2011-09 · NASA ASRS report 972667
Four Maintenance Technicians; including an Inspector; reported difficulties installing an Environmental Control System (ECS) Unit into a Bell 206L helicopter that resulted in the tail rotor push-pull control rod not being attached to a bellcrank clevis. Rod had separated during Operational Checks causing the Pilot to do a hovering auto-rotation.
We were closing up the aircraft after the Environmental Control Unit (ECU) installation. We looked in all the compartments for tools or any other items left in the aircraft. We looked at bolts and cotter pins and aggressively moved the flight controls to make sure the ECU installation hadn't caused any binding on any of them. We closed all the panels. We pushed the aircraft out: a pilot and one of the mechanics took it out for a ground run and an Operational Check flight. They came back with no problems noted other than the noise of the ECU and the tail-low attitude of the aircraft. Another Mechanic and I got into the aircraft with a different Pilot. We took off; flew around and listened to the ECU. It was really loud. The Pilot commented that the aircraft was holding a lot of pedal; more than he was used to. We were discussing whether this could be related to the aft Center of Gravity (C.G.). We were hovering at the end of the runway. The Pilot applied more pedal. There was a 'pop' and the pedals froze. The pilot rolled off the throttle to arrest the spin. The aircraft came to rest at the end of the runway with no damage to the aircraft or the passengers. We towed the aircraft back to the hangar; opened up the panels and found that when the bolt was installed in the bellcrank it failed to capture the bearing of the push-pull tube end. At least three Airframe/Powerplant (A/P) mechanics had looked inside this panel for tools and clearances of the [push/pull] tubes after the ECU installation and we had aggressively moved the pedals prior to the test flight. None of these actions revealed any problem. Corrective action recommended: Provide an easier way to connect push-pull tubes and to check the installation. The [access] hole is too small and can only be accessed from the side of the aircraft - the Mechanic must fully extend his arm to reach it.
We were tasked for the first installation of an Environmental Control System (ECS) Unit for a Bell 206 helicopter. This required a lot of removal of [flight] controls and [airframe] structural pieces for the new [ECS] Unit to fit. The job was tasked [scheduled] for five days; and was started in September and was finally ready for completion [approximately twelve days later]. My normal work schedule is five days on; two off. I started my shift five days before and worked thirteen more days; with no days off. There was not really [any] communication as to what we were doing. The helicopter had to be gutted as far as interior trim and flight control components. A sheetmetal guy did all the fabricating of the ECS Unit by cutting out frames; longerons; etc.; using approved drawings. When he was finished it was pretty much a puzzle for us to put the pieces back with all new trim work that had to be fitted along with all the flight controls and components that were removed. Three mechanics were needed to install one tail rotor flight control [push-pull] tube that was now obstructed by the newly installed ECS Unit; one Mechanic to shine a flashlight; the other to help guide the [push-pull] control rod end through the bellcrank and hold the wrench on the head [of the attach bolt]; while the third Mechanic installed the bolt washer; nut and torqued; then safetied [with a cotter pin]. Not properly installing the bolt was the reason the pilot noticed the stuck pedal while attempting to land. I feel many factors were present: fatigue; the long hours for the project; the difficulty of installing the bolt because of the ECS Unit installation taking up space that was normally there before; and the lack of guidance and knowledge for the installation of the ECS that has never been accomplished in the field.
After installation of the Environmental Control Unit (ECU) the noise level was so high with the ECU on during the Ground Run and Operational Checks; the sound level exceeded 119 decibels in the cabin. Reporter stated the added combination of noise levels; vibrations from the ECU; concerns about the aircraft's Center of Gravity (C/G) moving aft because of the weight of the ECU and thinking the control pedals were in a slightly different position than normal because of all the structural modifications; all came to a head when the pedals made a 'Pop' sound and froze. If they had only removed the push-pull control rod and reinstalled the same rod; without all the structural modifications during the ECU installation; mechanics would have noticed the pedal positions were not normal. Reporter stated the Maintenance Procedures for the ECU installation required physical structure modifications and additional supports to secure the ECU. Access for the installation of the ECU had to be accomplished through the Baggage door on the left side of the fuselage; through a small overhead ceiling panel; just aft of the passenger door. They could not access the ECU area from inside the cabin due to the location of all the medical equipment; oxygen hoses and medical vacuum machines.Reporter stated the tail rotor push-pull control rod tube is inserted into a close tolerance fit bellcrank clevis with the attach bolt going through three holes. The control rod hole did not line-up in the center of the clevis but was easily held there by the close tolerance fit. When the attach bolt was tightened; the clevis was squeezed just enough to hold the rod in position until the Pilot applied more pedal pressure and the rod 'popped' out; freezing the pedals. Mechanics now will not tightened the attach bolt until they are sure the push-pull rod end cannot be pulled from the bellcrank clevis.
Source: NASA Aviation Safety Reporting System (public domain). Reports are voluntary submissions and are not verified by NASA.
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