Aircraft
Certification Service Washington, DC U.S. Department of Transportation Federal Aviation Administration
SW-08-03
November 8, 2007
This is information only. Recommendations
aren’t mandatory.
Introduction
As a result of continued accidents due to loss of engine power
resulting from snow or ice ingestion on turboshaft powered rotorcraft,
we are reissuing this Special Airworthiness Information Bulletin (SAIB)
and are urging you to follow our recommendations.
This SAIB alerts owners and operators of turboshaft powered rotorcraft,
of the possibility of in-flight 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. This SAIB describes procedures to reduce the
probability of an engine in-flight shutdown due to ice and snow
ingestion.
Background
We have 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 without
the engine(s) operating or when the engine is 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.
Ground Operations
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 it 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 non-formation of ice 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 cowl, even when you use
proper inlet protection.
Inflight Operations
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 at all 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 [41F]. Pilots
must be aware that icing is possible in these ambient conditions and
should exit the conditions immediately by leaving the area of visible
moisture or by changing to a warmer altitude. (NOTE: This “warmer”
altitude may not always be a lower altitude.)
Recommendations
We highly recommend and strongly urge you to perform the following:
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 heavy snow.
Perform Basic Airmanship and
preflight by evaluating current and predicted weather briefings from
the area Flight Service Station. Recommended web sites include:
Icing tool: http://weather.aero/icing
HEMS flight tool: http://weather.aero/hems
When the aircraft is on the ground without the engines operating, install inlet and exhaust inserts or covers.
Prior to engine start, after
removing the inlet/exhaust inserts or covers, 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.
CAUTION: DO NOT remove ice
or snow by chipping or scraping! Use heated air or deicing fluid as
appropriate, in accordance with the manufactures 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; Available at: http://www.tc.gc.ca/ASL-SAN
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
For Further Information Contact
Matthew Rigsby, Continued Operational Safety (COS), FAA Rotorcraft
Directorate, Standards Staff, Fort Worth, Texas 76193-0110; phone (817)
222-5125; fax (817) 222-5961; email: matthew.rigsby@faa.gov