Page 27 - Volume 15 Number 4

determined by the governor, not by the position of the Low Pitch Stop. The propeller has not yet reached the state in which it is allowing us to bring it into reverse.
I should add here that this discussion about being impossible to reverse when airspeed is high began by mentioning the F90. I used the phrase “same propeller/ engine/airframe combination.” I lied a little, didn’t I? Compared to the C90 of its day, the F90’s wings are shorter, it has the T-Tail, it uses -135 engines instead of -21s, and it has four-blade props instead of the three- blades which were still used on the C90s of 1978 vintage. Yet, the relationship of airspeed to propeller speed at idle are still very similar, as I described.
Rest assured that although the 200-series uses 2,000 as its propellers’ maximum speed and the 300-series uses a mere 1,700 RPM, these models hit their LPSs quite easily due to their particular propeller’s size and shape. With power at Idle, they will be ready to reverse in almost all cases unless the speed at touchdown is much, much, too fast.
The “RVS NOT RDY” annunciator – Reverse Not Ready – illuminates when the landing gear handle goes down. It goes out when we push the propeller levers fully forward. Do you understand the significance of the reminder? Will extinguishing the light by advancing the prop levers guarantee that we can reverse the props? No.
This annunciator simply reminds us that selecting the highest propeller governor speed – which we are doing when the prop levers go fully forward – means that our moving of the LPS will more likely be successful since we are more likely to be in an underspeed condition if the governor is set for its highest governing speed.
You have all seen the placard on the power quadrant that states, “CAUTION: Reverse only with engines running.” At the start of this article I promised that my discussion would be in a “nonscientific, nonmechanical, non-engineering manner.” Let me try to explain why this caution exists and what it really means.
The only time the power levers can move the Low Pitch Stop to obtain Beta and Reverse is when the blade angle is actually sitting on the LPS. We might say that we need the propeller trying to go flatter, trying to restore the onspeed condition, trying to push the LPS flatter, to help us pull the LPS to smaller and smaller blade angles. If we don’t have this help, this push from the propeller, then we feel resistance as we pull back and try to move a LPS that is not yet ready to move. With enough force, we can elongate or stretch the reversing cable. If that occurs, in the least it can set the LPS to an incorrect, higher blade angle. In the worst case, it can cause the propeller to go to and stay in feather!
A sidenote: Most of us have pulled the propeller levers into feather at shutdown while making the mistake of leaving the power levers in Beta: An easy boo-boo to make, right? Well, don’t do it again but relax ... you probably did no harm. Unless you had the power levers quite deep into Beta – or at the Ground Fine position for those models that have it – combined with a very tight friction setting, the chance of damage is slim.
APRIL 2021
If you have followed our discussion this far, then it should be obvious that using Reverse in flight to increase the descent rate during an emergency descent is impossible. Power levers to Idle, prop levers fully forward, flaps to approach, landing gear down and we nose over to about -12 degrees pitch attitude to maintain the landing gear extended speed limit. Even with Idle power and maximum propeller speed (Np) selected, the high airspeed will cause the propellers to be solidly in the prop governing range. If we pull back into Beta now not only are we in violation of the limitation on lifting the power levers in flight but also all we will achieve is the possible stretching of the reversing cable since the blade angle is not even close to the LPS. KA
King Air expert Tom Clements has been flying and instructing in King Airs for over 46 years and is the author of “The King Air Book” and “The King Air Book II.” He is a Gold Seal CFI and has over 23,000 total hours with more than 15,000 in King Airs. For information on ordering his books, contact Tom direct at twcaz@msn.com. Tom is actively mentoring the instructors at King Air Academy in Phoenix.
If you have a question you’d like Tom to answer, please send it to Editor Kim Blonigen at editor@blonigen.net.
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