We are seeing some strange brake problems on the Twin Cessna line. This has recently shown up primarily on the 421 aircraft but we had a 340 aircraft showing the same problems.
Having been in numerous businesses, I spent many years operating a large repair facility for vehicles all the way up to large trucks. I had a large tire and service center and we did brake and alignment work from small vehicles to large vehicles. I understand brakes and tires and their associated parts.
The problem we are seeing involving the brakes do not have anything to do with “low fluid” (5606A) or air in the lines. It has nothing to do with the pads being thin. It has nothing to do with the calipers. It has to do with the master cylinders being out of round.
When I teach systems I spend a lot of time on the brakes, tires and gear. The brake problems we are seeing is a hard pedal that your holding down followed by a “spongy” pedal. It also can be a frozen piston assembly at the master cylinder that locks the plunger assembly in place. When this happens you land and as you slow at some point the brakes get locked on the rotor and you spin. It has happened in my 421C. It has happened to people who have taken training with us. We have the problem listed as problem number one in our handout that pilots get when they take our course.
What is the problem? These planes are fifty (50) years old and the master cylinders are getting warped (out of round) from repeated use. Nothing but replacing the master cylinder will solve the problem. One of our pilots was told by his repair facility after a 50 knot spin (YES 50 KNOTS) that it was the caliper and they needed to be rebuilt. IT DID IT AGAIN AT ANOTHER AIRPORT. I told him in my email to him, do not fly this plane until the master cylinder is REPLACED not REPAIRED. Sure enough he lost it again at another airport and refused to fly the plane. He then replaced the master cylinder and the problem was solved.
This is one of the many things we cover in our systems training. I and my other experienced instructors teach systems so you can ask questions. We dont give you a handout to fill out. We orally communicate the problems. We go over these problems until you understand and as our training is done, you “think out the solutions“.