Descent and Landing

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Descent and Landing
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Descent Profiles

• When operating piston and light turboprop
  aircraft descent planning is quite simple.
• These aircraft are relatively easy to slow down
  in the descent and configure for approach and
  landing. (propellers add drag)
• Jet aircraft are designed to offer minimal drag
  in order to achieve high cruising speeds.
• As a result they have a tendency to be slippery
  (resist deceleration)
• With larger aircraft momentum plays a big part in
  this reluctance to slow down.

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Choosing a Descent Point

• There are many factors involved in choosing a
  descent point
• Weather (icing, turbulence, wind)
• Fuel Burn
• Crossing Restrictions (ATC, STAR)
• Speed Limit Orders
• Descent should be delayed as long as possible to
  avoid prolonged exposure to turbulence or icing.
• Delaying descent also produces a more fuel
  efficient profile.
• Winds will affect the descent point by dictating
  a late descent in tailwind conditions or an early
  descent in headwind conditions.
• The descent point always hinges on the ability to
  get down, and get slowed down in time to execute
  an arrival and approach.

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• ATC will sometimes impose crossing restrictions
  which may result in starting the descent earlier
  than anticipated.
• STAR procedures often include specific crossing
  and speed restrictions which must be planned for
  and adhered to.
• The key is formulating a plan well ahead of time
  and adapting to changes which may arise during
  the descent.
• A failure to meet target speeds for flap
  extension in the descent will result in a
  requested level off or extended approach path. If
  close enough to the airport it could result in a
  missed approach.

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Rules of Thumb

• To plan your descent point for a 3 slope
  multiply altitude change (in thousands) by three
  to find required distance to start descent.
• 20,000-10,00010,000 to be lost
• 10330
• Begin descent 30nm back to cross fix at 10,000
• Descent rate required to meet crossing
  restriction is altitude to be lost divided by
  minutes to fix.
• 23000 to descend, 7 minutes from fix
  23000/73300/min.
• To plan a constant 300 per nm descent profile
  multiply ground speed by five to achieve required
  rate of descent. Or divide GS by 2 and add a 0.
  (3 descent path)
• At a ground speed of 450kts the required rate of
  descent is 2250 per minute.
• This rate of descent must be recalculated as
  ground speed changes.

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Exercise

• You are flying a Boeing 737 and have been cleared
  the KEINN SEVEN ARR, RWYS 08L and 08R are active.
  You are 30nm North at FL280 and proceeding direct
  TRENA.
• At what point should you start your descent to
  maintain a 3 descent profile?
• Considering a 370 knot ground speed what is the
  initial required rate of descent?
• What crossing restrictions must you meet?
• What routing will you fly? Give specific track
  information.
• What speed restrictions must you meet? List all
  and be specific.

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Emergency Descent

• An emergency descent is initiated when loss of
  altitude or a time to landing is of the essence.
• In the event of pressurization problems either in
  the form of rapid decompression or a smoke
  removal drill loss of altitude is the priority.
• In this case an emergency descent configuration
  which provides the greatest loss of altitude
  (highest rate if descent) will be initiated.
  (generally flaps and gear extended to increase
  drag)
• In the event of a time sensitive issue such as an
  uncontrollable engine or cabin fire the time to
  landing takes priority.
• In this case an emergency descent at maximum
  forward speed will be initiated.
• ATC must always be advised as soon as practical
  to avoid potential traffic conflicts.

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LANDING
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Fly The Numbers

• Landing large aircraft requires diligent speed
  control and handling.
• VREF speed is calculated for each approach and
  can vary greatly with weight.
• VREF is a result of stall speed for a given
  aircraft weight in landing configuration.
  (Normally 1.3VSO)
• Large aircraft require greater landing distances
  and take longer to slow down. Any deviation from
  the published speeds could result in landing
  long.
• The aircraft should cross the threshold at 50
  and VREF.

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• At 50 start the flare with a simultaneous power
  reduction.
• If a 3 glide slope is maintained throughout the
  wheels should touch down positively at the 1000
  markers.
• Attempting to milk it on will increase landing
  distances and possibly result in stalling just
  above the runway surface.
• See MD-80 video.

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Wind Adjustment

• VREF should be adjusted to account for gusty wind
  conditions.
• A gust factor must be added and is usually
  operator specific.
• An approach speed of VREF gust factor to a
  maximum of 15-20kts is fairly standard but
  operator specific.
• This gust factor correction provides a further
  buffer between VREF and stall speed to protect
  against performance degrading wind shear.

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Crosswinds

• Crosswind technique in aircraft with long
  wingspans and under wing engines is very
  demanding.
• In strong crosswinds the danger of striking an
  engine or wing tip is very real.
• Manufacturers publish approved crosswind
  techniques and limitations which account for
  these airframe restrictions.
• The preferred crosswind technique is to crab
  until just before touchdown at which point rudder
  and aileron input is used to straighten out the
  crab and maintain centerline.
• This technique avoids long periods of side slip
  and maximizes passenger comfort.
• In strong crosswinds it is possible for the
  pilots to be sitting over the grass just prior to
  touchdown, this requires a good feel for the
  dimensions of the aircraft.

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Landing Performance

• Calculating landing performance accurately
  becomes critical in large aircraft.
• Performance charts or company landing cards will
  be available to determine landing distance for
  prevailing conditions.
• Any abnormal situation will have an effect on
  landing distance required. (anti-skid failure,
  flap/slat malfunction, downslope, surface
  contamination, tailwind).

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Landing Distance Required

• For commuter and airline operators a dispatch
  restriction of 60 of landing distance (jets) and
  70 of landing distance (turboprops) is enforced.
• In order for a turboprop aircraft to be
  dispatched to an airport the landing distance
  required must be no more than 70 of the landing
  distance available.
• This restriction must be calculated and met
  before departure, but is not limiting upon
  arrival.

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Canadian Runway Friction Index

• The CRFI is a surface friction report measured
  with a decelerometer when available.
• CRFI is measured on a scale of 0 to 1 with 0
  representing the poorest braking action.
• The CRFI and its associated landing distance
  table contains advisory landing distance
  information for less than ideal runway surface
  conditions.
• In the absence of manufacturer published landing
  distances for contaminated runways the CRFI table
  corrections are available for use.

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• The CRFI will be given as part of an Aircraft
  Movement Surface Condition Report (AMSCR) when
  available.
• The AMSCR is issued to alert pilots to natural
  surface contaminants which could affect aircraft
  braking performance.
• A CRFI crosswind limit chart is also published.
• These tables are found in the AIM 1.6.6

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Hydroplaning

• A CRFI is not issued for runways contaminated
  with water alone.
• This standing water can have a significant impact
  on stopping distances.
• Hydroplaning has been estimated to increase
  stopping distances by as much as 700.
• The wet condition associated with rain may
  produce friction values of approx. CRFI 0.3 for
  a poorly drained surface but normally 0.5 for
  well maintained and drained surfaces.

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Questions

• At what speed will a C-172 start to hydroplane on
  takeoff? Landing?
• Will the nosewheel hydroplane at the same speed
  as the mains?
• At what speed will a B-95 start to hydroplane on
  takeoff? Landing?
• Will the nosewheel hydroplane at the same speed
  as the mains?
• Is hydroplaning more likely to occur on takeoff
  or landing? Why?
• Some large aircraft have a way to increase their
  landing hydroplane speed, what is it?

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Types of Hydroplaning

• Dynamic Hydroplaning occurs when there is
  standing water on the runway. Water is not
  displaced fast enough to allow the tire to
  contact the surface, and the tire rides on a
  wedge of water.
• Viscous Hydroplaning on smooth or contaminated
  surfaces (oil, rubber, dust, de-ice fluid, fuel)
  a thin film of water resists penetration by the
  tire and reduces braking action. Can occur at
  lower speeds.
• Reverted Rubber Hydroplaning as a tire skids and
  rubber melts it acts as a seal which traps water
  under the tire footprint where it is heated to
  steam which supports the tire off the runway
  surface.

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Rotating Tire 9vPSI
Non-Rotating Tire 7.7vPSI
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Reversers

• When contaminated runways reduce braking action
  thrust reversers can greatly improve stopping
  performance.
• The one area of caution is landings during
  reduced friction under crosswind conditions.
• Reverse is initially beneficial but caution must
  be used in the event of a skid.
• The reverse thrust vector will compound the skid
  by pulling the aircraft in the direction of the
  skid.
• If a skid condition is encountered reverse should
  be immediately disengaged, until the skid
  recovery is complete.

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Reverse compounds a skid