I was asked to write an article about preparing a King Air for winter weather. Initially, I brushed the idea aside because everything I would suggest is covered by the Phase Inspections in the Maintenance Manual. But when I had my shop, the majority of my customers flew less than 200 hours a year and subscribed to the alternate phase program. They came the same time every year, like clockwork, for two phases and other scheduled items. So maybe a cold weather check of your King Air is a good idea, especially if your phase inspections always come due in warm weather.
Checking Deice Boots
Speaking for myself, I would choose a day when the aircraft is not scheduled to fly so as not to delay takeoff with a lot of extra run-up items. The OAT must be below 75º F. I’d start with a really good walkaround and then take a very close look at the deice boots, paying 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 only 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. Make note of any cracks or splits observed in 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 allowing 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. I would look for 16-18 psi after the drop. If that doesn’t happen, I’d 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. However, eventually a boot will need to be replaced. 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 warning about boot dressing: I would never use anything but the manufacturer’s recommended product to dress the boots on any aircraft. Everyone wants their King Air to gleam in the sun with black shiny boots, but too often they go off the rails to achieve the look. I have seen people use car wax and even floor wax on their deice boots! Such products will dry out boots faster than no product at all. Likewise, tire dressing products are not designed for aircraft pneumatic boots. Make sure whoever cleans your King Air understands which product is to be used on the boots. 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 but 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 want to see it swing a couple of degrees at each change of switch position. The compass won’t swing if the OAT is too hot; again, it needs to be 75º F or below for this to work properly. If it cool outside and the compass doesn’t swing, then your windshield heat is not coming on. Have your shop look into this. [For more information on windshields and windshield heat see the article “Windshields 101” in the Mar/Apr 2010 issue of King Air magazine or send me an email.]
Fuel Vent Heat: These are the tubes on the bottom of the wings just outboard of the nacelles. They have a tendency 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 don’t 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, doesn’t it make sense to check your pitot tubes as well? 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. I’m not trying to insult anyone’s intelligence. There is nothing worse than having a routine and relatively minor check turn into a major fiasco in a matter of seconds. I formed the habit of taking the pitot covers off and putting my cellphone and car keys on top of them. This ensures that I put them 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 cuts the heat in half to compensate for lack of airflow. On those models if the tab gets warm you are good to go. Stall warning heat on model 90s is different. Its stall warning heat systems vary almost from aircraft to aircraft. It requires maintenance manual research by aircraft serial number to ascertain what configuration your 90 has. I could write a small book on just that subject. Suffice it to say that 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 of 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 in 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 written several articles on King Air prop heat and the problems with this test specifically. Two of those articles appeared earlier this year, in the February and April issues. 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 is the least crucial of the external heat items. It’s a tube located inside the engine cowlings by the fuel control. In 200s and 300s, the FCU heat comes on when the condition levers are moved forward. In the 90 models, there is an FCU heat switch in the cockpit for each engine. If the FCU heating element isn’t working, there is still plenty of heat inside the cowling, even in freezing conditions, for that engine to operate normally. 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 Phase Inspections.
Battery Off: As a friendly reminder, after checking all these items, don’t forget to turn your battery off. It’s easy to overlook when you are poking around your aircraft and not following a pre-flight or post-flight checklist. After years of waking at midnight and wondering if I left a battery switch on, I developed a habit to fix the problem. 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.
Speaking of checklists, my late father-in-law was an absolute stickler for them. He wouldn’t get within 50 feet of his aircraft without a checklist in hand. Were he alive to read this article, he would have made his own checklist with all of the above items on it; he would have gone to the airport on a brisk morning to make sure his aircraft was winter ready; and he would have carried his handmade checklist throughout each activity. Safety was paramount with him and ‘checklist’ was his middle name. Before his passing he was honored by the AOPA as a 62-year member. Allow me to raise a glass to all owners and pilots, wishing you a multitude of safe hours flying your King Airs.