The King Air Book Volume II eBook ReleasedPosted by KingAirNation — Friday, April 24, 2020
We covered the announcement of the paperback version back in February.
Original announcement post from author Tom Clements:
“It is finally done! It’s been ten years since The King Air Book first appeared and now Volume II is completed. As most BT Forum members know, I have been writing articles for King Air Magazine for over nine years. These 90+ articles form the basis of the new book. Unlike Volume I, the articles in Volume II are organized based on subject matter. In doing so, I believe topics of particular interest will be found more easily.
It’s big: 460 pages. It even has a few pictures! $59.95 is the cost. Order yours at http://www.thekingairbook.com. This link will direct you to the King Air Academy website where you will find buttons for both a print version and a digital, searchable version.”
Tom Clements has also provided a sample section of the book:
Testing Autofeather…The Correct Way
When I fly right seat with other King Air pilots, I get the opportunity to observe lots of different procedures and techniques, some good, some not so good. I have concluded that the test of the marvelous Autofeather system is a procedure that, more often than not, falls into the “not so good” category. How the procedure is written in the POH contributes to the errors, as well as how it is taught by some training providers. The purpose of this article is to teach you the way to do it correctly and easily, making sure that all the steps are covered.
For the Autofeather system to release oil from the propeller – allowing the feathering springs and blade counterweights to rapidly send the blade to feather, at or near a blade angle of 90° — requires four necessities. First, the Autofeather switch needs to be in the top, “Arm,” position. Second, both power levers must be advanced forward enough to trigger the electrical switches located inside the power quadrant, usually set near the 90% N1 (or Ng) position. Third, one side’s torque must be above about 400 ft-lbs (or 17%, for the 300-series). Fourth, the other side’s torque must be below about 200 ft-lbs (or 10%). (A different torque switch changed this to about 260 ft-lbs in later King Airs.) In The King Air Book I describe these requirements and explain in detail why each is important. To summarize, (1) the power lever position lets the system know that we want plenty of power on both engines; (2) the system knows we are getting significant power from the “good” side; and (3) the system also knows that the “bad” side is producing so little power as to be useless.
Have you ever considered this unlikely scenario? Climbing through, say, 5,000 feet after takeoff, with the Autofeather switch still in the Arm position, what will happen if both condition levers got pulled into Fuel Cutoff simultaneously? Would both propellers automatically feather, to set you up for the optimum glide, or would only one or neither side feather?
Referring back to the requirements for Autofeather to operate, we meet the first and second criteria…since the switch is Armed and both power levers are well-advanced. However, we don’t meet the third criterion since neither torque is above 400 ft-lbs. The fourth criterion is also not met since both side’s torques are very low, not just one side.
Can you figure out why the designers would not want to feather both sides automatically for you so as to optimize the glide? Well, before committing ourselves to a powerless glide to a landing, wouldn’t we want to attempt an airstart? Gee, I sure would! And are not windmilling airstarts generally easier and quicker than when we must use the starter? Yes, they are. So we have the chance – at 5,000 feet AGL in this example, or even at 1,000 feet AGL – to try for the restart before deciding that we really do need to glide to a touchdown.
The bottom, Test, position of the Autofeather switch eliminates the requirement to have both power levers advanced forward. The Test position, in other words, bypasses the power lever switches. By doing so, now we can use each power lever to initiate a loss of engine power without that action also turning off the Autofeather system.
In the olden days of standard three-blade propellers, the 500 ft-lbs of torque necessary to begin the Autofeather test did not spin the propellers fast enough to get into the governing range. For example, a C90 might experience about 1,700 RPM on the run-up pad at 500 ft-lbs, yet the lowest setting of the Primary Propeller Governor is 1,800 RPM.
Those with four-blade propellers, however, almost always find that the torque required at the start of the Autofeather test will indeed spin the propellers up into the governor’s operating range. Since it is torque we are after here, not power, I suggest you begin the Autofeather test by pulling both prop levers back to their lowest speed setting without going so far as to enter the feather detent. This will reduce the noise during the test, help prevent propeller erosion, and will even save an ounce or two of fuel!
While using your left hand to hold the Autofeather switch down into the Test position, slowly advance both power levers until you see both left and right Autofeather Armed annunciators appear. As my colleague, Dean Benedict, wrote in a King Air Magazine article recently, we must remember that we need to keep advancing both levers until both lights appear. Due to the nature of the wiring circuit, if the left light is illuminated but not the right, it probably means we need to push the left power lever further forward, not the right. Yes, that seems backwards but it is correct.
The lights should appear when the 400 ft-lb torque switches have been activated. Due to the nature of the pressure switch – that it typically takes more pressure to close the switch contacts than to open them – we may need to see 500 or even 600 ft-lbs of torque before the annunciators illuminate.
Once the lights are on, take the left power lever and pull it back s-l-o-w-l-y. Moving it too rapidly – a common mistake – prevents you from observing the two distinctly separate actions that you must now confirm. First, the opposite side’s annunciator must extinguish with nothing else happening. This verifies that no feathering will take place on the “bad” side until the “good” side is disarmed, preventing the feathering of the wrong side or of both sides. Second, as you continue slowly coming back on the left power lever, now the left annunciator should extinguish and the propeller speed – which has been slowly coming back along with the power lever – will now make a sudden decrease as the blades quickly start moving toward feather.
By now, the left N1 has decreased to near idle speed which has caused torque to go low enough to activate the feathering action. As the blade angle suddenly increases, moving towards feather, propeller speed slows and torque rises. In most cases, this is enough to deactivate the 200 ft-lb torque switch and stop further feathering. As oil flows back into the propeller and the blades flatten, RPM rises, torque falls, and the whole process repeats itself. Hence – unlike the manual feathering check during which propeller speed usually goes below 400 RPM with the engine idling and the propeller fully feathered – during the autofeather check the propeller speed rarely goes below 800 RPM, increasing and decreasing a couple of hundred RPM as it repeats the partial feathering cycles. In sync with this, the left autofeather annunciator will cycle off and back on.
In rare cases, there is enough “slop” in the 200 ft-lb torque switch that the rise in torque as the propeller feathers is not sufficient to deactivate the switch. The outcome is that the propeller makes it all the way to feather, ending up near 400 RPM with no annunciators on and no partial feather cycles taking place. I have observed this in perhaps five percent of the various planes in which I have conducted autofeather tests. Although unusual, it is not dangerous and does not nullify the test’s outcome.
While still holding the autofeather switch down to Test with our left hand and now having observed the two separate actions of (1) disarming the right side first, at near 400 ft-lbs of torque on the left side, and (2) starting the feathering action of the left propeller at near 200 ft-lbs, now we are done testing the left side and must bring the left power lever forward until both side’s annunciators are illuminated once again. This prepares us for repeating the test on the right side.
As we s-l-o-w-l-y retard the right power lever we are looking for the same distinctly separate actions as before: Disarming the left side first; Feathering the right side second. Unlike the left side’s test, however, we have no need to push the right power lever forward after we observe the feathering. We only did that on the left side so that we could test the right, but there’s not a third side to test! So, make your slow power lever reduction all the way to the Idle stop. This sets us up for the last part of the test, a part that is often overlooked or done incorrectly.
How we stand now is this: The right power lever is at Idle, the left power lever is still advanced enough to give us 500 – 600 ft-lbs of torque, the left annunciator is off, the right annunciator is cycling off and on, and the right propeller speed is, usually, rising and falling about 200 RPM as the partial feathering cycles take place. To complete the test correctly, pull the left power lever all the way back to the Idle stop while still keeping the autofeather switch pushed down.
What should be observed is that both left and right propellers return to their normal idle speed, with no autofeather annunciators illuminated and no feathering occurring. In other words, the retardation of the left power lever caused the right automatic feathering to cease. What we have just proven is that no feathering will take place during an aborted takeoff even if the 90% power lever position switches malfunction and remain activated! This goes back to our earlier statement that one side must be at relatively high power while the other side is at low power as one of the criteria for autofeather action. Thus, with both engines at low power simultaneously, the propellers need to keep windmilling. Can you imagine how much harder it would be to stop on the runway in an abort situation if both propellers went to feather?!
Although our presentation here has taught to test the left side first and the right side second, it makes absolutely no difference. If you want to reverse the order, it’s fine. No matter which side you begin with, however, the test isn’t complete until you verify that the feathering action of the second side ceases when the first side’s power lever also comes to Idle.
Three final comments: First, what the test does not check – since the switches are bypassed in the test – are the left and right 90% position power lever switches. Second, it is easy to make the mistake of not returning the autofeather switch to the top, “Arm,” position when the test is completed.
The pilot can verify that both of these potential oversights are correct by merely observing the annunciators illuminating before final takeoff power is set during the takeoff roll. With a crew, the non-flying pilot can/should include “Autofeather annunciators on” in his takeoff callouts. When flying single-pilot, we need to be making this important observation, too.
Third and last, realize that observing only one annunciator illuminated during some descents or while maneuvering in the approach area is not uncommon and does not indicate a problem. It just means that both power lever switches have not activated or deactivated at the exact same instant. Pull both power levers back a tad more, both lights will go off. Push both power levers forward a bit, both lights will appear. It’s quite normal.