737-300/400 LANDING GEAR

1. 737-300/400LANDING GEAR Main Menu Quit Next

2. Instrument Panels Landing Gear Panel

3. Landing Gear Panel LANDING GEAR Lever: UP – Retract landing gear. OFF – Hydraulic pressure is removed from the landing gear system. DN – Extend landing gear.

4. Landing Gear Panel • Red Landing Gear Indicator Lights: • Illuminated – • Respective landing gear is not down and locked when either or both forward thrust levers are retarded to idle. • Respective landing gear is in disagreement with LANDING GEAR lever, i.e. landing gear is in transit or is unsafe. • Extinguished – • Respective landing gear is up and locked with LANDING GEAR lever UP or OFF.

5. Landing Gear Panel • Green Landing Gear Indicator Lights: • Illuminated – • Respective landing gear is down and locked. • Extinguished – • Respective landing gear is not down and locked. • Note: Landing gear configuration warning horn is deactivated with all landing gear down and locked. See picture of main gear and nose gear indicator sensors

6. Landing Gear Panel LANDING GEAR LIMIT Speed Placard: Indicates maximum speed when operating the landing gear and after gear extension. See closeup picture of LANDING GEAR LIMIT speed placard

7. Landing Gear Panel LOCK OVERRIDE (Landing Gear Override) Trigger: Pull – Bypasses the landing gear lever locking system. Note: When the aircraft is on the ground, the air/ground sensing system engages the landing gear lever locking system and prevents the lever from moving to the UP position. When the aircraft becomes airborne, the air/ground sensing system disengages the landing gear lever locking system which allows the lever to be moved from DN to UP. It is possible, however, for the air/ground sensing system to remain in the “ground-mode” even though the aircraft is in flight. In this case, the locking system will remain engaged after takeoff and the landing gear lever will not move to the UP position. Non-normal procedures may recommend pulling the landing gear override trigger to bypass the locking system and consequently raise the gear (reference your company operations manual).

8. Manual Gear Extension

9. Manual Gear Extension Manual Gear Extension Handles: If “A” system hydraulics is inoperative, the landing gear may still be extended via the manual extension system. The manual gear extension handles are located in the flight deck floor, aft and to the left of the First Officer’s seat. When the extension handles are pulled to their limit, the respective gear will release from its locked position. Gravity and air loads will assist the gear in free-falling to the down and locked position. The main gear manual extension handles need to be pulled out approximately 14 to 16 inches (35 to 40 cm) with a force of about 60 pounds. The nose gear manual extension handle needs to be pulled out approximately 8 inches (20 cm) with a force of about 80 pounds. Down and locked verification can be made using the green landing gear indicator lights. Note: LANDING GEAR lever must be in DN or OFF position to prevent hydraulic lockup during manual extension.

10. Main Gear Viewer

11. Main Gear Viewer Plywood cover installed Plywood cover removed The main gear viewer is located in the main cabin floor. It is opposite the third window that is aft of the overwing exit, one foot left of center. After pulling back the carpet that is concealing the viewer, a plywood cover will be exposed and needs to be removed. The pilot will now position their eyes over the viewer. Two mirrors inside the viewer are used to ensure that the three red paint stripes on each main gear are visible and in horizontal alignment. It may be necessary to turn on the wheel well lights. Note: Depending on the aircraft seat configuration, some viewers may be positioned under an aisle seat.

12. Main Gear Paint Stripes See picture of main gear viewer mirrors The red paint stripes are located on the lower side strut of each main gear. When looking at the mirrors in the main gear viewer, the three red paint stripes should be visible and in horizontal alignment. This is an indication that the respective main landing gear is down and locked.

13. Nose Gear Viewer

14. Nose Gear Viewer Cover plate closed Cover plate open The nose gear viewer is located on the flight deck floor, just inside the door. Access to the viewer is made by opening the cover plate. Under the cover plate is a small circular viewing window. As the pilot looks into the viewing window, two red arrow heads should be visible. If the two red arrow heads are facing each other and appear to be in alignment (in contact), the nose gear is down and locked.

15. Nose Gear Arrow Heads See picture of viewing window in wheel well One nose gear arrow head is located on the nose gear lock brace and the other arrow head is located on the nose gear lock link. When looking into the nose gear viewing window the two red arrows should be visible. If the two red arrow heads are facing each other and appear to be in alignment (in contact), the nose gear is down and locked. It may be necessary to turn on the wheel well lights.

16. Instrument Panels Autobrake Panel

17. Autobrake Panel • AUTO BRAKE DISARM Light: • Illuminated – • RTO is selected on the ground. • When RTO is selected on the ground, the AUTO BRAKE DISARM light will illuminate while the braking system performs a self-test. One to two seconds later, the light will extinguish if the self-test was successful. • Manual brakes applied during RTO or landing. • A fault exists in the automatic braking system. • Antiskid has been selected off. • Thrust levers are advanced during an RTO or landing. • Landing made with RTO selected. • SPEED BRAKE lever moved to DOWN detent during an RTO or landing. • Extinguished – • Autobrakes armed. • AUTO BRAKE select switch is positioned to OFF.

18. Autobrake Panel AUTO BRAKE Select Switch: OFF – Automatic braking system deactivated. 1, 2, 3, or MAX – Selects desired deceleration rate for landing. Note: Switch must be pulled-out to select MAX deceleration. RTO (Rejected Takeoff) – At or above 90 knots during takeoff, automatically applies maximum brake pressure (3,000 psi) when thrust levers are retarded to idle.

19. Instrument Panels Antiskid Panel

20. Antiskid Panel • ANTI SKID INOP Light: • Illuminated – • The antiskid fault monitoring system has detected a system fault. • Antiskid switch is OFF. • Extinguished – • Antiskid system is operating normally.

21. Antiskid Panel • ANTISKID Control Switch: • ON (guarded position) – • Provides power to the antiskid unit for both inboard and outboard antiskid protection. • OFF – • Disables the antiskid system. • Illuminates the ANTI SKID INOP light. • Illuminates the AUTO BRAKE DISARM light if the autobrake system is armed.

22. Instrument Panels Hydraulic Brake Pressure Indicator

23. Hydraulic Brake Pressure Indicator • HYD BRAKE PRESS Indicator: • Indicates brake accumulator pressure. • Normal accumulator pressure – 3,000 psi • Maximum accumulator pressure – 3,500 psi • Normal accumulator precharge pressure – 1,000 psi • Note: The brake accumulator is attached to the aft wall in the main gear wheel well, aircraft right. The accumulator precharge is either compressed air or nitrogen. See picture of brake accumulator

24. Rudder/Brake Pedals Rudder/Brake Pedals: Push full pedal – Turns nose wheel up to 7° left or right of center. Push top of pedal only – Activates wheel brakes. Note: See the Flight Controls presentation for a description of the rudder.

25. Control Stand Parking Brake

26. Parking Brake PARKING BRAKE PULL Lever: Positioned forward – Parking brake is released. Pulled aft – Sets the parking brake when either Captain’s or First Officer’s brake pedals are fully depressed.

27. Parking Brake PARK BRAKE LIGHT: Illuminated – Parking brake is set. Extinguished – Parking brake is released.

28. Instrument Panels 1 AS INSTALLED 1 Nose Wheel Steering Switch

29. 1 AS INSTALLED 1 Nose Wheel Steering Switch NOSE WHEEL STEERING Switch: NORM (guarded position) – Hydraulic system “A” is providing power for the nose wheel steering system. ALT – Hydraulic system “B” is providing power for the nose wheel steering system.

30. Nose Wheel Steering Wheel

31. Nose Wheel Steering Wheel • Nose Wheel Steering Wheel: • Rotate – • Turns nose wheel up to 78° left or right of center. • Overrides rudder pedal steering. • Note: The nose wheel steering wheel is attached to the side wall, left of the Captain’s control column. The steering wheel is also known as the tiller.

32. Nose Wheel Steering Wheel Nose Wheel Steering Indicator: LEFT – Indicates nose wheel steering displacement left of center position. CENTER – Normal straight ahead position. RIGHT – Indicates nose wheel steering displacement right of center position. This concludes the review of the Landing Gear controls and indicators. The next section will discuss the system in greater detail. Click Next to continue.

33. Landing Gear Operation The aircraft has two main landing gear and single nose gear. Each gear is equipped with two tire and wheel assemblies. Each main gear wheel is fitted with disc-type hydraulic brakes which are modulated by the antiskid system. To absorb the impact on landing, air-oil type shock struts are installed on all three gear. “A” system hydraulics supplies power for normal retraction, extension, and nose wheel steering.

34. “A” system reservoir Return Hydraulic shutoff Engine driven pump Hydraulic heat exchanger To reservoir No. 1 fuel tank Motor Electric pump Supply “A” system pressure “B” system pressure Standby system pressure Case drain return Nose wheel steering Landing gear Landing gear transfer unit 737-300/400 Hydraulic Schematic (specific to landing gear) “A” system hydraulics supplies power for normal retraction, extension, and nose wheel steering.

35. “B” system reservoir Return “A” system reservoir Return Hydraulic shutoff Hydraulic shutoff Engine driven pump Engine driven pump Hydraulic heat exchanger Hydraulic heat exchanger To reservoir To reservoir No. 1 fuel tank No. 2 fuel tank Motor Motor Electric pump Electric pump Supply “A” system pressure “B” system pressure Standby system pressure Case drain return Nose wheel steering Landing gear Landing gear transfer unit 737-300/400 Hydraulic Schematic (specific to landing gear transfer unit) • A landing gear transfer unit is installed in the main gear wheel well. When all of the following conditions exist, “B” system hydraulics will retract the landing gear via the landing gear transfer unit: • Airborne • No. 1 engine drops below 56% N2 • LANDING GEAR handle in the UP position • Landing gear not up • When this becomes especially useful is during a loss of the No. 1 engine immediately after takeoff. With the No. 1 engine inoperative, the “A” system engine driven pump is also inoperative. Even though the “A” system electric pump is operating normally, the volume output of the pump is not great enough to raise the gear at a rate which is required during single engine operations. As the No. 1 engine N2 gauge drops below 56%, the landing gear transfer unit will connect “B” system hydraulics to the landing gear. “B” system will now raise the gear at a normal retraction rate.

36. Landing Gear Operation See picture of uplock hook and uplock roller The main gear is locked in the “down” position by a folding lock strut, and held in the “up” position by an uplock hook and uplock roller. When the LANDING GEAR lever is moved to the UP position, the main gear retracts inboard into the main gear wheel well. During retraction, main gear wheel rotation is stopped by “A” system hydraulics via the alternate brake metering valves. When the main gear is fully retracted, the doors are faired with the fuselage. Rubber blade-type seals and oversized hubcaps complete the fairing of the outboard wheels.

37. Landing Gear Operation See picture of snubbers The nose gear is locked in the “up” and “down” position by a folding lock strut. When the LANDING GEAR lever is moved to the UP position, the nose gear retracts forward into the nose gear wheel well. As the gear retracts, nose gear wheel rotation is stopped by tire contact with the snubbers. The snubbers are installed on the ceiling of the nose gear wheel well. The nose gear doors are mechanically linked to the nose gear and will fair with the fuselage when the gear is fully retracted.

38. Brake System See picture of one brake wear indicator pin. The brake system includes a normal brake system, an alternate brake system, one brake accumulator, an autobrake system, antiskid protection, and a parking brake. Each main gear wheel has a multi-disc hydraulic powered brake. Four brake wear indicator pins are provided on each main gear to indicate when the brakes need to be replaced.

39. Brake System Each brake is provided with pistons which actuate the brake when hydraulic pressure is applied. The brake system is manually controlled by the the Captain’s or First Officer’s brake pedals thru linkage and cables to the brake metering valve for each main gear. The intensity of pressure established in the brakes varies directly with the amount of pedal force maintained. The nose gear wheels do not incorporate any type of braking system.

40. “B” system reservoir Return Hydraulic shutoff Engine driven pump Hydraulic heat exchanger To reservoir No. 2 fuel tank Motor Electric pump Supply “A” system pressure “B” system pressure Standby system pressure Case drain return 737-300/400 Hydraulic Schematic (specific to the normal brake system) “B” system hydraulics supplies power to the normal braking system for each main gear wheel. Normal brakes

41. “B” system reservoir Return “A” system reservoir Return Hydraulic shutoff Hydraulic shutoff Engine driven pump Engine driven pump Hydraulic heat exchanger Hydraulic heat exchanger To reservoir To reservoir No. 1 fuel tank No. 2 fuel tank Motor Motor Electric pump Electric pump Supply “A” system pressure “B” system pressure Alternate Brakes Selector Valve Standby system pressure Accumulator isolation valve Case drain return 737-300/400 Hydraulic Schematic (specific to the alternate brake system) If “B” hydraulic system loses pressure, separate hydraulic lines are utilized to automatically supply “A” hydraulic system pressure to each main gear wheel. This is known as alternate brakes Alternate brakes Normal brakes

42. “B” system reservoir Return “A” system reservoir Return Hydraulic shutoff Hydraulic shutoff Engine driven pump Engine driven pump Hydraulic heat exchanger Hydraulic heat exchanger To reservoir To reservoir No. 1 fuel tank No. 2 fuel tank Motor Motor Electric pump Electric pump P Supply “A” system pressure “B” system pressure Hydraulic brake pressure accumulator Standby system pressure Accumulator isolation valve Case drain return 737-300/400 Hydraulic Schematic (specific to the accumulator braking) If “A” and “B” hydraulic system pressure is lost, the brake accumulator will supply trapped hydraulic fluid to each main gear wheel. Enough pressure exists in the accumulator for approximately six brake applications. Note: Antiskid protection is available during accumulator braking. Alternate Brakes Selector Valve Alternate brakes Normal brakes See picture of brake accumulator

43. Autobrake System The autobrake system provides automatic braking upon landing when a pre-selected deceleration rate (1, 2, 3 or MAX) is chosen. It also provides automatic braking in the case of a rejected takeoff (RTO) after a wheel speed of 90 knots is attained. The autobrake system operates utilizing “B” system hydraulics only. If the “B” hydraulic system is inoperative, the autobrake system is also inoperative. Antiskid protection is available during autobrake operation.

44. Autobrake System If automatic braking is desired upon landing, a deceleration rate must be selected while still airborne. When a rate is selected, a self-test is initiated and the AUTOBRAKE DISARM light will not illuminate unless the system has detected a fault. After landing, autobrake application begins when both forward thrust levers are retarded to idle and wheel speed of at least one wheel on each main gear is greater than 60 knots. Autobrake pressure will gradually increase during the first three seconds after touchdown. The system will then maintain a constant deceleration rate and, if allowed, will bring the aircraft to a complete stop unless braking is terminated by the pilot or a system fault is detected.

45. Autobrake System To maintain the selected deceleration rate, pressure from the autobrake system is reduced as additional drag (thrust reversers, spoilers) contributes to the total deceleration. The following deceleration rates are provided: “1” – 4 feet/second2 “2” – 5 feet/second2 “3” – 7.2 feet/second2 “MAX” – 14 feet/second2

46. Autobrake System If automatic braking is desired during a rejected takeoff, the AUTO BRAKE select switch must be positioned to RTO. After selecting RTO, the AUTO BRAKE DISARM light will illuminate while the braking system performs a self-test. One to two seconds later, the light will extinguish if the self-test was successful.

47. Autobrake System • To arm the RTO mode prior to takeoff, the following conditions must exist: • AUTO BRAKE select switch must be in the RTO position. • Aircraft must be on the ground. • Autobrake and antiskid circuits must be operational. • Both forward thrust levers must be positioned to idle. • Wheel speed must be less than 60 knots. • After a successful test, the autobrake system is now in an unarmed “waiting-mode.”

48. Autobrake System When wheel speed is greater than 60 knots, RTO mode is now in a “semi-armed” mode. However, if the takeoff is rejected with a wheel speed between 60 and 90 knots, automatic braking is not applied and the AUTO BRAKE DISARM light illuminates. Once wheel speed is greater than 90 knots, the autobrake system is “fully-armed.” If the takeoff is rejected and the forward thrust levers are retarded to idle, maximum braking (3,000 psi) is immediately applied to all four wheels. The system will bring the aircraft to a complete stop unless braking is terminated by the pilot or a system fault is detected.

49. Autobrake System If the takeoff was normal and an RTO was not initiated, the RTO mode is automatically disarmed when the right main gear strut extends (air/ground sensing system in “air-mode”). When this occurs, the AUTO BRAKE DISARM light will not illuminate and the select switch must manually be positioned to OFF. However, if a landing is made with the select switch still in RTO, automatic braking will not occur and the AUTO BRAKE DISARM light will illuminate two minutes after touchdown.

50. Antiskid Protection Antiskid protection is provided in the normal and alternate brake systems. The types of antiskid protection available include normal, touchdown, and locked wheel. When the pilot depresses the brake pedals, the brake metering valves open and hydraulic fluid is directed to the brakes via the antiskid valves.