Incident Description
A Boeing 717 sustained an in-flight thrust reverser deployment following a takeoff. The flight returned to the departure airport without further incident.
Maintenance Actions
After the prior flight, the thrust reverser had been unlocked but not deployed. During preflight, the flightcrew discovered the reverser unlock light. Unable to clear the indication, they contacted contract maintenance to lock out the reverser. The contractor was not familiar with the procedure and requested it be faxed. The contractor then used an incomplete set of procedures to lock out the reverser.
Inspection Findings
Post-incident inspection revealed that the thrust reverser doors had over deployed. Four locking pins and their fork-shaped locking triggers exhibited nicks and gouges on their mating surfaces.
Corrective Actions
Subsequently, Boeing revised their dispatch guide to include requirements that maintenance must verify "no more than one Thrust Reverser Proximity Sensor indicates Open" and that operators confirm the absence of the thrust reverser unlock indication and the presence of red lockout pins on the inoperative reverser.
After the incident, the overcenter links were redesigned. Boeing and the thrust reverser manufacturer issued service bulletins (SBs) to retrofit existing engines with the new link design, associated hardware, and rub plates. Aircraft in production will incorporate these changes. Boeing SB 717-78-004 stated, "Operators have reported five instances of thrust reversers failing to deploy and ten instances of side beam gouging. Inspections revealed that gouging had occurred between the over center link bolts and side beam assembly. One recent event resulted in a relatively new thrust reverser having side beam gouging so deep, it required a doubler to restore airworthiness. Rohr Incorporated Service Bulletin R715.78-008 provides instructions to modify the thrust reverser actuation system. The purpose of modifying the thrust reverser actuation system is to minimize the possibility of gouging and inadvertent in-flight thrust reverser deployment procedures given in this service bulletin."