Page 19 - Volume 13 Number 12

Winter Readiness
by Dean Benedict
Iwas 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 run­up 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 6­foot ladder, but for T­tails, 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 16­18 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,
DECEMBER 2019
eventually a boot will need to be replaced. They are not cheap and it is a labor­intensive 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
KING AIR MAGAZINE • 17
MAINTENANCE TIP