Sheaves and Winches Generally all sheaves should be free running, have no indication of turning of the lips, or indication of jamming by terminals. No slippage of the sheave on races should be evident, and any fault of this nature should be corrected. Winches should be checked for running and positioning. Both sheaves and winches should be kept clean of debris or foreign matter, and be regularly lubricated. BELOW DECKS–THE ARRESTING ENGINE The greatest safety factor in the operation of the arresting engine is constant attention to inspection, maintenance, and overhaul. Preventive maintenance is particularly necessary. Daily inspection, inspection after each arrestment, and depending on the unit involved, inspection and maintenance at regular intervals nullify many of the conditions that might arise to endanger operating and flight personnel. Always keep hands and body clear when engine is operating or in a condition to become operable. Weight Selector Settings The safe arrestment of incoming aircraft can be directly attributed to proper setting of the aircraft weight selector. Aircraft weight selector settings should always be made according to current aircraft recovery bulletins. Maximum efficiency is obtained from the arresting engine through proper weight settings.    There is one distinct error in arrestment that can be directly attributed to improper weight settings or error in the gross weight estimate. This error results in TWO-BLOCKING the engine. TWO-BLOCKING is a condition in which the weight selector is set too light for the incoming aircraft. This condition causes the ram to ride forward into the cylinder until the crosshead bangs into the mouth of the cylinder. A wooden block assembly, called a ram block, is positioned at the crosshead end of the ram to act as a shock absorber by preventing metal-to-metal contact between the crosshead and the mouth of the cylinder. BOUNCEBACK is the movement of an arrested aircraft backward and is caused by the stretch inherent in the purchase cables. Bounceback is desirable because the hook is disengaged, allowing rapid deck clearance for future landings. Pilots are instructed to allow for bounceback before braking. Control Valve Failure Prime failure, with resultant disastrous consequences, could be failure of the drive system that would result in improper opening or closing of the CRO valve. Cam alignment is equally important, as improper alignment would result in fluid flow through the CRO valve at a ratio different from that indicated on the aircraft weight selector indicator. Thus, while the operator would have an indication of a proper setting, actual flow control would be different. Drive System Hazards Much of the cable system is contained behind U-channels to protect personnel during operation. This cable, with connections, is subject to wear and fatigue and should be checked against failure. Failure of the drive system could cause serious injury to operating and aircraft personnel. Excessive Pressures The accumulator is built to take a 400-psi initial charge and such additional pressure as is developed during arrestment. This capacity provides for an overloading factor.    However, it is most important that the accumulator blow-down valve on the charging panel be kept open. Should leakage occur from high-pressure piping as the result of inadequate valving, this, with the additional compression loading during arrestment, could cause an extremely dangerous accumulator pressure. One operating indication of excessive accumulator pressure is retraction that exceeds normal speed. Initial accumulator pressure must be held at 400 psi. A safety diaphragm is installed on the air side of the accumulator to eliminate the possibility of an accumulator explosion. Fluid Level Indicator Safety When the engine is in BATTERY position, the fluid level indicator must read BATTERY. Should any other reading be indicated, the engine must not be operated until a battery indication is effected. Malfunctions and Safety Personnel must always be certain that their method of operation is not responsible for a malfunction. Possible malfunctions, causes, effects, and remedial action are listed in NAVAIR 3-66