Recent Topics - Rotate.Aero Thu, 18 Jul 2019 19:08:06 +0000 MYOB en-gb No Auto-Pilot Engagement - by: Mark
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.]]>
ATA 22 Auto-Pilot Fri, 12 Jul 2019 22:26:44 +0000
Twisted Pairs (Trips) - by: Mark
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.]]>
Electrical and Wiring Fri, 12 Jul 2019 21:03:03 +0000
Bad Day - by: Mark

Faces Wed, 19 Jun 2019 10:34:45 +0000
ATA 28-41, Fuel Quantity - by: Mark
Aircraft such as the 727, older 737's, DC-9's, DC-10's, and A300 use a total of three wires (tank to processor/indicator) for tank measurement. The tank probes are combined at the tank spar plug and only LoZ, HiZ, and Comp wires are needed beyond the tank itself.

Each individual probe on a 767/757 has its own LoZ input excitation wire. The HiZ output wires are all connected together. This does include the compensator output signal.

The fuel quantity processor unit looks at each probe separately by using millisecond "shots" down each LoZ wire. Only one probe receives excitation at a time, so the output HiZ signal can be measured for just that probe alone.

If a probe is lost, the processor uses a "sister probe" method for estimating the missing probe's value.

The good thing about this approach is that faults can be isolated down to the exact probe vs using a breakout box for tank probe troubleshooting on the aircraft mentioned above. The bad thing though........ many more chances of wires breaking.

ATA 28 Fuel Systems Thu, 20 Dec 2018 00:53:56 +0000