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Overview
The cowls are an aerodynamic part of the nacelle installed around the engine, between the engine air intake and the thrust revers. The engine cowls have an upper cowl and a lower cowl.
The upper cowl gives access to the Tt2 inlet air temperature sensor, the left and right engine control units (ECUs), and the monopole and thermal anti-ice (TAI) system components.
The lower cowl is installed around the bottom half of the engine and is hinged to the upper cowl. When closed the lower cowl gives access to the oil filling point and the air turbine starter. When open, the lower cowl gives access to all components on the bottom of the engine.
The upper and lower engine cowls protect and give access to the engine and nacelle systems. They are made from carbon plies bonded together. The cowls have a copper mesh embedded in the outer layer for additional high intensity radiated field (HIRF) and lightning protection, and a glass fibre interface for corrosion protection. The upper and lower cowls can be installed on the left or right engine.
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Upper Cowl
The upper cowl is installed around the top of the engine. The cowl leading edge attaches to the engine with eight screws. Two pin latches in the aft end of the cowl (one inboard and one outboard) attach the rear of the cowl to the engine.
Four tie-rods are installed on the inboard side of the upper cowl. These four tie-rods engage with the hook latches that are installed on the lower cowl.
Four hinge fittings are installed on the outboard side of the upper cowl. The four hinge fittings engage with the hinges that are installed on the lower cowl. Two pin latches (one forward and one aft) engage with two of the hinge fittings to keep the lower cowl closed.
A fire seal is installed on the inboard edge of the upper cowl, which seals the gap between the cowl and the pylon fairings. The seal is bonded to a Z-stiffener in the cowl structure.
A high intensity radiated field (HIRF) seal is installed along the outboard edge of the upper cowl to seal the gap between the upper cowl and the lower cowl.
The upper cowl has the panels that follow:
T2 Access Panel
The T2 access panel is installed on the left side of the upper cowl. This gives access to the engine inlet air temperature (Tt2) sensor. The panel is made from carbon plies that are bonded together.
Seven quick-disconnects are installed around the edge of the panel. The quick-disconnects have stud nuts which are installed in grommets. When the panel is installed, the stud nuts go into receptacles in the upper cowl.
ECU Access Panels
There are two ECU access panels installed on the upper cowl. These give access to the ECU units. The ECU access panels are installed on the left side and the right side of the upper cowl with stud nuts. They are made from composite plies that are bonded together.
A scoop assembly is riveted to each ECU access panel. This lets air into the nacelle to cool the ECU. Nineteen grommets are installed around the edge of each ECU access panel and stud nuts are installed inside each grommet. When the ECU access panel is installed, the stud nuts go into receptacles in the upper cowl.
Monopole and Thermal Anti-ice (TAI) Access Panel
The monopole and TAI access panel is installed at the top of the upper cowl.
The panel allows access to the following parts:
- TAI anti-ice valve
- TAI low-pressure switch
- Monopole electrical connectors
The panel is made from composite plies that are bonded together.
Nine quick-disconnects are installed around the edge of the panel. The quick-disconnects have stud nuts which are installed in grommets. When the panel is installed, the stud nuts go into receptacles in the upper cowl.
Ventilation Screen
A ventilation screen is installed on the top of the upper cowl, which operates as an HIRF screen and also supplies ventilation for the engine and nacelle systems. The screen is installed with 21 screws and nutplates and is sealed with a conductive jointing compound.
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Lower Cowl
The forward and aft pin latches (on the outboard side of the upper cowl) engage with two of the hinges in the lower cowl to keep the cowl closed. When the pin latches in the forward and aft hinges are removed, the cowl has to be lowered approximately four inches before the pins of the center hinges engage with the hooks in the upper cowl. On installation, the lower cowl has to be lifted from its position on the center hinges to engage the forward and aft hinges.
The lower cowl is also kept closed with a third pin latch. This is on the inboard forward edge of the lower cowl. In the closed position, the pin latch engages in a latch fitting on the rear bulkhead on the air inlet cowl.
Four hook latches on the inboard side of the lower cowl attach to tie rods on the upper cowl. A fire seal is installed on the edge of the lower cowl. This seals the gap between the lower cowl and the pylon fairings. The seal is bonded to a Z-stiffener in the cowl structure.
Twelve drain holes are formed in the bottom of the cowl skin. These let unwanted fluids (from the engine) drain from the cowl. The lower cowl has the panels/components that follow:
Oil Access Panel
The oil access panel is installed on the left side of the lower cowl. This gives access to the oil tank filler. The oil access panel is made of composite plies that are bonded together.
Four latches keep the panel closed against the lower cowl.
A hinge assembly is attached to the bottom of the oil access panel with five hi-lock fasteners, and to the cowl skin with five rivets. The hinge assembly lets the panel fold down flat against the cowl when open.
Air Turbine Starter (ATS) Access Panel
The ATS access panel is installed at the front of the lower cowl. This gives accesses the starter and ATS valve. The panel is made of composite plies that are bonded together.
Five quick-disconnects are installed around the edge of the panel. The quick-disconnects have stud nuts in grommets. When the panel is installed, the stud nuts go into receptacles in the upper cowl.
Hold-Open Rods
Two hold-open rods hold the lower cowl open. The rods pivot on bearings at each end and are hinged in the middle. The rods bend at the middle hinge and are stowed in the nacelle when not used. A lock pin keeps each rod in the locked-open position. A release collar on the shaft of the rod operates the locking pin. The forward rod is longer than the aft rod.
Drain Mast
A drain mast with a drain and collector are installed in the bottom of the lower cowl. The drain mast and collector are installed with eight screws and nutplates. The drain mast is sealed on the external side with a conductive jointing compound.
Lower Cowl Hinge
Four hinges are attached to the lower cowl. The four hinges have hooks that locate on the pins of the hinge fittings in the upper cowl. The hinges also include fail-safe devices that engage when the lower cowl is closed. The fail-safe devices prevent movement of the lower cowl if a hinge or pin fails.
Hook Latch
In the closed position, hook latches engage with keepers of the tie-rods (in the upper cowl). There are four hook latches, one for each tie-rod. To open the lower cowl, release and open the hook latches. The lower cowl will open to an angle of 110 degrees from the horizontal.
Generator Vent Duct
A generator vent duct is installed in the bottom of the lower cowl. This lets cooling air go into the generator. The duct is installed with 10 rivets.
Ventilation Screen
A ventilation screen for the ATS system is installed on the bottom of the lower cowl. This allows the removal of exhaust gases from the ATS. The screen is installed with 15 screws and nutplates and is sealed with a conductive jointing compound.
An additional ventilation screen operates as an HIRF screen and also supplies ventilation for the engine and nacelle systems. This screen is installed with 27 screws and nutplates and is sealed with a conductive jointing compound.
