R  C. Protection of the Pylon (Ref. Fig. 002, 003) This system is for the protection of the pylon. It operates if a duct of the pneumatic system breaks open or shows large leaks so that this can not endanger safe flight and landing of the aircraft. The system keeps the pressure to a limit. This prevents damage to the pylon structure and the components installed in the pylon.
 (1) The pressure relief doors prevent an uncontrolled increase of the pressure. They are installed in the leading edge of the pylon fairing and in the pylon/wing interface.
 (2) The leading edge of the pylon fairing and the pylon/wing interface have each one pressure relief door. The overpressure in this area is limited to 0.2 bar (2.90 psi) by the pressure relief doors. 
R  D. Protection of the Nacelles
 (Ref. Fig. 004) This system is made to protect the nacelle. It operates if a pneumatic duct breaks open or has a large leak, so that this can not endanger the safe flight and landing of the aircraft. The system keeps the pressure to a limit. This prevents damage to the nacelle structure and the components installed in the nacelle.
 - Core Compartment An overpressure in the core compartment can not cause any damage to the thrust reverser. If an IP or HP bleed duct breaks open or has a large leak, the pressure increases in the core compartment. The maximum overpressure is 2.90 psi (0.2 bar). The overpressure moves the thrust reverser. This movement increases the normal pressure relief area. - Fan Compartment A pressure relief door is installed in the fan cowl. This door will stay open to give a visual indication of the past abnormal internal pressure (differential pressure of 2.90 psi (0.2 bar)). 
R  4. Component Description_____________________ 
R  A. Ventilation of the Leading Edge 
R R  (1) NACA Ram-Air Inlet 
R R  The NACA ram-air inlet is forward of the drainage/bleed holes. Thus the released ventilation air can not flow back into the NACA ram-air 
R  inlet.

R R R R R R  (2) Piccolo Ducts The piccolo duct which is connected to the NACA ram-air inlet has a diameter of 38.1 mm (1.5 in.). It decreases continuously to 25.4 mm (1.0 in.) at the duct ends. The maximum internal pressure in the ducts is 0.19 bar (2.75 psi). To let the air out, the ducts have holes over their full length. They are forward of the piccolo ducts. 
R  B. Protection of the Wing Leading Edge
 (1) Pressure Relief Access Panels (Ref. Fig. 005, 006)
 The pressure relief panels are made of 3.5 mm (0.1377 in.) carbon fibre. Sections of nomex honeycomb or aluminum alloy angles reinforce the panels. The panels are attached to the wing structure at the leading and trailing edges. A 1.0 mm (0.0393 in.) aluminum alloy angle which is attached to the rear face of the sub spar holds the panels. When the pressure is too high the panel 'blows down' and thus bends the angle. The angle also contains the anchor nuts to attach the forward screws.
 The trailing edge of the panel is attached to a landing. It is attached to the forward edge of the lower skin of the torsion box. The landing is made of two back-to-back aluminum alloy angles. 2.4 mm (0.0944 in.) shear rivets, spacers and special washers hold this unit together. Smooth interfaces permit the landing angles to slide freely. The angle installed on the panel has a slotted hole for the rivet and the spacer. This permits the angle to move when the wing flexes and prevents that the rivet shears at an unwanted time. Also, the angle is castellated between the rivets to give a larger space for the air to flow through. When all rivets of the panels 2, 3, 4 and 5 shear, a 75 mm (2.9527 in.) dia. steel restraining lanyard connects the two angles of the landing. On access panel 1 is no restraining lanyard as the largest possible area is required to let the air out.
 The trailing edge of the panel and the landing are wet-assembled with sealant. This seals the trailing edge against air leakage. 
R  C. Protection of the Pylon (Ref. Fig. 002, 003) Two types of pressure relief doors are installed: - the one in the leading edge of the pylon (413BL,423BL) is spring loaded and made from titanium.
 - the one in the pylon/wing interface (471BL,482BR) is installed with shear rivets, a latch and a piano hinge.It is made of carbonhoneycomb core in sandwich construction.

 Pressure Relief Access Panel Operation Figure 006
 1EFF : 1 1R 1CES  ALL  1 11 1 36-14-00 Page 11 Aug 01/04

R  D. Protection of the Nacelles
 (Ref. Fig. 004)
 A pressure relief door made of aluminum honeycomb is installed in the
 right fan cowl of the left and right engine. It protects the core
 compartment against a differential overpressure of 0.90 psi (0.06 bar).
　
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