ATA 21

Bleed Line Over-pressurization
Your flight crew has returned from a routine flight and reported the illumination of the RED BLEEDLINE OVERPRESS warning light during the landing roll out. You perform an operational check of the bleed air system per the Aircraft Maintenance Manual. You are unable to duplicate the discrepancy. All functions appear normal and no abnormal indications are observed during the checks.

Questions:

1. What pneumatic system device(s) activate the BLEED LINE OVERPRESS warning light?
2. What bleed air control configuration may cause this condition (over-pressure/temperature in the bleed manifold) to occur during landing operations?
3. Why did the warning appear, and was it a true or false indication?

Answers:

1. The BLEED LINE OVERPRESS warning light is activated by either the over-temperature or over-pressure switch located on the bleed air common manifold upstream of the refrigeration unit.
2. If the cabin air selector is set to “RIGHT”, the ground bypass air valve will open upon landing because all conditions are met. When the crew deploys reversers and increases engine RPM with the piggyback lever(throttles are at idle), pressure and temperature in the bleed air common duct may rise above over-pressure switch or over-temperature sensor limits. As the right engine spools up, the open ground bypass air valve routes unregulated HP bleed air directly to the common manifold.
3. The BLEED LINE OVERPRESS warning will appear and it will be a “true” indication.

ATA 27

Flight Control Balance And Installation
We have recently discovered several aircraft that have been repainted, and the flight control hinge bolts were painted at the same time. Makes one wonder how the facility balanced the flight controls with them installed on the aircraft.
Customers are advised to ask the selected paint shop how they balanced the flight controls. The procedures require that special tooling be used. It has been our experience that most paint shops do not have this available and just use the old "knife edge" procedure. Nothing could be more wrong, because it results in substantial weight being added to the control surfaces.
Look at the flight controls prior to accepting the aircraft after painting. We find that the floating bushings are bottomed out at the hinge fittings and the controls are not shimmed properly, allowing the control to be loose on the hinges. The elevators will fit the stab hinges either way; however, the correct way is to have the large, rectangular hinge cutout on the bottom and the tapered cutout on the top. Otherwise, interference can result between the hinge and flight control skin. Contrary to what we heard, one shop tell thier customers it is NOT the customer's choice how the elevators are installed.

ATA 27

Flap Actuator Dust Seal
When accomplishing routine inspections in the area of the flap actuators, pay close attention to the dust seal in the end of the actuator. We find them split or missing. This allows dirt and water to be drawn into the actuator housing, which in turn, leads to corrosion and premature wear of the sleeve bearings and actuator shaft. The dust seal, P/N B132-116-2, is readily available fron the Worthington Aviation parts department.

ATA 77

Faulty Engine Oil Temperature Transmitter Can Affect Oil Pressure Indication
If you are a Westwind owner-operator who is experiencing high oil pressure indication at altitude and have exhausted your troubleshooting skills, here is one more thing you may not have thought of.
Recently, a customer arrived with this scenario, ground runs were performed with redundant gauges to verify the oil pressure was correct. We noticed the complaint was valid only as an indication problem after the oil temprature started to rise. It was found that the oil temperature transmitter was faulty. The result was the oil pressure indication becoming erratic on the ground and reading high at altitude. The oil pressure and temperature are displayed in the same gauge, and apparently, one can influence the other. Replacing the oil temperature transmitter fixed the problem.