The A-6 canopy jettisoning system is not actuated as part of the seat ejection sequence, but must be manually selected separately from the ejection process. Canopy jettison is a separate function because the normal procedures for using the ejection seat require ejection through the canopy unless special conditions dictate a deviation is necessary. In the A-6, a jettison sleeve is housed in the canopy actuator rod. Passages within the canopy actuator connect to a jettison cartridge that is mounted on the side of the cylinder head end. When the cartridge is fired, expanding gases create the necessary pressure to unlock the jettison sleeve from the rod end and force it and the canopy aft and off the aircraft (fig. 2-7). The jettison cartridge is fired by pneumatic pressure from a small (14.6 cu in.) air bottle pressured with nitrogen to 2,450 psi at 70 F prior to takeoff. Three air release valves are installed in the air-craft for jettisoning the canopy. One valve is actuated from the cockpit, the other two by their respective RESCUE handle on the engine intake air ducts. Opening any one of these valves directs nitrogen pressure from the bottle to the canopy actuator cap assembly (fig. 2-7) and fires the pneumatic jettison cartridge. To manually release the canopy actuator from the canopy attachment, pull either of the manual release handles located under access doors on the aft end of the canopy shell or the single manual release handle located on the canopy overhead center beam.

SYSTEM COMPONENTS

The main components of the canopy jettison system are shown in figure 2-6. The relief valve prevents excessive air bottle pressure increases due to thermal expansion and over-pressurization during charging. The valve cracks to relieve pressure at 3,800 psi and reseats at 3,400 psi. The air gauge provides a means of checking proper system precharge. The gauge is tapped into the pressure line between the air bottle and the cockpit air release valve. The vent bleeder check valve is located on the forward side of the left boarding ladder well. The valve is located downstream of the three air release valves and vents any low-pressure nitrogen that may have leaked past the air release valves, thus preventing inadvertent cartridge actuation. The vent bleeder check valve is normally open at 40 to 80 psi. When an air release valve is actuated, the bleeder valve closes and remains closed throughout the jettison operation. The bleeder valve will reopen when the pressure in the system is reduced below 40 psi. The bleeder valve also has a manual override that permits bleedoff of nitrogen pressure after jettison system testing as required during periodic inspections.

Figure 2-7.- Canopy jettison schematic.

NOTE: The canopy actuating and jettisoning cylinder is a primary concern of personnel CANOPY SEAL SYSTEM in the AMH rating. However, during AME Learning Objective: Recognize the purpose and operation of the canopy seal system. removal and/ or installation of the canopy, the cylinder can become damaged if the pro-cedures

provided in the MIM are not strictly followed. A canopy seal system (fig. 2- 8) provides an air-tight seal between the canopy assembly and the

Figure 2-8.- Canopy seal system.

aircraft structure to maintain cockpit pres-surization. The system, using cooled engine bleed air from the air-conditioning system, inflates the canopy seal in response to movement of the canopy locking linkage. The system deflates the seal when the can-opy is unlocked. There are many different types/ designs of pressure-maintaining seals used on naval aircraft. The main difference between canopy seal systems is the type of canopy seal pressure regulator used, elec-trical or mechanical. The F-14 inflatable seal will be discussed in the following para-graphs. The A-6 operates in a similar man-ner, but will not be covered in detail here. Refer to maintenance manuals for specifics.