Aircraft passenger seats having a backrest capable of being folded forward to change the seat to a bed mode position have been proposed. 
This type of aircraft passenger seat adopts a mechanism for locking the backrest at a normal upright position and at a bed mode position.  The lock mechanism has a function to fix the backrest by inserting pins provided at both sides of a backrest frame into receive members disposed on a fix-side frame. 
Lock pins are pushed into the receive members by springs, and in a state where a handle provided on a rear face of the backrest is operated, metal wires connected to the handle draw out the lock pins from the receive members against the springs, and the lock is released. 
FIGS.  4 and 5 are front and side views of the aircraft passenger seat to which the present invention is applied. 
An aircraft passenger seat 1 includes a seat assembly 100 surrounded by a back shell 10.  The seat assembly 100 includes a seat bottom 110, a backrest 120 and a headrest 130.  The seat assembly 100 can be used at two positions, an upright position U where the backrest 120 and the headrest 130 are positioned upright, and a bed mode position B where the backrest 120 and the headrest 130 are folded forward. 
A handle unit 200 is provided on the rear face of the headrest 130.  The handle unit 200 is coupled to lock pins 350 via metal wires 300, and in a state where the handle within the handle unit 200 is operated, the lock pins 350 are drawn out from the receive members, allowing the backrest and the headrest to be tilted. 
FIG.  6 is an explanatory view illustrating an outline of the lock mechanism. 
The lock mechanism fixing the aircraft passenger seat assembly 100 to the upright position and the bed mode position includes the handle unit 200 provided on a rear face of a headrest frame 132, two wires 300 connected to the handle unit 200 and arranged along a backrest frame 122, and two lock pins 350 operated by the wires 300. 
FIG.  7 is an external view of the handle unit 200.  The handle unit 200 includes a handle 230 stored within a handle bracket 205. 
FIG.  8 is an explanatory view illustrating a mechanism of a prior art handle unit 200. 
The handle 230 is attached swingably about a fulcrum 232 within a fixing bracket 210 coupled to the handle bracket 205.  The handle 230 is connected to one end portion of the link lever 240 via a pin 244.  The link lever 240 can pivot about a fulcrum 242, and the other end portion of the link lever 240 is coupled to terminal members 250 of the wires via pins 246. 
Each wire 300 adopts a structure where a metal wire 310 is slidably accommodated within an outer protective case, and the protective case is fixed to a housing 210 via a pair of nuts 330 and 332, with the metal wire 310 connected to the wire terminal member 250 via the stopper 320. 
According to this arrangement, in a state where the handle 230 is pulled up in a direction of arrow A, the metal wires 310 are drawn upward in an arrow F direction, and the lock pins 350 are drawn out from the receive members. 
FIG.  9 is an explanatory view of a step for removing the wires 300 from the handle unit 200 for maintenance. 
The wire terminal members 250 are connected to the link lever 240 via pins 246.  The pins 246 are retained by snap rings 247. 
The snap rings 247 are removed from the pins 246, and the pins 246 are drawn out. 
The wire terminal members 250 are removed from the link lever 240, so the nuts 330 are loosened, and the metal wires 310 of the wires 300 that are passed through holes 222 formed on a housing 220 are drawn out toward a front side of a wire mounting bracket 220 through slits 224, and the whole body of the wires 300 are removed from the handle unit 200. 
The arrangement of connecting the handle and the lock mechanism via metal wires is disclosed in the patent literatures listed below.