This article originally appeared in the September 2013 issue of this magazine. Some questions that I have recently received lead me to believe it is time for a repeat. Additionally, I have added a comment about the Shock Link in the nose wheel steering mechanism.
I am often asked by pilots transitioning into a King Air for the first time, “What should I look for? What systems or operations or mistakes commonly cause difficulties? If you were to make a list of things that could hurt me and/or the airplane, what would they be?”
To address those types of questions, this article will try to present a few important things that can get you if you’re not careful … some King Air “Gotchas.” They are to be studiously avoided!
First, Oil Dipstick Security. It takes little time for most PT6 engines to blow enough oil out of a loose or missing dipstick such that oil pressure drops out of the normal operating range, getting low enough, quickly enough, that engine damage is almost assured … unless the problem is recognized and an immediate return for landing or an in-flight shutdown is accomplished.
Most PT6s manufactured after about 2000 contain a ball checkvalve in the oil filler tube designed to prevent oil venting when the dipstick is missing – a nice improvement! You can recognize that your engine has this improvement by observing a shorter dipstick that only goes to “4 Quarts Low” instead of the longer “5 Quarts Low” older style dipstick.
Surprisingly, most King Air models do not contain a low oil pressure warning annunciator. Yes, the 300-series and F90-series do, but it is rare to find that useful light in other models. I believe both the British and French certification authorities required it to be added before the King Air could be approved in their countries, so some airplanes that originally went overseas, but have since returned and been recertified in the United States, have the annunciators.
Since it seems the time required to blow enough oil out of the tank to be problematic usually elapses soon after takeoff, get in the habit of doing a very careful scan of engine instruments as part of your After Takeoff flow pattern and checklist. None of us can fly a King Air without spending time looking at ITT, Torque, and Propeller Speed (Np) gauges. However, the remaining ones – at the bottom of the vertical stack, or over on the right side in the early birds with a horizontal row of gauges – attract our attention rather rarely. So now is the time to force ourselves to carefully scan those remaining three: Oil Temperature and Pressure, Fuel Flow, and Compressor Speed (N1 or Ng).
What’s that I see? Dang, the left Oil Pressure is low! Is there any supporting indication? Could it be merely a faulty gauge? Oh, double-dang! There’s oil streaming out of the aft seam of the cowling!
Not all, but most, King Air emergency checklists direct us to reduce power significantly when the oil pressure drops out of the green arc, but not necessarily to shut the engine down until it hits the lower redline limit. Why is that?
It seems logical that if the engine were not receiving the lubrication that it should, we should not run it hard … and perhaps that plays a role in the directive to reduce power. However, there is a more significant reason.
Remember that the torque instrument is actually an oil pressure gauge, reading the pressure in the torque chamber in the nose case of the engine, but displaying the pressure not in pounds per square inch (psi) but in the foot-pounds (ft-lbs) of twisting force on the propeller shaft that caused the psi value. (How that all works is a miracle of engineering, but it is a marvelous, mostly trouble-free, system.) When oil pressure drops too low, there comes a time when the torque meter becomes incapable of working correctly. Specifically, it will be limited in its ability to measure and display existing torque. For example, it may never read above 600 ft-lbs no matter how much more torque exists! This is the main reason for reducing torque when you observe low oil pressure.
Sometimes an unexplained decrease in torque indication has been the first thing that caught the pilot’s attention and led him or her to then notice a low oil pressure reading.
Since any gauge or sensor is capable of providing a false reading, it is always a good idea to attempt to get some verification before responding to the situation. For example, if you are fortunate enough to be operating a model with the Low Oil Pressure annunciator, and it illuminates, check the gauge. Is it showing a low reading? If the answer is “Yes,” you should throttle back and return for landing, even securing the engine if/when the oil pressure hits the red line. On the other hand, if the gauge reads properly, you may have only a faulty annunciator. Now’s the time to check the cowling carefully. Nice and dry, no oil seeping out? If so, you are rather sure there is no true oil pressure anomaly.
The next Gotcha is a badly bent Nose Wheel Steering Stop Block. I hope on your exterior preflight inspections that you are giving this item the attention it deserves. This is the metal tab with the three holes in it, located on the back side of the nose gear strut. Its purpose is to limit how far the nose wheel can turn when we make a tight turn while taxiing. Use of differential braking and/or differential power allows the pilot to turn the airplane “on a dime,” and when this is done the stop block is what is preventing any damage to the nose strut and steering linkage. It is strong enough that the pilot cannot force any further movement.
However, the leverage created by a sturdy tug and a long tow bar can easily overcome the resistance of the stop and permit a careless tug operator to go beyond the limits. When this takes place, not only will the stop block be deformed, but there is a chance that the strut itself will be fractured and/or that the nose wheel steering connection back to the rudder pedals will suffer damage. So, if ever you find the block distorted, I would suggest not flying until an A & P has inspected the strut and steering linkage carefully and given you a thumbs up that you’re good to go.
While you are down by the nose gear checking the stop block, occasionally also look up on the left sidewall of the wheel well and locate the shock link, the spring-in-tube assembly that is in the forward part of the nose wheel steering mechanism. Make sure that you can see and/or feel all four 90-degree spaced “ears” of the clip that prevents the spring from being released from its tubular housing. If the shock link comes undone, you lose nose wheel steering and may end up with the wheel deflected fully to one side. That makes the after touchdown rollout very exciting!
The third Gotcha is Loose Power Lever Friction Knobs. The vernier controls in Bonanzas, the one-friction-knob-controls-all-levers in Barons and Dukes … because of this past experience, a lot of pilots transition into a King Air without really having been taught much about friction locks. I would estimate that over 50 percent of King Air pilots pay scant attention, if any at all, to their friction knobs’ settings. This isn’t good!
Concerning the two power levers on King Airs, do you realize that a fairly hefty spring is attempting to pull each one back to idle at all times? As with any spring, the further it is stretched, the more force it applies … in this case, a force trying to return the power lever to idle.
If any work is done inside the cowling that involves the condition, power, or propeller cables, it is routine for the mechanic to turn the four cockpit friction knobs all the way counterclockwise, probably four or five complete 360-degree rotations, loosening them totally. By doing so, now he can move the engine-end of the cable easily, while the cockpit-end of the same control can move fore and aft with little resistance.
But woe be to the poor pilot who picks up the plane from the shop and does not do a thorough cockpit check, does not follow every checklist step, and who fails to retighten those power lever friction knobs! When his hand leaves the power levers to reach for the landing gear handle after liftoff, it is common now to find both power levers moving themselves back toward idle! In most cases, due to the shorter length of cable to the left engine than the right engine – and the resultant less resistance in the cable run – the left engine will lose more power than the right.
For those pilots who notice the power lever movement, the problem is rather easily corrected … the hand is moved back to the levers and returns them to the takeoff position. It can be almost comical to see the poor pilot trying to fly, keep the levers forward, get the gear handle up, and tighten the friction knobs all at the same time!
But if the operator does not notice this power lever migration toward idle, God help him! Suddenly the airplane is not climbing and accelerating as it should, rudder force is required to keep it straight, and autofeather (if installed) isn’t working! (Remember that autofeather is disarmed when either or both power levers move back.) I am positive that more than one fatal King Air takeoff accident has been caused by this very scenario.
To decrease the wear on the friction mechanism caused by moving the controls when the friction is tight, I personally fiddle with the friction knobs a lot … having them rather loose on the ground and then making sure they’re snugged up prior to adding takeoff power. When setting propeller speed for climb or cruise, for me it is a three-step process: twist the friction knob a half-turn or so counterclockwise, move the propeller levers, then snug the knob back up. When acting as a co-pilot or instructor in the right seat, I always have the index and middle fingers of my left hand resting at the base of the power levers when they are being pushed up for takeoff by the left-seat pilot … lightly enough that I won’t interfere with a possible abort, but firmly enough that there’s no way those levers are going to creep when the pilot’s hand leaves them to raise the gear or turn off the landing lights
Other pilots rarely ever change a friction setting and that’s fine, presuming they were set properly initially. Sure, maybe this causes fractionally more wear in the mechanism, but in the overall scheme of things that’s a tiny worry. But what about the pilot who is in the habit of not adjusting friction and then he or she flies another King Air, one that either just came out of maintenance with loosened friction or one operated by a pilot who routinely loosened them for ground operations? Unless the pilot tightens them back up to the position he is used to using prior to takeoff, the deck has been stacked for an embarrassing, comical, boo-boo soon after liftoff at best, or dead people and a destroyed airplane at worst!
Gotcha number four is the Upper Forward Cowling Not Properly Secured. It is not uncommon that one of the four latches that secure the upper forward cowling in place fails to engage properly when this cowling piece is installed. On my walk-around inspections, I use the palms of both hands to give this piece a firm upward hit, on each side, making sure that I cannot dislodge it. This is especially important if I know the cowling has been removed and reinstalled prior to this flight.
Even having done so, however, there may come a time or two when the air loads imposed on the cowling in flight cause the incorrectly fastened latch to finally let go. As you do your After Takeoff checks, you notice the upper forward cowl is lifted up an inch or so! I suggest you do three things.
First, slow the airplane down. The faster you fly, the more air loads are created and the chance of the cowling actually departing the airplane are increased, so keep the indicated airspeed down to no more than, say, 140 KIAS. Second, extend the ice vanes. The engine anti-ice system, the inertial separator, creates a venturi effect in the cowling when extended, reducing the inlet air pressure considerably. You will almost assuredly observe the loose cowling suck down a bit once you’ve extended the vanes. Third, return for landing. Taxi in, shutdown, and get a half-inch, thin walled socket and use it to tighten that temperamental latch properly.
Getting Too Slow at MDA is Gotcha number five. More and more, as WAAS-corrected GPS units allow us to have vertical guidance on almost every instrument approach, we are doing less of the non-precision, “dive and drive” type of approach. But if and when you find the need to level off with approach flaps and landing gear extended, there is a trap here waiting for the unwary.
The King Air exhibits considerable momentum, such that we can level off without adding sufficient power, yet the rate of airspeed decay is so slow and insidious that it can go undetected until we find ourselves far on the backside of the power curve, nearing stall speed. Close to the ground, perhaps still in IMC … this is not good! It has caused fatal accidents.
Here’s where knowing the “magic numbers” for your airplane is very important. If this term is unfamiliar to you, where have you been during training?! Anyway, the same power setting that yields 160 KIAS, clean, level, will be almost exactly what is required to hold about 120 KIAS, level, with flaps at approach and the landing gear down. (90-series, about 800 ft-lbs; 100-series, about 900 ft-lbs; F90 and 200-series, about 1,000 ft-lbs; 300 and 350 series, about 40 percent. All of these presume the propeller speed is at the normal cruise setting for the model.)
This magic number is important even on a severely clear day. You come abeam the touchdown point on your downwind leg, lower the gear in anticipation of starting down and turning base, and then the tower directs you to extend your downwind due to straight-in traffic. Don’t hesitate, just push the power levers up to the magic number, hold altitude, and continue ahead. It is comforting to know that your use of the correct power setting will never allow the airspeed to stray too far from exactly what you want.
Well, there you have them: My top five King Air Gotchas. There are others, certainly, but of decreasing frequency of occurrence. As we know, the King Air is an easy-flying, forgiving airplane in almost all respects, yet it, too, has the capability to bite the unwary. Be safe!
If you have a question you’d like Tom to answer, please send it to Editor Kim Blonigen at firstname.lastname@example.org