Ask the Expert: Beacons – Rotating or Not; Red or Not

Ask the Expert: Beacons – Rotating or Not; Red or Not

AskExpertIt is likely that the majority of operating King Airs in use no longer have a rotating beacon. A beacon? Sure. One with an electric motor that rotates the bulb(s)? Quite unlikely.

Those old beacon motors were a weak link in the system, often freezing in one position. One theory is that the grease in the bearings got very stiff when exposed to the cold temperatures up in the flight levels, leading to eventual binding of the mechanism.

Owners quickly tired of buying new beacons only to have them also fail in a frustratingly short period of time. Aircraft lighting manufacturers came out with new designs that eliminated the motor. Most of these have a pulsating device that makes the light rhythmically glow bright and dim, giving the appearance of a rotating bulb and hence attracting the same level of attention. These have become a popular retrofit item.

The black paint that is not the designer’s idea.
The black paint that is not the designer’s idea.

Others have chosen to replace the original rotating beacon with a strobe light. Although this is also an attractive option, there is almost universal finding of a minor, but annoying, problem when this change is made. Namely, when installed as a replacement for the beacon on the belly, the strobe capacitor’s charging and discharging cycles can usually be heard very clearly on the ADF. Having the NDB’s ident being overshadowed by the “Woosh-Snap-Woosh-Snap-Woosh-Snap” sound of the strobe is annoying! Who uses NDBs any longer? Yes, that’s a valid point, but the strobe sound also interferes with finding the score of the game on your favorite AM station! So if you still use an ADF at times, I suggest you avoid a belly strobe.

In the 1970s, when the model 200 was being certified, the FAA’s rules had been amended to require a brighter beacon, one having more candlepower. It was found that the easiest method of compliance with this new regulation was simply to replace the light’s red lens cover with a white one. You will notice that all 200s and later models leave the factory with white, not red, beacons.

This seemingly minor change led to an interesting “unintended consequence.” Beech’s test pilots for the 200 program reported that the beacons were now giving undesirable distraction when flying at night. Of course, as in airplanes with the less-bright red beacons, the switch could always be turned off when inside a cloud. But even in clear air, the pilots were finding too much distraction from the belly beacon reflecting its light from the lower nacelle area, from the back side of the propeller blades, and from the inboard gear door when the gear was extended.

The antennas that aren’t.
The antennas that aren’t.

Part of the solution was to paint the offending areas of the inboard nacelle and gear door with a flat black paint that absorbed the light reflection well. The solution for the propeller blades reflection was to add two blocking fins on the belly, to the left and right of the front side of the beacon, to block the light from reaching the propellers. (And you thought those fins were antennas, didn’t you?!)

So operators of later King Airs need to realize that the somewhat unattractive splotches of flat black paint that spoil the otherwise great look of their new paint job is not some designer’s whim, but rather they keep the airplane “legal” by reducing the cockpit light distraction to the level intended by the designers and the FAA.

I have seen lots of used King Airs with great new paint jobs that have raised doubt in my mind as to their “legality.” Few, if any, maintenance shops or FAA inspectors will likely be aware of the light shielding that is required with the white beacons and as long as the pilot(s) don’t find it overly distracting, who cares? But now you know why the “better” paint shops will inform you about the need for those weird black paint patterns that they must apply.

Another thing that raises doubt in my mind comes when the white beacons are replaced with red ones. Are they bright enough? Maybe so, but I would want the manufacturer to address that with me. I am quite sure that red strobes are plenty bright. So if the ADF interference is not an issue, this replacement path is probably fine.

Amazing, isn’t it? That something as simple as a rotating beacon can lead to such extra attention in FAA certification?

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