“What does that mean?”

 Peter Verrault

Winter weather can be a real problem for helicopters.  The most dangerous problem is ice.  When ice forms on the rotor blades of a helicopter the lift generated by the blades can be seriously reduced.  In a fixed wing aircraft it can get to the point where the aircraft cannot stay in the air.  The same thing can happen to a helicopter, although it very rarely gets to that point.

What usually happens is that the aircraft starts to feel “rough”.  This is caused by two factors.

1. Ice forms unevenly on the rotor blades so each blade is producing a different amount of lift.  This causes vibration.
2. As the ice forms, the flexing of the blades can cause it to shed.  If the ice sheds unevenly (and in my world it will) the blades become unbalanced because of the differing weight of ice on each blade.  This also causes vibration.  If there is a lot of ice on the blades and one sheds a large amount the vibration can become very violent very suddenly.

There are two other problems with ice.  Ice on the airframe adds weight to the aircraft.  This can amount to a substantial weight gain.  This will reduce performance and increase the power required.  Second, ice can form on the windshield.  This can happen suddenly and cause real visibilility problems.  On one flight my windshield iced over completely in about three seconds.  I had no vision out the front of the aircraft.  Luckily, as we descended the ice melted off.

Freezing rain is an obvious culprit.  Flying through clouds when it is below freezing is never a good idea.  I have even gotten ice flying in above freezing temperatures (7C) and hitting rain falling from very cold air above.  The water drops were super-cooled.  As soon as they hit the aircraft they froze.

Watch for ice forming on the windshield wiper arms, corners of the windows, door handles, basically anything sticking out into the wind.

If you are in ice, get out of it.  If you are not, stay out of it.