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Flickering Lights On Ground Power  
User currently offlineAnalog From United States of America, joined Jul 2006, 1900 posts, RR: 1
Posted (8 years 2 months 4 days 15 hours ago) and read 9047 times:

Last week I was on a CO 735 that had the most awful, seizure-inducing flickering cabin light. One of the bulbs was going bad (I assume). The flicker stopped when we pulled away from the gate. Why is this?

I assume that the flicker stopped when the aircraft stopped using ground power. Is this because ground power is at 60Hz and power generated on board is 400Hz? Or is it related to voltage (ground power or APU vs. generators on the engines)?

This wasn't the first CO 73x that had this problem. The previous one (733) flickered at the front of the F cabin where the FAs work. I can't believe that the FAs can live with this. If I were an FA I'd make damn sure to bitch and moan until these things were fixed. Sorry, I would bring this to the attention of the appropriate persons in an effort to resolve this maintenance issue.

15 replies: All unread, jump to last
 
User currently offlineTdscanuck From Canada, joined Jan 2006, 12710 posts, RR: 78
Reply 1, posted (8 years 2 months 4 days 14 hours ago) and read 9039 times:



Quoting Analog (Thread starter):
Last week I was on a CO 735 that had the most awful, seizure-inducing flickering cabin light. One of the bulbs was going bad (I assume). The flicker stopped when we pulled away from the gate. Why is this?

It sounds like a bad ballast in lamp (I'm assuming it was a fluorescent). Could be that ground power was just flaky enough to throw it off but aircraft power was OK.

Quoting Analog (Thread starter):
Is this because ground power is at 60Hz and power generated on board is 400Hz?

Ground power is 400 Hz too (plus or minus some tolerance).

Tom.


User currently offlineBartonsayswhat From Canada, joined Oct 2007, 445 posts, RR: 0
Reply 2, posted (8 years 2 months 4 days 14 hours ago) and read 9023 times:

yeah ground power constantly fluctuates, be it from bridge power or a diesel GPU. APU power is much more consistant, which is why most of the fmc updating is done on the APU, as a power surge can wipe out the whole thing, or so i've been informed. also does anyone know, just as a plane arrives or leaves the gate, when it is switched from GEN/APU to GPU the lights flick once?

User currently offlineHAWK21M From India, joined Jan 2001, 31875 posts, RR: 54
Reply 3, posted (8 years 2 months 4 days 11 hours ago) and read 8987 times:

Depoending on the condition of the GPU connected at that time.Its difficult to tell from here,but I presume the GPU could have had a voltage fluctuation issue.
regds
MEL



Think of the brighter side!
User currently offlineAirbus_A340 From Hong Kong, joined Mar 2000, 1567 posts, RR: 19
Reply 4, posted (8 years 2 months 4 days 8 hours ago) and read 8969 times:

Quoting Bartonsayswhat (Reply 2):
does anyone know, just as a plane arrives or leaves the gate, when it is switched from GEN/APU to GPU the lights flick once?

On the Airbus the Ground Power Control Unit (GPCU) produces what's called a 'reference frequency' used by the Ground Control Unit to provide sycronisation for No-Break-Power-Transfer (NBPT).

In English, that means u don't get the lights flickering or horrible 'clunk' sounds when you change from GPU to APU or APU to engine Gens, or vice versa that you would find on other older aircraft.

Usually APU is turned on about 20 minutes before departure, and turned off after pax have disembarked, unless it's a quick turnaround.

[Edited 2008-03-26 03:30:11]


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User currently offlineDALMD88 From United States of America, joined Jul 2000, 2891 posts, RR: 14
Reply 5, posted (8 years 2 months 4 days 4 hours ago) and read 8914 times:

Even relatively new ground power units can cause all sorts of strange happenings. Here in BOS our new terminal has new units at every gate. We frequently get calls in the morning about systems not testing correctly. The standard answer is switch to apu power and run the test again. If it is still a problem call back and will send someone out. I think the 737NG tends to have the most issues with flakey ground power.

User currently offlineAnalog From United States of America, joined Jul 2006, 1900 posts, RR: 1
Reply 6, posted (8 years 2 months 4 days 4 hours ago) and read 8902 times:



Quoting HAWK21M (Reply 3):
Depoending on the condition of the GPU connected at that time.Its difficult to tell from here,but I presume the GPU could have had a voltage fluctuation issue.

It was only 1 bulb out of many, though I guess "bad" power may well bring a marginal bulb/ballast over the edge.


User currently offlineHAWK21M From India, joined Jan 2001, 31875 posts, RR: 54
Reply 7, posted (4 months 1 week 3 days 10 hours ago) and read 4888 times:

Quoting Analog (Reply 6):
It was only 1 bulb out of many,

In that case look more like a Bulb/Ballast issue ....



Think of the brighter side!
User currently onlineZaphodHarkonnen From New Zealand, joined Jan 2015, 249 posts, RR: 0
Reply 8, posted (4 months 1 week 3 days 9 hours ago) and read 4874 times:

I would have thought the power would have been transformed for the lights and other internal systems, something like 120V or 240V AC. Or do all the lights and such run off the standard power bus? I'm not including flight management stuff in that as I'm sure that has its own power requirements.

User currently offlineShamrock137 From United States of America, joined Jul 2005, 236 posts, RR: 0
Reply 9, posted (4 months 5 days 7 hours ago) and read 4259 times:

Quoting Bartonsayswhat (Reply 2):
also does anyone know, just as a plane arrives or leaves the gate, when it is switched from GEN/APU to GPU the lights flick once?

Usually the transition from aircraft to ground power will cause a flicker or two.

Quoting Airbus_A340 (Reply 4):
In English, that means u don't get the lights flickering or horrible 'clunk' sounds when you change from GPU to APU or APU to engine Gens, or vice versa that you would find on other older aircraft.

I noticed the opposite, the A320 had a very audible clunk in the cockpit and front galley when transiting from aircraft to ground power.



Time to spare? Go by air!
User currently offlineglen From Switzerland, joined Jun 2005, 270 posts, RR: 2
Reply 10, posted (4 months 5 days 2 hours ago) and read 4159 times:

Quoting Shamrock137 (Reply 9):
I noticed the opposite, the A320 had a very audible clunk in the cockpit and front galley when transiting from aircraft to ground power.

The A330 and A340 have No-Break-Power-Transfer (NBPT), but the A320 does not and therefore has the clunk and short darkening. On the 330/340 you have smooth power transitions.



"The horizon of many people is a circle with zero radius which they call their point of view." - Albert Einstein
User currently offlineShamrock137 From United States of America, joined Jul 2005, 236 posts, RR: 0
Reply 11, posted (4 months 5 days 2 hours ago) and read 4148 times:

Quoting glen (Reply 10):
The A330 and A340 have No-Break-Power-Transfer (NBPT), but the A320 does not and therefore has the clunk and short darkening. On the 330/340 you have smooth power transitions.

Interesting! Now that you mention it I never noticed a transition on the larger Airbuses, I always assumed it was because the APU was started before boarding.

Edit* I also didn't realize this thread was 7 years old! HAWK21M is the champion of resurrecting old threads haha.

[Edited 2016-01-23 08:56:45]


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User currently offlinefr8mech From United States of America, joined Sep 2005, 6706 posts, RR: 16
Reply 12, posted (4 months 5 days 1 hour ago) and read 4130 times:

Quoting ZaphodHarkonnen (Reply 8):
I would have thought the power would have been transformed for the lights and other internal systems, something like 120V or 240V AC. Or do all the lights and such run off the standard power bus? I'm not including flight management stuff in that as I'm sure that has its own power requirements.

Really depends on the electrical architecture of the aircraft. Been a long time since I worked pax aircraft but, I seem to recall that the PSU lighting was 28VAC...and, I suspect that would vary by aircraft type.

The typical aircraft (not B787 or A350, as I understand, they are a little different electrically), there are a few different voltages:
-120VAC
-28VAC
-5VAC
-28VDC
-5VDC

It all runs at 400hz, except the DC stuff, of course. Anything requiring a different frequency, would change the frequency after the electricity makes it to the unit.

As for the issue the OP asked about, I suspect a marginal ballast. A 737-500 should be able to handle some frequency/voltage fluctuations without too much trouble. Newer technology aircraft have a harder time dealing with these fluctuations. Regardless of aircraft age, we will always put an aircraft on APU power if the electronics are exhibiting issues on pre-flight.

Let me add the standard disclaimer: while aircraft design tends to be consistent, within the regulations, there is variation based on manufacturer philosophy and customer preference.

[Edited 2016-01-23 09:51:58]


When seconds count...the police are minutes away.
User currently offlineCanadianNorth From Canada, joined Aug 2002, 3424 posts, RR: 7
Reply 13, posted (4 months 1 day 22 hours ago) and read 3627 times:

Was the cabin cold (first flight of the day after sitting outside on a cool night type deal)? Around here it's pretty normal when you power up a cold 737 the cabin lights will usually misbehave in a variety of ways, but once the heat has been on for a while and things warm up it seems 99% of the time the lights smarten up and work fine for the rest of the day.

Could also be as mentioned before a bad light or ballast, or a getting ready to be bad light or ballast combined with a GPU that's on the upper or lower end of tolerances. GPU power usually works fine enough but I have noticed over the years that APU power generally does seem more stable and consistent. Should all in theory be an even 120v 400 hz regardless of APU generator, engine generator or GPU, but as with most things there is a +/- tolerance.



What could possibly go wrong?
User currently offlineHAWK21M From India, joined Jan 2001, 31875 posts, RR: 54
Reply 14, posted (2 months 4 weeks 12 hours ago) and read 2255 times:

Quoting Shamrock137 (Reply 11):

Edit* I also didn't realize this thread was 7 years old! HAWK21M is the champion of resurrecting old threads haha.

I guess when some thread is interesting & worth a contribution it does get resurrected ..... Maybe Im guilty of this  
But on a serious note....there are some fantastic discussions on this forum, which are very educational & when read one does feel the need to add to it.Thats why I believe the Tec/Ops forum should never archive threads ever.

Quoting CanadianNorth (Reply 13):
, but once the heat has been on for a while and things warm up it seems 99% of the time the lights smarten up and work fine for the rest of the day.

Just curious does it apply to todays LED lights too



Think of the brighter side!
User currently offlineShamrock137 From United States of America, joined Jul 2005, 236 posts, RR: 0
Reply 15, posted (2 months 4 weeks 2 hours ago) and read 2190 times:

Quoting HAWK21M (Reply 14):
Thats why I believe the Tec/Ops forum should never archive threads ever.

Agreed, this is my favorite forum on the site.

Quoting HAWK21M (Reply 14):
Just curious does it apply to todays LED lights too

Not that I have noticed, although most of the aircraft I am familiar with don't use LED cabin lighting, just LED reading lights and galley lights. However they don't seem to run into the same issues as the florescent lights in the cold.



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