Sticky Autothrottle Button - Repaired — Flaps 2 Approach

oem autothrottle button. note the circular circlip

I noticed soon after the throttle quadrant arrived that the engine number one auto throttle button was a bit sticky. Depressing the button, it would stay pressed in for a few seconds even though pressure had been released. The autothrottle buttons are one-way buttons meaning that they are click buttons. It’s probable that after many hours of service, sweat, dead skin cells and dirt has built up on the inner button behind the spring mechanism; a friend suggested that DNA analysis of the built up debris would probably provide a list of suspect pilots!

Whilst the button was still in place, I attempted to loosen the built up material using a can of pressurized electronic cleaner fluid. The fluid, I hoped would dislodge any loose material before evaporating. Unfortunately, this didn’t work in the long run, although once lubricated with the evaporate solvent, the button operated correctly for a short time.

Circlip

The button is held in place within the throttle handle by a ½ inch circlip. Beneath the circlip and button there is a spring mechanism that pushes the button out after being depressed. Using a pair of circlip pliers, I very carefully removed the circlip making sure that the spring mechanism of the circlip didn’t propel my button out the window and into the garden!

With the circlip removed, the inner portion of the throttle handle slides out revealing the button and attached wiring. The button is a modular design (shaped to fit inside the throttle handle) and unfortunately cannot be disassembled further, Therefore, I reassembled the button and sprayed a small amount of silicone spray around the button, allowing the silicone solution to penetrate around the the edge of the button.

The silicon lubricant (which is non conductive, so there is no issue with power shorting) seems to have solved the problem as the button no longer sticks, however, this is only an interim solution. I'll search for a replacement button module. Sometimes the most simple solution will fix your problem.

No doubt I can purchase a new replacement from Boeing for err $800.00.... I think not. Eventually I'll find a disused button module in my travels.