Why do the lights go out?

[smoothkpilot]

Hi Guys, this is a question to all you pilots out there. I am a student pilot. I was wondering why is it, that when an aircraft( a passenger airliner) is taking-off or landing at night that the cabin lights are turned right down to very dim, and then once airbourne they are turned up again. Is this some strange safety measure. No explanation of this was presented in any of my ATPL courses. Please explain. Thanks.
Smoothk

[Angle of Attack]

I think its usually so the passengers eyes can adapt to the low light so in the event of an emergency or accident and an evacuation is nescessary you can see your way to the nearest exit more easily because the cabin at best would be very dim at night if the aircraft had sustained damage in an over run or something similar. Although not all airlines have the policy some have the lights on max for takeoff and landing, reason being rescue services can see the aircraft more easily if an accident occurs, hmm

[ICT_SLB]

Can't fault AoA's explanation but on some aircraft there's a system reason as well. On a lot of aircraft, the Auxiliary AC Busses are dropped at the same time as the electrical Hydraulic & Fuel Pumps are switched on automatically as the Flaps deploy (typically > 3 degrees). to avoid overloading the Generators. Lighting is a large percentage of total electrical load and the "mood" lights (upwash & downwash) are often on the Auxiliary Busses hence they're dropped automatically as the aircraft is set up in takeoff configuration (and landing of course).

In cruise (Flaps 0), all electrical pumps are switched off (the Engine Driven Pumps and motor flow Injectors do the job) and the Auxiliary loads (lighting, Galley Power etc) come back on line.

[Young Paul]

I won't disagree with the last answer except to say that it certainly doesn't apply to B737 or A320, whereas the first answer definitely does.

[smoothkpilot]

Thanks guys your replies are much appreciated. Now I have some reason as to why this is done on some flights.

Many Thanks,
Smoothk.

[QAVION]

This topic has been covered several times before, smoothpilot. Here's one of the message threads relating to this subject:


http://www.pprune.org/forums/showthread.php?s=&threadid=10521&highlight=cabin+light

Rgds.
Q.

P.S. I'd be a little concerned if the lights went out automatically on a Boeing 767 or a 747 if the aircraft was simply in takeoff/landing configuration (the 767 does have an engine start electrical loadshedding process, but shouldn't otherwise shed electrical loads unless a generator has failed... or the aircraft is dumping fuel).

[Rob767]

hi my mums cabin crew,
she told me that its for day savings. this helps over a/c in the area so they dint get blinded.
i hope this answer ur question

[FlapsOne]

What are day savings?

You've lost me!

[Slasher]

Flaps One! A fully-credited aircrew member like you and you honestly dont know what the non-blinding Day Savings procedure is and how it helps over aircraft in the area?

Unejamakated Phillistine! :D :p

[FlapsOne]

I feel soooooo inadequate!

[Slasher]

Getting back to the original question, it also serves for the cabin crews eyes to adjust to the night conditions so theyll be able to see clearley whats happening outside if an evac becomes necessary and determine wether that exit is suitable for use.

[Op checked Satis]

:) ICT, Just wondering which A/C you are refering to,generally speaking lighting is not part of any load shedding process i have come across unless your into major electrical failiure.