Aircraft Equipment Problem Less Severe; Flight Deck / Cabin / Aircraft Event Other / Unknown
Aircraft Aircraft Damaged; General Maintenance Action
Aircraft
I am filing this report as a general concern about an event on the Phenom fleet. From exchanges I have had with at least one of the pilots involved; a report from the crew involved was not filed. Therefore I am filing one to facilitate tracking of this event within the program. The aircraft in question had a failure of the main cabin door balancing mechanism as the door was opened from the exterior. This led to the door support cable apparently snapping; unloading the tension bar; and sending several metal shards and pieces of steel cable flying throughout the cabin. There were holes in several areas of the interior; including a seatback; sidewalls; and overhead panels. Had the crew been opening the door from the interior; or had there been passengers onboard; the potential for serious injuries would be quite high. For reference; the system description details the door balance mechanism as follows: The main door balancing mechanism is mainly composed of the torsion bar; gear sector; balance gearbox; balance cable; and balance drum. The main door balancing mechanism is responsible for equalizing the gravity action during the opening procedure and for providing mechanical assistance during the closing procedure. The torsion bar retains the elastic potential energy during the opening procedure. This energy results in a balance moment that equalizes the gravity action. When the main door is moving down; the door pulls the balance cable which is attached to the door. The balance drum rotates to load the torsion bar and keeps it at maximum tension. The accumulated potential energy of the torsion bar balances the door weight. While the door is in the fully down position; the torsion bar is under maximum stress; thus facilitating to pull the door upward. When the main door moves upward and reaches the near maximum closed position; the torsion bar keeps the balance cable slightly tensioned. When the main door is in the maximum open position; the balance cable is under maximum tension. I do not think that the average line pilot; prior to this event; had any idea how much destructive energy is stored right there at that cable drum on the door sill. From the few photos I have seen; this failure has the potential to cause serious injury to anyone in close proximity to that spool; even from the exterior; should parts be ejected as the door opens. If and when any investigation on this provides conclusive results; it should be shared with the fleet pilots without delay. It would be helpful to know if this is a design flaw; improper assembly; or improper maintenance; as well as if there is any mitigation that the crew can take while a fix is found.
The reporter made clear that he was not directly involved in the incident and was relaying information that was provided to him. The exact component that failed is unknown but thought to be the cable itself or the attachment to the door. This aircraft was also the oldest in the 505/Phenom 300 fleet.
Captain describes a failure of the main cabin door balancing mechanism as the door was opened from the exterior on an EMB505/Phenom 300. The cable apparently snapped throwing shards of metal from the cable into the cabin.