Page 24 - Volume 10 Number 9
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The change, therefore, was to add a flap position trigger into the unsafe warning circuit. In the King Air series, Beech added a switch beside the flap limit switches attached near the inboard track of the right inboard flap. This switch was adjusted to be activated whenever the flaps exceeded the approach position. So most King Airs, now, will have the horn blow and red lights illuminate whenever the flaps exceed approach if the gear is not correctly down, regardless of power lever position. There was no requirement to retrofit this flap trigger to earlier airplanes so many vintage King Airs still will not have it.
If you have operated a King Air for very many hours, I am sure you have experienced at least one case of “Two Green; No Red.” Huh? That ain’t right! By far, the most likely reason for this is a burnt out green light, right? Merely test the bulb by pressing it (or the module), verify it is bad, replace it with a spare bulb, and now we are relieved to see the “Three Green” that we were expecting. (If you are not 100 percent sure how to test and change the bulb, ask your mechanic or another pilot to show you the procedure!)
Unfortunately, there will come a time when the “Two Green; No Red” situation reveals that the bulb is good; it tests just fine! Now wait. How can that be?! If all three downlock switches must be activated to turn out the in transit red lights, how come that downlock switch is not also activating its greenie?
The answer comes from the fact that even though there is only one downlock switch per gear leg, that switch contains more than one set of contacts and has a lot more than just two wires attached to it. History has shown that it is not uncommon for the portion that deactivates the red lights to still function properly after the portion that activates the green light has failed.
In this situation, I like to say that we have a tie vote: One Aye and one Nay. The Aye vote – that the gear is safely down – comes from the absence of the in transit red lights. The Nay vote – that all three gear legs are not safely down – comes from the lack of that one Green. How do we break the tie?
Yes, you are correct: Use the gear warning horn. Pull one or both power levers back to idle, or go ahead and select full flaps. No horn? Whew, we are safe to land. We have two safe votes now and only one unsafe vote. I am not saying that the old tower fly-by is incorrect now, and feel free to do so if you prefer. But the situation I am describing is common enough in the King Air fleet that most experienced King Air pilots think the visual check is unnecessary.
Two more comments concerning this “Two Green, No Red” scenario: First, it is also quite common that sometime prior to touchdown the @%&! last green light will finally appear! The downlock switch contact had not totally failed but was just “sticky.” Second, for the older electro-mechanical systems, realize that all three gear jackscrews are driven from a common source, a common transmission that has torque tubes attached to the main jackscrews and a chain drive attached to the nose jackscrew. Unless there was a rather catastrophic failure of that transmission assembly, if one jackscrew has been driven properly to “full” extension then the chances are good that the other two are also fully extended. You didn’t hear a big, loud, “Sprong, Clackity-clack!” did you? If not, all three legs are likely operating together just fine.
Before I end this article, allow me also to review landing gear limit switches. It is surprising for a lot of King Air pilots and mechanics to find that the uplock and downlock switches play absolutely no role in telling the motor when to stop running! (With one exception that I will cover.) No, for the electro-mechanical system, the switches that tell the motor it’s time to quit are associated with that transmission/gearbox in the belly. If they activate too soon, the gear remains in transit without good contact on the uplock or downlock switches. Activate too late, and we put undesirable and possibly damaging stress on the jackscrews, torque tubes, and chain drive when they are asked to travel further than they should.
Lastly, what shuts off the motor that drives the fluid pump in the electro-hydraulic systems? Where is its “Limit Switch?” On the retraction side, the shutoff is triggered by a pressure-activated switch. As all three
22 • KING AIR MAGAZINE
SEPTEMBER 2016


































































































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