The cowling components attach together around the engine to make a nacelle. The function of the nacelle is to divide the airflow around the engine. The airflow that goes through the inlet cowl divides into the engine compressor and the fan bypass duct. The external surface of the nacelle makes an aerodynamic surface to give a smooth airflow around the engine.

The cowling components are part of a very strong but low-weight assembly which gives the engine protection.

The inlet cowl is at the forward part of the engine and has four main structural parts:

• The primary assembly
• The intake barrel assembly
• The aft bulkhead and
• The outer skins

The primary assembly is made of an aluminum alloy lipskin and a titanium forward bulkhead. The lipskin contains a TAI spray ring which is made of titanium and is attached to the forward bulkhead.

The intake barrel assembly is made of two carbon-fiber composite (CFC) sound-attenuation panels. These panels are connected longitudinally and are attached at the aft end to an aluminum alloy ring. This ring attaches the inlet cowl to the engine-fan-case forward flange.

The aft bulkhead is made of two CFC pieces connected by titanium straps. The aft bulkhead makes the forward firewall of the engine accessory zone. It also gives a mating surface for the upper and lower cowls at its outer edge.

The outer skins are made of two CFC panels with stiffeners and an aluminum alloy panel which holds the TAI system outlet-grille. The inlet cowl is not interchangeable between the left and right engines.

The upper cowl is made from CFC and gives protection to the upper half of the engine. It is installed between the aft edge of the inlet cowl and the forward edge of the thrust reverser. The upper cowl is held closed by five latches installed along the mating faces of the upper and lower cowls. It turns on two hinges and three forks attached to the fixed cowl. Door restraint latches on the forward and aft edges of the upper cowl make sure that it cannot open accidentally when the lower cowl is open.

The rate at which the upper cowl opens and closes is controlled by two damper struts. The upper cowl is held open by two struts which are attached to its inner surface. There is a door locator on the forward edge of the upper cowl. As the upper cowl is closed, the door locator engages with a receptacle on the inlet cowl. This makes sure that the upper cowl is aligned correctly.

The inner surface of the upper cowl also contains two "Y" shaped ventilation inlet ducts. These ducts are made of titanium and they let external air flow over the engine. The upper cowl is not interchangeable between the left and right engines.

The lower cowl is made from CFC and gives protection to the lower half of the engine. It is installed between the aft edge of the inlet cowl and the forward edge of the thrust reverser. The lower cowl is held closed by five latches installed along the mating faces of the lower and upper cowls. It turns on two hinges and three forks attached to the fixed cowl.

The rate at which the lower cowl opens and closes is controlled by two damper struts. The lower cowl is held open by two struts which are attached to its inner surface. There is a door locator on the forward edge of the lower cowl. As the lower cowl is closed, the door locator engages with a receptacle on the inlet cowl. This makes sure that the lower cowl is aligned correctly.

The lower cowl contains access doors for the TAI valve and the starter air valve. These two doors will blow out if the pressure in the nacelle becomes too high. On the left cowl only, there is an access door for the gearbox oil sight glass. The lower cowl contains a stainless steel drains dish, which lets unwanted engine fuel and oil drain overboard. There is also an air outlet grille, which is made from aluminum honeycomb. The lower cowl is not interchangeable between the left and right engines.

The fixed cowl is made from superplastically formed titanium and is on the inboard side of the engine, between the upper and lower cowls. The fixed cowl touches the engine pylon, and is attached at its forward edge to the inlet cowl by shear attachment brackets and bolts. At its aft edge, the fixed cowl is attached to the thrust reverser forward bulkhead by shear pins.

The upper and lower edges of the fixed cowl each have two hinges and three hooks which hold the upper and lower cowls. The forward and aft engine mounts, the thrust strut and different engine and aircraft systems go from the engine to the aircraft through the fixed cowl.

The forward engine mount is contained in a titanium firebox which is attached to the inner surface of the fixed cowl. The thrust strut and aft engine mount go through fireproof silicon rubber boots which are attached to the fixed cowl. The bleed air duct, the pre-cooler air duct and the main generator cables also go through fireproof seals on the fixed cowl.

The fixed cowl is not interchangeable between the left and right engines.