Milwaukee, WI, USA
N2410W
Boeing 717-231
A Boeing 717 sustained an in-flight thrust reverser deployment following a takeoff. The flight returned without further incident. After the prior flight the reverser was unlocked but not deployed. The flightcrew found the reverser unlock light during preflight. The crew could not clear the indication and contract maintenance was contacted to lock out the reverser. The contractor was not familiar and asked for the procedure to be faxed to him. The contractor used an incomplete set of procedures to lock out the reverser. Post incident inspection revealed the thrust reverser doors had over deployed. Four locking pins and their fork shaped locking triggers showed nicks and gouges on their mating surfaces. Subsequently Boeing revised their dispatch guide to include that maintenance would have to verify that "no more than one Thrust Reverser Proximity Sensor indicates Open" and that operators verify that the thrust reverser unlock indication is not present and red lockout pins are present on the inoperative reverser. Subsequent to the incident the overcenter links were redesigned. Boeing and the thrust reverser manufacturer issued service bulletins (SB) to retrofit the existing engines with the new link's design change, the link's associated hardware, and rub plates. Airplanes in production will incorporate the SB items as a production change. Boeing's 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."
On February 19, 2001, about 0730 central standard time, N2410W, registered as a Boeing 717-231, operated as Trans World Airlines (TWA) flight number 73, piloted by Airline Transport Pilot rated captain and copilot, sustained an in-flight thrust reverser deployment following a takeoff from General Mitchell International Airport (MKE), near Milwaukee Wisconsin. The flight landed at MKE without further incident. The scheduled domestic passenger flight was operating under 14 CFR Part 121. Visual meteorological conditions prevailed at the time of the incident. The 2 flight crewmembers, 3 cabin crewmembers and 62 passengers were uninjured. The flight was on an IFR flight plan. The flight was originating from MKE at the time of the incident and was destined for Lambert-Saint Louis International Airport, near Saint Louis, Missouri. Excerpts from that flight's debrief stated: During the cockpit preflight, the right engine's EPR display included an amber "T/R" light. The flight crew researched the QRH (quick reference handbook) and the flight handbook, and found no guidance for this problem. The Captain called the Kansas City maintenance coordinator (MCIMD) and discussed the problem with him. It was agreed that the engine would not be started with the T/R displayed. Two procedures were to be attempted by the flight crew before contract maintenance would be called: 1) pressurization of the hydraulics, followed by movement of the thrust reverse lever; and 2) an electrical "depowering" of the aircraft, followed by a total reboot of the computers. The loading was complete and the ramp service man was on the interphone; the Captain asked the agent to close the door and the flight blocked at 0614L. The flight crew completed the two procedures, with the ground crew verifying that the right engine's thrust reverse lever was not moving the buckets. Neither procedure cleared the problem T/R amber light; the flight was blocked-in at 0620 without having started an engine or moving the aircraft. (The gate in use at MKE does not involve a pushback.) The Captain phoned MCIMD and informed the coordinator that the procedures were not helpful and [contract maintenance] had been called. When the [contract maintenance] mechanic arrived, the Captain explained the problem and stated that the proposed solution was to lock out the right engine's thrust reverser and placard it as inoperative. The [contract maintenance] mechanic was careful and apprehensive as he reviewed the problem and stated that he would need a full hardcopy of the appropriate maintenance manual pages. He asked if there was one on the airplane, and the flight crew said there was not. The Captain explained that these pages are generally received by fax from MCIMD, which became the agreed-upon course of action. The [contract maintenance] mechanic explained his level of training (one day of ground school and no "hands on" experience with the B717) to MCIMD during a phone call as he requested a faxed, full copy of the procedure. The Captain had introduced the mechanic to the coordinator, who was a different individual as a shift change had occurred at MCIMD. The fax was sent to the MKE station manager's office and delivered to the [contract maintenance] mechanic by the MKE operations agent. The [contract maintenance] mechanic reviewed the procedure with the Captain; a placard and a circuit breaker collar were obtained from the station personnel. The [contract maintenance] mechanic completed the procedure that involved the "pinning" of the right engine thrust reverser, and the logbook signoff was reviewed with MCIMD. The amber T/R indication was still displayed in the cockpit. The flight departed the gate at 0720L. The takeoff was from runway 19R, followed by two turns to a westerly heading. Prior to slat retraction, at an altitude approximating 1400AGL and an airspeed of 200K, the right engine thrust reverser deployed. The airplane shuddered and rolled hard right; the T/R light was red. The Captain immediately closed the right throttle; the engine was secured shortly after the first officer was able to notify MKE departure control of an emergency and immediate need to return for landing. ATC cleared the flight for an immediate return with clearance to land on any runway. The wind at takeoff was southwesterly at 13 to 19 knots, which would require a landing on either 19R or 25L. The position of the flight was crosswind for 19R, and the distance to touchdown was shortest for 19R. A right turn to the downwind resulted in a call from the first officer of a 1500 fpm sink rate. To maintain a 1200AGL downwind and 200K, slats extended, the Captain forced the left engine thrust lever through the gate to obtain max thrust. (When time permitted, the first officer made a PA announcement to the cabin concerning our emergency condition; that we were returning and the cabin should be prepared for landing; and that we would be on the ground shortly.) A tight traffic pattern resulted in a safe landing after 6 minutes of airtime. ... When the Captain arrived in the MKE operations office a few minutes later, the [contract maintenance] mechanic was present and involved in a phone conversation with MCIMD. When he completed the phone call, he stated that MCIMD had not sent a fourth page that graphically depicted the pinning of the B717 thrust reverser. The B717 requires three pins to lock out the thrust reverser, and only one had been installed as had been normal with the DC9 and MD80. The thrust reverser was removed from the incident engine and shipped to the manufacturer for examination. A Federal Aviation Administration engineer oversaw the examination. Retrieved system data showed that after the prior flight the reverser, when stowed, moved to stowed position and did not lock. The examination revealed that the thrust reverser doors had over deployed. Four locking pins and their fork shaped locking triggers were inspected. Nicks and gouges were found on their mating surfaces. Subsequent to the incident, Boeing revised its 717 Dispatch Deviation Guide (DDG). The revised DDG included that maintenance would have to verify that "no more than one Thrust Reverser Proximity Sensor indicates Open" and that operators verify that the thrust reverser unlock indication is not present and red lockout pins are present on the inoperative reverser. Subsequent to the incident, Boeing revised its Flight Crew Operating Manual (FCOM) procedure for REVERSER DEPLOYED OR U/L OR REV DISPLAYED IN FLIGHT. A step was added to the FCOM to land at the nearest suitable airport. Subsequent to the incident the overcenter links were redesigned. Boeing and the thrust reverser manufacturer issued service bulletins (SB) to retrofit the existing engines with the new link's design change, the link's associated hardware, and rub plates. Airplanes in production will incorporate the SB items as a production change. An excerpt from Boeing's SB 717-78-004 stated: BACKGROUND 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. An excerpt from Rohr, Inc.'s SB R715.78-008 said: Based upon field experience and test data, it has been found necessary to introduce a number of thrust reverser actuation system improvements. This group of improvements will result in a better-functioning, more durable, more reliable thrust reverser actuation system. NOTE: This Service Bulletin provides terminating action for ALERT Service Bulletin R715.78-A008. ACTIONS: Install rub plates on the outboard surfaces of the side beams. Install new overcenter links (prevent in flight deployment) (greasable bearings). Install new overcenter link attach hardware (improve side beam clearance and provide lubrication facility). Modify the thrust reverser actuators. Modify deflector door seal retainers (lower profile for better deflector door overstow). Parties to the investigation were Boeing, the Federal Aviation Administration, and Trans World Airlines. Boeing reported that the Boeing and Goodrich service bulletins were completed for the entire fleet including stored aircraft by December 2003.
The failure of the operator to provide complete and comprehensive thrust reverser lock-out maintenance procedures and guidance to the contract maintenance personnel resulting in a partial and inadequate securing of the faulty thrust reverser and a subsequent inadvertent deployment following takeoff. Contributing to the incident is the failure of the contract maintenance personnel to verify that the maintenance instructions received where complete, accurate, and up to date.
Source: NTSB Aviation Accident Database
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