Pitot-Static Systems

Introduction:

Pitot Tube:

  • Pitot Tube
    Pitot Tube
  • Invented by Henri Pitot in 1732
  • Placed in front of the airfoil to prevent disturbed air from entering
  • Used only for the Airspeed Indicator (ASI)

  • Pitot Heat:

    • Pitot Tubes are often electrically heated, which can prevent and remove ice accumulation
    • Note that these devices should only be utilized during ground operations when necessary
      • Leaving them on unnecessarily can cause heat to the point of damage/malfunction

Static Port:

  • Static Port
    Static Port
  • Samples of ambient still-air atmospheric pressure
  • Normally flush mounted on the side of the aircraft where air is undisturbed
  • Senses movement of the aircraft through air both horizontally and vertically
  • Placed in one more places where the air is not disturbed
  • Some ports are heated
  • Dual ports remove errors due to slips and skids
  • Responsible for Airspeed Indicator, Altimeter, and Vertical Speed Indicators
  • The POH/AFM contains any corrections that must be applied to the airspeed for the various configurations of flaps and landing gear

  • Alternate Static Source:

    • On some aircraft, an alternate static air source valve is used for emergencies
    • If the alternate source is vented inside the airplane, where static pressure is usually lower than outside static pressure, selection of the alternate source may result in the following erroneous instrument indications:
      1. The altimeter reads higher than normal
      2. Indicated airspeed (IAS) reads greater than normal
      3. VSI momentarily shows a climb
    • Many POHs provide a correction table and aircraft-specific instructions
    • In any case, the alternate static source is not corrected for non-standard pressure (as it is with an altimeter's Kollsman window)
    • The use of alternate static sources may impact other instruments that rely on static pressure (i.e., autopilots, TCAS, transponder, etc.)
    • The use of alternate static sources can also decrease the accuracy beyond the 75 feet recommendation outlined in the Aeronautical Information Manual
  • Instrument Flying Handbook. Figure 3-1, A Typical Electrically Heated Pitot-Static Tube
    Instrument Flying Handbook, A Typical Electrically Heated Pitot-Static Head
  • Instrument Flying Handbook. Figure 3-1, A Typical Electrically Heated Pitot-Static Tube
    Instrument Flying Handbook, A Typical Electrically Heated Pitot-Static Head
  • Static Port
    Static Port

Pitot-Static System Anomalies and Malfunctions:

  • Blockages in the system can cause a variety of errors
  • To prevent these errors, you must complete a thorough pre-flight
  • Blockages can occur from FOD, striking an object, insects, and icing
  • Consult the Pilot's Operating Handbook/Airplane Flight Manual (POH/AFM) to determine the amount of error

  • Pitot-Tube Blockage (static open):

    • At the altitude where the Pitot tube becomes blocked, the airspeed indicator remains at the existing airspeed and doesn't reflect actual changes in speed
      • At altitudes above where the Pitot tube became blocked, the ASI displays a higher-than-actual airspeed, increasing steadily as altitude increases
      • At lower altitudes, the ASI displays a lower-than-actual airspeed, decreasing steadily as altitude decreases

  • Pitot-Tube Drain Hole Blockage:

    • Would cause ASI to malfunction

  • Pitot-Tube and Drain Hole Blocked:

    • Would cause ASI to malfunction

  • Static Port Blockage:

    • Would cause ASI, altimeter, and VSI to malfunction
    • If in a real emergency, malfunctions can be corrected with alternate air or breaking the glass on a Pitot static instrument (VSI)
    • If the static ports become blocked, the ASI would still function but could produce inaccurate indications
    • At the altitude where the blockage occurs, airspeed indications would be normal
      • At altitudes above which the static ports became blocked, the ASI displays a lower-than-actual airspeed continually decreasing as altitude is increased
      • At lower altitudes, the ASI displays a higher-than-actual airspeed, increasing steadily as altitude decreases
    • The trapped pressure in the static system causes the altimeter to remain at the altitude where the blockage occurred
    • The VSI remains at zero
    • Pilots should use alternate static sources per the pilot operating handbook

Common Training Aircraft Pitot-Static System Characteristics:

  • Piper Arrow:

    • Composed of a heated Pitot tube on the lower left wing
    • Two static ports are located on each side of the fuselage
    • Alternate static air (below the pilot control yoke) provides static pressure from inside the cabin

  • Cessna 172:

    • Composed of a heated Pitot tube on the lower surface of the left wing
    • An external static port is located on the lower left side of the forward fuselage
    • Pitot Tube consists of a heating element, a 5-amp switch/breaker, and associated wiring
    • Alternate static (below throttle) provides pressure from inside the cabin

Private Pilot - Operation of Aircraft Systems Airman Certification Standards:

  • To determine that the applicant exhibits satisfactory knowledge, risk management, and skills associated with the safe operation of systems on the airplane provided for the flight test
  • References: FAA-H-8083-2, FAA-H-8083-3, FAA-H-8083-23, FAA-H-8083-25; POH/AFM
  • Lesson Plan

Operation of Aircraft Systems Knowledge:

The applicant must demonstrate an understanding of:

Operation of Aircraft Systems Risk Management:

The applicant demonstrates the ability to identify, assess, and mitigate risks, encompassing:

  • PA.I.G.R1:

    Failure to detect system malfunctions or failures

  • PA.I.G.R2:

    Improper management of a system failure

  • PA.I.G.R3:

    Failure to monitor and manage automated systems

Operation of Aircraft Systems Skills:

The applicant demonstrates the ability to:

  • PA.I.G.S1:

    Operate at least three of the systems listed in K1a through K1l above appropriately

  • PA.I.G.S2:

    Use appropriate checklists properly

Private Pilot - Systems and Equipment Malfunctions Airman Certification Standards:

  • To determine that the applicant exhibits satisfactory knowledge, risk management, and skills associated with system and equipment malfunctions appropriate to the airplane provided for the practical test and analyzing the situation and take appropriate action for simulated emergencies
  • FAA-H-8083-2, FAA-H-8083-3; POH/AFM

Systems and Equipment Malfunctions Knowledge:

The applicant must demonstrate an understanding of:

Systems and Equipment Malfunctions Risk Management:

The applicant demonstrates the ability to identify, assess, and mitigate risks, encompassing:

  • PA.IX.C.R1:

    Failure to use the proper checklist for a system or equipment malfunction

  • PA.IX.C.R2:

    Distractions, loss of situational awareness, or improper task management

Systems and Equipment Malfunctions Skills:

The applicant demonstrates the ability to:

  • PA.IX.C.S1:

    Describe appropriate action for simulated emergencies specified by the evaluator, from at least three of the elements or sub-elements listed in K1 through K5 above

  • PA.IX.C.S2:

    Complete the appropriate checklist

Conclusion:

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