Vikkyvik From United States of America, joined Jul 2003, 6060 posts, RR: 27 Posted (5 years 6 months 1 week 4 days 4 hours ago) and read 1108 times:
Pretty simple questions here, so feel free to utilize this thread for any sort of airfield/obstacle lighting discussions and questions you may have.
1.) Why are runway centerline lights typically offset by about a foot or two to one side?
2.) I've been noting the lights on various buildings, towers, and other obstructions, both near airports and distant from them. Sometimes, the lights are steady red, sometimes they're flashing red, and sometimes they're flashing white (typically the white flashes are more like strobe flashes, while the red are more like a rotating beacon-type). Are there any particular guidelines as to what color/type of light to put on any given obstruction?
Thanks for all responses.
~Vik
The spirit of Massachusetts is the spirit of America!
N8076U From United States of America, joined Jun 2006, 425 posts, RR: 12 Reply 1, posted (5 years 6 months 1 week 4 days 4 hours ago) and read 1099 times:
Quoting Vikkyvik (Thread starter): 1.) Why are runway centerline lights typically offset by about a foot or two to one side?
I believe they do this so the aircraft's nose wheel(s) won't constantly be running over the lights. By offsetting them just a little, they avoid getting battered as much as they would if they were dead center. The little "bump, bump, bump" noise from running over the lights is irritating as well.
Vikkyvik From United States of America, joined Jul 2003, 6060 posts, RR: 27 Reply 2, posted (5 years 6 months 1 week 4 days 4 hours ago) and read 1097 times:
Quoting N8076U (Reply 1): I believe they do this so the aircraft's nose wheel(s) won't constantly be running over the lights. By offsetting them just a little, they avoid getting battered as much as they would if they were dead center. The little "bump, bump, bump" noise from running over the lights is irritating as well.
See, I thought this might be the reason, but then I thought, well, most aircraft have a double nose wheel. Which means each wheel is already offset by a couple feet to each side. So wouldn't this actually tend to put the flush (or semi-flush, whatever) lights right under one of the wheels?
Oh well.
~Vik
The spirit of Massachusetts is the spirit of America!
Meister808 From United States of America, joined Jan 2000, 968 posts, RR: 2 Reply 3, posted (5 years 6 months 1 week 4 days 4 hours ago) and read 1092 times:
Centerline lights are offset to prevent a really annoying thump-thump-thump from the nosewheel on takeoff and rollout.
As for obstruction lighting, there are a lot of guidelines. In general, red lights are for nighttime use, and white lights are for daytime use. Most towers will have a 2-part light on top that uses a white strobe during the daytime and then switches over to the red pulse at sunset. As for whether or not the light flashes or is steady, I think the steady lights are required on obstructions between the 'non-lighted' and 'flashing light required' within an airport safety zone. If I recall correctly, 75' high is where the flashing lights become mandatory, but I could be very wrong. The FAA's Advisory Circular 70 covers Obstruction Lighting and Marking. It is pretty interesting, because it lays out guidelines for every light you see on towers and buildings and stuff. You can find the latest edition online here:
Undehoulli From , joined Dec 1969, posts, RR: Reply 4, posted (5 years 6 months 1 week 4 days 4 hours ago) and read 1092 times:
Really, it's no problem to keep your nosewheel off the centerline lights. The noise and bumps can be really annoying if you don't!
Yes, most larger aircraft have a double nosewheel, but it's not like it's 6' from one side to the other. When I'm taking off or landing, I keep the nose gear slightly to the other side of the centerline markings and I've never had a problem avoiding the "bump..bump..bump" noise.
KELPkid From United States of America, joined Nov 2005, 5515 posts, RR: 5 Reply 5, posted (5 years 6 months 1 week 4 days 3 hours ago) and read 1070 times:
Quoting Vikkyvik (Thread starter): 1.) Why are runway centerline lights typically offset by about a foot or two to one side?
Fly into PDX at night in a Grumman Cheetah, hit a few of these on takeoff with the nosewheel, and freak out your backseat pax and you'll know why Probably more for us GA types that might use the runway than anything else...
Quoting Vikkyvik (Thread starter): 2.) I've been noting the lights on various buildings, towers, and other obstructions, both near airports and distant from them. Sometimes, the lights are steady red, sometimes they're flashing red, and sometimes they're flashing white (typically the white flashes are more like strobe flashes, while the red are more like a rotating beacon-type). Are there any particular guidelines as to what color/type of light to put on any given obstruction?
The FAA has (had?) an advisory circular on recommended lighting practices for fixed hazards. It's been a long time since my broadcast engineering assistant days, where one of my jobs was to ensure that new construction broadcast towers were properly marked, or that a particular lighting system was appropriate for a proposed tower.
Tower owners like flashing white (high-intensity) strobes the best, as the usual maintenance on them was to replace a circuit board at ground level when and if it acted up (they eliminated the need to pay a highly-trained and well-qualified individual to scale the tower and change a bulb. Also, many stations must reduce power anytime someone is up the tower doing work ). However, I have known of many instances where high-intensity strobes have made bad neighbors out of the tower owners...so there is some give and take.
Towers with old lighting (and marking!) systems are grandfathered in, and will typically only require upgrade if the owner "tops" the tower (makes it higher).
Towers are required, by law, to be painted aviation orange/white in many instances as well (not all towers are required to be marked...). Guy wires will bring about the need to paint the tower, however many self-supporting towers (i.e. no guy wires) are required to be painted as well. The tower owner will like to aviod this, if possible, as paint adds to a tower's maintenance costs. High-intensity lighting is required on towers above a certain height (1000'?). Of course, the FAA won't complain if the tower owner decides to exceed the requirements
Off of the top of my head, the FAA starts to care about towers when their height above ground level exceeds 200'. Of course, they care immensely when the tower is located in the safety area of a runway, within a mile of an FAA designated landing area, and especially when the obstruction is located on the extended centerline of a runway
EDIT: they will care about the tower even if it is shorter than 200' given the extenuating circumstances listed in the last paragraph above!
EDIT: Also, in many instances, high-intensity strobes that are in use during daylight hours will eliminate the need to paint the tower, but it will run the electric bill up.
[Edited 2006-08-07 21:50:53]
[Edited 2006-08-07 21:58:54]
Celebrating the birth of KELPkidJR on August 5, 2009 :-)
KELPkid From United States of America, joined Nov 2005, 5515 posts, RR: 5 Reply 6, posted (5 years 6 months 1 week 4 days 2 hours ago) and read 1025 times:
Quoting Vikkyvik (Thread starter): 2.) I've been noting the lights on various buildings, towers, and other obstructions, both near airports and distant from them. Sometimes, the lights are steady red, sometimes they're flashing red, and sometimes they're flashing white (typically the white flashes are more like strobe flashes, while the red are more like a rotating beacon-type). Are there any particular guidelines as to what color/type of light to put on any given obstruction?
It is also interesting to note, that when placing a structure, if you suspect it may be a "hazard to air navigation" (FAA's words), you are required to submit to the FAA a study request form, and the FAA will determine for you if the proposed structure is indeed a hazard to air navigation, and what steps must be taken to mitigate the hazard (like lighting and marking the tower).
If you are making an FCC application (for example: broadcast station, cell phone tower, etc.), and that application proposes a new tower, you are required to submit such a request for study to the FAA concurrent with your application.
Celebrating the birth of KELPkidJR on August 5, 2009 :-)
Vikkyvik From United States of America, joined Jul 2003, 6060 posts, RR: 27 Reply 7, posted (5 years 6 months 1 week 3 days 10 hours ago) and read 941 times:
Sorry for not getting back here quicker (I tend to sometimes forget that I started a topic ).
Thanks for all the responses, especially KELPkid for your plentiful information. Meister808, I haven't had a chance to look at the link yet, but I will soon.
Thanks again!
~Vik
The spirit of Massachusetts is the spirit of America!
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From United States of America, joined Jul 2003, 6060 posts, 
Probably more for us GA types that might use the runway than anything else...
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