Date: 201807
Local time of day: 1801-2400
Light: Night
Aircraft: B737-700
Operator: Air Carrier
Operating under: Part 121
Flight plan: None
Mission: Passenger
Flight phase: Parked
Aircraft component: Trailing Edge Flap
Component problem: Improperly Operated
Reporter organization: Air Carrier
Reporter function: Technician
Reporter qualification: Maintenance Airframe; Maintenance Powerplant
Human factors: Situational Awareness; Communication Breakdown
Second reporter function: Technician
Anomaly: Deviation / Discrepancy - Procedural Maintenance; Deviation / Discrepancy - Procedural Published Material / Policy; Ground Event / Encounter Object
Detector: Person Maintenance
Result: Aircraft Aircraft Damaged; General Maintenance Action
Contributing factors: Procedure; Human Factors
Primary problem: Procedure

Narrative: I was working pax window inspection on aircraft. The cabin check had the APU on along with the packs for cooling the cabin. I had my ear plugs because I was working the pax window inspection card outside. I was inspecting the windows on the left side of aircraft fwd of the eng. A mechanic called down and asked if the wings were clear for flaps; I looked at both wings and gave him the clear sign. Several minutes went by I completed the window inspection fwd of the wing so I moved the ladder and tool box to the aft side on wing. I positioned my ladder to continue with the inspection. I climbed the ladder and started with the inspection again. With ear plugs in APU running and packs on I didn't hear him call out or see him for movement of the flaps and I couldn't see the beacon on because I was up against the fuselage. Once I saw the flaps moving down I jumped off the ladder but could not move out of the way before the flaps contacted the ladder. A person needs to keep in eyesight with all flaps moving; and be in contact with the person who is moving flaps and to the position that they are moving to.


Second narrative: I was in the cockpit working on some Avionics cards on the cabin visit. Another mechanic said they needed the flaps lowered. I asked if they were clear; he responded they were clear but he said; let him double check. When he told me they were clear; I lowered them. He then said to stop because he lost sight of someone at the wing. He then came back and told me they were clear. I lowered the handle and they began to move. While in transit to full down I heard people yelling STOP! I then moved the flap handle towards up while killing the hydraulic pump. By then it was too late. Someone had moved a ladder under the flaps and the left inboard trailing edge flap came down on the ladder and broke the trailing edge flap.This was a breakdown in communication between myself; the mechanic clearing the flaps and the mechanics on the ground. I should have had a spotter I could see out the First Officer's window the whole time before I lowered the flaps. Someone could have been injured by this incident. The aircraft damage was later found to have a broken bellcrank and bent pushrods that drive the trailing edge; as well as the flap trailing edge.


Synopsis: B737 Maintenance Technicians reported the flaps were lowered onto a ladder that was positioned under the trailing edge of the flaps.