ATA 27

Flap Limit Switches
With the issuance of Service Bulletin 1124-27-153, Mandatory Replacement of the Inboard Flap Actuators, it is an excellent time to inspect the position switches on the actuators. The left actuator has six and the right has two. Pay particular attention to the rollers; check them for flat spots and ease of turning. A drop of LPS 1 on each one will help prevent further problems. Make sure the arms are true and not bent; if they are bent, now is a great time to replace them. Wringing out the switches can also be done at this time. Make sure the 0°, 40°, and 42° switches are good; if high resistance is noted, replace the switch. If you find multiple problems, you would be money and time ahead to replace the entire switch rack.

ATA 27

Flaps Extended, No Retract
Your aircraft has landed at a facility with no maintenance operations on site. The pilot reports the flaps are full down and the flap unbalance light is illuminated. There is not an apparent physical asymmetry between left and right flap surfaces. The fault unbalance condition is thought to be a result of an electrical fault, not a mechanical failure in the flaps drive system.

Question:

1. What action may be taken to retract the flaps to 0° in order to return the aircraft to home base?
2. Once the flaps are retracted, what must be accomplished to render the flaps system inoperative?
3. When the flap unbalance indication exists in flight, is it safe to cycle the flap unbalance test switch in an attempt to clear the fault?

Answer:

1. A maintenance technician may temporarily disconnect the flap comparator asymmetry box electrical connector. This will allow the flaps to be retracted, since the flap comparator relay will be de-energized and allow flap operation. Extreme care must be taken when operating the flaps in this condition. If a true mechanical asymmetry exists, the condition must be thoroughly investigated and the aircraft should not be ferried.
2. The flap comparator box connector must then be re-connected. This will ensure the flaps will not operate if inadvertently commanded to run.
3. No, the unbalance switch should never be used in flight. If the flaps test switch is reset while a true failure exists in flight, the fault may progress to an actual flap asymmetry with negative aerodynamic effects.