Procedures Reduce Probability Of An Engine Shutdown
The FAA has revised and reissued a
Special Airworthiness Information Bulletin (SAIB) alerting owners
and operators of turboshaft powered rotorcraft of the possibility
of inflight engine loss of power due to the ingestion of ice and
snow. Accumulation of ice and snow can occur in the area of
the airframe engine inlet while the rotorcraft is on the ground or
in the air.
The FAA has determined that ingested ice and snow accumulation
in the airframe engine inlet can cause the engine to lose power.
This has resulted in accidents and fatalities. Snow and ice can
build up in the engine intakes and plenums when the rotorcraft is
on the ground with the engine(s) not operating or are operating at
a low power setting for extended periods. When a pilot increases
engine power during takeoff, the accumulated snow and ice can
separate from the airframe inlet surface and be ingested into the
engine, resulting in decreased power or complete engine failure.
Some of the early turboshaft engines with axial inlets are
particularly susceptible to loss of power due to ice and snow
ingestion.
On the ground with the engine(s) operating at a low power
setting, ice and snow can accumulate on the airframe cowl forward
of the inlet, on the inlet lip, and inside the inlet. Under extreme
conditions, usually when the rotorcraft is on the ground waiting
for clear weather, the buildup of ice and snow can be enough
to cause the engine(s) to lose power or fail completely if the ice
or snow is ingested.
On the ground with the engine(s)
not operating, proper use of inlet inserts (pillows) or inlet
covers can eliminate the accumulation of snow, but these measures
cannot fully guarantee that ice will not form in the inlet. Ice can
also develop in the inlet area when water seeps into the
inlet from rain or snow melting on a warm cowling, even when
proper inlet protection is used.
Some rotorcraft require a snow protection kit for the airframe
engine inlet in order to successfully operate in falling and
blowing snow. Operation in snow without the kit is prohibited and
can be especially risky when hovering in snow and then
transitioning to takeoff when weather conditions
clear. Snow may accumulate on or in the engine inlet area during
hover, and then be dislodged and ingested into the inlet during
takeoff. Pilots should not believe they have escaped the danger
following successful hover in snow with an unprotected inlet. If
possible, land the aircraft immediately after the hover and
thoroughly inspect the engine inlet prior to takeoff. If terrain
will not allow an immediate safe landing, transition to takeoff as
smoothly as possible when the weather clears with minimum
application of engine power. Land and inspect the inlet area as
soon as practical.
Most rotorcraft are NOT approved for flight in known icing
(FIKI) conditions. For rotorcraft not approved for FIKI conditions,
a pilot can expect icing any time when operating in visible
moisture, such as fog, rain, or clouds, when the temperature is
below 5°C [41°F]. Pilots should be aware that icing
is possible in these ambient conditions and should immediately
leave the area of visible moisture or change to a warmer altitude.
(NOTE: This “warmer” altitude may not always be a lower
altitude.)
The FAA highly recommends the following procedures:
- Review the aircraft Flight Manual for Limitations and
Operations guidance in falling/blowing snow and/or icing. Many
aircraft are prohibited from operating in known icing and/or
falling and blowing snow.
- Perform basic airmanship and preflight by evaluating current
and predicted weather briefings from the area Flight Service
Station.
- When the aircraft is on the ground without the engines
operating, install inlet and exhaust inserts or covers.
- Prior to engine start, remove the inlet/exhaust inserts
or covers and perform a complete inlet/exhaust inspection (using a
flashlight). The inspection should include surfaces inside the
inlet, the cowl area forward and around the inlet, and the area
behind the particle separator or screen (if installed). Remove all
accumulated snow or ice.
- Do not remove ice or snow by chipping or scraping! Use heated
air or deicing fluid as appropriate, in accordance with the
manufacturer’s procedures. In freezing temperatures, pay
particular attention to sheet ice on the bottom and forward of the
inlet. This ice can also form behind particle separators. Engine
preheating may be required.
- Review Transport Canada Aviation Safety Letter Issue 4/2007
article 'Helicopter Operations: The Icing Factor'.
If it is necessary to keep the rotorcraft on the ground for an
extended period (i.e., waiting for clear weather), you should
shutdown the engine(s). Prior to takeoff, you should accomplish a
detailed preflight inspection, removing any snow/ice build-up. You
should perform the inspection even if the rotorcraft is fitted with
some form of inlet protection, such as screens or baffles.