T/R Not Fully Stowed

General information about Thrust Reversers can be found  here .

CF6-80C's use pneumatic air to open and close the Thrust Reversers during the landing roll-out. Each engine has two reverser halves. We had a problem with a aircraft when upon landing both T/R halves would deploy, but one side did not fully stow.

Please note: one supply of air is used for both halves. There are two CDU's or Center Drive Units, one for each half that do the "work" of actually moving the T/R.

The email I sent to Maintenance Control should explain what we found:

Others and I have been going at this as more of a mechanical issue vs. electrical. We switched gears and went after the electrical side in earnest today.

The center drive position switches are wired in parallel. Pins 5, 6, 7, and 8 should continuity check to each other between the two CDU plugs. Pins 7 & 8 are used on the deploy cycle. 5 & 6 are used for the stow. For either deploy or stow, these switches provide 28 VDC to the T/R Valve to supply muscle air to the CDU's.

When we approached the aircraft today, we had no continuity between pin(s) 5 of the CDU plugs. We found a wiring problem with the right side harness that connects to the right CDU.

This would explain the right half not stowing completely. The left hand T/R is faster than the right. When it reaches its full stow position, the internal switch on pins 5 & 6 opens.  The 28 VDC to the valve goes bye-bye and the air supply stops (along with the right T/R half movement). The internal switch on the right CDU is still made, but the wiring to keep the valve powered is not in the circuit.

This would make sense because when you watch a stow cycle, the left half stows with about 8 inches more to go on the right.
  
    

Nice work Mark, I find the 80c thrust reverser to always be a pain especially, when more often than not the bypass switch for ground operations never works.

From recently completed training: The PRSOV has to have a "Reverse Flow Solenoid" installed for the switch to work.

This is an extra cost during overhaul, so..... more often than not, it is omitted.