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Question About Emergency Lighting

Mon Aug 23, 2004 3:05 pm

How long is the emergency lighting designed to stay on?

The reason I ask this is last night I was disembarking a UA 757-200 and as soon as the door was opened, all the lights went out. Maybe 30 seconds later, the emergency lights came on. Only a minute after that, they went out, so we all had to disembark in absolute darkness.

So I was curious as to whether the emergency lighting was turned off for some reason or if it should go out after a minute. A minute seems awfully short for emergency lights to stay on.

I must add that the green floor lighting was a particularly attractive color.
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RE: Question About Emergency Lighting

Mon Aug 23, 2004 3:22 pm

I can't remember for sure but I think it is designed to last for 30 minutes. I know the time is mandated by the FAA I'm just not sure if it is 30 mins. Anybody else confirm or refute?

As for whether or not the emergency lights were turned of in this case they probably were. Flight crews and MX are pretty judicious about turning off emergency lights when not absolutely necessary. There are several battery packs that power them and all have to be changed if the lights are on for very long. Better to avoid that if possible.

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RE: Question About Emergency Lighting

Mon Aug 23, 2004 3:25 pm

As far as I know, all aircraft above a certain weight (7 metric tons I think, but I'm not sure) have to have emergency batteries that can power essential flight instruments and emergency lighting for AT LEAST 30 minutes. In the case you described, I'd put my money on the lighting being turned off, though the reason for this is unclear to me.
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RE: Question About Emergency Lighting

Mon Aug 23, 2004 11:44 pm

How long is the emergency lighting designed to stay on?

I think in your case on the 757 someone forgot to set the switches correctly before the main door was opened and the lights disarmed. If the aircraft senses a power loss when armed, the lights will turn on. I've done it before while doing a MX taxi and forgot the disarm them. You just need to reset the switches and power and the lights will go out.

I know the time is in the FAR's, so I'll do some digging and try and get back to you.
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RE: Question About Emergency Lighting

Tue Aug 24, 2004 8:17 am

I know one thing is you never want to see F/A's or Cabin Cleaners using the emergency lights when they don't have ground power. That used to drive us crazy. They would discharge all the emergency batteries and then MX would have to crawl on the floor trying to replace all the battery packs before the flight left. That happened more than a few times.
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RE: Question About Emergency Lighting

Tue Aug 24, 2004 11:59 am

The emergency lights are supposed to deliver light for 30 minutes from their own battery packs. If armed, these lights will illuminate as soon as there is no power on the plane. The batteries are constantly recharged by trickle chargers if the plane is powered up. If the batteries are empty, it will take about 12 hours to recharge them. Since a non working emergency light system is a no go item and since changing the battery packs is such a pain in the neck (if the station mx has any in stock at all), the pilots probably switched them off as soon as he noticed them on.
Probably the GPU was faulty, causing the plane to loosde power after the engines and APU were shut down.

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RE: Question About Emergency Lighting

Mon Aug 30, 2004 2:13 am

According to my cabin crew manual, the emergency lighting on the 737-300/700 and 757 is designed to illuminate for 12 minutes. I'm guessing that's a worst case scenario as long as the batteries have had a good charge, but are getting on a bit (that's a technical term!) Similarly, flight crew tell us that the flight deck EROS oxygen masks will deliver anything up to 10 times the length of oxygen supply than is written in our manuals which is a minimum guaranteed supply.

There's one Aviance GPU at Gatwick that has a loose plug. I can't remember how many times we've pulled on stand at night, shut down the engines, plugged in the GPU, shut down the APU, and the cabin is plunged into darkness, to the amusement of all the passengers. At least they get to see what the emergency lighting looks like! BTW - the emergency lighting should come on immediately the cabin lighting fails, not after 30 seconds. In an emergency, the evacuation would be well underway by the time the lights came on!
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RE: Question About Emergency Lighting

Mon Aug 30, 2004 2:44 am

Having been the "victim" of a falty GPU at JFK when onboard a 767, I noticed the emergency lighting came on almost immediately. I didn't time it but it was no more than 1-2 seconds.
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RE: Question About Emergency Lighting

Fri Sep 10, 2004 5:41 am

On a similar note - my airline, and a huge number of others, have removed emergency exit floorpath lights and replaced them with SafTGlo photoluminescent strips. This is incredible stuff, it requires no power, it lasts hours (30 min of cabin lighting charges it to last approx 12hrs of darkness) and it can't break - inoperative floorpath lighting is a no-dispatch item, and electrical systems are very vulnerable to damage from people/trolleys in the aisle.

When you've seen SafTGlo in action in a darkened cabin it's amazing - far brighter and clearer than conventional systems. This photo doesn't do it justice; It is that bright but in a completely dark cabin it's incredible.

More information and some photos and diagrams on the STG Aerospace website.

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RE: Question About Emergency Lighting

Fri Sep 10, 2004 10:49 pm

So does this mean that SafTGlo will also light up when the lights are turned off during night flights?
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RE: Question About Emergency Lighting

Sat Sep 11, 2004 12:10 am

Hkg_clk: It will almost certainly light up at all times, it just requires darkness for it to be noticed. The website does not indicate whether this is phosphorescence or fluorescence, but either way, the chemical absorbs energy from existing lighting (or sunlight) and then emits energy as light continually for, in this case, 12 hours or more with no additional light input. Doesn't seem like it should be too much of an annoyance for sleeping pax, especially if you have to get to the head.

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RE: Question About Emergency Lighting

Mon Sep 13, 2004 10:30 am

Is this the same stuff they use for the material that glows on the subway trains in nyc when the lights go out?
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RE: Question About Emergency Lighting

Tue Sep 14, 2004 8:18 am

The relevant standard is FAR 25.812 which states:

The energy supply to each emergency lighting unit must provide the required level of illumination for at least 10 minutes at the critical ambient conditions after emergency landing.

Of course this is a minimum performance standard and the actual aircaft system may exceed this minimum time.

I have yet to see an airplane that has emergency lighting over 15 minutes. (Not saying it doesn't exist...but I'd say its rare)

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