TM 1-1520-240-102-1-92-1-21. Shoulder Harness Inertia Reel Lock Lever.A two-position shoulder harness inertia reel lock lever is onthe left side of each seat (22, fig. 2-1-3) The lever positionsare LOCKED (forward) and UNLOCKED (aft). The lock maybe moved freely from one position to the other. When thelock lever is in UNLOCKED position, the reel harness cableis released to allow freedom of movement. However, thereel will automatically lock if a horizontal impact force of 2 to3g is encountered. When the reel is locked in this manner,it stays locked until the lock lever is moved forward toLOCKED and then returned to UNLOCKED. When the leveris at LOCKED, the reel is manually locked so the pilot isrestrained from bending forward. When a crash landing orditching is anticipated and time permits, manual locking ofthe shoulder harness inertia reel provides added safety be-yond the automatic feature of the inertia reel. Depending onthe pilot’s seat adjustment, it may not be possible to reachall switches with the inertia locked. Each pilot should checkand adjust the shoulder harness in locked position to deter-mine whether all switches can be reached.2-1-22. Self -Tuning Dynamic Absorbers.The helicopter is equipped with three sel-tuning dynamicabsorbers. One absorber is in the nose compartment andthe other two absorbers are under each pilot’s seat belowthe cockpit floor. All three absorbers serve to maintain aminimum vibration level through the normal operatingrotor RPM range of the helicopter. The self-tuning featureof the the dynamic absorber functions as follows: eachdynamic absorber consists of tuning mass suspended bysprings, and electronic measuring circuit, accelerome-ters, counter-weights, an electrical actuator and a self-test box. The accelerometers sense and compare thevibration phases of the helicopter and the spring-mounted mass. When the measured vibration phasesdiffer from a built-in phase relationship required to assureproper tune, the electronic circuit extends or retracts theelectrical actuator to reposition the counterweightswhich, in turn, increases or decreases the resonant fre-quency of the spring-mounted mass. The dynamic ab-sorbers are constantly being adjusted (tuned) to mini-mize helicopter vibration. A self-test box is in the heatercompartment to provide maintenance personnel with anintegral testing capability for self-tuning feature of thedynamic absorbers. Power is supplied by the No. 2 ACbus through the VIB ABSORB-LH, CTR and RH circuitbreakers in the No. 2 PDP.Figure 2-1-6. Canted Console (Typical)
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