ICING INFLIGHT HELICOPTER

1. INFLIGHT
ICING
GUILLERMO SÁENZ SAN BARTOLOMÉ
CAP. ANTARCTICA & SAR PILOT

2. ICING IN
HELICOPTERS
Icing is defined as the formation of
ice that occurs on an helicopter
under certain circumstances.
In order to icing to occur, it is
necessary that there be liquid
water and that its temperature is
less than 0º.
This means that there is
supercooled water in the
atmosphere. The icing occurs
when the helicopter or parts of it
come into contact with the drops,
which instantly freeze on the
surface of the helicopter.

3. TYPES OF ICING
GRANULAR ICE: It is opaque, white, porous granular
texture, weighs little and adheres little, releasing easily.
It is formed when the aircraft comes in contact with
small supercooled drops. This type of icing can occur
up to fairly low temperatures (on the order of -20 ° C).
CLEAR ICE: This is the type of icing that can be
considered as more dangerous for the flight. It is
dense, crystalline and transparent, and detaches with
difficulty due to its adhesion. It forms when the aircraft
comes into contact with large, supercooled drops.
Generally forms when the temperature is between 0°
and -10° C and is especially intense and adherent near
0°, when the number of supercooled drops is higher.

4. TYPES OF ICING
WET SNOW: It is a fact that dry snow does not
adhere to a dry aircraft, but if the snow is wet, that
is, it is formed by supercooled drops and ice
crystals, then it adheres, forming the icing.
FROST: It is a typical phenomenon of winter that
occurs when the layer of air in contact with the
ground very rich in humidity, the night cooling
does lower the temperature below 0º. Then the
water vapor is sublimated, transforming into ice.
This type of icing, which occurs without clouds,
with clear sky, can become important if the
helicopter stays out of the hangar. To avoid this,
an exhaustive pre-flight review of it should be
done.

5. EFFECTS OF
INFLIGHT ICING (I)
The first effect of the icing comes from the increase in
weight that causes, taking into account the density
altitude to which we are flying, we will need more power
to maintain the same flight line, which can aggravate the
situation of high power requirement, because it reduces
the available power range.
The second factor is aerodynamic, since the ice formed
in the blades will break the profile of the blades, causing
a significant loss of lift and increased resistance.

6. EFFECTS OF
INFLIGHT ICING (II)
In addition, the formation is not
symmetrical in the blades, reason why it
will produce a dissymmetry that will be
translated in vibrations, the stronger the
greater the dissymmetry.
The third factor is the icing of surfaces
such as the pitot tube, producing
instrument errors, such as anemometer,
altimeter and variometer, which are so
important in flight.

7. EFFECTS OF
INFLIGHT
ICING (III)
Recall that these instruments are
based on the Bernoulli theorem and
as the pressure variations are
altered, the indications of the
instruments are distorted; the icing
of the antennas, making both
reception and communication
difficult, since the ice formed in the
antenna "bridges" with the
insulators at the ends and forms
mass with the structure of the
helicopter.
Finally the problem of icing the
cabin windows, making it difficult to
see the flight, especially in final
approach and has not given time to
unfreeze them

8. RECOMMENDATIONS
 Most flight manuals prohibit helicopter flight under known icing
conditions. There are also manufacturer's procedures for exit to
and authorized time under freezing conditions described in the
RFM.
 Planning the mission for routes and altitudes that do not cause
icing and always have alternative routes, either in VFR or IFR.
 Provide anti-ice devices and protection devices against snow
ingestion to prevent both icing and possible engine stoppage due
to ice ingestion and blade breakage.
 Check MEL and the operation of the different systems that the
helicopter carries, Pitot systems, glass heaters, etc. and follow the
Company´s SOP´s.