I’ve been corresponding with a King Air owner about an oil temp problem he has wrestled with for awhile. On one engine, the oil temp is not warming up to where it should be. Initially he worried about icing in the oil-to-fuel heater, but we have since ruled that out. This started my thinking about King Airs in winter conditions and a good time to reiterate points on my recommended Cold Weather Checklist.
All the items I have in mind are addressed at some point in one of the four Phase Inspections and some are addressed at every one. But if you’re like the majority of owner-operators flying less than 200 hours per year, your King Air is on the alternate phase program: You take it to your shop once a year for two phases plus the additional scheduled items coming due. For many, their phases are done during mild or hot weather every year, when cold weather readiness is less of a concern. Regardless of when your inspections come due, it never hurts to double check these cold weather items to make sure they are ready to go when you really need them.
I suggest you choose a day when your King Air is not scheduled to fly and the OAT is below 75ºF. This way you are not cramming a bunch of extra items into your pre-flight checklist and distracting yourself from your normal routine – never a good idea. Do it in February – make a date with your King Air and show it a little love.
Deice Boot Check
Starting with a good walk-around, take a very close look at all the deice boots. Pay particular attention to the leading edge where splits and cracks are most likely to occur. Don’t forget the horizontal stabilizer. For a model 90 you’ll need a 6-foot ladder, but for T-tails, if you don’t have a safe way to get up there, you’ll have to leave it to your shop. You can at least check the wings and make note of any cracks or splits observed on the boots as you’ll need to have those addressed by maintenance.
After the visual inspection, run the aircraft at high idle and select auto cycle on the deice switch while keeping an eye on the vacuum and pneumatic gauges. You want to see those gauges drop and then come back up. The deice switch (auto cycle) opens the pneumatic deice valve and allows air into the boot, causing the gauges to drop. Once the boot is inflated and the air is trapped, the pressure goes back up and so do the gauges. You are looking for 16-18 psi after the drop. If you don’t get it, you should be worried about leaks in the boots. Take a closer look for cracks or weather checking and alert your shop accordingly.
Obviously if a boot doesn’t inflate properly, it can’t bust the ice off the leading edge. In the case of most cracks, your shop can patch them with no problem. The sooner you catch a crack in a boot, the easier it is to patch. A properly installed patch should last a long time; but if it starts to come loose, it usually can be redone. Multiple patches on a boot are not uncommon. Eventually, however, boots need replacement. They are not cheap and it is a labor-intensive job, so paying attention to your boots on a regular basis is good preventative maintenance.
A stern warning about boot dressing: Never use anything but the manufacturer’s recommended product to dress the boots on any aircraft. If you want your King Air to gleam in the sun with shiny black boots, you must rethink this obsession. Any product not specifically designed for your aircraft deice boots will surely hasten their demise, if not utterly destroy them.
I have seen people use car wax and even floor wax on their deice boots. Such products dry out boots faster than no product at all. Likewise, tire dressing products are designed for automobile tires, not aircraft pneumatic boots. Make sure whoever cleans your King Air understands implicitly which product they may use on the deice boots and that no substitutes are allowed. I cannot emphasize this point strongly enough.
External Heat Items
Windshield Heat: To test windshield heat, start with the battery on and select windshield heat. The different King Air models have a variety of windshield heat switches; the point is to cycle the switch through its various positions with a hesitation between each selection. While doing this, look at your magnetic compass – you’ll want to see it swing a couple of degrees with each change of position. The compass won’t swing if the OAT is too hot. It needs to be 75ºF or below for this to work properly. If it’s cool outside and the compass doesn’t swing, then your windshield heat is not coming on. Have your shop look into it.
I have written articles on windshields and windshield heat for this magazine. See “Windshields 101” in the Mar/Apr 2010 issue [Volume 4, Number 2] and “More on Windshields” in the April 2015 issue [Volume 9 Number 4]. Send me an email if you can’t find them.
Fuel Vent Heat: These are the tubes on the bottom of the wings just outboard of the nacelles. They tend to erode on the leading edge and sometimes the fine wires come unglued causing failure to heat. With the battery on, feel the tubes for heat but be careful not to burn your fingers. If it doesn’t get hot, add it to your squawk list.
Pitot Heat: As long as you are checking your fuel vents, you might as well check your pitot tubes. Just remember to take the pitot covers off before flipping that switch or you will have a big, melted mess on your hands! Believe me, I’ve done it myself and it’s a miserable experience.
There is nothing worse than having a routine and minor check turn into a major fiasco in a matter of seconds. My preventative measure is to take the pitot covers off and put my cell phone and car keys on top of them. This ensures that I put the covers back on when I’m done and I don’t get distracted by my phone while focusing on the aircraft.
Stall Warning Heat: On King Air 200s, 300s and 350s the stall warning vane only gets half heat on the ground because the squat switch reduces the heat to compensate for lack of airflow. On those models, if the tab gets warm, but not hot, you are good to go.
Stall warning heat on the model 90s is completely different. Its stall warning heat systems vary from aircraft to aircraft. It requires maintenance manual research by aircraft serial number to ascertain what configuration your 90 has. Suffice it to say, some 90s heat the vane all the time and others cycle the heat on and off. Allow ample time for heating in case yours is on a cycle, but don’t just go up and grab it. You could burn your fingerprints off! Especially if your stall warning heats continuously.
If a couple minutes have gone by and you haven’t blistered your fingers, add stall warning heat to your squawk list. And while you are at it, make a note for your shop to research what kind of stall warning system is on your 90.
Prop Heat: Although the prop heat boots are an external heat item, you are better off checking this in the air. The manual check done on the ground takes two people – one to turn the prop and feel the prop boots while the other is in the cockpit operating the system and monitoring the gauges. Although recommended by the maintenance manual, I’ve seen this test fall short on many occasions.
I’ve also written articles regarding prop heat and problems with this test specifically. See “Prop Heat” in the February 2019 issue and “Heated Argument – More on Prop Heat” in the April 2019 issue [Volume 13, Numbers 2 and 4 respectively].
Testing your prop heat in flight requires a clear understanding of the type of system installed in your King Air and keeping a keen eye on your prop amp gauge.
FCU Heat: This tube located inside the engine cowl connected to the fuel control carries compressor discharge air (P3 air) which is super hot. This is the least crucial of the external heat items due to the extremely hot air running through it – freezing is highly unlikely. In fact, King Airs with 60-series PT6s (such as 300s, 350s and those with a 60-series Blackhawk mod) do not have FCU heat.
In 200s, the FCU heat comes on when the condition levers are moved forward. The same is true for later model 90s. Earlier 90 models have an FCU heat switch for each engine in the cockpit.
The only time a malfunction of FCU heat becomes an issue is in reverse or in an over-torque situation. FCU heat is checked at every Phase Inspection.
Battery Off
As a friendly reminder, after checking all these items, don’t forget to turn your battery off. It’s easy to overlook this when you are poking around your aircraft and not following a preflight or postflight checklist. After years of waking up at midnight and wondering if I left a battery switch on, I came up with a surefire remedy. When working on a King Air with a dual bus system, I leave the beacon switch in the “on” position. The flashing beacon is a constant reminder that the battery is on.
Try it yourself. As you get ready to leave the hangar and you look back at the aircraft on your way out the door, if that beacon is still going, you will happily turn your battery off and be thrilled you didn’t drain it dead. When I’m working on a King Air with a triple feed bus, I use the nav lights as my “battery reminder” since the beacon bus is not powered with the battery on.