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Helicopter Safety - Technical Issues

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Mechanical problems

All of the mechanical parts of a helicopter are stressed due to wear and (physical) strain. Mechanical parts should be regularly inspected, and will, ultimately, have to be replaced. Helicopters are more sensitive to mechanical failure than airplanes because of the rotor system generated vibrations. To avoid mechanical problems, proper maintenance is mandatory.

  • Follow the manufacturer’s maintenance schedule and instructions
  • Always use certified replacement parts.
  • Beware of the status of your helicopter after maintenance. The chances of mechanical failure are higher in the period immediately after maintenance has been carried out. This paradoxical situation occurs because maintenance can also cause faults by, e.g. procedures not being followed or a problem during re-assembly, etc.
  • Always take any deviation from your normal operating experience seriously; it can be an early warning. 
  • Carry out pre-flight inspections. You, as a pilot, are responsible!
  • Carry out post-flight inspections.

Lost of tail rotor authority

This is a very serious problem, since without tail rotor authority the helicopter will almost certainly start to spin around the rotorshaft axis. This spinning is caused by the fact that the engine produces torque to rotate the rotorshaft. As a result, the rotor will start turning in one direction and the fuselage in the opposite direction. The tail rotor compensates for this rotating movement. Therefore, without the tail rotor force in place, the helicopter starts spinning.

As a loss of tail rotor authority can only come about by application of the engine power, a counter measure is therefore to remove engine power. Because this will also result in (rapidly) low rotor rpm, the collective should be lowered too.

  • Start autorotation; be sure to remove engine power.
  • When tail rotor thrust is still in place, but cannot be controlled (no yaw control, e.g. obstructed), yaw can, to some degree, be influenced by changing torque, thus by applying more or less engine power.

Loss of power

In the event of a loss of engine power, rotor RPM will quickly diminish. The rate at which this occurs depends on the amount of kinetic energy that is stored in the still moving rotor system. Fortunately, helicopters can fly without engine power by lowering the collective completely. The catch, however, is that the time between power loss and the lowering of the collective should be minimal. The amount of time available is dependent on the amount of stored kinetic energy in the rotor system. Larger rotor systems (heavier, more blades) have an advantage here, because they store more energy. A helicopter with too low RPM will, undoubtedly, be lost.

A helicopter with collective complete lowered can fly due to the shape of the rotor blades. They are designed such that the innerpart wil drive the rotors while the middle part of the rotors provide the required thrust vector. Of cource, the rotor system isn't as effective (from a pilot point of view) as in powered condition. The descent rate is quite high. However, it is perfectly possible to fly and land every helicopter in autoration, if practiced.


Don't Get Caught in a Fatal Trap!

A vital resource for pilots, technicians, and helicopter enthusiasts, this book analyses every possible helicopter accident in detail. It looks at accidents that have been caused by a broad range of factors, such as technical problems, weather influences, mechanical failures, human factors, and many more. The treatment and analysis of each cause is dealt with in depth. What makes this text invaluable is that throughout this work an attempt is made to analyze accidents with a view to finding common causes, solutions, and enabling preventive measures to be defined. This makes 'Fatal Traps for Helicopter Pilots' a potential life saver.

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HeliStart is authored by Peter Goossens.


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