Normal 28-volt alternating-current power from transfer bus 1 is lost. What allows the flight-safety-related captain and first-officer instrument lighting to remain available?, The Master Dim and Test system automatically transfers all flight-compartment lighting to the 28-volt direct-current battery bus., The standby relays de-energize and connect the 28-volt alternating-current standby bus through the standby transformer, which supplies 5-volt alternating current to the applicable instrument and panel lights., The variable transformers mechanically bypass the lighting modules and connect transfer bus 2 directly to the affected lamps., The main-panel floodlights remain illuminated following loss of the normal 115-volt alternating-current transfer-bus supply, but the crew can no longer vary their brightness. Why is this behaviour expected?, Loss of normal power de-energizes the standby relay, causing fixed standby resistors rather than the normal bright/dim control to set the floodlight intensity., The floodlights transfer to direct-current battery power, which can support illumination but cannot operate the dimmer-control units., The Master Dim and Test system commands maximum brightness whenever normal transfer-bus power is unavailable., A technician selects TEST on the Master Dim and Test switch. How does the system illuminate both ground-seeking and power-seeking indicator circuits despite their opposite operating logic?, The test relay supplies the appropriate power and ground paths simultaneously so all applicable indicating lights illuminate brightly., The test switch reverses the polarity of every power-seeking indication so that all indicator circuits temporarily become ground-seeking circuits., The annunciation and dimming module removes all system inputs and directly powers only the amber and red warning indications., Several passenger-compartment lights downstream of one particular light assembly stop responding to scene and colour commands, but electrical power remains available. Why should the apparently failed downstream lights not immediately be replaced?, All lights on a channel share a single electrical power return, so any downstream failure must originate at the final light in the electrical series circuit., The Attendant Control Panel intentionally removes addressing from downstream lights whenever one light reports an internal fault., Passenger-lighting data is transmitted serially from one light assembly to the next, so an upstream light or wiring failure can prevent downstream assemblies from receiving commands even though those downstream assemblies remain serviceable., A new window light has been installed in a passenger-compartment lighting channel. It has electrical power and a valid data connection but remains inoperative. Which missing condition could independently prevent the light from operating?, The light has not been selected as the termination resistor for its Telecommunications Industry Association 485 channel., The light has not received a valid location address through the address/token procedure., The light has not received a direct command from both the forward and aft Attendant Control Panels simultaneously., The FASTEN SEAT BELT switch is in AUTO, the landing gear is not down, and the passenger oxygen indication relay is not energized. The trailing-edge flaps move away from the UP position. What should occur?, The FASTEN SEAT BELT and RETURN TO SEAT signs illuminate and a low chime sounds., Only the FASTEN SEAT BELT signs illuminate because RETURN TO SEAT indication requires the landing gear to be down., No sign changes occur until either the landing gear is selected down or the passenger oxygen system operates., The flight-compartment emergency-exit-light switch is ARMED and the aft Attendant Control Panel switch is NORMAL. What event causes the emergency-light power supplies to automatically energize their connected lights?, The 28-volt direct-current bus 1 voltage decreases below 12 volts., Either alternating-current transfer bus decreases below 100 volts., The passenger-compartment utility relay opens while the aircraft is airborne., A single Light Emitting Diode fails in the left air-conditioning-compartment lighting system. Why should the remaining compartment lights continue to operate normally?, The Light Emitting Diodes are electrically connected in parallel, so failure of one light does not interrupt power to the others., Each Light Emitting Diode has an internal battery that automatically supplies the remaining lights after a failure., The right air-conditioning-compartment lighting switch automatically supplies a redundant serial power path to all left-side lights., The forward cargo-compartment light switch is ON, but the cargo door is moved to the locked condition. Why do the cargo lights extinguish even though the light switch remains selected ON?, The Proximity Switch Electronics Unit detects the locked-door condition and energizes the cargo-light control relay, which removes illumination., The door-lock mechanism mechanically opens the light-switch power circuit., The cargo-light control relay is de-energized by the locked-door input, connecting the lights directly to ground., The TAXI light switch is in AUTO and all landing/taxi light arrays are operating at their lower taxi-power level. The nose landing gear subsequently leaves the down-and-locked condition. What should happen without further crew selection?, Only the outboard arrays extinguish while the inboard arrays remain illuminated for taxi operation., The light arrays automatically increase to the landing-mode power level., Both left and right main light arrays automatically extinguish.

ATA 33

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