Narrative:

I was assigned to run the engines on aircraft for the operational check-out for the engine thrust control module. Per the aircraft maintenance manual (amm) task for installation it required me to perform an operational check of the thrust reversers (TR) with the engines running per [our aircraft maintenance manual reference a]. This reference told me to start the engines per amm tasks; (engine operation - safety precautions); and [amm reference]; (start the engines - operation). Prior to starting the engines I reviewed all the amm references looking for steps; cautions; and warnings that pertained to operating the engines in reverse. After reviewing I determined that there was only 1 warning and 1 step in the safety precautions task and 2 steps in the TR operational check-out that gave me any information about the operation of the engine in reverse. The warning out of the safety procedures told me to keep all people and equipment out of the fan air path when the TR operates due to possible injuries to personnel or damage to equipment from the high volume of fan air coming out during reverse. The step out of the safety procedures told me that I could run the engine in reverse for maintenance with the aircraft parked and the engine in idle. The 2 steps out of the TR check-out task told me to move the thrust lever up and aft until the interlock position and make sure not to move the thrust lever off the idle position. There were no other steps or warnings that I found in any of the tasks that were noted for this check-out.I proceeded to the aircraft to do my normal pre-engine start walk around and noticed how close the #1 engine was to the jet bridge. I looked thru the safety precautions for a definition of the inlet hazard area with the engine in reverse but there were only illustrations for the inlet hazard area in forward thrust. Using these as a minimum I felt that the jet bridge was to close and contacted management to have the bridge pulled off the aircraft. I also had a pre-run conference with the ground crew to notify them that we were going into reverse and to watch the jet blast. I notified the mechanic standing at the nose about the warning out of the safety precautions and we decided it would be best if he moved to the opposite side away from the motor that was going into reverse. After this was completed I went into the aircraft and the jet bridge was pulled as far forward and outboard of the #1 engine as it could be moved. The normal start procedures were used to start both engines in preparation for the ops check of the thrust reverser. Once the engines were up and running I went thru the procedures for the operational check-out steps 1(a) and (B) for engine 1 with no issues and then I went to move the TR handle per step 1(C) thinking that I just needed to pull the TR lever back to the first detent and not advance the throttles off of idle. When I deployed the TR I pulled up and aft and with what I felt was very little resistance the lever moved thru the interlock position to what I eventually determined was max reverse. The throttles never left the stops and the engine rapidly advanced thru 76% N2 before I was able to re-stow the TR. The aircraft nose jumped up and the aircraft swung side to side moving what felt like 3 feet left to right; if there hadn't have been 167;000 pounds of fuel still on board; or the jet bridge had not been repositioned I believe there would have been serious damage to both the aircraft and the jet bridge. Also if the mechanic standing ground was in the air path of that engine when it went to max reverse he could have been seriously injured. When I read the step that told me not to advance the engine throttles off of idle I was under the impression that if I didn't move the throttles forward off of idle; that the engine would stay at idle in reverse. I now understand that all I have to do is extend the reverser lever to the full travel and I will advance the engine to 80% N2 with nomovement of the throttle. There should be a note or warning letting the mechanics know that there is no mechanical detent to stop them at the interlock position only a resistance of approximately 35 ft pounds to identify the interlock position and if you pull the lever past the interlock position you will take the engine to max reverse without advancing the throttles. Also there should be an illustration for the inlet and exhaust hazard areas for the engines included in the safety precautions task of the amm.

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Original NASA ASRS Text

Title: When maintenance performed a Reverser Operational Check on a B787-8 Aircraft in the terminal area; the Technician exceeded the reverse thrust idle position causing the engine to exceed the thrust limit for the check.

Narrative: I was assigned to run the engines on aircraft for the operational check-out for the engine thrust control module. Per the Aircraft Maintenance Manual (AMM) task for installation it required me to perform an operational check of the Thrust Reversers (TR) with the engines running per [our Aircraft Maintenance Manual reference A]. This reference told me to start the engines per AMM tasks; (Engine operation - Safety Precautions); and [AMM reference]; (Start the Engines - Operation). Prior to starting the engines I reviewed all the AMM references looking for steps; cautions; and warnings that pertained to operating the engines in reverse. After reviewing I determined that there was only 1 warning and 1 step in the safety precautions task and 2 steps in the TR operational check-out that gave me any information about the operation of the engine in reverse. The warning out of the safety procedures told me to keep all people and equipment out of the fan air path when the TR operates due to possible injuries to personnel or damage to equipment from the high volume of fan air coming out during reverse. The step out of the safety procedures told me that I could run the engine in reverse for maintenance with the aircraft parked and the engine in idle. The 2 steps out of the TR check-out task told me to move the thrust lever up and aft until the interlock position and make sure not to move the thrust lever off the idle position. There were no other steps or warnings that I found in any of the tasks that were noted for this check-out.I proceeded to the aircraft to do my normal pre-engine start walk around and noticed how close the #1 engine was to the jet bridge. I looked thru the safety precautions for a definition of the inlet hazard area with the engine in reverse but there were only illustrations for the inlet hazard area in forward thrust. Using these as a minimum I felt that the jet bridge was to close and contacted management to have the bridge pulled off the aircraft. I also had a pre-run conference with the ground crew to notify them that we were going into reverse and to watch the jet blast. I notified the mechanic standing at the nose about the warning out of the safety precautions and we decided it would be best if he moved to the opposite side away from the motor that was going into reverse. After this was completed I went into the aircraft and the jet bridge was pulled as far forward and outboard of the #1 engine as it could be moved. The normal start procedures were used to start both engines in preparation for the ops check of the thrust reverser. Once the engines were up and running I went thru the procedures for the operational check-out steps 1(A) and (B) for engine 1 with no issues and then I went to move the TR handle per step 1(C) thinking that I just needed to pull the TR lever back to the first detent and not advance the throttles off of idle. When I deployed the TR I pulled up and aft and with what I felt was very little resistance the lever moved thru the interlock position to what I eventually determined was max reverse. The throttles never left the stops and the engine rapidly advanced thru 76% N2 before I was able to re-stow the TR. The aircraft nose jumped up and the aircraft swung side to side moving what felt like 3 feet left to right; If there hadn't have been 167;000 LBS of fuel still on board; or the jet bridge had not been repositioned I believe there would have been serious damage to both the aircraft and the jet bridge. Also if the mechanic standing ground was in the air path of that engine when it went to max reverse he could have been seriously injured. When I read the step that told me not to advance the engine throttles off of idle I was under the impression that if I didn't move the throttles forward off of idle; that the engine would stay at idle in reverse. I now understand that all I have to do is extend the reverser lever to the full travel and I will advance the engine to 80% N2 with nomovement of the throttle. There should be a note or warning letting the mechanics know that there is no mechanical detent to stop them at the interlock position only a resistance of approximately 35 FT LBS to identify the interlock position and if you pull the lever past the interlock position you will take the engine to max reverse without advancing the throttles. Also there should be an illustration for the inlet and exhaust hazard areas for the engines included in the safety precautions task of the AMM.

Data retrieved from NASA's ASRS site and automatically converted to unabbreviated mixed upper/lowercase text. This report is for informational purposes with no guarantee of accuracy. See NASA's ASRS site for official report.