Recent Topics - Rotate.Aero Sun, 18 Aug 2019 03:01:27 +0000 MYOB en-gb Cargo Pit Lights - by: Mark
The light installed on the door receives this same power. We had an aircraft with the door light inop. A new bulb was no help. Checking for power and ground on the bulb wires revealed that power was present.... but no ground.

All door control wires and light power use one harness.

On this particular aircraft, power used pin 20 and ground pin 21. We checked continuity from the door side receptical to the light itself. These wires were good. The aircraft side of the harness enters the airframe at the top rear section of the door hinge.

The harness does "not" have a corresponding disconnect plug on the aircraft side. It's "hard wired" down to the door light control box on the aircraft's right side-wall. We started gutting both the overhead and side-wall looking for the ground stud associated with the pin 21 wire.

After an hours' worth of (needless) work, we opened the door disconnect plug. There was no wire connected to pin 21. A long pair of needle-nose retrieved this....

The re-pin and insertion was quite difficult as the harness elbow did not allow much room. We were lucky we didn't bust any of the other wires.]]>
ATA 33 Lights Wed, 14 Aug 2019 17:54:42 +0000
Kenric O Smith - by: Mark

Faces Wed, 14 Aug 2019 17:03:49 +0000
Check Your Work Area - by: Mark

This safety wire can was in the right core cowl. It was crispy, but it didn't look like there was any actual fire.

I try (but fail sometimes) to check all my tools and the complete work area before job completion. Having a second set of eyes to look things over is a good idea also.]]>
Be Aware Mon, 12 Aug 2019 15:17:16 +0000
ATA 76-11, Engine Fuel Conditioning - by: Mark
The pneumatic start valve was operational. The spar fuel valve was also working correctly. The engine fuel valve was not opening and valve indication light stayed on.

We hung a replacement Fuel Conditioning Unit, which was no help. The conditioning unit has an actuating piston which is attached to the fuel control (or MEC - Main Engine Control as it is usually called). Fuel is allowed to flow with the piston extended.

We noticed the installed unit and the replacement had "maybe" an inch worth of travel distance. To be sure this was enough, we opened up the other engine. We noticed twice (maybe three times as much) piston travel on the known good conditioner. We hung the replacement unit on the good engine, which also moved this greater distance.

A conditioner control relay (K168) was tried which was no help. Open command voltage at the conditioner plug was significantly lower than 28VDC.

The problem turned out to be high resistance on the fire control handle switch. After a few cycles of the fire handle, all valve operations were normal. A dirty fire handle switch contact was restricting current flow. The piston moved... just not enough.

Power for the conditioner goes through the fire handle switch first. Next in line is the fuel shut-off handle, followed by the control relay. Two situations are represented by the engine valve light. With the shut-off handle up and the conditioner not fully extended, the light will be on. With the shut-off handle down and the conditioner not fully retracted, the light will be on.]]>
ATA 76 Engine Controls Wed, 07 Aug 2019 21:55:45 +0000
31-31, Digital Flight Data Acquisition Unit - by: Mark QAR - Quick Access Recorder card with no data during the download process. "No Memory" was noted under the Non-Mandatory/Recording section of the DFDAR status screen.

After a good card was installed. The "Recording" section showed a blank screen (meaning a functional card).
Subsequently..... the bad card was marked......

ATA 31 Instruments Wed, 07 Aug 2019 18:28:26 +0000
Position Sensor Break-Out Cable - by: Mark
A "huge" issue during a sensor nulling was knowing the output voltage during the adjustment. You could have someone in the E&E or at the elevator position indicator reading a VOM and relaying by radio the values, but this turned out to be pointless. The sensors were extremely sensitive. Just grasping it with your hand would cause values to change. Adjustments were tedious using two people.

I found out that there was a means of using a break-out test harness right at the sensor during the procedure. With the sensor in one hand and a meter in the other, a null could be accomplished quite quickly.

727's are pretty much gone now, but 757's and 767's (possibly others) use these exact same sensors for elevator and rudder position indication. These sensors are not used in the auto-flight system, but they do require adjustment at times. After referencing some prints, the same pin-outs are used on 75's and 6's.

There should be no reason why this harness couldn't be used for adjustment on these newer aircraft types. Two plugs, two alligator clips, and some wire is all that is needed to build one. Pins 4 & 5 are the taps.

The plug part numbers are: Plug (female pins) BACC63BN10-5S (or 48-63N10C5S) Jack (male pins) MS24264R-10B5PN. The back-shells (2 ea) are MS27291-1.

Further information on the sensors can be found here. ]]>
Tools Mon, 05 Aug 2019 17:53:59 +0000
Digital Flight Data Acquisition Unit - by: Mark Systems such as auto-pilot/flight-director, hydraulics, pneumatics, fuel, flight controls, and many others usually have a controller of some type. Controllers use subsystem response and feedback to verify proper operation and if need be, reconfigure or render inoperative a failed component/system.

Flight Control Computers and System Controllers store faults that can be retrieved for troubleshooting by maintenance.

The flight recording system functions in a slightly different manner. It receives and records aircraft data, but plays no role in operation. Flight recorders basically receive data from "all" major systems installed on the aircraft.
The main workhorse in retrieval of this data is the DFDAU or Digital Flight Data Acquisition Unit. The DFDAU can receive digital, analog, or discrete signals. Teledyne Controls lists 64 Arinc-429, 54 analog, and 180 discrete inputs are capable on their DFDAU unit.

The DFDAU sends this data to the Flight Recorder which stores 17+ hours of data in a continuous updating loop. The DFDAU can also send data to the ACARS system for real time operation and fault reporting. Aircraft without ACARS often have a QAR or Quick Access Recorder which records data to a retrievable storage card.

Digital Flight Data Acquisition Unit Sun, 04 Aug 2019 23:14:04 +0000