Inbound (pissed off) crew write-up of all three auto-pilot systems inoperative.

Numerous interface flight faults which were also noted during ground tests.

Problem was with one of the FCC's. When the unit failed, the unit's cross-talk 429 bus data, locked up the other two FCC's. The Flight Director bars operated, but no auto-pilot engagement. This problem persisted with the suspect unit in all three positions.

We also noted a "Stab Trim" message on the EICAS page that could not be removed.



A replacement FCC cleared the message and restored all three auto-pilot's functionality.

767 tank rear spar fuel quantity connectors and HiZ bussing plug.




The standard (from old 727, 737, and 747 days) three pin connectors are used. The LoZ and Comp pins are not used. The wider (shielded) HiZ pin is.

All LoZ and Comp wiring go through the upper plug.

As stated above..... more wires have advantages for usage (tank quantity reliability) and troubleshooting (isolation of single bad probe), but...... there is a whole bunch more crap that can break.

A question was posed to me today about Boeing's depiction of shielded twisted pairs and twisted triples on their wiring prints.

The wires can be shown with an oval or a figure 8 representing the shield.



Of all the aircraft types referenced (737, 757, and 767), the oval shielding is always grounded and the figure 8 shield is always open.

Either way..... these wires should "all" be twisted. I have never seen two (three) conductor wires inside a shield that are not twisted. The drawings can possibly make you think that the oval shield wires aren't.

Standard colors are red and blue for twisted pairs. Red, blue, and yellow for twisted triples. Wiring prints sometimes show a R,B, or Y behind the wire number.

Wow, never seen that kind of damage around nose gear!