Event: CPT 4

Last updated: 7 April, 2003 1:28
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  1. Main drive shaft failure - The main drive shaft, also known as the barbell shaft, connects the engine to the transmission. It has a flexible splined coupling on each end, giving it its name. The aft end is connected to the freewheeling unit. Then the shaft passes through the firewall and connects to the transmission input pinion. Failure of this shaft would unload the freewheeling compressor and leave the rotor transmission, and consequently, the rotor, underpowered. [Systems 4-6]

  2. Engine restart in flight - An engine restart in flight would most likely result from a malfunction of the fuel control unit or fuel system. The decision to attempt an engine restart during flight is the pilot's responsibility and is dependent upon the pilot's experience and the operating altitude. Consideration must be given to the cause of the failure prior to attempting restart. Engine Restart [NATOPS 14.5] included below.

  3. Vibration identification - It is important to note that sources of vibrations can only be from rotating or moving parts.

    1. Low frequency vibrations - Classified as one or two beats per revolution. Most commonly caused by the main rotor. Vertical "One per" is caused by an out-of-track condition, which causes more lift on one blade than another at the same point of rotation. Lateral "One per" vibrations are caused by a difference in weights of blades (spanwise imbalance) or a misalignment of blades (chordwise imbalance). Two-to one vibrations are inherent in two-blades systems at about 100 to 110 kts.
    2. Medium frequency vibrations - Classified as 4 to 6 beats per revolution, they are also inherent in helicopters. If there is an increase, it may be because of a change in aircraft's ability to absorb noise, or a loose part vibrating with rotor system.
    3. High frequency vibrations - Felt as a "buzz" due to high speed. Always present as well, it is caused by anything that vibrates at a speed higher than that of the tail rotor. Common problems are tail rotor out-of-track, out-of-balance, or worn tail rotor components. [NATOPS 11-9, AERO 5-12]
  4. Mast bumping - The result of excessive rotor flapping. If flapping exceeds the maximum allowed angle, a static stop will violently contact the mast, causing mast damage or separation.

    The most influential causes:
    1) Low G maneuvers (below 0.5 g's)
    2) Rapid, large cyclic movements (especially forward)
    3) Flight near longitudinal / lateral CG limits
    4) High slope landings.
    Less influential causes:
    1) Max sideward/rearward flight
    2) Sideslip
    3) Blade stall conditions

    Warning • Should mast bumping occur in flight, catastrophic results are probable. Since conditions causing rotor flapping are cumulative, improper pilot response/recovery techniques to flight situation approaching or favorable to mast bumping can aggravate the situation and lead to in-flight mast bumping and mast separation. [NATOPS 11.5]

    Low G flight, such as crossing a ridgeline, masking and unmasking, acquiring/staying on a target, and recovery from a pull-up, allows thrust to be unloaded from the rotor head. Incorrect pilot inputs for engine failure and tail rotor failure can also lead to excessive flapping. Recover should be made by reapplying thrust to the rotor head again, usually through aft cyclic. [System 5-11]

    Indications: Sharp two-rev knocking

    During high speed sideward or rearward flight:
    1. Cyclic - Immediately Apply Smoothly Toward CENTER
    2. Pedals - Immediately Apply as Req. to Align the Nose with the Direction of Travel
    3. Land immediately

    During other flight conditions:
    1. Cyclic - Immediately Apply AFT to Establish Positive G Load on Rotor, Then Center Laterally
    2. Controls - As Required to Regain Balanced Flight
    3. Land immediately

    Cyclic: Move to stop bumping
    Rear/Side flight:
    Cyclic: Move slightly toward center
    Pedal: Align nose w/ direction of travel
    Slope Landing:
    Cyclic: Move toward center to stop bumping; reestablish hover
    Engine failure,
    high forward airspeed
    Cyclic: Move aft to maintain positive G (positive thrust), retain Nr, and avoid mast bumping during auto entry
    Collective: As req. to maintain Nr
    Low G maneuvers
    < 0.5G
    (Other than nose high)
    Cyclic: Aft, then center laterally to regain positive g (positive thrust) on rotor and maintain Nr
    Collective: Judiciously increase, if possible
    Pedal: As req.
    Nose high,
    low airspeed
    Cyclic: Neutral
  5. Ditching

      Once the decision has been to made to ditch:
      1. Passengers and crew - Alert
      2. Shoulder harness - Locked
      3. Mayday/IFF - Transmit/EMER
      4. Perform a normal approach to 3 to 5 feet hover
      5. Doors - Jettison
      6. Nonessential personnel - Execute Emergency Egress
      7. Helicopter - Move, Safe Distance Away
      8. Vertical landing - Perform
      9. Twist grip - Close
      10. Collective - Increase Slowly to Maximum Pitch
      11. Cyclic - Maintain Helicopter Upright As Long As Possible
      12. Emergency Egress - Execute
      13. Lifevest - Inflate (when well clear of helicopter)

      Time permitting:
      1. Autorotate
      2. Shoulder harness - Locked

      If time and altitude permits:
      3. Crew/passengers - Alert
      4. Mayday - Transmit On Guard
      5. Squawk - EMER
      6. Doors - Jettison

      WARNING • Do not abandon helicopter until rotor blades have stopped. Do not inflate lifevest until well clear of the helo.

      7. Underwater egress - Execute



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(none for this event)


    Indications: increase in Nr, Nf, Ng, TOT, Right yaw, Engine noise increase

    1. Collective - Increase (to maintain Nr in operating range)
    2. Twist grip - Reduce (to maintain Nf in operating range)
    3. Collective/twist grip - Readjust
    4. Land as soon as possible

    Note • The Nf overspeed must be continually controlled by coordinating collective and twist grip.

    Indications: Low Nr, Low Nf

    If Nr can be maintained at 90% or higher in level flight, it is safe to proceed to a suitable landing site. Terrain permitting, a sliding landing offers the lowest power required. Do not decelerate below the minimum airspeed of 50 KIAS while executing the power check. If some usable power exists but level flight cannot be maintained, that power, if sufficient, may be utilized to effect a landing or minimize rate of descent en route to a more suitable site for autorotation.

    1. Collective - Adjust to maintain Nr within limits
    2. Twist grip - Full Open
    3. GOV RPM - Full Increase
    4. Check power available with Nr in limits
    If power is not sufficient:
    5. Autorotate
    If sufficient power is available:
    6. Land as soon as possible
    Indications: Popping or rumbling noise, Vibrations, Rapid rise in TOT, Ng fluctuation, Loss of power

    1. Collective Reduce (maintain Nr within limits)
    2. Reduce severity of maneuver
    If TOT within limits:
    3. Land as soon as possible
    If TOT not within limits:
    4. Twist grip Reduce to maintain TOT within limits
    5. Check power available with Nr within limits
    If power is not sufficient:
    6. Autorotate
    If sufficient power is available:
    7. Land as soon as possible

    Be prepared for a complete power loss.
    When accelerating the rotor system during the initial rotor engagement or after a full autorotation, exceeding 40% torque may induce compressor stall or engine chugging.

    Slight power (collective) reduction will often eliminate compressor stalls.
    Mild compressor stalls may occur that will allow powered flight if TOT is within limits.

  4. ENGINE FAILURE [Adapted NATOPS 14.1]
    Indications: Nr decrease, Rapid settling, Left yaw, Low rotor rpm caution light and audio, Engine-out caution light and audio

    Immediately upon engine failure, rotor rpm will decay and the nose will swing to the left, because of loss of power and torque. Except when near surface, it is mandatory that autorotation be established by immediately lowering the collective pitch to minimum. Right pedal decreases tail rotor thrust. High gross weights, increased g loads, and higher altitudes and temperatures will cause increased rpm, which other than that specified for maximum glide {94-95%}, will cause increased rates of descent. At 75 to 100 feet, a cyclic flare should be established to reduce airspeed, rate of descent, and increase rotor rpm. Caution should exercised to avoid striking tail; level skids before ground contact.

    The best glide airspeed is 72 KIAS. The minimum rate of descent airspeed is 50 KIAS. Do not exceed 100 KIAS in sustained autorotation.
    If time and altitude permit, engine restart may be attempted. The decision to attempt a restart is the pilot's responsibility and is dependent upon the pilot's experience and operating attitude.
    All autorotative landings should be made into the wind at a suitable landing site.

    An engine restart in flight would most likely result from a malfunction of the fuel control unit or fuel system. The decision to attempt an engine restart during flight is the pilot's responsibility and is dependent upon the pilot's experience and the operating altitude. Consideration must be given to the cause of the failure prior to attempting restart.

       If attempting a restart, proceed as follows:
    1. Autorotate
    2. Fuel valve Check On
    3. Starter Engage
       If light off occurs:
    4. Land as soon as possible

    If Ng is allowed to fall below a minimum of 15% Ng the close the twist grip and perform a normal start.
    Do not attempt to start above 12,000 feet as TOT rises too fast to control.

    Ng will not decrease below minimum starting speed within 10 seconds because of rotational inertia plus possible ram effect. The twist grip can be left in the full open position since fuel flow during the start will be on the normal acceleration schedule.
    Indications: Loadmeter/DC Voltmeter show excessive load, Smoke, Fumes, SparksPrior to shutting off all electrical power, the pilot must consider the equipment that is essential to the particular flight environment that will be encountered (e.g., flight instruments and fuel boost pumps).

    [NATOPS 14.16.1]
    1. BAT switch OFF
       © 2. STANDBY GEN switch OFF
       © 3. STBY ATT ID switch OFF if in VFR Conditions
    4. MAIN GEN switch OFF
       If fire persists:
    5. Land immediately
       If fire extinguishes:
    6. Land as soon as possible

       If the electrical power is required to restore minimum required equipment for continued flight, proceed as follows:
    7. All circuit breakers Out
       © 8. Check BAT RELAY CB In
    9. BAT switch ON
    11. MAIN GEN switch Reset, then ON
       ©12. STBY GEN switch ON
       ©13. STBY IND ATT switch ON
    14. Circuit breakers for essential equipment In One at a Time in Order of Importance

    Ensure corresponding bus supply circuit breakers are in to provide power to desired electrical equipment.
    Voltmeter will not indicate battery voltage until battery bus supply and voltmeter circuit breakers are in.
    Flight operation can be maintained without battery and generator. Instruments powered by the 28V DC power system, however, will be inoperable.

    1. Affected equipment Secure
    2. Affected C/B's Pull
       If fire persists:
    3. Electrical Fire Unknown Origin Proc. Execute
       If fire extinguishes:
    4. Land as soon as practicable {Because cause of fire known and extinguished}
    Indications: Nr decrease, Nf/Ng rpm increase, Left yaw, Loud bang/noise

    1. Autorotate
    2. Twist grip Adjust to maintain Nf/Ng in operating range
       When on deck:
    3. Emergency shutdown Complete

    The engine must continue to operate to provide tail rotor drive. Tail rotor drive effectiveness may be lost if Nf is allowed to go below 80%.


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  1. All FAM stage checklists and voice reports - PRESTART CHECKLISTS
  2. Normal starting/shutdown procedures - PRESTART CHECKLISTS
  3. Abnormal starts - same as from CPT1
  4. Generator/electrical malfunctions - same as from CPT3
  5. Hydraulic system failure - same as from CPT3
  6. Chip light - same as from CPT3
  7. Post shutdown fire/internal - same as from CPT1

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