2.23.4 Engine Chip Detector. The chip detector is on the forward side of the accessory gear box. It consists of a housing with integral magnet and electrical connector, with a removable screen surrounding the magnet. The detector attracts magnetic particles at a primary chip detecting gap. A common oil discharge from the scavenge pump is routed to a chip detector wired to a cockpit caution legend marked CHIP #1 ENGINE or CHIP #2 ENGINE. If chips are detected, a signal is sent to the cockpit to light a caution legend, marked CHIP #1 ENGINE or CHIP #2 ENGINE. Power to operate the engine chip detector system is from the No. 1 and No. 2 dc primary buses respectively, through circuit breakers marked WARN LTS, under the general headings NO. 1 ENG and NO. 2 ENG.
2.24 ENGINE START SYSTEM.
The pneumatic start system uses an air turbine engine start motor for engine starting. System components consist of an engine start motor, start control valve, external start connector, check valves, controls and ducting. Three pneu-matic sources may provide air for engine starts: the APU, engine crossbleed, or a ground source. When the start but-ton is pressed, air from the selected source is directed through the start control valve to the engine start motor. The #1 ENGINE STARTER or #2 ENGINE STARTER caution legend will go on at this time and remain on until the starter drops out. As the engine start motor begins to turn, an overrun clutch engages causing the engine to motor. As the engine alternator begins to turn, electrical current is supplied to the ignition exciter. Ignition will con-tinue until either the ENGINE IGNITION switch is moved to OFF or starter dropout occurs. The ENG POWER CONT lever is advanced to IDLE detent for light-off and acceleration. A starter speed switch terminates the start cycle when cutoff speed is reached (52% to 65% Ng SPEED) and turns off the starter caution legend and engine ignition. Malfunction of the starter speed switch may be overcome by manually holding the start button pressed until reaching 52% to 65% Ng SPEED. To drop out the starter, manually pull down on the ENG POWER CONT lever. To abort a start, pull down on the ENG POWER CONT lever and move to OFF in one swift movement. Power to operate the No. 1 engine start control valve is from the dc essential bus through a circuit breaker marked NO. 1 ENG START. Power to operate the No. 2 engine start control valve is from the No. 2 dc primary bus through a circuit breaker marked NO. 2 ENG START CONTR.
2.24.1 Engine Ignition Keylock. An ENGINE IGNI-TION keylock is installed on the side of the lower console (Figure 2-7), to short out and prevent ignition exciter cur-
rent .ow when the switch is OFF and the starter is engaged. The switch is marked ENGINE IGNITION OFF and ON. When the switch is ON, the shorts are removed from both engine alternators, allowing exciter current to .ow when the engine alternator begins to turn. The ENGINE IGNI-TION is normally ON during .ight and turned OFF at shutdown. One switch serves both engines. If the switch is OFF, neither engine can be started, although motoring capability remains. When an engine is to be motored with-out a start, make certain the ENGINE IGNITION switch is OFF. To prevent a possible hot or torching start never turn the ENGINE IGNITION switch ON after motoring has started. Abort start procedures must be done to remove excess fuel from the engine if a start was attempted with the switch OFF.
2.24.2 APU Source Engine Start. The APU provides an on-board source of air and auxiliary electrical power. The APU bleed-air output is enough to start each engine individually at all required combinations of ambient tem-peratures and enough to start both engines simultaneously within a reduced range of ambient temperatures (Figure 5-2). The AIR SOURCE HEAT/START switch must be at APU. Refer to Section XII for complete APU descrip-tion.
2.24.3 Crossbleed Engine Start System. Crossbleed engine starts are used when one engine is operating and it is desired to start the other engine from the bleed-air source of the operating engine. To make a crossbleed start, the oper-ating engine must be at least 90% Ng SPEED. When the AIR SOURCE HEAT/START switch is placed to ENG, both engine crossbleed valves will open. Pressing the start button for the engine not operating will cause the start valve for that engine to open at the same time the crossbleed valve for the starting engine will close, and remain closed until starter dropout occurs. At 52% to 65% Ng SPEED, the starting engine start valve will close, stopping bleed-air .ow to the starter. Power to operate the bleed shutoff valve is from No. 1 dc primary bus through a circuit breaker marked AIR SOURCE HEAT/START.
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