Hydraulics Flashcards
(88, 90) Functions of AUX hydraulic pump switch:
• Aux pump in the right system, provides addt’l source of hyd pressure.
• Operation controlled by auxiliary pump (AUX) switch located on FO’s instrument panel.
- ON – Turns on electrical hyd auxiliary pump.
- OFF – Turns off electrical hyd auxiliary pump.
- OVRD – (Momentary – must be held in OVRD) –
Bypasses thermal protective circuit & activates pump.
• Auxiliary pump is protected by thermal switch that automatically shuts pump off if normal operating temp range is exceeded.
(88, 90) Functions of the hydraulic transfer pump, positions of switch:
On / off switch
- HYD PUMP TRANS Switch open/closes shutoff valve on each side of transfer pump.
- Transfer pump mechanically connects left and right hydraulic systems and enables hydraulic pressure to be transferred from higher to lower side (higher pressure side operates as a motor and low pressure side acts as a pump).
(88, 90) Meaning of an illuminated HYD QTY LOW light before and after engine start:
Amber HYD QTY LOW lts on system display panel illuminate when:
MD-88:
• Left quantity < 8 qts or right quantity < 9 qts.
• After engine start, if either sys. quantity < 4 qts
MD-90:
• Left quantity < 9 qts or the right quantity < 10 qts.
• After engine start, if either sys. quantity < 6 qts
(88, 90) Will engine driven hydraulic pumps operate during electrical failure?
• Engine driven HYD pumps operate during electrical failure regardless of switch position.
(88, 90) Minimum hydraulic quantity for dispatch:
MD-88:
• Left minimum – 8 qts, Right minimum – 9 qts
MD-90
• Left minimum – 9 qts, Right minimum – 10 qts
(ALL) How many independent hydraulic systems are on the MD-88/90? How are they designated?
• Airplane has 2 independent hyd systems (left and right) utilizing fire-resistant hyd fluid.
(88, 90) Minimum hyd pressure necessary to set the parking brake:
• Minimum of 1400 psi (88) / 1700 psi (90) on BRAKE PRESS gauges is required prior to setting the parking brake to ensure adequate brake holding power.
(88, 90) Meaning of amber ABS light:
- Landing gear handle is down
- AUTO BRAKE selector is moved out of the OFF position
- AUTO BRAKE ARM/DISARM switch is in DISARM.
(88, 90) Conditions for availability of antiskid braking:
Antiskid system is elec. controlled and is operational when:
- Switch in ARM position
- Gear handle down or alt gear handle pulled
- Parking brakes released
- Wheel speed greater than 10 knots
Note: Anti-skid braking is not available if the left / right DC busses are unpowered.
(All) Recall auto brakes are available in normal brake system only:
When should autobrakes not be used?
When is ABS unavailable?
- The anti-skid system must be armed and operational for ABS operation.
- With left and/or right hydraulic system failure, do not use Autobrakes.
- ABS is unavailable with flaps < 26° for landing or if the accumulators are the only source of hydraulics.
(ALL) Conditions required for autobrake RTO system operation:
• ABS takeoff mode is activated during rejected takeoff upon spoiler handle extension.
Note: If spoiler handle fails to deploy automatically, manual spoiler handle deployment will activate ABS.
- If a rejected takeoff is initiated < 70 kts (88) / 90 kts (90), ABS reverts to landing mode operation and MIN braking is provided.
- At speeds > 70 kts (88) / 90 kts (90), max dual-system auto braking is applied immediately without any time delay.
Note: Full right and left brake system pressure is applied to the brakes and maximum deceleration is limited only by anti-skid operation.
(ALL) Conditions required for ABS operation during landing:
• ABS landing mode is activated when
(1) spoiler handle is deployed either automatically or manually,
(2) throttles retarded and
(3) brake pedals released.
• Auto braking is delayed after spoiler deployment for ~ 1” in MAX position and ~ 3” (88) / 1” (90) in MIN or MED positions. ABS landing mode is inhibited if throttles are not retarded towards idle.
Note:
- With MED selected, brake system pressure is modulated to brakes by land manifold to maintain a fixed level of deceleration.
- With MAX selected, full right brake system pressure is applied to brakes; maximum deceleration is limited only by anti-skid operation
(88, 90) Brake pedal deflection that will disengage automatic braking (autobrakes):
MD-88
• Autobrakes are disarmed at any speed by depressing brake pedals beyond 25% travel.
MD-90
• Below 90 knots, 25% pedal deflection is required to disengage autobrakes.
• Above 90 knots, 90% pedal deflection is required to disengage autobrakes.
(88, 90) Maximum brake temperatures for takeoff and setting the parking brake: (MD-88)
MD-88:
• Max brake temp for setting parking brake: 300°C
• Prior to takeoff, verify brake temp < 205°C and OVHT light extinguished.
(88, 90) Maximum brake temperatures for takeoff and setting the parking brake: (MD-90)
MD-90:
• Max brake temp for setting parking brakes is 500°C.
• Prior to takeoff, verify OVHT light extinguished and BRAKE TEMP gauge < 250°C for airport elevations up to 2,200’ MSL.
• Corrections to takeoff brake temperature limits:
- When OAT exceeds 32°C, subtract 5°C for
each 1°C above 32°C.
- For each 1 knot of tailwind, subtract 15°C.
• For takeoff from higher airport elevations or higher brake temperatures refer to guidance in VOL.1 NP and ODM.
