Not long ago, I had four King Airs in a row that had flap issues. Three of them were in the hangar at same time. A contagion of flap failures? Flap Cooties? Let’s hope not.
F90 – No Washers
First, there was an F90 in for a pre-buy inspection, and we found that most of the flap roller bearings were worn out. We had to replace six out of the eight bearings. Worse yet, every roller bearing was missing the all-important Teflon washer – not one to be found! Also, the flaps were wildly out of rig. The only thing more shocking was the fact that just 10 hours earlier, this King Air had been through a Phase 1-4 inspection (at an authorized service center, no less)! Good thing the prospective buyer arranged his own pre-buy in spite of the recent inspections, because this King Air had plenty of other issues to be worked out before the deal closed.
Model 300 – Roller Bearings
Concurrent with the F90 issues, a King Air 300 was in for a phase inspection and needed all of its roller bearings replaced – making it another four roller bearings we changed. The 200s, 300s and 350s have the Teflon washer/roller bearing setup on the outboard flaps only; the 90s and 100s have it on all four flaps. Each flap takes two washers and two bearings.
I wasn’t surprised at having to replace all the roller bearings on this 300. They caught my attention at the last inspection and I knew they were nearing the end of their useful life. You can’t tell if a bearing is bad just by looking at it though, you have to hold it in your hand and feel it.
The outer ring must slide smoothly around the center post with no grinding or rough patches, and the center post must stay firmly in place. The center post in a worn out bearing is wobbly and shifts back and forth.
A B100 – Damaged Flap Track
Across the hangar, a King Air B100 in for phase and gear inspections had one seriously messed up flap with a bad roller bearing and no Teflon washer. Actually, the washer was installed on the wrong side of the flap track where it does no good and does not fit. The washer’s interior hole is nearly one inch in diameter to accommodate the center post of the roller bearing. Installed on the wrong side of the flap track, this comparatively giant washer was hanging on a bolt less than one-fourth-inch in diameter.
Without the Teflon washer in place to protect the side surface of the flap track, the shoulder of the roller bearing gouged into it, metal-on-metal. This is the worst possible situation, and the damage looked pretty profound. There is a diagram of the flap track assembly in the maintenance manual (see example above); the aft flap track is on the right. The shaded gray area on the diagram is where the roller bearing shoulder scrapes and gouges if the Teflon washer is worn out or missing. The maximum allowable wear to the flap track side surface is .050 inch. It wasn’t looking good and I was worried.
The flap track assembly extends pretty far into the wing structure. If condemned, it means big bucks to change it as many hours of labor are required. To be absolutely certain about this flap track, we stripped the paint and measured carefully. It was exactly at max limits for wear.
Whew! The owner dodged a big expensive bullet on that one! But if there is no more leeway left on this flap track, how much longer will it last? I don’t have a crystal ball, but it will last longer than you’d think provided it is regularly inspected and properly maintained. The washer and bearing should be replaced before they get really bad, and the dry lube called for by the maintenance manual must be applied.
The odd thing about this squawk on the B100 is that the other seven roller bearings were fine; they had Teflon washers properly installed. Only one out of eight was bad, and it was really bad. To do that much damage to the flap track, it had been that way for a while. I wonder how many mechanics, supervisors, inspectors and QC personnel missed it. No shop is perfect, but this was another shocker. About 65 hours prior to our discovery, this King Air went through a Phase 1-4 pre-buy inspection and an Airworthiness Certification, as it had been out of the United States prior to the sale. It was inspected and certified by a company-owned shop that had the aircraft for seven months.
The B200 – Failed Bearing
On the heels of the three other King Airs, came a B200 for a Phase 1-2 inspection. We found a failed roller bearing at the inboard position of the R/H outboard flap. The bearing had just begun to scrape the flap track bracket. This is a sure sign of bearing failure and easily found upon close inspection. I wasn’t expecting to find a bad bearing on this King Air, but it is exactly why we do regular inspections!
Some things degrade slowly and you can keep a watchful eye until it fails or is out of limits, as in the 300 discussed earlier. Other times failure is sudden and unanticipated. Periodic inspections coupled with the proper remedy help keep sudden problems from escalating into extensive and expensive repairs.
Flap Self-Check
You can check your own King Air for Teflon washers and you can see if the washers and rollers are in the correct position. For a 90 or 100 model, put the flaps down and stand at the trailing edge of any flap. For a 200, 300 or 350, choose either outboard flap.
Forget inboard versus outboard and left wing versus right wing. Just look at the flap from the trailing edge. A flashlight may be helpful. There’s a flap track on each side, coming out of the wing structure. It runs between two brackets which are attached to the flap itself. The brackets closest to the outside edge of the flap I’m calling the outer brackets and the ones closer to the center of the flap I’m calling the inner brackets.
Shift the flap to the right to get a better view of the flap track on the left side. Between the track and the inner bracket, you can glimpse the roller bearing; the edge of the shoulder looks silvery. The Teflon washer is skinnier than the shoulder and white-ish. It goes around the bearing and lies flat between the bearing shoulder and the flap track.
Now shift the flap to the left and check the right flap track. The set-up should be a mirror-image of the other side. The roller bearing is between the inner bracket and the track; again, the shoulder is thicker than the washer and has a silver appearance. The thin white Teflon washer lies between the bearing shoulder and the track.
This is the proper set-up, regardless of whether it’s an inboard flap or an outboard flap. The roller bearing is always between the flap track and the inner flap bracket. The Teflon washer is always between the bearing shoulder and the track. That wasn’t hard, was it?
Flap Movement
You just saw that the flap will shift a little bit, side to side. This is normal and desirable. The flap should also move up and down a tad, maybe an eighth- to a quarter-inch of movement. It shouldn’t be totally rigid in place. If it is, the flap rigging needs attention. Put this on your squawk list.
Wind Load
Your flaps take a beating at all times during flight. When they’re down, they get maximum wind load. The wind pushes against the flap which presses the bearing against the top edge of the flap track slot.
When the flaps are up and you are cruising at altitude, the flaps are still getting buffeted about in all directions: up, down and side to side. In fact, the greatest wear and tear on the flap track slot happens in the flaps-up position. Over thousands of hours of flight time, there is gradual wearing away of the flap track slots.
Of much greater concern, however, is a damaged flap track or bracket caused by failed roller bearings and/or bad or missing Teflon washers. This damage is preventable with good and regular maintenance. You can add the flap self-check described earlier to your pre-flight routine. Why not? You know the saying about an ounce of prevention versus a pound of cure?
I’d hate to see your flaps create a flap.
Happy flying.
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