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ENGINE COWLING - DESCRIPTION AND OPERATION
1. General
A.  The engines are covered by cowl panels to provide a smooth airflow over the engines and to protect exterior engine components from damage. The cowl panels for each engine include a nose cowl, left and right hinged removable cowl panels and a fixed fairing. (See figure 1.) A nose dome is also fitted to each engine. Titanium and steel fireshields are bonded to the inside of the outer skin in areas in which a fire may occur.
2.  Engine Removable Cowl Panels
A.  The engine left and right cowl panels fair with the engine nose cowl, with the fixed fairing attached to the engine, and with the thrust reverser fairing. Six hook latch fasteners attach the left and right cowl panel to the fixed fairing and serve as cowl hinges. (See figure 1.) Two of these six latches on each cowl panel are safety latches which prevent an open cowl from being removed until the latches are depressed. The safety latches automatically trip into the locked position when the panels are closed. Hold open rods, installed in each panel, allow the panels to be propped in the open position. Safety pins are provided to lock the rods in either the open or stowed position. Six other hook latch fasteners join the left and right cowl panels together at the underside of the engine. A pin latch near the forward lower corner of the right cowl panel engages a fitting on the left cowl panel to provide a positive safety backup.
B.  Port openings are provided in the cowl panels for the engine gear case breather, engine accessory draining, and exhausting engine accessory cooling air. An overboard drain mast, installed on the bottom of the left cowl panel, discharges engine drain fluids. Access doors are fitted on the left cowl for servicing the engine oil tank and the constant speed drive . Pressure relief doors are provided to relieve excessive pressure which could develop within the cowling during a fire or as a result of serious bleed air or pneumatic leakage. The side panels are interchangeable between the nacelles.
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REFER TO EXHAUST, CHAPTER 78
NOT REQUIRED ON ENGINES WITH
PLUGGED P&D VALVE DRAIN PORTS

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3.  Engine Nose Cowl
A.  The nose cowl is bolted to the forward flange of the engine inlet case. It is shaped to obtain a smooth airflow over the engine and to provide an optimum airflow to the engine compressor inlet (Fig. 2). There are two kinds of nose cowl, early configuration and later configuration nose cowl. The early configuration nose cowl has six secondary air inlet doors arranged around the outer face of the nose cowl. These doors open, when inlet pressure is low, to provide additional airflow to the engine on the ground and in certain pitch attitudes. On some airplanes, water drain holes are provided for the doors located at the 4 and 8 o’clock positions. Later configuration nose cowls do not have secondary air inlet doors.
B.  An anti-icing air inlet is located on the rear face of the nose cowl at approximately the 5 o’clock position. The nose cowl is anti-iced by engine bleed air (Ref Chapter 75, Air).
C.  The nose cowl also contains tubing and exhaust nozzles for the engine gravel protection system (Fig. 2). This system discharges high velocity 13th-stage bleed air through exhaust nozzles located in the end of a tube suspended beneath the bottom of the cowl to prevent dirt, gravel, and other debris from entering the engine inlet (Ref Chapter 75, Air).
4.  Engine Fixed Fairing
A.  A two piece fixed fairing, attached to the engine, fairs with the left and right side cowl panels (Fig. 1). The fairing provides attach and hinge structure for the removable side cowl panels. Forward, mid, and aft fairings are attached to the wing and enclose the engine mounting installation. Design of the engine cowling and fairings allows for motion of the engines relative to the wing. On some left fixed fairings an access door is installed to facilitate servicing the PS3 bleed system filter without engine removal.
5.  Nose Dome
A.  A nose dome is mounted on each engine to provide a smooth airflow over the front accessory drive housing (Fig. 2). There are two kinds of nose domes in use. The early configuration nose dome is shorter than the later configuration dome and is used only in conjunction with early configuration nose cowls. The later configuration nose dome is a longer drooping nose dome and is used only with the later configuration nose cowls. The nose dome covers the N1 tachometer generator. An inlet pressure sensing probe (Pt2) is mounted in the center of the nose dome. The nose dome is anti-iced by engine bleed air.
　
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