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CHAPTER 5

NAVY AIRCREW COMMON EJECTION SEAT (NACES)

Chapter Objective: Upon completion of this chapter, you will have a working knowledge of the Navy Aircrew Common Ejection Seat (NACES), including functional description, physical description, component identification, and maintenance concepts.

The incorporation of the Navy Aircrew Common Ejection Seat (NACES) in Navy aircraft represents a significant improvement in ejection-seat design that takes advantage of the latest escape system technology. The NACES system gives the aircrew improved chances for escape in all ejection situations, reduced potential for injury, extended preventive maintenance intervals, and a significant reduction in life-cycle costs. This Martin-Baker ejection seat will be fitted to the new Grumman F-14D Tomcat, the McDonnel Douglas/British Aerospace T-45A Goshawk two-seat trainer, and the McDonnel Douglas F/A-18C and D aircraft.

The purpose of the common ejection seat is to ease the logistics and maintenance problems on the Navy's inventory of aircraft. The new seat will increase the standardization and reliability of aircraft emergency escape and aircrew and ground crew training. The electronically controlled NACES represents the state-of-the-art in escape system technology, and it has been selected as the future standard of the U.S. Navy. The NACES series was engineered from the outset for future growth potential. The ejection seat is designed for simple reprogramming or modification to ensure that it maintains current technology.

As a senior AME, you already have the prerequisite knowledge and experience to understand ejection seat theory. New ideas have been incorporated into the NACES. Now all that is required is your willingness to learn these new ideas so that NACES characteristics become as familiar as previous Martin-Baker ejection seats.

SYSTEM DESCRIPTION AND COMPONENTS

Learning Objective: Recognize the functional and physical description of the NA-CES and the components within the system.

The NACES system uses a flexible configuration to meet the exact requirements of the crew station designer. Although this is a common ejection seat, the designator number for the seat versus aircraft types are different, as shown below.

Although the physical description may differ between the seats used in the F-14D as compared to the F/A-18 and T-45 (fig. 5-1), the functions of all the seats are the same. In this chapter we will use the F/A-18 ejection seat to discuss system description, operation, function, and component identification.

FUNCTIONAL DESCRIPTION

WARNING

The emergency escape system incorporates several explosive cartridges and rockets containing propellant charges. Inadvertent firing of any of these may result in serious or fatal injury to personnel on, or in the vicinity of, the aircraft.

Figure 5-1.-Forward ejection seat; (A) right-hand view, (B) left-hand view.

Ejection control handle safety pins and safe/armed handles are provided to render the ejection seats safe when the aircraft is parked between flights and at all other times on the ground. The ejection control handle safety pins are removed by the aircrew before flight and installed by the plane captain after flight. Movement of the safe/armed handle is the responsibility of the aircrew.

Before entering the cockpit, personnel should ensure that the correct safety precautions have been applied.

The F/A-18 aircraft is equipped with a type SJU-17(V)1/A ejection seat. The F/A-18D

aircraft is equipped with a type SJU-17(V)2/A and a type SJU-17(V)1 /A ejection seat installed in the forward and aft cockpits, respectively. The seats are interconnected by a command sequencing system. The two types of seat are essentially the same, but with differences to suit the two cockpit installations. For convenience, the description that follows applies equally to both ejection seats, except where noted. Where reference is made to the aft seat configuration on the F/A-18D, the description applies equally to the single seat (F/A-18C) installation.

All NACES seats incorporate fully automatic electronic sequencing and are cartridge operated and rocket assisted. Safe escape is provided for most combinations of aircraft altitude, speed, attitude, and flight path within the envelope of

Figure 5-1.-Forward ejection seat; (A) right-hand view, (B) left-hand view-Continued.

zero speed, zero altitude in a substantially level attitude to a maximum speed of 600 knots estimated air speed (KEAS) between zero altitude and 50,000 feet.

Ejection is initiated by pulling a seat firing handle situated on the front of the seat bucket between the occupant's thighs. The parachute container is fitted with canopy breakers to enable the seat to eject through the canopy should the jettison system fail. After ejection, drogue deployment, man/seat separation, and parachute deployment are automatically controlled by an onboard multimode electronic sequencer. A barostatic harness release unit caters for partial or total failure of the electronic sequencer, and an emergency restraint release (manual override) system provides a further backup in the event of failure of the barostatic release.

The seat is ejected by action of the gas pressure developed within a telescopic catapult when the cartridges are ignited. An underseat rocket motor situated under the seat bucket is fired as the catapult reaches the end of its stroke, and sustains the thrust of the catapult to carry the seat to a height sufficient to enable the parachute to deploy even though ejection is initiated at zero speed, zero altitude in a substantially level attitude. The seat is stabilized and the forward speed retarded by a drogue and bridle system, followed by automatic deployment of the personnel parachute and separation of the occupant from the seat. Timing of all events after rocket motor initiation is controlled by the electronic sequencer, which uses altitude and airspeed information to select the correct mode of operation.







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