C. Those systems using engine bleed air and containing coverage in other chapters are as follows:
SYSTEM CHAPTER
Pneumatic Starting System 80
Engine Fuel Deicing 73
Pneumatic System 36
*[1] GJ ALL EXCEPT B-2509 AND B-2510 PW 732, 742, 752, 761, 762 AND 772
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75-00 Page 1
K92334
Engine Air Bleeds 515
75-00 Figure 1 Jun 20/85
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BOEING PROPRIETARY - Copyright . - Unpublished Work - See title page for details.
ENGINE GRAVEL PROTECTION SYSTEM - DESCRIPTION AND OPERATION
EFFECTIVITY
GJ ALL EXCEPT B-2509 and B-2510
1. General
A. The engine gravel protection system is provided for the two engines to prevent dirt, gravel and other debris from getting into the engines. The system uses 13th stage engine bleed air ducted through the nose cowl and discharged at a point below the inlet of the engine through air nozzles (Fig. 1).
B. The system uses 28-volt dc power from the P6 load control center.
C. The system consists of a gravel protection boom, gravel protection valve, GRAVEL PROTECT or ENG ANTI-FOD light, and a pressure switch for each engine, and a GRAVEL PROTECT or ANTI-FOD switch for the two engines.
D. The GRAVEL PROTECT or ANTI-FOD switch at the P5 overhead panel controls the operation of the system and permits testing valve operation during flight. System operation is indicated at the control cabin by the GRAVEL PROTECT or ENG ANTI-FOD light at the center instrument panel. A press-to-test feature checks the circuit continuity of the GRAVEL PROTECT or ENG ANTI-FOD light (Fig. 2).
E. The landing gear module (M338) through the air-ground switch allows operation of the system while the airplane is on the ground. When the airplane lifts off the ground the system is automatically de-energized even though the GRAVEL PROTECT or ANTI-FOD switch is ON.
2. Engine Gravel Protection Boom
A. The engine gravel protection boom conveys bleed air from the engine and discharges it to the ground through nozzles located at its end. The boom is located below the nose cowl and extends from a point slightly forward of the aft end to a few inches beyond the inlet end. The boom has a forward strut support which is provided with internal air lines for anti-icing the strut (Fig. 1).
B. The nozzles in the boom direct the air at an angle towards the rear of the engine. The high velocity air prevents dirt, gravel and other debris on the area below the engine inlet from being sucked into the engine.
C. For removal/installation of the gravel protection boom, refer to Engine Nose Cowl, 71-11-31.
3. Engine Gravel Protection Valve
A. The engine gravel protection valve controls the flow of air that goes through the air nozzles in the gravel protection boom. It is a solenoid- piloted, pressure-actuated regulating valve.
B. The valve is located below the engine just aft of the nose cowl. It is connected to the gravel protection air ducts by means of couplings.
5C8
Oct 20/85 75-09-100 Page 1
BOEING PROPRIETARY - Copyright . - Unpublished Work - See title page for details.
K92339
Engine Gravel Protection System Component Location 5A7
75-09-100 Figure 1 Oct 20/83
Page 2
BOEING PROPRIETARY - Copyright . - Unpublished Work - See title page for details.
C. The valve is opened by positioning the GRAVEL PROTECT or ANTI-FOD switch at the P5 overhead panel to ON. This allows 13th stage engine bleed air to pass through the valve and then to the air nozzles in the boom. Air pressure downstream of the valve is monitored by means of an air sensing line tapped on the duct a few inches away from the outlet end of the valve and connected to the valve body. Air pressure beyond the minimum or maximum pressure limits at which the valve has been set will increase or decrease the opening of the valve thereby regulating the flow of air.
D. The valve has an indicator which can be used in checking valve position during maintenance. A regulating screw on the valve permits adjustment of the downstream air pressure to the recommended value (Ref Adjustment/Test).
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