The airspeed/ altitude sensor (A/ AS) must be removed from the aircraft to perform the check-out procedure. The following paragraphs describe the steps of the test procedure. Figures 6-50 and 6-51 show portions of the test. 1. Place the A/ AS in the mounting fixture and secure it to the workbench. Screw the pitot

Figure 6-51.- Airspeed/ altitude sensor function check.

hose from the manifold assembly onto the pressure port of the A/ AS. After you remove the static port filter, screw the altitude hose from the manifold assembly into the static port of the A/ AS. Then connect the pitot pressure hose of the test set to the airspeed port of the manifold assembly. Set the pressure temperature test set controls to the positions listed in table 6-1.

WARNING The TTU-205-C/ E test set must be properly grounded to prevent injury to personnel.

2. Connect the test set electrical plug to a 115-volt ac, 400 Hz, single-phase power source. Set the test set power switch to ON. When the pressure stabilizes, the static pressure ready light and the pitot pressure ready light will illuminate. Rotate the static pressure vent and pitot pressure vent controls full clockwise. Position the airspeed knots control to 500. Vary the airspeed trim control as necessary to obtain 500 on the airspeed knots indicator. It will take a few minutes for the airspeed knots indication to increase to 500.

3. Position the airspeed leak test switch to ON. Allow the pitot pressure to stabilize. At this point, you should ensure that the pitot pressure light goes out and that the leak rate is not more than 15 knots in 5 minutes. Position the airspeed leak test switch to OFF. The pitot pressure light should illuminate and the airspeed knots should return to 500. Position the airspeed knots control to 280. Vary the airspeed trim control to obtain 280 on the airspeed knots indicator.

WARNING To prevent injury, make sure personnel are clear of the A/ AS plunger during actuation.

4. Attach a 0-to 150-pound spring scale to the arming key. Apply a straight pull on the scale and remove the sensor arming key. The arming key should release between 6 to 16 pounds of force and the sensor plunger should remain extended.

5. Extend the plunger with the pull tool and reinstall the arming key. Position the airspeed knots control to 250 and vary the airspeed trim control to obtain 250 on the airspeed knots indicator. Remove the A/ AS arming key and observe the A/ AS plunger retract. Again, use the pull tool to extend the plunger and reinstall the arming key.

6. Position the airspeed knots control to 50. After the airspeed knots indication decreases to the set value, position the test set power switch to OFF. Rotate the static pressure vent and pitot pressure vent controls full counterclockwise. Disconnect the test set pitot hose from the manifold and test set. Remove the pitot hose assembly from the airspeed port of the manifold and connect it to the altitude port of the manifold assembly. Plug the airspeed port of the manifold.

7. Rotate the static pressure vent and pitot pressure vent controls full clockwise. Position the

Table 6-1.- TTU-205-C/ E Tester Control Settings

test set power switch to ON. Position the ALTITUDE x 1000 FEET control between 7 and 8. The altitude feet indication should increase to approximately 7750. You may have to vary the altitude trim control to obtain 7750 on the altitude feet indicator. Remove the A/ AS arming key. The A/ AS plunger should remain extended.

8. Use the pull tool to extend the plunger and install the arming key. Set the ALTITUDE x 1000 FEET control between 6 and 7. Vary the altitude trim control to obtain 6250 on the altitude feet indicator. The arming key should release with a pull of 6 to 16 pounds of force and the A/ AS plunger should retract.

9. Again, you should use the pull tool to extend the plunger and reinstall the arming key. Position the altitude control to zero. After the altitude feet indication decreases to the set value, position the test set power switch to OFF. Rotate the static pressure vent and pitot pressure vent controls full counterclockwise.

10. Remove the manifold assembly from the A/ AS and disconnect it from the test set. Disconnect the static pressure hose from the test set. Disconnect the power source and remove the test set.

If the A/ AS passes the functional check, you may install it on the seat. If the A/ AS is faulty, you should forward it to depot-level maintenance for repair.