INADVERTENT IMC
Whether it is a corporate or HEMS operation, helicopter
pilots sometimes operate in challenging weather
conditions. An encounter with weather that does not
permit continued flight under VFR might occur when
conditions do not allow for the visual determination of
a usable horizon (e.g., fog, snow showers, or night
operations over unlit surfaces such as water). Flight in
conditions of limited visual contrast should be avoided
since this can result in a loss of horizontal or surface
reference, and obstacles such as wires become perceptually
invisible. To prevent spatial disorientation, loss
of control (LOC) or CFIT, pilots should slow the helicopter
to a speed that will provide a controlled
deceleration in the distance equal to the forward visibility.
The pilot should look for terrain that provides
sufficient contrast to either continue the flight or to
make a precautionary landing. If spatial disorientation
occurs, and a climb into instrument meteorological conditions
is not feasible due to fuel state, icing conditions,
equipment, etc., make every effort to land the helicopter
with a slight forward descent to prevent any sideward or
rearward motion.
All helicopter pilots should receive training on
avoidance and recovery from inadvertent IMC with
emphasis on avoidance. An unplanned transition
from VFR to IFR flight is an emergency that involves
a different set of pilot actions. It requires the use of
different navigation and operational procedures,
interaction with ATC, and crewmember resource
management (CRM). Consideration should be given
to the local flying area’s terrain, airspace, air traffic
facilities, weather (including seasonal affects such
as icing and thunderstorms), and available
airfield/heliport approaches.
Training should emphasize the identification of circumstances
conducive to inadvertent IMC and a
strategy to abandon continued VFR flight in deteriorating
conditions.3 This strategy should include a
minimum altitude/airspeed combination that provides
for an off-airport/heliport landing, diverting
to better conditions, or initiating an emergency
transition to IFR. Pilots should be able to readily
identify the minimum initial altitude and course in
order to avoid CFIT. Current IFR en route and
approach charts for the route of flight are essential.
A GPS navigation receiver with a moving map provides
exceptional situational awareness for terrain
and obstacle avoidance.
Training for an emergency transition to IFR should
include full and partial panel instrument flight,
unusual attitude recovery, ATC communications, and
instrument approaches. If an ILS is available and the
helicopter is equipped, an ILS approach should be
made. Otherwise, if the helicopter is equipped with
an IFR approach-capable GPS receiver with a current
database, a GPS approach should be made. If
neither an ILS nor GPS procedure is available use
another instrument approach.
Upon entering inadvertent IMC, priority must be given
to control of the helicopter. Keep it simple and take one
action at a time.
- Control. First use the wings on the attitude indicator
to level the helicopter. Maintain heading
and increase to climb power. Establish climb airspeed
at the best angle of climb but no slower
than VMINI.
- Climb. Climb straight ahead until your crosscheck
is established. Then make a turn only to
avoid terrain or objects. If an altitude has not been
previously established with ATC to climb to for
inadvertent IMC, then you should climb to an
altitude that is at least 1,000 feet above the highest
known object, and that allows for contacting
ATC.
- Communicate. Attempt to contact ATC as soon
as the helicopter is stabilized in the climb and
headed away from danger. If the appropriate
frequency is not known you should attempt to
contact ATC on either VHF 121.5 or UHF
243.0. Initial information provided to ATC
should be your approximate location, that inadvertent
IMC has been encountered and an
emergency climb has been made, your altitude,
amount of flight time remaining (fuel state),
and number of persons on board. You should
then request a vector to either VFR weather
conditions or to the nearest suitable airport/heliport
that conditions will support a successful
approach. If unable to contact ATC and a
transponder code has not been previously
established with ATC for inadvertent IMC,
change the transponder code to 7700.
3 A radio altimeter is a necessity for alerting the pilot when inadvertently going below the minimum altitude. Barometric altimeters are subject
to inaccuracies that become important in helicopter IFR operations, especially in cold temperatures. (See Appendix B.)
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