Why do they dim the lights on airplanes for take off and landing?
They say that it is to conserve power for the engines. Frankly I can’t see it making that much difference… but just what i’ve heard…
I’ve heard that but don’t know why they need to conserve power for landing …
I think the pilot wants to impact as many of the passengers’ senses as possible. Dimming the lights seems to reinforce the audible announcement and say: “Hey, we’re really landing/taking off. Seriously!” Helps get the passengers in a better frame of mind and awareness, especially those for who the announcement may go in one ear and out the other.
Welcome to the Boards by the way.
Yeah, seems a little iffy. Maybe the braking takes a shit-load of power. Not too sure…
So you can’t see the Tommyknockers?
I was under the assumption that large (737 and larger) passenger jets used 'APU’s to generate onboard electricity, so I don’t see where the power-conservation comes into play.
Err…Langoliers.
Perhaps in the situation where they need to abort the landing and takeoff again.
I always assumed it was so that you could see out the windows if there was a problem. With the glaring lights on inside the plane, in an emergency, you need to be able to see which exits are OK, which might open into the water, etc.
That’s certainly the reason you’re supposed to have the shades up during takeoff and landing, so I assume the same with the lights.
Just as an addition, that is related to the reason for the tray-tables and seat-backs in upright position: so that the person next to you (or behind you, respectively) can get out quickly in case of emergency evacuation.
My wag is it’s a throwback to the days where every oz of power was needed for takeoff and a little insurance that every oz of power is available, more so pease of mind then something critical.
They dim the lights now? Is this something new? I haven’t been on a plane for a few years, but I don’t recall this as SOP for all takeoffs. On night flights, AFTER takeoff, the cabin lights would dim so people could sleep; I often wished they would dim them sooner so I could start sleeping faster.
Nope. The APU is used only when the engines are not running and there is no ground service available. Each engine has a large generator (not an alternator like current automobiles) and the higher the electrical load, the harder the generator has to work to produce electricity. During testing of new airplanes, tests are run to measure the generator output during no load, light load, and heavy load conditions. During take off and land the lights are dimmed to reduce the load. About 2 years ago Boeing added a switch to all of the airplanes they build that allows the pilot to shut off all non essential electrical items. Things like vacuum waste, galley power, and cargo lights can be shut off with the flick of a switch. It reeked havoc at my work, I might be running a test that required the switch to be on, someone else would need it off. The engines also have to run hydraulic and air pumps, items that you want running at maximum during takeoff and landing. It is just a matter of placing the airplanes resourses where they are needed the most.
They can’t squeeze a little more power for the cabin lights?
So, when the engines are starting to fail and you’re heading towards the side of a mountain at 600MPH the last thing the pilot does in a desperate bid to save his plane is switch off the thing that keeps all the wee jobbies from flying back out of the toilet!* :eek:
What a way to go…
That does make your spelling mistake (reeked havoc) incredibly appropriate though.
*Copyright B. Connoly
I agree that the upright position is a plan-for-disater idea. But I think the main part is to prevent injury from people crashing into them. Easy evacuation would be secondary.
Well, I’m not going to speculate on why (I’ll ask the F/As on my next trip) its done, but if it IS for electrical power reasons, then it is a throwback to earlier times, because that is a very small player these days.
The cabin lights are a relatively minor drain on the electrical system. Things that use up a lot of power are the galleys (coffemakers and ovens), windshield heat, and the landing lights. The only time that galley power is actually turned off under normal conditions is during engine starting.
Most airliners flying today have “smart” electrical systems (or they have a flight engineer !
). For example, if I lose an engine in my jet (and the generator associated with that engine) the electrical system automatically switches everything essential over to the operating generator and dumps the unneeded stuff (ie galleys). So if things get bad, we will NOT be futzing around with the “LAV OFF” switch and fly into the ground!
:NOTE - detailed explantion coming up:
That being said, the cabin lights obviously do put a load on the system, but it’s not much. A jet engine generator works by taking the rotation of the engine and through a (very complicated) series of gears translates that into rotation of a generator. The best way to think about this is to remember back to when you rode a bike, and those headlights you hooked up and used the rotation of your wheels to power. Same concept, on a much larger scale. Remember how when you slowed down the light got dimmer? Well, one of the purposes of the gears (called a CSD, or Constant Speed Drive) is to take varying speeds of the engine and maintain a constant rotation speed on the generator. Constant generator speed = clean, constant power. Very neat.
Now, if you remember those bike headlights you also remember that turning it on caused you to pedal MUCH harder than normal. This was due to two things: inefficient electrical system, and spindly kid legs 
. The electrical system on an airplane is much more efficient, and turning that generator takes a very small portion of the engine’s power. Using your bike wheel as an example, say it weighs about two pounds and cruising through your neighborhood it turns at about 300 RPM (a WAG on my part). The drain of that light is pretty significant. A jet engine (depending on the airplane) can weigh 2,000 to 5,000 pounds, and at cruise the high-speed turbine rotates at upwards of 30,000 RPM (yes, 30,000 not 3,000). Since the generator is always turning (and thus drawing a load from the engine), the added demand from the generator for powering the cabin lights is very small.
:NOTE - detailed explanation over:
Of course, even though it is very small, it is STILL an added load, which means that extra energy is going to power the generator instead of going out the exhaust and helping to keep me airborne. I don’t think that it would ever make a difference in an emergency, but then again, I’ll take every advantage I can get!
Sorry this is not definitive; like I said, I’ll ask the F/As on my next trip and see what they get told in training.
After reading this thread a few weeks ago I specifically asked this question of the pilots on my Southwest Airlines flight on Tuesday, 6/10/2003. The pilot replied that it was not because of the power drain on the engines. In fact on the plane we were to be flying, a Boeing 737, he said there is enough power from the engines to power a small city. The pilot said the reason for dimming the lights is in case of an emergency where the lights might go out, the passengers and flight attendents eyes would already be adjusted to the darker conditions making it safer to move around in the plane without having to wait for your eyes to adapt to the darkness.
This seems logical to me.