Recent Topics - Rotate.Aero Sat, 19 Jan 2019 08:50:23 +0000 MYOB en-gb ATA 28-43, Fuel Tank Temp - by: Mark
We had an aircraft reading -40C. The temp bulb resistance measured 80 ohms. (Actual outside temp was just above freezing.)

When compared to a functioning aircraft showing a temp of 1C, the temp bulb read 93 ohms.

Double plug indicators: P3900 pins 8 and 9.
Triple plug indicators: P3896 pins 12 and 13 (13 being ground). P3896 is the middle smaller plug.

AMM Task 28-43-00-715-018-002 shows low end resistance (-30C) as 80 ohms and high end resistance (60C) as 112 ohms.]]>
ATA 28 Fuel Systems Mon, 07 Jan 2019 09:56:57 +0000
ATA 24-20, Dead Left A/C Bus - by: Mark
No related faults on Bus Power Control Unit and a swap of Generator Control Units did not help.

Problem was isolated to a drained main battery. Unit only showed 1.5 VDC.

No actual description in the AMM, but from digging through the prints, it was noted that power for the Left Tie Bus Contactor "close" coil comes from a Battery Bus breaker. This control voltage goes through the Left GCU, a Auto-Land relay, and the relaxed contacts of the Left Generator Contactor.

The Right Tie Bus Contactor does not need to see battery voltage which explains why that bus was powered.

As a guess..... I'm assuming that because the left bus plays a part in standby power, the system must see a functional battery before the left side will come up.

767-300 SSM 24-20-01]]>
ATA 24 Electrical Power Thu, 03 Jan 2019 05:39:10 +0000
ATA 34-11, Altimeter Splits - by: Mark
These systems are extremely accurate. Altimeter splits of a hundred feet or more at 35K were normal with older bellows based airspeed, altimeter, and air data systems. With digital's, 40 feet or more at 35K are uncommon.

If a crew reports an altimeter split beyond acceptable limits, the possibility of a leak must be considered.

The usual path by maintenance is to replace the suspect altimeter or air data computer first. If both those components have been tried and the problem persists, chances are....... there's a leak.

The easiest way to at least verify a leak is to tape over the static ports, close the aircraft up, and pressurize it. The suspect system will have a altimeter that starts to drive down. This doesn't find the leak, but it does verify that you've got one.

Pressurizing the line to 10psi or so and using leak detector would be my preferred method of leak isolation.]]>
ATA 34 Navigation Mon, 31 Dec 2018 12:38:31 +0000