIT

• Critical mach number is the flight speed at which
  airflow reaches the speed of sound over any part
  of the airframe.
• The compressibility of air at high speeds causes
  a shock wave to form.
• At MCRIT a small shockwave starts to form on the
  upper, forward surface of the wing.
• As speed increases beyond MCRIT the shockwave
  becomes more pronounced and creates a drag rise.

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Maximum Mach Operation MMO

• Limiting maximum speed for flight operations.
• As speed increases beyond MCRIT the shockwave
  grows and moves further aft.
• MMO is the maximum speed the aircraft can fly
  without encountering the dangerous flight
  characteristics associated with boundary layer
  separation.
• These include mach buffet, mach tuck, and dutch
  roll.
• An airspeed limitation indicator (barber pole)
  automatically adjusts for temperature changes.
• An aural warning (clacker) actuates if the speed
  is exceeded.

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Coffin Corner

• As an aircraft gains altitude stall speeds
  increase while Maximum Mach speed decreases.
• At high altitude the separation between these
  speeds narrows and defines the aircrafts maximum
  operating altitude for a specific weight.
• The buffet margin is the airspeed range between
  the stall buffet and the high-speed buffet.
• When operating with a narrow buffet margin the
  danger of misdiagnosing adverse flight
  characteristics is always present. (initiating a
  stall recovery when mach buffet is encountered)
• As aircraft weight decreases throughout the
  flight higher altitudes become available.

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Stick Shakers and Pushers

• Stick Shaker A stall warning device installed in
  large turbine powered aircraft to warn against
  approach to stall. The control column will
  literally begin to shake as the aircraft
  approaches the stall.
• Stick Pusher Some aircraft are equipped with a
  device which will automatically lower the pitch
  of the aircraft when stall is imminent. The stick
  pusher will manipulate the control column or the
  elevator control surface depending on
  installation.

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Altitude Selection

• Choosing the optimum cruising altitude is
  critical for long range flights.
• A less than optimum altitude will result in more
  fuel burn.
• Altitude can and should be changed as aircraft
  weight is decreased.
• ATC will accommodate as well as they can in order
  for operators to maximize efficiency.
• Other things to consider when choosing a cruising
  altitude are weather, turbulence, buffet
  boundaries.
• Modern airlines have sophisticated dispatch
  centers which compile and generate flight plans
  for the flight crews.
• This information is computer generated and very
  accurate.
• It is still the pilots responsibility to verify
  this planning information and make any necessary
  changes en-route due to other than forecast
  conditions.
• Another pilot aid on sophisticated aircraft are
  FMS.
• Flight management systems will continually
  recalculate optimum performance parameters as
  conditions change in order to maximize
  efficiency.

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ETOPS

• Extended Range Twin-Engine Operation
• In the past longer transoceanic trips were
  limited to aircraft with more than two engines
  due to strict regulations imposed on twin engine
  aircraft.
• With the introduction of the 757/767 and their
  proven capability and reliability the governing
  bodies provided a certification program called
  ETOPS.
• The operator and aircraft must adhere to strict
  reliability and maintenance schedules in order to
  become ETOPS certified.
• An ETOPS certified operator is able to fly
  twin-engine aircraft on routes otherwise
  prohibited.

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120 min and 180 min ETOPS