FMS 9.2-5 Rev 6 (current) Inlet Barrier Filter System
GENERAL
The Inlet Barrier Filter (IBF) system is installed to remove foreign objects such as sand, dust or other particles from the engine inlet air stream in order to prevent premature erosion of compressor blades and other engine components.
The IBF system consists of two completely separated filter frames, which are installed so that each engine intake in front of the firewall is completely covered. The filter frame creates two passageways for the air to enter the engine: Through the filter element and via a bypass door.
The filter element allows air to pass through the filter while effectively retaining most foreign matter. The filter element is made of cotton gauze soaked with oil and can be easily replaced and cleaned through a maintenance action. Water entering through the filter can escape through two drain ports at the bottom of each frame.
The bypass doors are installed to prevent excessive performance detriments and engine flame out when the filter element is clogged. The bypass doors are controlled by an electric actuator, which is connected to the essential bus.
Filter element clogging is measured through a static pressure port located in the filter frame. The pressure difference between the filter frame and aircraft static ports is an indication of the degree of filter contamination (clogging). The pressure measurement is presented as a clogging level in percent on the VMS page. This percentage level is calculated from the pressure loss taking into account altitude, airspeed and power setting.
Despite these corrections, slight clogging indication variations can still occur.
IBF SYSTEM OPERATION
The switches for operation of the IBF system are located in the overhead panel.
The IBF system is operated through two separate IBF switches with three switch positions:
NORM, OPEN and CLOSE.
The IBF RECALL switch allows the maximum clogging level that was encountered since the last reset to be displayed by momentarily placing the switch in the RECALL position. Each time a new or cleaned filter is installed, the RECALL value shall be reset to zero (by holding the switch in the RECALL position for more than 15 seconds).
NORM
The IBF system is active, the bypass door is closed. The engine is protected from foreign matter.
When an OEI condition is detected in flight (power split condition), both bypass doors will open automatically.
When dangerously excessive clogging is detected (equivalent to about 140% clogging), the bypass doors will open automatically to protect the engines from being damaged or surging.
OPEN
IBF system is inactive, the bypass door is open. The engine is not protected from foreign matter.
CLOSE
The bypass doors are closed and will not open automatically in case of OEI condition or dangerously excessive clogging.
This mode can be used to override an automatic opening of the bypass doors in case of OEI, to protect the remaining engine.
SAFETY INFORMATION NOTICE No. 3515-S-71 Rev 1
Airbus Helicopters was informed of a HEMS mission in the year 2020 in conditions close to a temperature of 0 °C, during which a sudden engine flame-out occurred on a helicopter equipped with an Inlet Barrier Filter (IBF). The event occurred during flight with the IBF bypass closed. A successful engine restart was performed in flight and the helicopter could safely continue to its destination.
Although fuel or engine related malfunctions could be eliminated as a root cause, the exact reason for the flame out could never be determined. Following this event, Revision 0 of this Safety Information Notice (SIN) was published to raise awareness with flight crews about a potential partial IBF icing when operating at OAT < 3 °C and in visible moisture.
A further incident occurred recently, where a helicopter equipped with IBF was hovered prolonged in falling snow, followed by a long period on ground in snow with the collective lever raised to prevent sinking in. Shortly after take-off, engine #1 flamed out. After the crew managed to land the helicopter safely in OEI conditions, engine #2 flamed out after the engine was switched to IDLE. Both IBF bypass doors were opened well before the flame out.
Investigations to determine the root cause of this recent incident are ongoing. However, partial icing of the IBF engine intake cannot be excluded as a reason for the flame out.
Purpose of Revision 1 of this SIN is to inform flight crews that the following has been decided as a protective measure for helicopters with IBF installed:
Flights in falling or blowing snow shall be prohibited
Flights at or below 5 °C OAT when visible moisture is present shall be avoided. Visible moisture can be precipitation (snow, sleet, ice crystals) or fog/cloud reducing the visibility below 800 m.
Partial icing of the IBF engine intake can occur even when no signs or only light traces of snow or ice are visible on the helicopter (windshield wiper, pitot tube attachment).
A temporary revision of the IBF Flight Manual Supplement (FMS 9.2-5) will be issued in due time to re-define the environmental limitations within which operation with IBF shall be conducted. In the meantime, Airbus Helicopters is further investigating the situation and expects to provide an update of this SIN within the coming weeks.
The standard air intake provides better protection in the case of inadvertent entry in potential icing conditions. Customers wishing to uninstall the IBF during winter time may do so in accordance with the AMM.
AMM 71-64-00,7-1 Removal - IBF System - INLET BARRIER FILTER SYSTEM
Remove the IBF system LH and IBF system RH as follows:
NOTE
The procedures to remove the IBF system LH and the IBF system RH are the same. The procedure that follows gives the removal procedure of the IBF system LH.
Remove the IBF filter assembly AMM 71-64-00,4-2.
Remove the IBF tray assembly AMM 71-64-00,4-3.
If you plan to operate the helicopter without IBF detachable parts installed, do as follows:
CAUTION
THE IBF DIFFERENTIAL PRESSURE SENSORS CAN BE DAMAGED IF STATIC PRESSURE IS ONLY APPLIED TO THEIR LOW PRESSURE PORTS. DO NOT OPERATE THE HELICOPTER WITHOUT INSTALLED ELBOW UNIT ASSEMBLY.
Install the elbow unit assembly AMM 71-64-00,4-13.
Install the cover and the frame (3) on the main gearbox cowling (2) AMM 71-64-00,4-8.
Install the compressor inlet screens AMM 71-31-00,4-2.