Civil Aviation Safety Alert (CASA) No. 2013-03

ATTENTION:
PERSONS OPERATING AS350/EC130 HELICOPTERS

Issuing Office: Standards Branch Document
No.
:
CASA 2013-03
File Classification No.: A 5258-37 P/A P/A Issue No.: 03
RDIMS No.: 8847976 Effective Date: 2013-11-05

POTENTIAL FOR AS350/EC130 ENGINE INLET (PLENUM) ICING

PURPOSE:

This Civil Aviation Safety Alert (CASA) is meant to inform persons operating AS350/EC130 type helicopters of the potential of engine inlet (plenum) icing and subsequent engine failure during “Operations in Cold Weather”.

BACKGROUND:

Service history with the AS350/EC130 family has shown that sudden in-flight engine failure is possible if the engine inlet is not free of snow, water and ice prior to engine start.  Accidents have resulted when sudden engine flame-out occurred shortly after take-off.  Engine flame-outs have been caused by ice accumulation in the engine inlet plenum, and the ice suddenly being ingested by the engine.  In some cases the helicopter had been shut-down after a previous flight and the inlet covers had not been used. In other cases the snow accumulated on the upper surface of the helicopter, including the engine intake, and was not removed nor was the intake plenum inspected prior to engine start.  In one case the intake covers were installed overnight, the snow removed, but clear ice in the plenum was not detected until after a post start flame-out.

Eurocopter Safety Information Notice (SIN) No. 2645-S-30 states in part:

“...EUROCOPTER has participated in investigations concerning an accident which occurred following sudden engine flame-out in flight.  The investigations revealed that the engine flame-out occurred shortly after take-off and was due to a snow and ice accumulation in the engine air intake plenum, and the snow/ice mixture suddenly being ingested by the engine.  The aircraft had been shutdown after a previous flight and the inlet covers had not been used. Several centimeters of snow accumulated on the upper surface of the sand filter prior to engine start. The snow was not removed from the upper surface of the particle separator and the engine air intake was not inspected prior to engine start.

A turbine engine has a good rainwater or falling-snow absorption capacity in continuous operation. However, the engine is sensitive to the absorption of an instantaneous volume of water, snow or ice, because this quantity (even if it is limited) can exceed the instantaneous absorption capacity of an operating engine.

When operated in accordance with the Flight Manual, the engine air intakes are designed to prevent - in flight or on the ground with the engine running (rotor spinning or not) - an accumulation which could lead to this type of engine flame-out.  When an area close to the engine air intake or the air intake itself is not cleaned on the ground, an instantaneous volume of water, snow or ice may detach. The design of the engine air intakes (including those equipped with a sand filter) does not ensure correct engine operation in these conditions.

EUROCOPTER would like to remind you that the check of the engine air intakes is required in all Ecureuil Flight Manuals. In order to underline the importance of this check, EUROCOPTER will progressively introduce the modifications below in all the Ecureuil Flight Manuals.

The following condition will be added to the forbidden conditions in section 2 "Limitations": "Engine starting when snow or ice accumulations are in or around the engine air intake".

The following "Warning" will be added to the "Pre-flight check" part of section 4, in the "Sand Filter" and "Use in cold weather" supplements: "WARNING: Ice or snow accumulations that remain in or around the engine air intake may be ingested and can cause a sudden in-flight engine failure".

The pre-flight check will be adapted as follows: "Engine air intake………………Clean - No foreign objects or accumulations of ice or snow in or around the engineair intake and no stagnant water at the drain hole".
“Exhaust cover…………………Removed”.

The following complementary information will be added in the "Use in cold weather" supplement: 
- General: This supplement details the procedures to be followed when the aircraft is operated in cold weather (OAT ≤ 0°C) and/or when the aircraft is or could be exposed to falling or blowing snow.
- NOTE: In falling or blowing snow conditions the engine air intake should be checked at the end of the exterior checks. The further checks before engine starting should then be performed without major delay.

EUROCOPTER also reminds you that after arriving on a parking area in cold weather and snowy conditions or falling rain, it is recommended that you install the engine air intake cover rapidly after engine shutdown...”

To allow inspection and cleaning of the engine inlet (plenum), the engine cowling must be elevated and supported, or, where installed, the grill that covers the filter must be removed and reinstalled, which is time consuming and not considered to be Elementary Work that can be accomplished by a pilot.

It is necessary to be very safety conscious when inspecting the engine inlet as not to injure yourself, damage the airframe, or introduce Foreign Object Damage (FOD) within the engine inlet (plenum).

RECOMMENDED ACTION:

Persons operating AS350/EC130 type helicopters should review Eurocopter Safety Information Notice (SIN) No. 2645-S-30 Subject: ICE AND RAIN PROTECTION, “Recommendations in case of snow/ice accumulation in and around the engine air intakes”  This document is available on the internet: www.eurocopter.com/techpub

The Manufacturer’s instructions for inspection of the engine inlet (plenum) of the AS350/EC130 type helicopter before start up should be fully complied with when prevailing meteorological conditions are conducive to engine inlet ice formation. 

Engine flameout may still occur when the aircraft has been standing outside and exposed to conditions where moisture can collect in the engine inlet filter components that may not be detected by the pilot during inspection.  Avoid towering take-offs or any high hovering flight during the initial departure that may place the helicopter within the shaded area of the H-V diagram.  Engine flameout from ice or water ingestion is sudden, occurs without warning, and will result in rapid main rotor rpm decrease and stall if immediate action is not taken to lower the collective and enter autorotation. In most cases, there will not be sufficient time to attempt a restart.

After arriving at a parking area in cold weather with snowy conditions or rain, it is recommended that you install the engine air intake blank rapidly after engine shutdown.

NOTE:

Eurocopter has convened a Working Group tasked with improving manufacturers’ procedures for engine inlet (plenum) inspections.

CONTACT OFFICE:

For more information concerning this issue, contact a Transport Canada Centre; or contact Alex Roberts, Commercial Flight Standards in Ottawa, by telephone at 613-990-1090 or by e-mail at alex.roberts@tc.gc.ca

Original signed by Matthew Weeks for

Aaron McCrorie
Director
STANDARDS BRANCH

The Transport Canada Civil Aviation Safety Alert (CASA) is used to convey important safety information and contains recommended action items. The CASA strives to assist the aviation industry's efforts to provide a service with the highest possible degree of safety. The information contained herein is often critical and must be conveyed to the appropriate office in a timely manner. The CASA may be changed or amended should new information become available.

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