Let’s talk about your preflight routine. Did you know there are some simple tasks you can add to your preflight checklist that could ultimately save you thousands of dollars in maintenance costs? Your flaps are one example—do you check your flaps regularly?
Remember the old adage: “An ounce of prevention is worth a pound of cure.” That’s especially true in aviation maintenance because when preventive measures are not taken in time, the cure weighs much more than a mere pound. It’s, unfortunately, more like a ton.
Playing With Flaps
What’s the first thing I do when I walk up to a King Air? I check for play in the flaps. Most likely they’re in the “up” position, so I wiggle the trailing edge up and down a little bit. If the flap is rigid with no play at all, it is a red flag. I’m looking for a little bit of movement.
Next, put the flaps in the “down” position and do the same thing. You want the same outcome as in the up position. Wiggling the trailing edge up and down, you are looking for about a quarter-inch of movement. The down position check is the most critical, as you never want to be stranded in the boondocks with your flaps stuck in the down position!
A rigid flap is usually bottomed out in the flap track. If not detected and remedied, this will cause the flap flex shaft to fail and/or the flap motor to jam or burn up. These expensive problems are easily avoided by regularly checking for a little play in your flaps.
Limit Switches Have Limits
A flap that bottoms out in the flap track has limit switches out of rig. The righthand (R/H) inboard flap is the “master” flap on all King Airs, and on many models the limit switches are found there.
You can see them with your flaps in the down position. On some older King Airs, the limit switches are mounted on the flap track assembly. On newer King Airs, an arm runs a shaft with cams that activate the switches. The flap switch in the cockpit controls the flap motor and the limit switches prevent the flaps from moving too far.
Over time, as the linkage and bushings start to wear down, the limit switches go out of rig. A flap that bottoms out repeatedly will eventually break the flap flex shaft or burn up the motor and gearbox. Avoid these problems by checking your flaps regularly and alerting your shop at the first sign of flap stiffness. Bushings can be replaced and the cam or switches can be adjusted to stop the flaps a little sooner and prevent them from bottoming out. Crisis averted.
Watch Your Washers
While you still have your flaps in the down position, there is another thing to check: the Teflon® washer installed on each of the aft flap track roller bearings. Figure 1 (lead photo) shows the thin, white Teflon washer positioned under the roller-bearing shoulder, which is thicker and appears more silver.
On King Air models 200/250 and 300/350, these washers are found in the outboard flaps only, nestled between each flap track and its corresponding roller bearing. On King Air 90s, both flaps on each wing have the Teflon washer setup. You can slide the flap slightly from side to side to get a better view of the washer. A flashlight may be helpful.
See the flap in the down position in Figure 2, above, and note the two flap track assemblies that jut out from the wing structure. They flank the central area of the flap. The correct positioning of the roller bearings and Teflon washers is relative to the center area of the flap as viewed from the trailing edge. The roller bearing is always between the flap track and the inside bracket adjacent to the center area of the flap.
Figure 3, left, shows the flap track to the left of the center flap area, with the roller bearing on the right side of the flap track, closer to the center flap area. The single Teflon washer is sandwiched between the flap track and the roller-bearing shoulder.
Figure 4, right, portrays the flap track to the right of the center flap area. The setup is a mirror image of the other side—the roller bearing positioned on the left of the flap track, adjacent to the center flap area, with the Teflon washer installed between the flap track and the roller bearing.
What You Are Looking For
You want to see that: A) the Teflon washers are there; B) the washers are correctly positioned next to the flap track, under the roller bearing shoulder; C) there is only one washer per roller bearing; and D) the washers are in good condition (not warped or deformed, worn or discolored).
These washers keep the roller-bearing shoulder from gouging into the flap track. Repair or replacement of flap tracks is something you want to avoid. It is very labor-intensive, and the parts are crazy expensive. By comparison, those Teflon washers at less than $10 each are the bargain of the century. You can’t afford not to check them!
It just so happens that the first article I wrote for this magazine in 2009 was on this topic of checking for play in your flaps as part of your preflight routine. Whenever I have the opportunity to walk around a King Air with an owner or pilot (such as at King Air Gatherings), I am forever checking flaps for play and more often than not, I find flaps that are too stiff!
The time it takes to check your flaps as I have described is a very small price to pay when compared to the alternative. If your flaps are bottoming out or those Teflon washers are missing or worn out, you are looking at thousands of dollars in parts and labor, plus downtime for your King Air. In this case, an ounce of prevention really is worth a ton of cure. So, give your flaps a little jiggle during your preflight routine and keep an eye on those washers.
Happy flying.
Note: Other flap-related articles can be found in May/June 2013 and October 2016 issues.