Q: I live in Florida. How often should I do a compressor wash on my PT-6?
A: Pratt & Whitney recommend that you do a compressor wash at least once a week if the airplane is exposed to occasional salt air.
The Importance of Preflighting your King Air
I recently trained a student that experienced an interesting event while flying an E-90. While cruising at FL210, the upper door latch failed from fatigue. The upper portion of the door opened about six inches resulting in an explosive decompression. The pilot stated one of the more unusual aspects of the rapid loss of cabin pressure was the amount of dirt and sand that was sucked out of the carpet. The airplane was a 1972 model with approximately 10,000 hours. As the King Air fleet ages, it’s important to thoroughly preflight the airplane. On older models, pay particular attention to the door pin brackets and the possibility of fatigue cracks.
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Split Flap Procedures
QUESTION: Are there any split flap procedures on the C-90?
ANSWER: I get this question frequently in ground school. There are no emergency procedures for a split flap situation. If the wing flaps are inoperative, the airplane should be landed in the existing flap configuration. If you have a flap malfunction, ensure flap position is visually inspected prior to resetting the flap handle to the previous position. Once reset, the flap motor CB should be pulled to prevent inadvertent flap movement. It should be noted that the military flight tested the aircraft under all possible asymmetric flap configurations and found the airplane to be fully controllable.
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Prist Does Not Kill Microbes
Prist does not kill fuel microbes. Although the King air rarely experiences fuel system icing, many pilots order Prist when re-fueling in the mistaken belief that any microbial growth in the tanks will be killed. Prist is a Biostat. A Biostat can keep an outbreak of microbes from continuing to grow, but it won’t kill them. Only a Biocide can eradicate growth in fuel tanks. How do you know that you have growth in your fuel tanks? The signs can vary. Obviously clogged filters, contaminated tank bottoms, or fuel samples that have green or brown slimy formations are all definitive signs of bacterial growth. Untreated, this problem can lead to corrosion and damage to the structural integrity of the airplane. Of course, the worst-case scenario is the loss of an airplane due to engine failure. So, what exactly are these microbes? The scientific names for organisms that live in jet fuel are Cladosporium Resinae and Pseudomonas Aeruqinosa. I doubt, however, these names will catch on with King Air pilots. These microbes live and multiply in the water found in jet fuel. By living in the water, they can feed off the hydrocarbons in the fuel. As they grow, they form dark colored mats that appear gel – like. Their waste products include acids, sludge and water. Not content with feeding off of just hydrocarbons, they also consume rubber gaskets, hoses, tank linings, and O-rings. Pilots should be aware of the signs of microbial growth in their airplanes. If growth is suspected a microbial detector kit is the most effective way to test for microbial infestation. If an infestation is present, a Biocide can eradicate the growth. Fortunately for those pilots that rarely sump their fuel tanks, most FBO’s treat their stored fuel with a Biocide prior to selling it.
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Reflective Heat Shields
QUESTION: Should I place reflective heat shields in the windshield of my BE200 when I leave it parked on the ramp?
ANSWER: Unlike your car, the windshield of the King Air has a polyvinyl layer sandwiched between two plates of glass. Using sunscreens to reflect the heat back outside the cockpit can damage this inner layer of the windshield. Of course, this can lead to premature failure of the windshield. So my advice is not to use them.
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Cycles Defined
Many King Air pilots are confused about how to define an aircraft cycle. For maintenance purposes a cycle is defined as the period of time from initial start to shutdown of the engine that includes a start up, an increase to full power required for a flight regime and then a complete engine shutdown. So in normal operations, the number of landings is equal to the number of aircraft and engine cycles. Of course, keeping track of these numbers is important for maintenance events and should be reported to your shop prior to any inspections.
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The Secret to Keeping your Windshield Shatter Proof
QUESTION: Will using windshield heat consistently reduce the chances of my windshield cracking?
ANSWER: King Air windshields are constructed of two layers of glass separated by a polyvinyl inner layer. Contrary to popular belief, turning on the windshield heat does not
cause or prevent the windshield from cracking. Most windshield crack when the
heat is turned on because of pre-existing physical damage to the outer ply. Turning on the heat causes a stress fracture and the windshield cracks. A study conducted of King
Air pilots in England where they are required to consistently use windshield heat for a
bird-proofing reveal maintenance reports that do not differ much from US reports. In other words, their windshield crack at approximately the same frequency as ours, even though we have no consensus on when to operate the windshield heat. So what is causing the failures?
According to PPG, (they manufacture most windshields) it is the penetration of water through the primary weather seal. The primary weather seal is area just outside of the
transparent part of the window. The hydraulic pressure of rain, snow or ice
crystals can erode a poorly maintained weather seal and work its way into the vinyl interlayer of the windshield. Once there, delamination can occur. I’ve seen numerous King Air’s with yellow delamination spots dotting the windshield. These spots are the warning signs that water may have penetrated the interlayer. This leads to heating system failure and possible shattering of the outboard window glass. Proper maintenance can slow down or even stop moisture caused deterioration. Schedule seal maintenance during you normal phase inspections because the sealant usually requires 48 hours to cure. Of course,
some pilots recommend turning on the heat just prior to take off and turning
off after landing. There is nothing wrong with this procedure, but it is not
required.
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FOD or “When to Deploy the Ice Vanes”
During ground school, several students have told me about their engines having to go into maintenance for first-stage compressor F.O.D. In each instance, a single blade has been bent with the damage being caused by a soft or dull object. I’m sure it was ice. The King Air intake system is the result of a millions of flying hours coupled with a thorough research program. Closed circuit television cameras located in the intake has shown the effectiveness of deploying the ice vanes in a timely manner. Yet, every year Pratt & Whitney issues a bulletin informing pilots on the need to extend the ice vanes. I’m going to throw in my two cents and hopefully save a few PT-6 engines. The King Air flight manual is explicit when it comes to icing. “Temperature requiring Engine Anti-Ice” +5ºC or lower in visible moisture. The pilot’s interpretation of what is icing conditions is sometimes used as justification to delay deployment of the ice vanes. Many King Air pilot’s wait until the see ice appear on the bottom of the windshield wiper before considering extending the ice vanes. Flying at night adds to difficulty in ascertaining if icing is present. To correctly deploy the ice vanes, you have to understand how the FOD is getting into the engine. It doesn’t build-up on the engine intake and then suddenly break off and go through the engine screen into the engine. The mass of the ice will stop it from turning the corner and hitting the screen. But if the ice vane is not extended moisture will collect under the screen and freeze. Then as you descend into warmer air, a piece breaks off and FOD’s the engine. Snow will do the same thing. So the key to eliminating this problem is to extend the ice vanes at +5º C when in visible moisture. If its night and you can’t tell if visible moisture is present, extend them anyway!
Of course, FOD isn’t only ice induced.
The following actions should be taken by pilots to reduce the potential of F.O.D. during ground operations:
1, Following maintenance, ensure that the mechanic hasn’t left anything in the intake. Even a small safety wire clipping can F.O.D. an engine.
2. Avoid run-ups in areas containing loose gravel or sand.
3. Avoid use of reverse at low ground speeds.
4. Do not use reverse to position the aircraft on the ground.
5. In newer King Airs, consider extending the ice vanes just prior to landing, especially if you are planning on using heavy reverse.
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Why is my cabin door hard to close with the engines running?
QUESTION: I recently flew into PDK and dropped off two passengers. It was a quick drop off so I left the engines running. After they deplaned, it was very hard to close the cabin door. I noticed the door seal was still inflated. Why is my cabin door hard to close with the engines running?
ANSWER: The reason the door is hard to close pertains to changes and improvements in the cabin door inflatable seal installation on a block of early C-90’s, E-90’s and F-90’s. A service bulletin came out in 1978 explaining the operation of the door seal but judging from the persistent reoccurrence of this question during ground school, perhaps it is not fully understood.
The cabin door seal on these early airplanes was originally pressurized with unregulated, low-pressure air tapped off downstream of the left hand flow control valve. This worked fine, but an in-flight engine shutdown or flow control valve loss allowed the seal to deflate and then cabin pressurization could not be maintained. To rectify this problem, starting, at LJ-587 and LW-55, the door seal air source was moved to the bleed air manifold in the belly so that either flow control valve would supply air to the door seal. A 1.0 psi air regulator was also attached at the door frame to supply a regulated pressure. Now the problem was that, with either engine running, the door was difficult to close due to the inflated seal. To solve this problem, starting at LJ-765 and LW-272 a normally open electric solenoid, wired to the left hand “squat switch”, was incorporated to block bleed air to the door seal while on the ground. Also, the 1.0 psi regulator was replaced with a 4.0 psi air regulator to give a tighter seal.
The bottom line to all this is that the cabin door on LJ-587 thru 764 and LW-55 thru 271 airplanes can be hard to close with the engines running. This could lead to improperly latched doors and a subsequent in-flight door opening. Maybe the best solution is to shut down the engines when boarding or deplaning passengers!
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