Landing lights are dimmed (heated)

[Hardy Heinlin]

Forum cleanup: Slightly off-topic posts moved here from Networkers subforum.


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Impressive attention to detail Hardy  

Note that the landing lights are dimmed (heated) in certain situations, even if the switches are off.

I don't understand what you mean here, - what is meant by dimmed (heated) ?

Thanks in advance

Kurt


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In order for  the filaments and other parts of the lamp not to get a huge thermal shock when they go from glowing temperature to minus 60C to glowing, they are being kept on during the whole flight. And it is not just a vague red wire you see, they really look like car parking lights. I had the pleasure of working on a 777 recently that we had put into air mode while on the ground, and the landing lights really stood out on the wings.


Hoppie


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what is meant by dimmed (heated) ?

For preventing thermal shock, when the landing lights are turned off, 28 volts AC is supplied to the landing light power transformer circuits to keep the landing light lamp filaments warm (instead of the normal 115 volts AC).
This function is activated on some 747-400s by the landing gear lever (in UP or OFF) or on other 747-400s by the air-ground sensing system ("weight-on-wheels").

This heating function is is an airline option, however, so not all 747-400s will have this feature.

Rgds
JHW


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Thanks both of you, - makes sense

BR

K


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Slightly related - I have a distant memory that airliners flying through the narrow corridor allowed for flights from western Europe to (for example) Tokyo keep their landing lights on all the way since there is incomplete radar tracking coverage in this corridor.  The theory is that flights heading into a collision path would see each other better if they keep their "headlights" on.

As interesting as this theory is, I have wondered if the bulbs would last that long if they are fully powered up for an extended period of time.  Perhaps these are not ordinary light bulbs and thus it isn't stressful to leave them on for 10+ hours.  Or, perhaps this is just a nonsensical rumor and not even approximately true?

Can anyone confirm or deny this trans-Russia collision avoidance system/s use?  I can't recall where I read it...

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Best wishes,

Phil Bunch


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They are not fully powered -- full power comes only when you lower the landing gear, I believe.

Over Dark Afrika, aircraft even routinely blink their landing lights at each other while talking on the radio, to give absolutely positive confirmation to each other that yes, this is me, there is not an unknown third guy nearby.


Hoppie


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