AVSIG: Strobing Runway Lights wwswsigarch.jpg (7236 bytes)

✈ . . . . . . ✈ . . . . . ✈ . . . . ✈ . . . ✈ . . ✈ . ✈ . . ✈ . . . ✈ . . . . ✈ . . . . . ✈ . . . . . . Touch-and-Go to our Live Forum (This is a Read-only Archive of the 2004-2017 AVSIG Forum)


AVSIG Discussion Sections >> Training & Proficiency

Pages: 1 | 2 | 3 | 4 | >> (show all)
Scott Dyer [HPN/NY]
Top Gun


Reged: 01/11/03
Posts: 20065
Strobing Runway Lights
      #445860 - 12/15/17 04:25 PM

No, I'm not referring to the rabbit. Here's a report of how LED runway/centerline lights may cause some problems for arriving aircraft. (CALLBACK is great, and this month's issue had some especially interesting reports...including this one).
--------------------

Now You See it, Now You Don’t

A Bonanza Pilot became distracted and confused when he perceived the runway edge and centerline lights cycling on and off while ATC assured him that they were on steady.

■ I was transiting the final approach path of…Runway 16R and observed the runway edge and center line lights cycle on and off…at a rate of approximately 1 per second. It was very similar to the rate of a blinking traffic light at a 4-way vehicle stop. The [3-blade] propeller speed was 2,400 RPM. This was observed through the entire front windscreen and at least part of the pilot side window. I queried ATC about the reason for the runway lights blinking and was told that they were not blinking. It was not immediately obvious what was causing this, but I did later speculate that it may have been caused by looking through the propeller arc.

The next day [during] IFR training while on the VOR DME Rwy 16R approach, we observed the runway edge and center line lights cycle on and off…at a rate slightly faster than 1 per second. The propeller speed was 2,500 RPM. I then varied the propeller speed and found that at 2,700 RPM, the lights were observed strobing at a fairly high rate, and at 2,000 RPM the blinking rate slowed to less than once per second. This was observed through the entire approach that terminated at the Missed Approach Point (MAP). The flight instructor was also surprised and mentioned that he had not seen this before, but he also doesn’t spend much time behind a 3-blade propeller arc.

I would speculate that the Pulse Width Modulation (PWM) dimming system of the LED runway lights was phasing with my propeller, causing the observed effect. I would also speculate that the effect would…significantly differ at other LED dimming settings…and behind a 2-blade propeller.

I found the effect to be entirely confusing and distracting, and would not want to make a landing in such conditions.

--------------------
www.scottdyercfi.com


Post Extras: Print Post   Remind Me!   Notify Moderator  
Ray Tackett
Top Gun


Reged: 04/30/04
Posts: 8892
Loc: Philadelphia, USA
Strobing Runway Lights [Re: Scott Dyer [HPN/NY]]
      #445862 - 12/15/17 05:19 PM

The Law of Unintended Consequences strikes again. I'll bet all the test
flights were jets or multi-engine props.

--------------------
Ray,

Owner, Lake Wood Be Gone

Turning quality lumber into sawdust and noise since 2013.


Post Extras: Print Post   Remind Me!   Notify Moderator  
Russell Holton
AVSIG Member


Reged: 07/07/05
Posts: 14136
Re: Strobing Runway Lights [Re: Scott Dyer [HPN/NY]]
      #445863 - 12/15/17 06:20 PM

Quote:

I would speculate that the Pulse Width Modulation (PWM) dimming system of the LED runway lights was phasing with my propeller, causing the observed effect.




Maybe. Doing the math, 3 blades x 2400 Rev/min x 1/60 min/sec = 120 cycles/sec. Exactly what you'd expect for a light powered by the 60Hz mains.

Yes, standard dimmers use a type of PWM for dimming, but I don't think that's the real issue. The problem is the LEDs "flicker" in time to the AC mains that the old incandescent (being a heat-based device) couldn't.

The problem here might be retrofitting dimable LED bulbs on a conventional circuit. I haven't looked to see how dimable 120V LED bulbs work, but I'd imagine they have to be responsive to the "PWM"/dimming of the conventional system to function properly. Simply rectifying and smoothing the incoming voltage is going to result in a bulb with really strange dimming characteristics. (Normal brightness until below 50% and then rapid dimming as the cycle drops.) As a result, a strong 120Hz strobe is quite likely.

An LED system designed from the ground up to be LED may run at a higher PWM speed and not cause that problem.


Post Extras: Print Post   Remind Me!   Notify Moderator  
Jeff Hartmann CIC
Top Gun


Reged: 05/18/04
Posts: 7323
Loc: Chico,CA
Re: Strobing Runway Lights [Re: Scott Dyer [HPN/NY]]
      #445864 - 12/15/17 06:23 PM

When Concord NC revamped their runway lights with LED side and centerline...touchdownzone, the works, initially they only ran on high beam.

When landing at night especially with low vis, the tendency was to flare a little high. But you can really see the runway!

--------------------
Jeff

nothing clever to say right now...


Post Extras: Print Post   Remind Me!   Notify Moderator  
Ralph Jones
Top Gun


Reged: 08/31/01
Posts: 21214
Loc: 4CO2
Re: Strobing Runway Lights [Re: Scott Dyer [HPN/NY]]
      #445865 - 12/15/17 06:25 PM

The wagon wheel effect strikes again...;-)

You should make a video and put it on reddit/aviation. (although the cellphone video scan might muddy the waters a bit).

--------------------
Ralph Jones
LS-4a N49LS 6R


Post Extras: Print Post   Remind Me!   Notify Moderator  
Scott Dyer [HPN/NY]
Top Gun


Reged: 01/11/03
Posts: 20065
Re: Strobing Runway Lights [Re: Ray Tackett]
      #445867 - 12/15/17 06:32 PM

Quote:

The Law of Unintended Consequences strikes again. I'll bet all the test
flights were jets or multi-engine props.




That Law also can take out EV systems from seeing those lights...they may need to have an IR emitter in each lamp.

(It's amazing to me how EV systems have penetrated the bizjet market)

--------------------
www.scottdyercfi.com


Post Extras: Print Post   Remind Me!   Notify Moderator  
Ray Tackett
Top Gun


Reged: 04/30/04
Posts: 8892
Loc: Philadelphia, USA
Strobing Runway Lights [Re: Scott Dyer [HPN/NY]]
      #445869 - 12/15/17 08:13 PM

Indeed. My professional photographer friend who is also a retired electrical
engineer built a bunch of LED light fixtures for his studio. Shortly
thereafter, he found out that the camera he had modified for IR didn't see
much.

--------------------
Ray,

Owner, Lake Wood Be Gone

Turning quality lumber into sawdust and noise since 2013.


Post Extras: Print Post   Remind Me!   Notify Moderator  
Scott Dunham (RDU)
Top Gun


Reged: 04/29/04
Posts: 6470
Loc: Chapel Hill, NC
Re: Strobing Runway Lights [Re: Jeff Hartmann CIC]
      #445873 - 12/15/17 08:27 PM

Wen Delta landed a 767 on the taxiway at Atlanta a few years back, turned out that the airport had edone the taxiway lights with LEDs but the runway lights were still incandescent. The LEDs were a lot more conspicuous, and the crew misidentified the taxiway as the runway. All downhill from there...

Post Extras: Print Post   Remind Me!   Notify Moderator  
Randy Sohn
Gradn Exlated Ordre of teh Fyling Fingres


Reged: 08/31/01
Posts: 23187
Loc: Savage, MN - U.S.A.
Re: Strobing Runway Lights [Re: Scott Dunham (RDU)]
      #445874 - 12/15/17 08:57 PM

Quote:

All downhill from there...




Meb'be not "downhill" in a technical sense but - oohwhee - concur with your comment!

best, randy


Post Extras: Print Post   Remind Me!   Notify Moderator  
Scott Dyer [HPN/NY]
Top Gun


Reged: 01/11/03
Posts: 20065
Re: Strobing Runway Lights [Re: Scott Dunham (RDU)]
      #445877 - 12/15/17 10:15 PM

Scott -- I hear there have been issues calibrating the intensities of LED runway lighting, too.

--------------------
www.scottdyercfi.com


Post Extras: Print Post   Remind Me!   Notify Moderator  
Pages: 1 | 2 | 3 | 4 | >> (show all)



Extra information
0 registered and 48 anonymous users are browsing this forum.

Moderator:  Mike Overly 

Print Topic

Forum Permissions
      You cannot start new topics
      You cannot reply to topics
      HTML is disabled
      UBBCode is enabled

Rating:
Topic views: 6513

Rate this topic

Jump to

Contact Us AVSIG

Powered by UBB.threads™ 6.5.5

Logout   Main Index    AVSIG Aviation Forum