Maintenance Powerplant; Maintenance Airframe
Maintenance Technician 30
Communication Breakdown
Aircraft Equipment Problem Less Severe
General None Reported / Taken
Chart Or Publication; Equipment / Tooling; Procedure; Human Factors
While the APU was suspended in the lifting sling; it 'flipped over' to an upside down position. High center of gravity while APU is in cradle/sling. Cradle/sling assembly is allowed to pivot; therefore allowing APU to flip over. Sling pivot points should not be able to move. Hangar. APU removal/installation sling.
Reporter stated the APU cradle is mounted to four attach points on the Honeywell RE220 APU and two cables on each side form an 'A' shape that connect to a single point above the APU at the CRJ-900's internal structure. There are also two hand crank assemblies; one on each side that are used to lower the APU from it's compartment. There are four turnbarrels to level the APU as the Honeywell unit is lowered from the APU compartment. The APU tends to be nose heavy due to components on the forward end. As they were adjusting the turnbarrels to maintain a level position; the APU suddenly rotated nose down at the two side pivot points and flipped 180-degrees; basically turning upside down without anyone pushing on the unit. Reporter stated that because of the APUs weight and the Center of Gravity (CG); if the APU starts to flip; he doesn't think anyone can stop the movement. There was discussion afterwards about attaching a third cable for the third Mechanic to help guide and maintain a balancing effect; but mechanics feel that procedure would only mask the real issue which is a design problem that Bombardier has yet to improve. The CRJ-700 uses similar equipment and procedures to Remove and Replace (R/R) that aircraft's APU. Reporter believes a design change is necessary to prevent serious injury or death of technicians.
An Aircraft Maintenance Technician (AMT) reports that a Honeywell RE 220 APU unit 'flipped over' to an upside down position as the unit was being lowered from the APU compartment of a CRJ-900 aircraft.