Flashing Landing Lights

[DC Meatloaf]

Sorry in advance for this question from a decidedly non-pilot perspective...

I work in Washington, DC, and my daily commute across the 14th street bridge (usually in heavy traffic) gives me plenty of time to take advantage of the great view of the aircraft either taking off or landing at National.

On a couple of occasions in the last year, I've noticed aircraft on approach flashing their landing lights (not just the usual anti-collision ones). Does this signify anything in particular?

By the way, the view of the aircraft when they're landing to the south at National is particularly spectacular from the bridge, especially around sunset. Easily the highlight of my commute. That right-hand turn just before touching down looks like fun...

[Luftwaffle]

I can think of three reasons. Only the first one is really applicable at the Washington DC airport.

* Many aircraft have a pulse system in their landing lights to make them flash automatically. It is an anti-collision measure. A lot of jets around here have a system that flashes the landing lights alternately on each side. Very attention-getting. Does that match what you're seeing?

* At night if a pilot has a radio failure, or doesn't have a radio to begin with, he may flash the lights to acknowledge ATC transmissions or signals.

* Air traffic controllers who do not have radar sometimes ask a pilot to flash the landing lights, so they can be sure they have identified the correct airplane.

I'll edit this into being a tech question and ask someone on the tech side: how do pulsing light systems affect the life of the light bulbs?

[This message has been edited by Luftwaffle (edited 22 March 2001).]

[matspart3]

Easier to see from the Tower
Probably scares birds away?

[DC Meatloaf]

Thanks for refining my question into something relevant to the forum. :)

Yes, what I've seen appears to be an automatic pulsing of the both landing lights simultaneously. The lights flash with a regular rhythm and do so for as long as I can see them (usually until it's time for me to change lanes or otherwise get back to driving my car...). I was curious as to whether that signalled something out of the ordinary or was just a standard procedure on some aircraft....

Thanks again for the input!

[RRAAMJET]

DC: as nobody with a radio failure is going to be anywhere near the National ( I hope !), it is probably the lights of a corporate aircraft ( I've noticed the Falcon's flash ) or Southwest Airlines. All their 737's have flashing landing lights; yes, the right turn into DCA is as close to the old Hong Kong Kai Tak IGS 13 approach as you'll find these days. Great fun on a gusty day...

I've just thought - do SWA fly into DCA?

[Royan]

What you are seeing are the strobe lights the way I understand your explanation. They flash white and normally they are three synchronized lights, one on each wing tip and one below the tail cone. http://www.pprune.org/ubb/NonCGI/Forum3/HTML/001629.html

[This message has been edited by Royan (edited 23 March 2001).]

[SixDemonBag]

I'm pretty sure this guy's clued in enough to know they are not strobes...

[HugMonster]

Several types of aircraft (including, I believe, 737's) can be retrofitted with a device that will flash the landing lights.

This is intended as a bird-scaring device.

I believe that EZY are looking into the effectiveness of this at the moment.

[DC Meatloaf]

Royan, thanks for the info, but they're definitely not strobes--they're the landing lights (the big headlight-ish sorta things). :)

The corporate aircraft theory probably most closely matches what I saw. The last aircraft I saw flashing appeared to be something Lear-sized, I think. It's possible that one of the other times may have been a 737, but I didn't get a close enough look to tell. (Oh, and SWA doesn't fly into DCA...at least, I've never been able to get a flight outta DCA on SWA -- always BWI).

Anyway, thanks to all for the info!

[Cyclic Hotline]

What you are most likely seeing is the Pulselight, as described by Luftwaffle. They are a common (if not essential) piece of equipment for aircraft operating VFR in congested areas. In Alaska, they are a primary piece of our operating equipment, and we install them in all our aircraft before they enter service.

The fact they caught your attention as you drove down the road, is testament to their ability to be seen. They are quite remarkable for the visibility they create, to often otherwise invisible aircraft!

With a combination of high intensity strobes and a Pulselight, this is the most effective method of enhancing the ability of other traffic spotting you. The systems are simple to install, esentially maintenance free, and are claimed to actually enhance bulb life. In a decade of operating this equipment in a variety of aircraft, I would say that bulb life is certainly no shorter (kinda hard to say it's longer!).

Very good piece of equipment, highly recommend it to anyone.
http://www.pulselite.com/

[Tor]

How is it operated. I mean is there an extra switch to turn the pulsing off at night?

[cossack]

Saw it on a Citation 750 a few weeks back - very attention grabbing!

Question - Why do some pilots leave their landing lights off until you clear them to land?
Switch them on earlier please it gives the traffic lining up an incentive!

[Denti]

In our company it's a procedure to switch on the outboard landing lights after cleared to land/cleared for take-off.

Denti

[HugMonster]

There are several theories about when you turn landing lights on/off.

One says that to leave them off until cleared takeoff/land shows the tower you are aware you have not received clearance.

The other is that they should be on for visibility at all times anywhere near the runway.

Personally, I favour a hybrid. I would prefer landing lights to come on after clearance to take off, then to stay on until >10,000, and come on again passing 10,000 in the descent. To leave them on when stationary on the runway (i.e. with no cooling airflow over them) tends to overheat them and result in much lower bulb life, and I believe that white strobes are sufficient for visibility on the runway. Below 10,000 it aids visibility with slower VFR traffic wandering around.

There is unconfirmed evidence (one case, I believe) of birds being attracted to landing lights, leading some people to suspect that leaving them on in the air may result long-term in a higher bird-strike rate. This is the reason for the development of the "flashing" lights.

None of the above represents my company's views - my personal opinions only! :)

PS - in cloud at night, of course, you would normally switch them off until VMC and about to land (e.g. Cat II/III approaches).

[This message has been edited by HugMonster (edited 24 March 2001).]

[Cyclic Hotline]

The Pulselight system can be selected ON as required. The other position leaves the light operating as a normal landing light.

[Canuck_AV8R]

On our A/C (B737-200) most have pulse lights installed. They are very effective as you have mentioned and function as follows.

They have a seperate switch on the overhead lighting panel which when selected ON and the landing light switches are OFF causes the inboard and outboard landing lights to pulse. Pulsing can be stopped in one of two ways, by turning OFF the pulse lights or by turning ON the landing lights, obviously when the landing lights are selected ON then the lights stop pulsing and remain on steady.

Hope this explains in Readers Digest format how the system works.

BTW the bridge you are watching from is that the (in)famous 14th Street Bridge that claimed the Air Florida B737 back in the 80s ??

[This message has been edited by Canuck_AV8R (edited 26 March 2001).]

[Luftwaffle]

HugMonster, Transport Canada tells us that birds tend to see aircraft with landing lights on sooner, and take avoiding action. I think these birds should get together on their operating procedures.

Perhaps at night, the birds fly towards aircraft lights because they see insects in the beam.

[DC Meatloaf]

Canuck_AV8R,

It is indeed the very same bridge; although, I guess, technically there are several spans. From what I understand (the crash you mention predates my time in the area), the northbound-side bridge -- the one closest to DCA -- was the one most involved.

As I spend a considerable portion of my commute on that bridge, I'm thankful that the view of the aircraft either taking off or landing is so dramatic...though I often wonder (usually while gazing out the sunroof at the overflying landing gear) how much the view contributes to the traffic. :)

[maxmobil]

Hugmonster, Luftwaffle:

the theory which I learned is quite interesting and seems somehow logical:
If in danger, animals, especially birds try to escape into the direction of the sun, because if they can see the sun there can't be an obstacle or enemy inbetween.

If an aircraft (especially those with only one landing light or lights so close together they look like one light only from a distance) has it's landing lights on then the bird would firts try to escape in the direction of this would-be sun, until only in the very last moment it might realize that in fact the big bird behind the light also means danger.

That's why ABC lights (anti-bird-collision) are not on steadily, but have a frequency which is changing all the time, to prevent from being mixed up with the steadily shining sun.

You can see the same effect when driving at night with deer/game crossing the road. When You switch to high beam, the deer will stay on the road or even run to Your car; when You dip the headlights and flash them a few times, they run away.



------------------
This Airbus is o.k., but why did it come with a RENAULT key ??