Helicopter Tail Rotor Failure

On January 9, 2004, a 1984 Aerospatiale AS350BA helicopter crashed in the Gulf of Mexico. The NTSB listed the probable cause as the failure of a passenger to properly secure the cargo compartment door before takeoff, allowing baggage to be ejected into the tail rotor when the door opened during flight. The primary defendant, the cargo compartment supplier, filed a third-party complaint against the latch manufacturer alleging the latch mechanism on the aft cargo door failed, causing the crash.

The helicopter had been retrofitted with an aftermarket cargo compartment on the right hand side of the fuselage. The cargo compartment door was hinged along the upper edge and secured with two over-toggle button latches. The standard practice was for passengers to stow their equipment in the cargo hold and secure the two latches before boarding the helicopter. In a like manner, disembarking passengers were responsible for securing the cargo door after retrieving their equipment. The pilot and copilot did not routinely check the security of the cargo door.

On the day of the crash, the cargo door opened up in flight with cargo compartment contents spewed into the path of the tail rotor. While damage to the tail rotor blades was light, it was concluded that the impact was sufficient to shear the tail rotor shaft. Loss of tail rotor control resulted in the helicopter crashing into the Gulf.

The failure investigation focused on the two latches which were intact after the crash. Witness marks on the paint opposite the forward latch suggested that at one time the cargo door was closed with the forward latch closed but not secured to the corresponding strike plate - not unlike closing the lid of a hard-shell suitcase with the first latch already shut so that the lid seats at an angle and is secured by only the second latch. Immediately following the accident the forward latch was indeed closed and the door open. It is feasible to conclude that the last passenger simply failed to properly secure the cargo door and that the lone remaining latch failed to keep it closed during flight.

While this explanation is certainly feasible, another possible scenario may be that loose equipment in the cargo compartment came into contact with the over-center mechanism of the forward latch, triggering it to release.

The button latches used in this application incorporate an over-toggle lever that helps maintain them in the locked position, provided they are adjusted with sufficient preload. However, the levers of the button latches in this application were on the inside of the cargo hold and not protected against loosely-stowed baggage. A 12-oz. hammer dropped from a height of 4" is enough to un-toggle a button latch, so it is entirely possible that this could have occurred and not left a witness mark.

One basis of the lawsuit against the latch manufacturer had to do with the latch manufacturer not warning the cargo compartment supplier to provide shielding over the latches to prevent inadvertent triggering by loose cargo. The lawsuit asserted that the latch manufacturer had knowledge of the application, an assertion denied by the latch manufacturer.

The case was settled in arbitration in 2006.

Consultant Conclusion

Whether the cargo door was improperly secured by the last boarding passenger or not, the retrofit cargo compartment was inadequate in that it was prone to inadvertent release by loosely secured cargo. Either a different style of latch should have been used or the button latches should have been fitted with protective shields.

To see the resume of the expert associated with this case study, see the link below.